JP3849876B2 - Semiconductor laser device and manufacturing method thereof - Google Patents

Description

The present invention relates to a semiconductor laser device provided with a striped ridge (convex portion). In addition, the semiconductor laser device of the present invention has a group III-V nitride semiconductor (InbAldGa1-b-dN, 0 ≦ b, 0 ≦ d, b + d <1) that is GaN, AlN, InN, or a mixed crystal thereof. ).

  Today, semiconductor laser devices using nitride semiconductors are increasingly demanded for use in optical disc systems capable of recording and reproducing information with a large capacity and high density, such as DVDs. For this reason, research on semiconductor laser elements using nitride semiconductors has been actively conducted. In addition, it is considered that a semiconductor laser element using a nitride semiconductor can oscillate in a wide wavelength range of visible light from ultraviolet to red, and its application range is not limited to the light source of the optical disk system, It is expected to be a wide variety of light sources such as laser printers and optical networks.

  In particular, various studies have been made on the laser element structure, and various proposals have been made on structures that allow suitable control of the transverse mode. Among them, a particularly promising structure is a ridge waveguide structure, which is also used in nitride semiconductor laser devices that have been shipped for the first time in the world.

  As the structure of the semiconductor laser element, the ridge waveguide structure has a simple structure, so that laser oscillation can be easily performed. However, variations in characteristics are likely to occur during mass production. This is because the characteristics of the ridge waveguide structure change depending on the mesa stripe size variation, but the mesa stripe shape variation depends on the etching accuracy. It is because it is not possible. In a semiconductor laser device using a semiconductor material that is damaged due to etching of the active layer, or the active layer surface is exposed to the etching atmosphere, a complete refractive index is obtained by etching deeper than the active layer to form a ridge. If an attempt is made to construct a waveguide type semiconductor laser device, the laser characteristics deteriorate due to damage caused by etching of the active layer and the surface of the active layer. Therefore, in such a semiconductor laser device, an effective refractive index type waveguide structure in which stripes are provided at a depth that does not reach the active layer must be used. However, in the effective refractive index type waveguide structure, the change in the element characteristics due to the variation in the stripe shape described above becomes remarkable, and the variation in the element characteristics becomes large during mass production.

  In a laser element using a nitride semiconductor, as a next problem for realizing application in the above-described field, it is an essential item to provide an element of stable quality by mass production.

  However, in the currently known laser device structure, the formation of a ridge waveguide is a hindrance. This is because, usually, a ridge waveguide is formed by growing a nitride semiconductor to be an element structure and then removing a part of the nitride semiconductor by etching from the upper layer to form a waveguide. This is because the etching accuracy at this time greatly affects the element characteristics of the obtained laser element as described above. That is, the transverse mode is controlled by the shape of the convex portion forming the ridge waveguide, particularly its height and width, and the F.D. F. P. This is because the (far field pattern) is determined, and thus, when the ridge waveguide is formed by etching, the control error of the depth is a major factor that directly causes variations in device characteristics.

  Conventionally, dry etching such as RIE (reactive ion etching) is known as a nitride semiconductor etching method. However, these etching methods can fundamentally solve variations in device characteristics. It was difficult to control the etching depth with this accuracy.

  Furthermore, in recent element designs, a large number of layers controlled in units of several atomic layers such as a superlattice structure are provided in the element structure, which is a cause of variations in element characteristics due to the etching accuracy. It has become. That is, in the formation of each layer constituting the element structure, the thickness of each layer is controlled with extremely high accuracy, and a ridge or the like is formed using an etching method inferior to several orders of magnitude. This makes it difficult to realize a highly designed element structure, and becomes a bottleneck for improving element characteristics.

  For example, in a laser device using a nitride semiconductor, a high power type nitride semiconductor laser device is realized by a refractive index waveguide structure in which a ridge waveguide is provided on the active layer without etching the active layer. Therefore, the accuracy in the etching depth direction needs to be controlled with an accuracy of 1/100 of the effective refractive index difference between the active layer portion directly under the ridge and the other active layer portions. In order to realize the accuracy, in the layer immediately above the active layer, for example, if it is a p-type cladding layer, the depth is controlled with an accuracy of 0.01 μm or less until only a part of the p-type cladding layer remains. The ridge must be formed by etching. Further, with respect to the width of the ridge waveguide, it is necessary to control the etching with an accuracy of 0.1 μm although the accuracy is lower than that.

  Further, when RIE is used as a method for etching a nitride semiconductor, the etched exposed surface and the exposed layer tend to be damaged, leading to deterioration of device characteristics and device reliability. As an etching method, there is a method using wet etching in addition to dry etching, but a wet etching solution that can be used for a nitride semiconductor has not been developed yet.

  As described above, the high accuracy of laser elements using nitride semiconductors and the realization of mass production with little variation in characteristics are greatly affected by the accuracy of the ridge waveguide formation in the etching process. The formation of an excellent ridge waveguide is an extremely important issue.

  In view of the above circumstances, the inventor of the present invention has realized a stable transverse mode control, even if a semiconductor laser element having a stripe shape is a semiconductor laser element having a resonator excellent in oscillation and waveguide, F. P. Thus, the present inventors have invented a laser element or an end surface light emitting element that can obtain a laser beam excellent in quality and has little element variation even during mass production, and a manufacturing method thereof.

  That is, the semiconductor laser device of the present invention can achieve the object of the present invention with the following configuration.

A first semiconductor laser element according to the present invention includes a first conductive type semiconductor layer, an active layer, and a second conductive type semiconductor layer different from the first conductive type, which are sequentially stacked. In a semiconductor laser device comprising a structure, wherein a waveguide region that guides light in a direction orthogonal to the width direction by limiting the spread of light in the width direction in the active layer and the vicinity thereof is formed.
The waveguide region has a first waveguide region and a second waveguide region,
The first waveguide region is a region in which light is confined in the limited active layer due to a difference in refractive index between the active layer and a region on both sides thereof by limiting the width of the active layer. And
The second waveguide region is a region in which light is confined by effectively providing a refractive index difference in the active layer.

  Thus, in the first semiconductor laser device according to the present invention configured as described above, the waveguide region includes a first waveguide region, and in the first waveguide region, an active layer, regions on both sides thereof, and Since a refractive index difference is actually provided between the active layers so that light is confined in the active layer, generation of a transverse mode can be more reliably suppressed in the first waveguide region, and beam control can be performed. Can be performed reliably. F. P. Excellent laser light can be obtained.

  Further, since the first semiconductor laser element includes a second waveguide region configured by forming a region having an effective refractive index in the active layer, the second waveguide region Since the waveguide can be formed without directly exposing the active layer functioning as the waveguide to the outside, the lifetime of the element can be improved and the reliability can be improved. As described above, the first semiconductor laser element according to the present invention can be a laser element having both the characteristics of the first waveguide region and the second waveguide region.

  In the first semiconductor laser device according to the present invention, the active layer in the first waveguide region is formed by forming a first ridge including the active layer, thereby limiting the width of the active layer. The region having an effectively high refractive index can be formed by forming a second ridge in the second conductivity type layer.

  In the first semiconductor laser device according to the present invention, the first ridge is formed by etching both sides of the first ridge until the first conductivity type layer is exposed, and the second ridge is formed. Can be formed by etching so as to leave the second conductivity type layer on the active layer on both sides of the second ridge.

  In the first semiconductor laser device according to the present invention, the film thickness of the second conductivity type layer located on the active layer on both sides of the second ridge is 0.1 μm or less. Preferably, this enables more reliable control of the transverse mode.

  Furthermore, in the first semiconductor laser device according to the present invention, it is preferable that the second ridge is longer than the first ridge, whereby the reliability can be further improved.

  Still further, in the first semiconductor laser device according to the present invention, it is preferable that the first waveguide region includes one resonance end face of the laser resonator. F. P. Excellent laser light can be obtained.

  In the first semiconductor laser device according to the present invention, it is preferable that the one resonance end face is an emission face. F. P. Excellent laser light can be obtained.

  Furthermore, in the first semiconductor laser element according to the present invention, the length of the first waveguide region is preferably 1 μm or more.

  Still further, in the first semiconductor laser element according to the present invention, the first conductive type semiconductor layer, the active layer, and the second conductive type semiconductor layer are each formed of a nitride semiconductor. be able to.

  In the semiconductor laser device, the active layer can be composed of a nitride semiconductor layer containing In, thereby allowing laser oscillation in a visible light region and an ultraviolet region having a relatively short wavelength.

  In the first semiconductor laser device according to the present invention, insulating films are formed on both side surfaces of the first ridge and both side surfaces of the second ridge, and the insulating films are formed of Ti, V, Zr, Nb, Hf, Ta oxides and at least one selected from the group consisting of SiN, BN, SiC, AlN are preferable.

In the second semiconductor laser element according to the present invention, a first conductivity type layer, an active layer, and a second conductivity type layer having a conductivity type different from the first conductivity type layer are sequentially stacked. In the semiconductor laser device having a stripe-shaped waveguide region in the stacked structure, the stripe-shaped waveguide region is provided with a stripe-shaped waveguide having a perfect refractive index in the cavity direction. It has at least a waveguide region C ₁ and a second waveguide region provided with a stripe-shaped waveguide by an effective refractive index. With this configuration, the laser element of the present invention has the second waveguide region C ₂ excellent in device reliability, and the first waveguide region C ₁ excellent in lateral mode controllability and beam characteristics. The laser element takes advantage of both characteristics, and various laser elements can be obtained depending on the application without complicated and complicated element design changes. This is because the effective refractive index type waveguide is provided with a stripe-shaped convex portion on the second conductive type layer above the active layer, so that the active layer can be kept in a growth state. When the element is driven, the waveguide is not deteriorated and the element reliability is excellent. Further, the transverse mode can be easily controlled by providing the _first waveguide region C ₁ of the refractive index type in which the refractive index difference is provided on both sides of the waveguide region by etching deeper than the active layer. By having this as the waveguide of the laser element, it is possible to easily change the transverse mode in the waveguide. In this specification, in order to avoid confusion between the waveguide constituting the first waveguide region and the effective refractive index type waveguide, a complete refractive index type waveguide or a true refractive index type waveguide is used. Let it be a waveguide.

In the second semiconductor laser device according to the present invention, the complete refractive index of the _first waveguide region C ₁ is provided so as to include the first conductivity type layer, the active layer, and the second conductivity type layer. The striped convex portion can be realized, and the effective refractive index of the second waveguide region can be realized by the striped convex portion provided in the second conductivity type layer. With this configuration, since the first waveguide region C ₁ and the second waveguide region C ₂ can be easily provided in the laser element, the laser element can have various element characteristics by a simple element design. .

In the third semiconductor laser device according to the present invention, a first conductivity type layer, an active layer, and a second conductivity type layer having a conductivity type different from the first conductivity type layer are sequentially stacked. In the semiconductor laser device having a striped waveguide region in the laminated structure,
In the resonator direction, the stripe-shaped waveguide region has a second conductive type layer in which a part of the second conductive type layer is removed and a stripe-shaped convex portion is provided in the second conductive type layer. The first conductive type layer, the first conductive type layer, the active layer, and the second conductive type layer are partially removed from the waveguide region and the first conductive type layer to provide a striped convex portion. And at least a waveguide region C ₁ . With this configuration, a stripe-shaped waveguide is formed by a region where the part of the active layer is removed (first waveguide region C ₁ ) and a region where the active layer is not removed (second waveguide region). Damage to the active layer caused by the removal can be limited to a part of the waveguide, and the device reliability is improved. Damage partial removal of the active layer, the element reduced reliability, in a large semiconductor material of the device property deterioration, since the first waveguide region C ₁ is part, occupied by the first waveguide region C ₁ Part By designing the ratio, a laser element having desired element reliability and element characteristics can be obtained. Further, by changing the length (ratio constituting the waveguide) and position of the first waveguide region C ₁ and the second waveguide region C ₂ , laser elements having various element characteristics can be obtained. In particular, a laser element having desired beam characteristics can be easily obtained.

In the second and third semiconductor laser elements, a part of the stacked structure is removed to form a ridge waveguide composed of stripe-shaped convex portions, whereby the first waveguide region C ₁ and the second waveguide region C ₂ may be configured. . With this configuration, laser elements having various characteristics can be obtained in a ridge waveguide structure laser element composed of stripe-shaped convex portions.
In the second and third semiconductor laser elements, it is preferable that the stripe length in the _second waveguide region C2 is longer than that in the _first waveguide region C1. With this configuration, a semiconductor material that is greatly deteriorated by providing the _first waveguide region C ₁ , for example, a semiconductor material that is damaged by removing a part of the active layer or being exposed to the atmosphere, has excellent element reliability. It becomes a laser element.

In the second and third semiconductor laser elements, at least one of the resonator surfaces of the semiconductor laser element is formed at an end of the _first waveguide region C1. It is preferable. With this configuration, by providing the first waveguide region C ₁ having excellent controllability in the transverse mode on one side of the resonator surface, it becomes possible to control the waveguide of light more effectively than at other positions. Laser elements having various element characteristics can be obtained.
In the second and third semiconductor laser elements, the resonator surface formed at the end of the _first waveguide region C1 is preferably an emission surface. With this configuration, by providing the first waveguide region C ₁ with excellent lateral mode controllability on the laser light emission surface, the beam characteristics can be directly controlled. F. P. A laser element having an aspect ratio of laser light can be obtained.
In the second and third semiconductor laser elements, the stripe length of the _first waveguide region C ₁ having a resonator surface at the end is preferably at least 1 μm. With this configuration, more reliable F.I. F. P. Control of the aspect ratio of the laser beam is realized, and a laser element with little element variation in these characteristics can be obtained.

In the second and third semiconductor laser elements, the first conductive type layer, the active layer, and the second conductive type layer can be formed using a nitride semiconductor. With this configuration, laser elements having various characteristics can be obtained in a laser element using a nitride semiconductor in which it is difficult to form a buried structure by ion implantation and regrowth layers. Nitride semiconductors also have a practically useful laser element consisting of a complete refractive index waveguide that removes part of the active layer because the lifetime of the element is greatly reduced when part of the active layer is removed by etching or the like. However, since a part of the waveguide becomes the first waveguide region C ₁ , it is possible to obtain a laser element with excellent lateral mode controllability while suppressing a reduction in element life.

  In the second and third semiconductor laser elements, the active layer can be formed using a nitride semiconductor layer containing In. With this configuration, a laser element having a wavelength from the ultraviolet region to the visible light region can be obtained.

  The second and third semiconductor laser elements may include an n-type nitride semiconductor in the first semiconductor layer and a p-type nitride semiconductor in the second semiconductor layer.

  In the second and third semiconductor laser elements, the second waveguide region has a p-type cladding layer containing a p-type nitride semiconductor, and the stripe-shaped convex portion of the second waveguide region. However, it is preferable that the thickness of the p-type cladding layer is less than 0.1 μm. With this configuration, a laser element having a low threshold current and excellent lateral mode controllability can be obtained. Here, the film thickness of the p-type cladding layer refers to the exposed surface of the p-type cladding layer in the region where no protrusion is provided and the adjacent layer in contact with the p-type cladding layer in the film thickness direction. The distance between the active layer and the adjacent layer is located above the active layer. That is, when the active layer and the p-type cladding layer are provided in contact with each other, the exposed surface / planar surface has a depth that the p-type cladding layer remains with a film thickness of greater than 0 and equal to or less than 0.1 μm. Is formed. Further, as in Example 1 described later, when a guide layer or the like is provided between the active layer and the p-type cladding layer, the exposed surface / plane is disposed on the active layer and the active layer. It is provided above the interface between adjacent layers and below the position where the thickness of the p-type cladding layer is 0.1 μm, or between the active layer and the p-type cladding layer.

In the second and third semiconductor laser elements, the nitride semiconductor is exposed on the stripe-shaped convex side surface of the _first waveguide region C1 and the stripe-shaped convex side surface of the second waveguide region. And an oxide film comprising at least one element selected from the group consisting of Ti, V, Zr, Nb, Hf, and Ta. Or at least one selected from the group consisting of SiN, BN, SiC, and AlN. With this configuration, in a laser element using a nitride semiconductor, a laser element having a stripe-shaped waveguide region that can provide a favorable refractive index difference to the stripe-shaped convex portion and has excellent lateral mode controllability. Is obtained.

In the second and third semiconductor laser elements, it is preferable that a width of the stripe-shaped convex portion is 1 μm or more and 3 μm or less. With this configuration, in the first waveguide region C ₁ and the second waveguide region C ₂ , a stripe-shaped waveguide region having excellent lateral mode controllability can be formed in the waveguide layer. In the current-light output characteristics, the laser element is free of kinks.

  The semiconductor laser device manufacturing method of the present invention can achieve the object of the present invention with the following configuration.

  The manufacturing method of a semiconductor laser device according to the present invention includes a stacking step of forming a stacked structure in which a first conductive type layer, an active layer, and a second conductive type layer are stacked in order using a nitride semiconductor. And forming a stripe-shaped first protective film after forming the laminated structure, and etching the laminated structure in a portion where the first protective film is not formed, Forming a third protective film through a first protective film on a part of the surface exposed in the first etching process, the first etching process for forming a stripe-shaped convex portion on the layer, A second etching step of etching a portion of the laminated structure where the third protective film is not formed to form a stripe-shaped convex portion in the first conductive type layer; and a material different from the first protective film The second protective film having an insulating property is formed on the stripe-shaped convex portion. Surface, and a step of forming the nitride semiconductor plane exposed by etching, after forming the second protective film, characterized in that it comprises the step of removing the first protective film.

The laser element of the present invention has a first waveguide region C ₁ and a second waveguide region C _{2 in the} direction of the resonator as a waveguide, and thus has excellent device reliability and lateral mode controllability. ing. Further, according to the present invention, laser elements having various element characteristics can be provided by simple design changes.

Conventionally, it has been difficult to achieve both excellent device characteristics such as device reliability that can withstand practical use and stable transverse mode oscillation. However, the laser device of the present invention has excellent productivity and reliability, and the device It is possible to obtain a laser element having excellent characteristics. In addition, by providing a part of the _first waveguide region C1 on the emission surface side of the resonance surface, it becomes possible to extract beams having various spot shapes and aspect ratios. That is, according to the present invention, various beam characteristics can be realized, and the effect is great in expanding the application range of the laser element.

Conventionally, in a laser element using a nitride semiconductor, it is difficult to regrow crystals and implant ions such as protons. Therefore, only a stripe laser element can withstand manufacturing yield and productivity. When an active layer having a nitride semiconductor containing is exposed to the atmosphere, the damage is large and the lifetime of the element is greatly reduced. Therefore, only an effective refractive index type laser element can be selected. However, the laser device of the present invention has the first waveguide region C ₁ and the second waveguide region C ₂ , so that the laser has excellent lateral mode controllability and beam characteristics while ensuring device reliability. It is possible to obtain an element, and the element structure can be manufactured with an excellent yield even in mass production, so that it is possible to apply a laser element using a nitride semiconductor, and to dramatically spread it. be able to. In addition, as a light source for a high-density recording optical disk system, there is no movement in the transverse mode in both the optical output areas at the time of data reading (5 mW) and at the time of data writing (30 mW), and it exceeds 1000 hours even when driven at 30 mW. With a laser element, an excellent laser element having an aspect ratio in the range of 1.0 to 1.5 can be provided as a light source.

  Hereinafter, semiconductor laser elements according to embodiments of the present invention will be described with reference to the drawings.

As shown in FIG. 1A, the semiconductor laser device according to the embodiment of the present invention includes a first waveguide region C ₁ , a second waveguide region C _2, and a stripe-shaped waveguide region. It is what has.

Here, as shown in FIG. 1C, the first waveguide region C ₁ is activated by forming a ridge (first ridge 201) so as to include the active layer 3 so as to include the active layer. This is a waveguide region in which light is confined in the active layer 3 by providing a difference in refractive index between the layer 3 and regions on both sides thereof (in the atmosphere here). In this specification, a waveguide region in which light is confined by actually providing a refractive index difference between the active layer and the regions on both sides thereof is referred to as a perfect refractive index type waveguide in this specification.

Further, as shown in FIG. 1B, the second waveguide region C ₂ is formed by forming a ridge (second ridge 202) in the semiconductor layer located on the active layer. This is a waveguide region in which the effective refractive index of the active layer 3 positioned under 202 is made higher than that of the active layers on both sides thereof so that light is confined in the active layer 3 having a high effective refractive index. In this specification, the waveguide region in which the refractive index difference is effectively provided between the active layer and the regions on both sides to confine light is referred to as an effective refractive index type waveguide in this specification.

  As described above, the semiconductor laser device according to the present invention is characterized by having a waveguide having a complete refractive index type waveguide and an effective refractive index type waveguide. .

As a specific structure, a stacked structure in which a first conductivity type layer, an active layer, and a second conductivity type layer different from the first conductivity type layer are stacked is formed. A second waveguide region C ₂ is formed by forming a stripe-shaped second ridge (projection) 202 in the second conductivity type layer 2 at a depth that does not reach the second conductivity type layer 2. The first waveguide region C ₁ is formed by forming a stripe-shaped first ridge (projection) 201 so as to include a part of the active layer 3 and the first conductivity type layer 1. is there.

As described above, the semiconductor laser device according to the present invention has the first waveguide region C ₁ and the second waveguide region C ₂ in the waveguide, thereby obtaining laser devices having various device characteristics. Is possible. In addition, the semiconductor laser device according to the present invention includes a first waveguide region C ₁ and a second waveguide region C as shown in FIGS. 3 (a), (b), 4 (a) and (b). ₂ can be formed in various forms. Here, FIG. 3A shows a perspective view and a partial cross-sectional view of a laser element having a structure in which stripe-shaped convex portions are provided by removing a part of the laminated structure. 3 (b) is observed from the direction of the white arrow in FIG. 3 (a), and FIGS. 4 (a) and 4 (b) show a waveguide structure having a form different from that in FIG. It is.

As shown in FIGS. 3A, 3B, 4A, and 4B, in the present invention, the first waveguide region C _{1 in the} resonator direction (longitudinal direction of the convex stripe). A structure in which the _second waveguide region C ₂ is variously arranged can be employed. Of course, the semiconductor laser device of the present invention may have a waveguide region other than the _first waveguide region C ₁ and the second waveguide region C ₂ . For example, as shown in FIG. 4 (a), the first waveguide region C ₁ and the first waveguide region C ₁ and the second waveguide region and C ₂ between the second waveguide region C ₂ Different waveguide regions 203 may be provided. 3A and 3B, the first waveguide region C ₁ is provided so as to include one resonator surface of the resonator, and the second waveguide is included so as to include the other resonator surface. It has a structure in which the region C ₂ is provided. In FIG. 4A, the first ridge 201 constituting the _first waveguide region C ₁ and the striped second ridge 202 constituting the _second waveguide region C ₂ are perpendicular to each other. This is a semiconductor laser element having a structure bonded via a waveguide region 203 formed so as to be inclined with respect to (a direction orthogonal to the resonator direction). Thus, the first waveguide region C ₁ and the second waveguide region C ₂ are formed substantially continuously in the resonator direction as shown in FIGS. 3 (a) and 3 (b). Alternatively, as shown in FIG. 4A, other regions may be sandwiched therebetween.

In the present invention, the width of the first ridge 201 and the width of the second ridge 202 are not necessarily the same. For example, as shown in FIGS. 1A to 1C and FIG. 3A, when the side surface of each ridge is inclined, it is provided to form the _first waveguide region C1. The width of the bottom portion of the first ridge 201 and the width of the bottom portion of the second ridge 202 provided to form the _second waveguide region C2 are necessarily different. The side surface of the first ridge and the side surface of the second ridge are preferably located on the same plane. In FIG. 1A and FIG. 3A, among the mesa type in which the side surface of the stripe-shaped convex portion is inclined, the forward mesa type is inclined so that the width decreases from the lower layer to the upper layer. On the contrary, a reverse mesa type inclined so as to increase in width toward the upper layer may be used, or both sides may be the same mesa type or different mesa types.

  Further, the width of the upper surface of the first ridge 201 and the width of the upper surface of the second ridge 202 may be different. Furthermore, the width of the first ridge 201 and the width of the second ridge 202 when viewed in a horizontal section change discontinuously at the boundary between the first ridge 201 and the second ridge 202. May be different.

[Resonator structure]
In the semiconductor laser device of the present embodiment, a part of the laminated structure is removed to form a convex portion, thereby forming a striped waveguide. That is, as shown in FIGS. 1 and 3, in the element structure in which the first conductive type layer 1, the active layer 3, the second conductive type layer 2 and the like are laminated, both sides of the ridge portion are removed by means such as etching. Thus, it is a structure suitable for a so-called ridge waveguide laser element in which a resonator structure is formed by forming stripe-shaped convex portions. And this invention can improve a beam characteristic by providing at least _1st waveguide area | region C1 and _2nd waveguide area | region C2 by the stripe-shaped convex part, respectively. It is possible to obtain laser elements having various element characteristics, such as being able to be controlled to an arbitrary shape from an ellipse to a perfect circle. At this time, the stripe-shaped ridges (convex portions) are not limited to the forward mesa shape as shown in FIGS. 1 and 3 as described above, and may be a reverse mesa shape or a vertical mesa shape. It may be a stripe having side surfaces. That is, in the present invention, the shape of the ridge can be changed according to the required laser characteristics.

In the semiconductor laser device of the present invention, in order to form the _first waveguide region C ₁ and the second waveguide region C ₂ , the stripe-shaped convex portions 201 and 202 are formed, respectively, Crystals may be regrown on both sides of the ridge to embed the ridge.

Thus, since the present invention is premised on the ridge waveguide structure having the striped ridges, not only the low-cost manufacturing is realized, but also the first waveguide region C ₁ and the _first waveguide region are formed in the waveguide. By arranging the _two waveguide regions C ₂ in various combinations, laser elements having various characteristics can be realized. . For example, since the beam characteristics can be controlled, a good FFP can be obtained without using a beam correcting lens or the like.

In the laser element of the present invention, the stripe-shaped first and second ridges 201 and 202 provided in the _first waveguide region C ₁ and the second waveguide region C ₂ are shown in FIG. The shape is as shown in (c).

  Further, the present invention can be applied to an end surface light emitting element such as a light emitting diode other than the laser oscillation element. In this case, in the configuration shown in FIG. 1 and the like described above, the device can be operated as a light emitting diode by driving the element below the oscillation threshold, and the waveguide end face is not perpendicular to the waveguide end face. By tilting the waveguide from the direction perpendicular to the end face, an element that emits light from the end face without laser oscillation can be obtained.

[Laminated structure]
Next, a detailed configuration of the first conductivity type layer, the active layer, and the second conductivity type layer in the semiconductor laser device of the present embodiment will be described.

  First, in the semiconductor laser device of this embodiment, as shown in FIG. 1, the first conductive type layer 1 and the second conductive type layer 2 have cladding layers 5 and 7, respectively. Light is confined in the thickness direction by sandwiching the active layer 3 between the cladding layers 5 and 7. In this way, light is confined in the laminated structure by confining light in the width direction (direction perpendicular to the thickness direction and perpendicular to the resonance direction) by the ridge and confining light in the thickness direction by the cladding layers 5 and 7. A waveguide region is provided. In the semiconductor laser device of the present invention, various types of conventionally known semiconductor materials can be used for each semiconductor layer. For example, GaAlAs-based, InGaAsP-based, and GaAlInN-based materials are appropriately selected and used. Can do.

  Thus, in the semiconductor laser device of the present invention, the stripe-shaped waveguide region corresponds to the first conductive type layer, the active layer sandwiched between the second conductive type layers, and the vicinity mainly corresponding to the ridge. At this time, the longitudinal direction of the stripe and the light propagation direction substantially coincide with each other. That is, the stripe-shaped waveguide region is mainly composed of the active layer in which light is confined as described above, but a part of the light is guided to spread in the vicinity thereof. A guide layer may be formed between the cladding layers, and a region including the guide layer may be an optical waveguide layer.

[Second waveguide region C ₂ ]
The second waveguide region C ₂ of the present invention, in the waveguide of the semiconductor laser element, a region which is provided as a waveguide effective refractive index type, specifically, in the stacked structure, the active layer 3 The upper second conductive type layer 2 is provided with stripe-shaped convex portions 201, and an effective refractive index difference is provided in the surface direction (width direction) of the active layer to provide a stripe-shaped waveguide region. It is a thing.

As shown in FIG. 2A, an effective refractive index type laser element having a waveguide composed only of the second waveguide region C ₂ is provided with a mask 20 after each semiconductor layer is formed. The stripe-shaped convex portions 202 were formed by etching. However, since the stripe-shaped convex portion 202 is formed by etching that does not reach the active layer and an effective refractive index difference is provided in the active layer (waveguide layer), FIG. The device characteristics are greatly influenced by the width Sw of the stripe shown, the height of the ridge (projection) Sh ₁ , and the distance Sh ₂ from the etching bottom surface to the top surface of the active layer. This causes a serious variation in device characteristics in the manufacture of laser devices. That is, in FIGS. 2C and 2D, the error Hd with respect to the height of the protrusion (etching depth) and the error Wd with respect to the stripe width due to the etching accuracy directly cause variations in device characteristics. Is. This is because the waveguide region formed in the active layer (waveguide layer) is formed by the stripe-shaped ridge (convex portion) 202 provided on the active layer due to an effective refractive index difference corresponding to the ridge 202. This is because the shape of the convex portion described above greatly affects the effective refractive index difference. Further, the error Hd with respect to the height of the convex portion is also an error with respect to the distance between the active layer top surface and the etching bottom surface. Distance Sh ₂ between the active layer top and etching bottom, so the effective refractive index difference becomes too large decreases, greatly affects the device characteristics such as light confinement is weakened. As described above, the effective refractive index depends on the convex shape and the distance between the upper surface of the active layer and the bottom surface of the etching.

  10, 11 and 12 show the yield rate, drive current value, and laser lifetime with respect to the etching depth in a conventional effective refractive index type laser element. As can be seen, the characteristics of the laser element change extremely sensitively with respect to the etching depth.

The laser element of the present invention has the second waveguide region C ₂ etched to a depth not reaching the active layer as a part of the waveguide, so that the second waveguide region C ₂ Since the active layer can be prevented from being damaged by etching, the reliability of the device can be improved. Further, in the case where the active layer is exposed to the atmosphere, a material whose element characteristics are greatly deteriorated is provided with the _second waveguide region C ₂ , so that a decrease in the reliability of the element can be suppressed.

[First waveguide region C ₁ ]
As described above, the laser element of the present invention has various characteristics by forming the _first waveguide region C ₁ in addition to the _second waveguide region C ₂ as the striped waveguide region. A laser element can be easily realized. This is because the first waveguide region C formed by forming a stripe-shaped first ridge (convex portion) 201 including a part of the active layer and the first conductivity type layer 1 in the laminated structure. ₁ is an effect brought about by excellent controllability in the transverse mode.

That is, the first waveguide region C ₁ limits the width itself of the active layer by the first ridge, since the confinement of light by real refractive index difference between the active layer and both sides of the region It becomes possible to confine light more strongly.

  Thereby, generation | occurrence | production of an unnecessary transverse mode can be suppressed more reliably, and transverse mode can be controlled more reliably.

  As described above, in the present invention, by providing the first waveguide region having excellent lateral mode controllability in a part of the waveguide region, generation of unnecessary transverse modes in the first waveguide region is suppressed. As a result, it becomes possible to easily obtain laser elements having various beam characteristics by making the overall lateral mode controllable.

In the laser device of the present invention, the first waveguide region is formed at one end portion so as to include one resonator surface of the laser resonator, thereby making it easier to form a beam having a desired shape. Can get to. In other words, as shown in FIGS. 3B, 4A, and 4B, the laser resonator surface 4 is formed so as to coincide with the end surface of the _first waveguide region C1. Is preferred. This is because when the region near the resonator surface is the first waveguide region C ₁ , the light can be laterally controlled before and after reflection on the resonator surface and provided in other regions. This is because the transverse mode control functions more effectively in the waveguide than in the case.

In the laser element of the present invention, the end face of the _first waveguide region C ₁ is a laser resonator surface, and the laser resonance surface is an emission surface. F. P. It is possible to obtain a laser element having an excellent aspect ratio and beam characteristics. This is because, by providing the _first waveguide region C ₁ on the exit surface side, it is easy to control the transverse mode in the _first waveguide region C ₁ , and thus the beam characteristics of the laser light that is easily emitted. It is because it becomes possible to control. As shown in FIGS. 3 and 4, when the _first waveguide region C ₁ is composed of a stripe-shaped first ridge (convex portion) 201, the stripe width of the first ridge 201 is set as follows. By adjusting, the transverse mode can be easily controlled, and desired beam characteristics can be obtained with high accuracy.

At this time, the length of the _first waveguide region C ₁ provided on the emission surface may be formed with a length of at least one wavelength of the obtained laser light, but a functional surface for controlling the transverse mode. Is preferably provided with a length of several wavelengths of laser light, whereby desired beam characteristics can be obtained.

  Specifically, it is preferable to form the first waveguide region with a length of 1 μm or more, and this enables favorable transverse mode control. In consideration of the manufacturing surface, it is preferable to set the first waveguide region to 5 μm or more because the stripe-shaped ridge (projection) 201 can be formed with good accuracy.

  Further, the active layer width (length in the direction perpendicular to the resonator direction) may be 10 μm, but is preferably 50 μm or more, and more preferably 100 μm or more. This active layer width corresponds to the width of the chip in a configuration in which a pair of positive and negative electrodes are arranged opposite to each other with a substrate interposed therebetween. In a structure in which a pair of positive and negative electrodes are provided on the same surface side, an electrode is provided on the first conductivity type layer. Therefore, the length of the chip is reduced by subtracting the width of the portion removed to form the exposed surface from the width of the chip.

[Configuration of waveguide]
The laser device according to the present invention is characterized in that the striped waveguide region has at least a first waveguide region C ₁ and a second waveguide region C _2, and has a complicated device structure. Even without the design change, the characteristics of the laser element can be easily changed by arranging and distributing these waveguide regions in the resonator in various ways. Specifically, as described above, by arranging the _first waveguide region C1 on the resonator surface, the beam characteristics can be easily controlled and desired characteristics can be easily obtained. Further, by reducing the ratio of the _first waveguide region C ₁ in which the side surface of the active layer constituting the waveguide is exposed in the waveguide to be smaller than that of the _second waveguide region C ₂ , element reliability is improved. An excellent laser element can be obtained. This is because the ratio of the active layer that is not damaged by etching can be increased by providing a large number of _second waveguide regions C ₂ in the waveguide. As a result, the device life can be improved, and the variation between devices in the device life can be reduced.

The laser element of the present invention has at least a _first waveguide region C ₁ and a second waveguide region C _{2 as} waveguides, but in addition, the first waveguide region C ₁ , A waveguide region having a form different from that of the _second waveguide region C ₂ may be provided. For example, as described above, as shown in FIG. 4A, the configuration region is defined by the plane 203 formed by being inclined between the _first waveguide region C ₁ and the second waveguide region C _2. It may be provided. Thus, in addition to the first waveguide region C ₁ and the second waveguide region C ₂ , a waveguide region different from them may be provided. Furthermore, the first waveguide region C ₁ and the second waveguide region C ₂ suffice if they exist at least one in the waveguide. As shown in FIG. A plurality of may be provided. Further, it is not necessary to provide anything between the _first waveguide region C ₁ and the second waveguide region C ₂ as shown in FIGS. 3 and 4B. An inclination opposite to (a) may be provided so that the first waveguide region C ₁ and the second waveguide region C ₂ partially overlap each other.

In the laser device of the present invention, as shown in FIG. 13, in addition to the first waveguide region C ₁ and the second waveguide region C ₂ , the active layer side surface (waveguide layer side surface) 204 is arranged in the resonator direction. A structure having a _third waveguide region C ₃ formed so as to be inclined with respect to the surface may be employed. Here, FIG. 13A is a schematic perspective view for explaining the element structure, and FIG. 13B is a cross-sectional view showing the vicinity of the bonding surface between the upper clad layer 7 and the active layer 3. At this time, the third waveguide region C ₃ shares the stripe-shaped ridge (convex portion) 202 on the upper cladding layer 7 with the second waveguide region C _2, and the end face of the active layer (waveguide layer). (Side surface) 204 is provided with an inclination. In the laser device configured as described above, as shown in FIG. 13B, the angle α formed by the resonator direction AA and the side surface direction BB of the active layer is adjusted, and the light is guided by the side surface 204. it is possible to totally reflect the light, the first waveguide region C ₁ striped, can be guided. Specifically, by setting the angle α to 70 ° or less, the light guided in the resonator direction AA can be set to an incident angle of 20 ° or more with respect to the end face 204, and thus total reflection without loss can be expected. . Therefore, the angle α can be selected in the range of 70 ° to 0 according to the purpose. For example, by setting the angle α to 20 ° or less, the light guided in the resonator direction AA can be made to have an incident angle of 70 ° or more with respect to the end face 204. In this case, total reflection without loss is also achieved. I can expect. In the second waveguide region C ₂ , a stripe-shaped waveguide region is formed in the active layer (waveguide layer) plane due to an effective refractive index difference. There is also light that is guided out of the way, and the light is reflected at the end of the _second waveguide region C2.

At this time, if the loss of light increases, the output decreases, which causes the slope efficiency of current-light output to decrease. When the second waveguide region C ₂ is wider than the _first waveguide region C ₁ , the third waveguide region C ₃ is replaced with the second waveguide region C ₂ and the first waveguide region C _1. The above-described loss of light can be reduced, and good light can be guided at the junction with the _first waveguide region C ₁ as shown in FIG. it can.

In the laser element of the present invention, the stripe-shaped ridges (projections) 201 and 202 constituting the _first waveguide region C ₁ and the second waveguide region C ₂ may have different stripe widths. . In this way, the beam can be set to various aspect ratios by changing the stripe width. Therefore, in the semiconductor laser device of the present invention, the first ridge and the second ridge can be formed with a width according to the purpose. For example, the accuracy of the width control is questioned by making it thinner, but it is possible to obtain characteristics such as an FFP that is closer to a perfect circle, or the width of the beam depending on the width. It is also possible to change the degree. As a specific example, as shown in FIG. 15, the width at the part 205 of the _second waveguide region C ₂ is gradually narrowed to reduce the stripe at the junction with the _first waveguide region C _1. The width can be made the same as the stripe width S _w2 , and various modes of laser light can be extracted corresponding to the width of the first waveguide region. In FIG. 15, a portion where the width of the _second waveguide region C ₂ is gradually reduced is shown as a _third waveguide region C ₃ .

In FIG. 15, in order to form the _second waveguide region C ₂ , the first ridge (convex portion) having a width S _w1 wider than the stripe width S _w2 of the first ridge constituting the _first waveguide region C _1. ) 202 to provide a waveguide having a small characteristic change with respect to an effective refractive index change, and in the third waveguide region C ₃ , the waveguide regions having different stripe widths can be well joined. A region 205 having an inclined stripe width is provided to minimize loss at the junction. In addition, the ridge for forming the _third waveguide region C3 may be provided above the active layer as shown in the drawing, or the first ridge may be provided in the same manner as the _first waveguide region C1. It may be provided by etching to a depth reaching the conductivity type layer, or may be provided between them.

As described above, the stripe-shaped ridges for forming the first and second waveguide regions of the present invention can be formed in various shapes, for example, in a taper shape having different stripe widths in the stripe direction (longitudinal direction of the stripe). Also good. As a specific example, as shown in Examples 1 or 15, in the waveguide structure where the first waveguide region C ₁ is disposed on the exit side end, a large second waveguide region C ₂ of the stripe width , the closer it from the narrower first waveguide region C ₁ of the stripe width, the stripe width is made smaller, can the structure of narrowing the optical waveguides before the junction therebetween. Such tapered stripes may be partially formed in the stripes of each waveguide region, or may be tapered in all regions in the stripe direction, and the stripe widths are increased as they approach both ends of the stripes. It is also possible to provide a plurality of different tapers that are narrowed.

[Stripe in nitride semiconductor]
Hereinafter, a case where the semiconductor laser device according to the present invention is configured using the first conductive type and second conductive type semiconductors and the nitride semiconductor in the active layer will be described.

  The nitride semiconductor used in the laser device of the present invention includes GaN, AlN, InN, or a III-V group nitride semiconductor that is a mixed crystal thereof (InbAldGa1-b-dN, 0 ≦ b, 0 ≦ d, b + d). ≦ 1). In addition, a mixed crystal in which B is used as the group III element or a part of N of the group V element is substituted with As or P can be used. Further, such a nitride semiconductor can be made to have a desired conductivity type by adding impurities of each conductivity type. As the n-type impurity used in the nitride semiconductor, specifically, a group IV or group VI element such as Si, Ge, Sn, S, O, Ti, Zr can be used, and preferably Si, Ge, Sn is used, and most preferably Si. Specific examples of the p-type impurity include Be, Zn, Mn, Cr, Mg, and Ca, and Mg is preferably used. Hereinafter, a laser element using a nitride semiconductor will be specifically described with respect to the laser element of the present invention. Here, a laser element using a nitride semiconductor means that a nitride semiconductor is used for any one of the layers of the laminated structure in which the first conductive type layer, the active layer, and the second conductive type layer are stacked. Yes, preferably for all layers. For example, a cladding layer made of a nitride semiconductor is provided in each of the first conductivity type layer and the second conductivity type layer, and a waveguide is formed by providing an active layer between the two cladding layers. More specifically, the first conductive type layer includes an n-type nitride semiconductor layer, the second conductive type layer includes a p-type nitride semiconductor layer, and the active layer includes a nitride semiconductor layer containing In. Shall be.

(Active layer)
In the present invention, when a semiconductor laser device according to the present invention is configured using a nitride semiconductor, the active layer includes a nitride semiconductor layer containing In, so that a wavelength from blue to red in the ultraviolet region and the visible region. In the nitride semiconductor layer containing In, when the active layer is exposed to the atmosphere, there is a case where extremely serious element deterioration is caused in driving the laser element. Since the second waveguide region C ₂ constituted by the first ridge (convex portion) 202 provided at a depth that does not reach the active layer is included, it is possible to minimize such element deterioration. It is. Because, since In has a low melting point, a nitride semiconductor containing In is a material that easily decomposes and evaporates, is easily damaged during etching, and has a crystallinity in processing after the active layer is exposed. This is because it is difficult to maintain the resistance, and as a result, the lifetime of the element is reduced.

  FIG. 12 is a diagram showing the relationship between the etching depth when forming the stripe-shaped convex portion and the element lifetime. As can be seen from the figure, in the active layer having a nitride semiconductor containing In, the device life is drastically reduced by etching at a depth reaching the active layer, and the active layer is exposed to the atmosphere. It can be seen that the reliability of the device is extremely deteriorated.

In the laser element of the present invention, there is a concern about deterioration of characteristics by exposing the active layer to the atmosphere by having the _first waveguide region C ₁ and the second waveguide region C _{2 as the} waveguide. Even in a semiconductor laser element using a nitride semiconductor, it is possible to provide a laser element having excellent element reliability. This is because the first ridge (projection) 201 for forming the _first waveguide region C ₁ is only part of the waveguide, and it is possible to prevent deterioration in element reliability. Because. For example, in the laser device using the nitride semiconductor according to the present invention, the length of the first ridge (convex portion) 201 in the stripe shape for configuring the _first waveguide region C ₁ with the resonator length of about 650 μm. When the thickness is 10 μm, it is confirmed that there is no decrease in device reliability due to the active layer exposed in the first ridge, and a life of several thousand hours can be secured in driving at 5 mW.

In the laser device using the nitride semiconductor of the present invention, the width of the stripe of the ridge constituting the _first waveguide region C ₁ or the second waveguide region C ₂ is preferably set to 0.5 to 4 μm, More preferably, by adjusting to the range of 1 to 3 μm, oscillation in the transverse mode that is stable in the basic (single) mode becomes possible. If the ridge stripe width is less than 1 μm, it is difficult to form the ridge, and if it is 3 μm or more, the transverse mode may become multimode depending on the laser oscillation wavelength. If it is 4 μm or more, a stable transverse mode is obtained. It may not be possible. In the present invention, further adjustment to the range of 1.2 to 2 μm makes it possible to effectively stabilize the transverse mode in a region with a higher light output (effectively suppress the occurrence of unnecessary transverse modes). In the present invention, the width of the ridge stripe may be such that at least one of the _first waveguide region C ₁ and the second waveguide region C ₂ is within the above range, When one waveguide region C ₁ is provided, it is preferable to provide the stripe-shaped first ridges (convex portions) 201 of the first waveguide region C ₁ with a width in the above range. Further, the present invention is not limited to such a narrow stripe structure, but can be applied to stripes having a stripe width of 5 μm or more. Further, in the configuration in which the _first waveguide region C1 is disposed at the end of the waveguide, the second waveguide is mainly used to control the optical characteristics of the laser light with the _first waveguide region C1. stripe width of the region C ₂ can be freely set relatively.

In the laser device using the nitride semiconductor of the present invention, the end face of the _first waveguide region C ₁ is a resonator face (outgoing face), so that the controllability of the transverse mode, which has not been obtained conventionally, F. P. A laser element having an excellent aspect ratio and excellent element reliability can be obtained. As described above, etching is performed deeper than the active layer, and the first waveguide region C ₁ is provided on the exit surface side of the resonator surface, so that the light emitted from the laser element is controlled immediately before the emission. This makes it possible to obtain laser beams having spots of various shapes and sizes.

Here, the active layer may have a quantum well structure, in which case either a single quantum well or a multiple quantum well may be used. A quantum well structure is preferably used, so that a laser element and an edge emitting element having excellent light emission efficiency and high output can be obtained. Further, the stripe-shaped second ridge (convex portion) 202 for forming the _second waveguide region C ₂ is formed by etching at a depth that does not reach the active layer. In this specification, the fact that the second ridge 202 is positioned above the active layer means that the second ridge 202 is formed by etching at a depth that does not reach the active layer. That is, the stripe-shaped second ridge (convex portion) 202 constituting the _second waveguide region C ₂ is positioned above the interface between the active layer and the layer provided in contact therewith. Provided.

As described above, a nitride semiconductor containing In is preferably used as the active layer of the nitride semiconductor. Specifically, Al _x In _y Ga _1-xy N (0 ≦ x ≦ 1, 0 It is preferable to use a nitride semiconductor represented by <y ≦ 1, x + y ≦ 1). In this case, the active layer having the quantum well structure means that the nitride semiconductor shown here is preferably used as the well layer. In the wavelength region from near ultraviolet to visible light green (380 nm to 550 nm), In _y Ga _1-y N (0 <y <1) is preferably used, and longer wavelength region (red). However, similarly, In _y Ga _1-y N (0 <y <1) can be used, and at this time, a desired wavelength can be obtained mainly by changing the In mixed crystal ratio y. In a short wavelength region of 380 nm or less, since the wavelength corresponding to the forbidden band width of GaN is 365 nm, the band gap energy needs to be approximately the same as or larger than that of GaN. For example, Al _x In _y Ga _1-xy N (0 <x ≦ 1, 0 <y ≦ 1, x + y ≦ 1) is used.

  When the active layer has a quantum well structure, the specific well layer thickness is in the range of 10 to 300 mm, preferably in the range of 20 to 200 mm to reduce Vf and the threshold current density. Can be made. Further, from the viewpoint of crystal growth, when the thickness is 20 mm or more, a layer having a relatively uniform film quality without large unevenness in film thickness can be obtained. It becomes possible. The number of well layers in the active layer is not particularly limited and is 1 or more. At this time, when the number of well layers is 4 or more, if the thickness of each layer constituting the active layer increases, the active layer Since the entire film thickness is increased and Vf is increased, it is preferable to keep the film thickness of the active layer low by setting the film thickness of the well layer to 100 mm or less. In high-power LDs and LEDs, it is preferable that the number of well layers is 1 or more and 3 or less because an element with high luminous efficiency tends to be obtained.

The well layer may be doped with p-type or n-type impurities (acceptor or donor), or may be undoped or non-doped. However, when a nitride semiconductor containing In is used as the well layer, the crystallinity tends to deteriorate as the n-type impurity concentration increases. Therefore, the well layer should have a good crystallinity by keeping the n-type impurity concentration low. Is preferred. Specifically, the well layer is preferably grown undoped in order to maximize the crystallinity, and specifically, the n-type impurity concentration should be 5 × 10 ¹⁶ / cm ³ or less. preferable. The state where the n-type impurity concentration is 5 × 10 ¹⁶ / cm ³ or less is a state where the impurity concentration is extremely low. In this state, it can be said that the well layer is substantially free of n-type impurities. In addition, when the n-type impurity is doped in the well layer, if the n-type impurity concentration is doped in the range of 1 × 10 ¹⁸ or less and 5 × 10 ¹⁶ or more, the deterioration of crystallinity is suppressed and the carrier concentration is reduced. Can be high.

The composition of the barrier layer is not particularly limited, and a nitride semiconductor similar to the well layer can be used. Specifically, a nitride semiconductor containing In such as InGaN having a lower In mixed crystal ratio than the well layer, or A nitride semiconductor containing Al such as GaN or AlGaN can be used. At this time, the barrier layer needs to have a larger band gap energy than the well layer. As a specific composition, In _β Ga _1-β N (0 ≦ β <1, α> β), GaN, Al _γ Ga _1-γ N (0 <γ ≦ 1) or the like can be used. the _{in β Ga 1-β N (} 0 ≦ β <1, α> β), the barrier layer can be formed with good crystallinity by using GaN. This is because, when a well layer made of a nitride semiconductor containing In is directly grown on a nitride semiconductor containing Al such as AlGaN, the crystallinity tends to be lowered and the function of the well layer tends to be deteriorated. Because. When Al _γ Ga _1-γ N (0 <γ ≦ 1) is used as the barrier layer, a barrier layer containing Al is provided on the well layer, and the In _β Ga _{1− β N (0 ≦ β <1} , α> β), can be avoided this by a barrier layer of a multilayer film using the barrier layer of GaN. As described above, in the multiple quantum well structure, the barrier layer sandwiched between the well layers is not limited to one layer (well layer / barrier layer / well layer). As the barrier layer, a plurality of barrier layers having different compositions and impurity amounts may be provided, such as “well layer / barrier layer (1) / barrier layer (2) /... / Well layer”. Here, α is the In composition ratio of the well layer, and it is preferable that the In composition ratio β of the barrier layer is smaller than that of the well layer, with α> β.

The barrier layer may be doped with an n-type impurity or may be non-doped, but is preferably doped with an n-type impurity. At this time, the n-type impurity concentration in the barrier layer is preferably at least 5 × 10 ¹⁶ / cm ³ or more, and the upper limit is 1 × 10 ²⁰ / cm ³ . Specifically, for example, in the case of an LED that does not require high output, it is preferable to have an n-type impurity in the range of 5 × 10 ¹⁶ / cm ^{3 to} 2 × 10 ¹⁸ / cm ³ , For high-power LEDs and high-power LDs, a range of 5 × 10 ¹⁷ / cm ^{3 to} 1 × 10 ²⁰ / cm ³ , preferably a range of 1 × 10 ¹⁸ / cm ^{3 to} 5 × 10 ¹⁹ / cm ³ In the case of doping in such a high concentration, it is preferable that the well layer is substantially free of n-type impurities or is grown undoped. At this time, a normal LED, a high output LED (high power LED), and a high output LD (such as an LD of 5 to 100 mW output) have different n-type impurity amounts. This is because a high carrier concentration is required to obtain a high output when driven with a large current. By doping in the preferred range, as described above, it is possible to inject high concentration carriers with good crystallinity.

On the contrary, in the case of nitride semiconductor elements such as low output LDs and LEDs that are not high output, some barrier layers in the active layer are doped with n-type impurities, or all barrier layers are used. It may be substantially free of n-type impurities. When doping an n-type impurity, all the barrier layers in the active layer may be doped, or some barrier layers may be doped. When some of the barrier layers are doped with n-type impurities, it is preferable to dope the barrier layers disposed on the n-type layer side in the active layer, and specifically, n is counted from the n-type layer side. Doping the second barrier layer B _n (n = 1, 2, 3...) Allows electrons to be efficiently injected into the active layer, resulting in an element having excellent light emission efficiency and internal quantum efficiency. This applies not only to the barrier layer but also to the well layer. When both are doped, the n-th barrier layer B _n (n = 1, 2, 3... Counting from the n-type layer). ), Doping the m-th well layer W _m (m = 1, 2, 3...), That is, doping from the side closer to the n-type layer, the above-mentioned effect tends to be obtained.

  The thickness of the barrier layer is not particularly limited, and can be 500 mm or less, and more specifically, the range of 10 to 300 mm can be applied as in the case of the well layer.

  In the laser element using the nitride semiconductor of the present invention, the stacked structure includes an n-type nitride semiconductor in the first conductivity type layer and a p-type nitride semiconductor in the second conductivity type layer. Preferably, specifically, an n-type cladding layer and a p-type cladding layer are provided on each conductive type layer to constitute a waveguide. At this time, a guide layer, an electron confinement layer, or the like as described later may be provided between each cladding layer and the active layer.

(P-type cladding layer)
In the laser device using the nitride semiconductor of the present invention, a p-type cladding layer including a p-type nitride semiconductor (first p-type nitride semiconductor) is used as the second conductive type layer or the first conductive type layer. It is preferable to provide it. At this time, an n-type cladding layer including an n-type nitride semiconductor is provided in a conductive type layer different from the conductive type layer provided with the p-type cladding layer, and a waveguide is formed in the stacked structure. The nitride semiconductor used for the p-type cladding layer only needs to have a sufficient refractive index difference for confining light, and a nitride semiconductor layer containing Al is preferably used. Further, this layer may be a single layer or a multilayer film. Specifically, as shown in the embodiment, it may have a superlattice structure in which AlGaN and GaN are alternately stacked. Then, crystallinity can be made favorable, which is preferable. Further, this layer may be doped with a p-type impurity, or may be undoped. As shown in the examples, in the multilayer film layer, at least one of the layers is doped. May be. In a laser element having a long oscillation wavelength of 430 to 550 nm, the cladding layer is preferably GaN doped with a p-type impurity. Further, the film thickness is not particularly limited, but it is formed in a range of 100 to 2 μm, preferably in a range of 500 to 1 μm, and functions as a sufficient light confinement layer.

  In the present invention, an electron confinement layer and a light guide layer, which will be described later, may be provided between the active layer and the p-type cladding layer. At this time, when the light guide layer is provided, it is preferable to provide a light guide layer also between the n-type cladding layer and the active layer so that the active layer is sandwiched between the light guide layers. In this case, the SCH structure is obtained, and the Al composition ratio of the cladding layer is made larger than the Al composition ratio of the guide layer to provide a refractive index difference, so that the light is confined in the cladding layer. When the cladding layer and the guide layer are each formed of a multilayer film, the magnitude of the Al composition ratio is determined by the Al average composition.

(P-type electron confinement layer)
The p-type electron confinement layer provided between the active layer and the p-type cladding layer, preferably between the active layer and the p-type light guide layer, is a layer that also functions as confinement of carriers in the active layer. It contributes to easy oscillation by lowering the threshold current. Specifically, AlGaN is used. In particular, a more effective electron confinement effect can be obtained by providing a p-type cladding layer and a p-type electron confinement layer in the second conductivity type layer. When AlGaN is used for the p-type electron confinement layer, the function can be exhibited more reliably by doping with a p-type impurity. It has a function. The lower limit of the film thickness is at least 10 mm and preferably 20 mm. Further, the above effect can be sufficiently expected when the film thickness is 500 Å or less and the composition of Al _x Ga ₁ -xN is x is 0 or more, preferably 0.2 or more. An n-side carrier confinement layer that confines holes in the active layer may also be provided on the n-type layer side. The confinement of holes can be performed without providing an offset (difference in band cap from the active layer) as much as when confining electrons. Specifically, the same composition as the p-side electron confinement layer can be applied. Further, in order to improve the crystallinity, it may be formed of a nitride semiconductor that does not contain Al. Specifically, almost the same composition as the barrier layer of the active layer can be used. In this case, the n-side barrier layer for confining carriers is preferably disposed on the n-type layer side most in the active layer, or may be disposed in the n-type layer in contact with the active layer. Thus, the p-side and n-side carrier confinement layers are preferably provided in contact with the active layer, so that carriers can be efficiently injected into the active layer or the well layer. In this case, the layer in contact with the p-side and n-side layers may be a carrier confinement layer.

(P-type guide layer)
In the present invention, an excellent waveguide in a nitride semiconductor can be formed by providing an optical waveguide by providing a guide layer sandwiching the active layer inside the cladding layer. At this time, the thickness of the waveguide (the active layer and both guide layers sandwiching it) is specifically set to 6000 mm or less to suppress a rapid increase in the oscillation threshold current, and preferably to 4500 mm or less. With a low oscillation threshold current, continuous oscillation with a long lifetime in the fundamental mode is possible. Moreover, it is preferable to form both guide layers with substantially the same film thickness, and the film thickness of the guide layer is preferably set in the range of 100 mm to 1 μm, more preferably 500 mm to 2000 mm. A good optical waveguide can be provided. Furthermore, the guide layer is made of a nitride semiconductor, and may have a sufficient energy band gap to form a waveguide as compared with a clad layer provided on the outside thereof. Either a multilayer film may be used. In addition, as a light guide layer, it is possible to form a good waveguide by using a band gap energy that is substantially the same as that of the active layer, preferably larger than that, and in the case of a quantum well structure, The band gap energy is larger than that of the layer, and preferably larger than that of the barrier layer. Furthermore, by providing the light guide layer with a band gap energy of about 10 nm or more than the emission wavelength of the active layer, a waveguide excellent in light guiding can be formed.

Specifically, as the p-side light guide layer, it is preferable to use undoped GaN when the oscillation wavelength is 370 to 470 nm, and to use a multi-layer structure of InGaN / GaN in a relatively long wavelength region (450 μm or more). Thereby, in the long wavelength region, the refractive index in the waveguide constituted by the active layer and the light guide layer can be increased, and the refractive index difference from the cladding layer can be increased. In the short wavelength region of 370 nm or less, since the absorption edge of GaN is 365 nm, it is preferable to use a nitride semiconductor containing Al. Specifically, Al _x Ga _1-x N (0 < x <1) is preferably used, and a multilayer film made of AlGaN / GaN, a multilayer film in which these layers are alternately stacked, and a superlattice multilayer film in which each layer is a superlattice can be used. The specific structure of the n-type guide layer is the same as that of the p-type guide layer. In consideration of the energy band gap of the active layer, GaN and InGaN are used. If a multi-layered film in which InGaN and GaN are alternately stacked is provided, a preferable waveguide is obtained.

(N-type cladding layer)
In the laser element using the nitride semiconductor of the present invention, the nitride semiconductor used for the n-type cladding layer may be a refractive index difference sufficient to confine light, as in the p-type cladding layer. A nitride semiconductor layer containing Al is preferably used. This layer may be a single layer or a multilayer film. Specifically, as shown in the embodiment, it may have a superlattice structure in which AlGaN and GaN are alternately stacked. In addition, this n-type cladding layer acts as a carrier confinement layer and a light confinement layer, and in the case of a multilayer film structure, as described above, a nitride semiconductor containing Al, preferably AlGaN is grown. It is good to let them. Further, this layer may be doped with an n-type impurity or may be undoped. As shown in the embodiment, in the multilayer film layer, at least one of the layers is doped. May be. In the laser element having a long oscillation wavelength of 430 to 550 nm, the cladding layer is preferably GaN doped with an n-type impurity. Further, the film thickness is not particularly limited as in the case of the p-type cladding layer, but it is sufficient to form a film with a thickness of 100 to 2 μm, preferably with a thickness of 500 to 1 μm. Functions as a confinement layer.

  Here, in the laser element using the nitride semiconductor, the position where the stripe-shaped ridge is provided is in the nitride semiconductor layer containing Al, and the insulating film is provided on the exposed nitride semiconductor surface and the convex side surface. Good insulation is achieved, and a laser element free from leakage current can be obtained even if an electrode is provided on the insulating film. This is because the nitride semiconductor containing Al has almost no material that can make a good ohmic contact, so even if an insulating film, an electrode, or the like is provided on the surface of the semiconductor, there is almost no generation of leakage current. Is to be made. Conversely, if an electrode is provided on the surface of a nitride semiconductor that does not contain Al, an ohmic contact is likely to be formed between the electrode material and the nitride semiconductor, and the electrode is provided on the surface of the nitride semiconductor that does not contain Al via an insulating film. If the insulating film is formed, the insulating film and electrode film quality may cause leakage when the insulating film has minute holes. Therefore, in order to solve them, it is necessary to consider such as forming an insulating film with a film thickness sufficient to ensure insulation, or not covering the exposed semiconductor surface with the electrode shape and position. In the design of the structure, a great restriction is added. Also, the position where the ridge (projection) is provided becomes a problem because the nitride semiconductor surface (plane) on both sides of the ridge exposed when the ridge (projection) is formed is compared to the side surface of the ridge (projection). It occupies an extremely large area, and by ensuring good insulation on this surface, it becomes a laser element with a high degree of design freedom in which various electrode shapes can be applied and the electrode formation position can be selected relatively freely, This is extremely advantageous in the formation of ridges (convex portions). Here, as the nitride semiconductor containing Al, specifically, AlGaN or the above-described superlattice multilayer structure of AlGaN / GaN is preferably used.

Here, as the first waveguide region C ₁ and the second waveguide region C ₂ , stripe-shaped first ridges (projections) 201 and second ridges 202 are provided as shown in FIG. It is formed by removing both sides of each ridge as shown in 1 (c). The convex portion 202 is provided on the upper clad layer 7. At that time, in the region other than the convex portion, the surface / plane position where the upper clad layer 7 is exposed is the etching depth.

[electrode]
In the laser element of the present invention, the present invention is not particularly limited by the shape of the electrodes provided on the striped first ridge and the second ridge. For example, as shown in FIGS. 1 and 7 and the like, the first waveguide region C ₁ and each of the striped first ridge 201 and second ridge 202 provided as the _second waveguide region C ₂ are provided. A structure provided on almost the entire surface may be used. Further ,, for example, the second electrode only the waveguide region C ₂ is provided, it may be preferentially inject carriers into the second waveguide region C _2, the first waveguide and vice versa a structure providing an electrode only to the region C _1, may be functionally separated in the waveguide in the resonator direction.

[Insulating film]
In the laser element of the present invention, when a part of the laminated structure is removed and a stripe-shaped ridge is provided to form a resonator, the stripe side surface and the planes (convex) on both sides of the ridge are continuous. It is preferable to form an insulating film on the surface where the portion is provided. For example, after providing a stripe-shaped ridge as shown in FIG. 1, it is provided from the side surface of the ridge to the surfaces on both sides of the ridge.

  In the laser element of the present invention, when a nitride semiconductor is used, it is preferable to provide a second protective film 162 as an insulating film as shown in FIGS.

The material of the second protective film is a material other than SiO ₂ , preferably an oxide containing at least one element selected from the group consisting of Ti, V, Zr, Nb, Hf, Ta, SiN, BN, SiC, It is desirable to form at least one of AlN, and among these, it is particularly preferable to use an oxide of Zr or Hf, BN, or SiC. Some of these materials have a property of being slightly dissolved in hydrofluoric acid, but when used as an insulating layer of a laser element, the reliability tends to be considerably higher than that of SiO ₂ as a buried layer. In general, oxide thin films formed in the gas phase such as PVD and CVD are not easily converted into oxides in which the element and oxygen are equivalently reacted. Although the above elements selected in the present invention are PVD, oxides by CVD, BN, SiC, and AlN are more excellent in reliability regarding insulation than Si oxides. In addition, it is very convenient as a buried layer of a laser element when an oxide whose refractive index is smaller than that of a nitride semiconductor (for example, other than SiC) is selected. Furthermore, when the first protective film 161 is formed using Si oxide, the Si oxide is removed by hydrofluoric acid, so that the first protective film is formed only on the upper surface of the ridge as shown in FIG. 7B. A film 161 is formed, and a first protective film 161 is selectively formed by successively forming a film 161 thereon, a side surface of the ridge, planes on both sides of the ridge (etch stop layer), and a second protective film 162. When removed, a second protective film 162 having a uniform film thickness can be formed on the surface other than the upper surface of the ridge, as shown in FIG.

  The film thickness of the second protective film is specifically in the range of 500 to 1 μm, preferably in the range of 1000 to 5000 μm. The reason is that if the thickness is less than 500 mm, it is difficult to ensure sufficient insulation at the time of forming the electrode, and if it is 1 μm or more, the uniformity of the protective film is lost and a good insulating film is not obtained. . Moreover, by being in the preferable range, a uniform film having a good refractive index difference between the ridge (convex portion) and the ridge is formed.

The second protective film can also be formed of a buried layer of nitride semiconductor, semi-insulating, i-type nitride semiconductor, conductivity type opposite to the ridge of each waveguide region, for example In the first second waveguide region C ₂ , an embedded layer made of an n-type nitride semiconductor can be formed, and the embedded layer can be used as the second protective film. In addition, specific examples of the buried layer include confining light in the lateral direction by providing a refractive index difference between the ridge and a current blocking layer by using a nitride semiconductor containing Al, such as AlGaN. And a good optical characteristic as a laser element is realized by providing a difference in light absorption coefficient with a nitride semiconductor containing In. When a layer other than i-type and semi-insulating is used for the buried layer, the second waveguide region may be a buried layer of the first conductivity type different from the second conductivity type. On the other hand, in the first ridge constituting the first waveguide region, the first and second conductivity type layers are formed in a stripe shape with the active layer interposed therebetween, so that the first conductivity type layer or The regions on both sides of the first conductivity type layer and the active layer are buried layers of a second conductivity type different from the first conductivity type, and the second conductivity type layer, or the second conductivity type layer and the active layer In this region, a buried layer of the first conductivity type different from the second conductivity type is used. As described above, the buried layer may have a different layer structure in the first waveguide region and the second waveguide region. The buried layer is formed on a part of the side surface of the stripe, preferably almost the entire surface, like the second protective film. Furthermore, the buried layer is preferably formed continuously on the side surface of the ridge and the surface (plane) of the nitride semiconductor on both sides of the ridge, so that better light confinement and current confinement functions can be exhibited. . Further, after forming the buried layer, a nitride semiconductor layer is further formed on the buried layer and / or on the stripe, and a ridge constituting each waveguide region is disposed inside the device. You can also

  The resonator length of the laser element using the nitride semiconductor in the present invention is preferably in the range of 400 to 900 μm, and the drive current can be lowered by controlling the reflectance of the front and rear mirrors.

[Production method]
As described above, the laser element using the nitride semiconductor according to the present invention can realize good element characteristics, and the stripes serving as the _first waveguide region C ₁ and the second waveguide region C ₂ are as follows. By forming by this method, the stripe-shaped waveguide region in the laser element of the present invention can be manufactured with high accuracy and high yield. In addition, a highly reliable laser device can be manufactured by the following manufacturing method. Hereinafter, the manufacturing method will be described in detail.

  As shown in FIGS. 8 and 9, when manufacturing an element in which a pair of positive and negative electrodes are formed on the same surface of a different substrate, as shown in FIG. 7, an n-type contact for forming a negative electrode is used. In order to expose the layer, etching is performed up to the depth, and then etching for forming a striped waveguide region is performed.

(Method 1 of forming striped ridge (convex portion))
FIG. 5 is a schematic perspective view showing a part of a wafer on which an element structure using a nitride semiconductor is formed for explaining the steps of the electrode forming method of the present invention, and FIG. 6 is a similar view. FIG. 7 is a diagram for explaining a process after the formation of the second protective film, and FIG. 7B is a diagram for explaining the second embodiment in the present invention. 2 shows a cross-sectional view of the _second waveguide region C ₂ , and FIG. 7C shows a cross-sectional view of the _second waveguide region C _{2 in} FIG. 7D. In the manufacturing method of the present invention, as shown in FIG. 5A, after each semiconductor layer constituting the element structure is stacked, the stripe shape is formed on the contact layer 8 in the second conductivity type layer as the uppermost layer. The first protective film 161 is formed.

The first protective film 161 may be any material as long as it has a difference from the etching rate of the nitride semiconductor, regardless of the insulating property. For example, Si oxide (including SiO ₂ ), photoresist, or the like is used. Preferably, it is more soluble in acid than the second protective film in order to provide a solubility difference from the second protective film to be formed later. Select a material that has the property of being easily processed. As the acid, hydrofluoric acid is preferably used. Therefore, it is preferable to use Si oxide as a material that is easily dissolved in hydrofluoric acid. The stripe width (W) of the first protective film is adjusted to 3 μm to 1 μm. The stripe width of the first protective film 161 roughly corresponds to the stripe width of the ridge for constituting the waveguide region.

  FIG. 5A shows a state where the first protective film 161 is formed on the surface of the laminated structure. That is, the stripe-shaped first protective film as shown in FIG. 5A is formed by first forming a second protective film on almost the entire surface of the laminated structure, and then using a photolithography technique to obtain a desired shape. Is provided on the surface of the first protective film, and a stripe-shaped first protective film 161 is formed on the surface of the contact layer 8.

  Further, a lift-off method can be used to form the stripe-shaped first protective film 161 as shown in FIG. That is, a photoresist having a shape in which stripe-shaped holes are formed is formed, a first protective film is formed on the entire surface of the photoresist, and then the photoresist is dissolved and removed to contact the contact layer 8. This is a means for leaving only the first protective film 161. Rather than forming the stripe-shaped first protective film by the lift-off method, a stripe having a substantially vertical end face and a uniform shape tends to be easily obtained by etching as described above.

  Next, as shown in FIG. 5B, using the first protective film 161 as a mask, a portion where the first protective film 161 is not formed is etched from the contact layer 8 to form the first protective film. Striped ridges corresponding to the shape of the protective film are formed immediately below 161. When etching is performed, the structure and characteristics of the laser element differ depending on the position of the etch stop.

As means for etching a layer formed using a nitride semiconductor, for example, dry etching such as RIE (reactive ion etching) is used, and in order to etch the first protective film made of Si oxide, CF It is desirable to use a fluorine-based gas such as ₄ , and in the second step, Cl ₂ , CCl ₄ , SiCl, which are often used in other III-V compound semiconductors to etch a nitride semiconductor, are used. _Use of a chlorine-based gas such as ₄ is desirable because the selectivity with Si oxide can be increased.

Subsequently, as shown in FIG. 5C, a third protective film 163 is formed so as to cover a part of the stripe-shaped ridge (FIG. 5E shows the third protective film 163 in FIG. 5C). Sectional drawing of the part covered with the protective film 163 of FIG. As the third protective film 163, a generally known resist film having dry etching resistance can be used as the resist film, and specifically, a photocurable resin or the like can be used. At this time, the stripe-shaped ridge covered with the third protective film 163 becomes the second ridge 202 for constituting the _second waveguide region C ₂ and is not covered with the third protective film. Then, a first ridge (projection) 201 for forming the first waveguide region C ₁ is formed. Using the third protective film 163 and the first protective film 161 thus provided as a mask, etching is performed at a depth reaching the cladding layer 5 in the laminated structure in which those masks are not formed, Striped ridges (first ridges) having different depths are formed. Thereafter, the third protective film 163 is removed, and the first protective film 161 is left on the first ridge and the second ridge as shown in FIG. 5D (FIG. Sectional drawing of the 2nd ridge part in d).

  Next, as shown in FIG. 7A, a second protective film 162 which is made of a material different from that of the first protective film 161 and has an insulating property is etched into a striped ridge (convex portion) side surface and etched. The exposed layer (in FIG. 7, the clad layers 5 and 7) is formed on the plane. The first protective film 161 is formed of a material different from that of the second protective film 162, and the first protective film 161 and the second protective film 162 have selectivity with respect to the etching means. Therefore, if only the first protective film 161 is removed later with, for example, hydrofluoric acid, the upper surface of the ridge is opened as shown in FIG. 7B, and the surfaces of the cladding layers 5 and 7 (exposed by etching). The second protective film 162 can be formed continuously on both the plane of the nitride semiconductor and the side surface of the ridge. In this way, high insulation can be maintained by forming the second protective film 162 continuously. In addition, when the second protective film 162 is continuously formed from above the first protective film 161, it can be formed with a uniform film thickness on the cladding layers 5, 7, and thus non-uniform film thickness hardly occurs. Also, current concentration due to non-uniform film thickness does not occur. In this process, since the etch stop is in the middle of the clad layers 5 and 7, the second protective film 162 is formed on the plane (exposed upper surface) of the clad layers 5 and 7 in FIG. Needless to say, when the etch stop is set below the cladding layers 5 and 7, the second protective film is naturally formed on the plane of the etched layer.

  In the next step, as shown in FIG. 7B, the first protective film 161 is removed by lift-off. Thereafter, an electrode is formed on the second protective film 162 and the contact layer 8 so as to be in electrical contact with the contact layer 8. In the present invention, since the second protective film having the stripe-shaped opening is formed on the ridge first, when forming this electrode, the electrode is formed only on the contact layer having a narrow stripe width. There is no need, and a continuous electrode can be formed in a large area on the second insulating film from the contact layer exposed in the opening. Accordingly, an electrode material that also serves as an ohmic contact can be selected, and an electrode that serves as an ohmic contact and an electrode that can serve as a bonding electrode can be formed together.

In a laser element using a nitride semiconductor, when forming a striped waveguide region, dry etching is used because etching is difficult by wet etching. In dry etching, since the selectivity between the first protective film and the nitride semiconductor is regarded as important, SiO ₂ is used as the first protective film. However, if it is also used for the second protective film formed on the top surface of the SiO ₂ etch-stopped layer, the insulation is insufficient and the first protective film is the same material, so that only the first protective film is used. It becomes difficult to remove. For this reason, in the present invention, the second protective film is made of a material other than SiO ₂ to ensure selectivity with the first protective film. In addition, since the nitride semiconductor is not etched after the second protective film is formed, the second protective film is not a problem with respect to the etching speed with the nitride semiconductor.

(Stripe-shaped convex part forming method 2)
FIG. 16 is a schematic perspective view showing a part of a wafer on which an element structure using a nitride semiconductor is formed, for explaining the steps of another method for manufacturing a semiconductor laser according to the present invention. Each step is performed in substantially the same manner as the above-described forming method 1, but here, the end face of the resonator is formed at the same time as etching is performed to expose the n-type contact layer forming the negative electrode. That is, the order in which each part is formed is different from the formation method 1. In the formation method 2, the n-type contact layer is first exposed (FIG. 16A). At this time, the resonator end face is also formed at the same time. Next, the step of forming the stripe-shaped ridge (projection), the first and second waveguide regions, and the electrode is performed in the same manner as in the formation method 1 (FIG. 16B). Thus, by first forming the resonator end face by etching, it is possible to cope with a case where a good resonator end face cannot be obtained by cleavage.

As described above, in the laser element of the present invention, the stripe-shaped second ridge (convex portion) 202 for forming the _first waveguide region C ₁ and the second waveguide region C ₂ is made efficient. The electrode can be formed on the surface of the ridge of the laminated structure.

(Etching means)
In the manufacturing method of the present invention, as the nitride semiconductor etching means, for example, when dry etching such as RIE (reactive ion etching) is used, the first protective film made of Si oxide frequently used in the first step It is desirable to use a fluorine compound-based gas such as CF ₄ for etching, and in the second step, it is often used in other III-V compound semiconductors to etch nitride semiconductors. It is desirable to use a chlorine-based gas such as Cl ₂ , CCl ₄ , or SiCl ₄ because the selectivity with Si oxide can be increased.

(Chip)
FIG. 17 is a schematic cross-sectional view for explaining a cutting position when the laminated structure formed on the wafer as described above is formed into chips. FIG. 17A shows a case where only the substrate is divided, and FIG. 17B shows a case where the substrate and the n-type layer are divided. In addition, the region where the pair of electrodes is formed is set as one unit, and I, II, III, and IV from the left as shown in the figure. In FIG. 17A, Ia, IIa, and IVa have the first waveguide region directed to the right side, and IIIa directed to the opposite. In FIG. 17B, Ib, IIb, and IIIb have the first waveguide region directed to the right side, and IVb directed to the opposite side. In addition, a suitable arrangement can be selected for such an arrangement before division according to a process or the like.

  By dividing at the AA cutting position, the resonator end face formed by etching can be left as it is. In I and II, after dividing along the AA cut surface and further dividing along the BB cut surface, the resonator end surface on the light reflection side becomes a cleaved surface. Further, II is divided by the DD cut surface, so that the resonator end surface on the light emission side also becomes a cleavage plane. Further, when divided by the CC cut plane, the resonator end faces on the light reflection side of IIIa and IVa are simultaneously formed as cleavage planes. Similarly, when divided by the EE cut surface, the resonator end surfaces on the light emission side of IIIb and IVb are simultaneously formed as cleavage surfaces. Thus, the end face and the resonator face of the element can be an etching end face or a cleaved end face depending on the cutting position.

  Here, in order to ensure that only the substrate exists between the resonator end surface of Ia and the resonator end surface of IIb as between Ia and IIa shown in FIG. 17A, FIG. It can be obtained by further etching the resonator end face formed by etching as shown in FIG. The reason for etching up to the substrate in this way is to prevent the semiconductor layer from cracking during the division. Here, if the substrate is exposed by one etching without passing through FIG. 16A, the etching surface in the vicinity of the active layer exposed first becomes rough because the etching time is long, and a good resonator is obtained. It becomes difficult to obtain the end face. However, by performing the etching process up to the n-type layer as shown in FIG. 16A and then the etching up to the substrate in two steps, a good resonator end face can be obtained, and , Can also be divided easily. FIG. 16D is a view obtained by cutting FIG. 16C at the position of the arrow, but a protruding region such as D in the figure is generated by performing the etching process twice as described above. When etching up to the substrate, it is necessary to reduce the protrusion of the protrusion region D in the light emission direction. This is because when the width of D (the length of protrusion) is increased, the light emitted from the light exit surface is blocked and good F.D. F. P. It is because it becomes difficult to obtain. In this case, there is no problem as long as D on the end face on the light emission side is small.

(Reflective film)
FIG. 18 is a schematic diagram for explaining a method of forming a reflective film provided on the end face of the resonator. As shown in FIG. 18, the semiconductor divided into bars is placed so that the end surface on the light reflecting side or the end surface on the light emitting side faces the material of the reflecting film, and the reflecting film is formed by a method such as sputtering. In this way, a high-quality reflective film that has a uniform quality and is unlikely to deteriorate even when it is formed into a multilayer film by dividing it into bars and forming the divided surface so as to face the raw material of the reflective film and forming it by sputtering. Can be formed. Such a reflective film is more effective when used in an element that requires high output. In particular, a reflective film that can withstand high output can be obtained by using a multilayer film. The reflection film on the end face can be formed by sputtering from the upper part of the electrode or by wrapping around the resonator end face on the side face. However, in that case, although there is a merit that the process of forming a bar shape and facing the end face upward can be omitted, it is formed so as to wrap around from the lateral direction to the end face, so a uniform film, particularly a multilayer film Is difficult to obtain, and the film quality is slightly inferior. Such a reflective film may be provided on both the light reflecting end face and the light emitting end face, or only one of them or a different material may be used.

  In the present invention, other device structures such as active layers and cladding layers are not particularly limited, and various layer structures can be used. Specific embodiments of the device structure include, for example, the device structures described in the examples described later. Moreover, an electrode etc. are not specifically limited, A various thing can be used. Further, the nitride semiconductor of each layer used as the laser element is not particularly limited to the composition, and is expressed by the above-described composition formula (InbAlcGa1-b-cN, 0 ≦ b, 0 ≦ d, b + d <1). A nitride semiconductor can be used.

  In the present invention, a nitride semiconductor is grown by MOVPE, MOCVD (metal organic chemical vapor deposition), HVPE (halide vapor deposition), MBE (molecular beam vapor deposition) or the like. All methods known to can be applied.

Examples of the present invention will be described below.

  The following examples are laser elements using nitride semiconductors, but the laser element of the present invention is not limited to this, and it goes without saying that the present invention can be implemented on various semiconductors.

[Example 1]
Hereinafter, the laser element of Example 1 will be described. Specifically, as in Example 1, the laser device comprising the second waveguide region C ₂ having a sectional structure shown in FIG. 8, the first waveguide region C ₁ having the sectional structure shown in FIG. 9 Is made.

Here, in the first embodiment, a sapphire substrate, that is, a heterogeneous substrate different from a nitride semiconductor is used as the substrate, but a substrate made of a nitride semiconductor such as a GaN substrate may be used. Here, as the heterogeneous substrate, for example, an insulating substrate such as sapphire or spinel (MgA1 ₂ O ₄ ) whose main surface is any one of the C-plane, R-plane, and A-plane, SiC (6H, 4H, 3C). , ZnS, ZnO, GaAs, Si, and an oxide substrate lattice-matched with the nitride semiconductor can be used. Preferable heterogeneous substrates include sapphire and spinel. Further, the heterogeneous substrate may have a surface inclined from a low index surface that is normally used (off-angle). In this case, if a substrate that is off-angled stepwise is used, the growth of the underlying layer made of gallium nitride is performed. Can be grown with good crystallinity.

  Further, in the case of using a heterogeneous substrate, after growing a nitride semiconductor serving as an underlayer on the heterogeneous substrate and before forming an element structure, the heterogeneous substrate is removed by a method such as polishing to remove only the underlayer. The element structure may be formed using the base layer as a single substrate of a nitride semiconductor, or the heterogeneous substrate may be removed after the element structure is formed.

As shown in FIG. 8, when a heterogeneous substrate is used, an element structure made of a good nitride semiconductor can be formed by forming an element structure after forming a buffer layer and a base layer. Here, FIG. 8 is a sectional view for explaining the element structure in the _second waveguide region C ₂ , and FIG. 9 is a sectional view for explaining the element structure in the _first waveguide region C ₁ .

(Buffer layer 102) In Example 1, first, a heterogeneous substrate 101 made of sapphire having a 2 inch φ and C-plane as a main surface was set in a MOVPE reaction vessel, and the temperature was set to 500 ° C., and trimethylgallium (TMG) was used. ), And using ammonia (NH ₃ ), a buffer layer made of GaN is grown to a thickness of 200 mm.

(Underlayer 103) After growing the buffer layer 102, the temperature is set to 1050 ° C., and a nitride semiconductor layer 103 made of undoped GaN is grown to a thickness of 4 μm using TMG and ammonia. This layer is formed as a base layer (growth substrate) for forming an element structure. In addition, a nitride semiconductor grown by ELOG (Epitaxially Laterally Overgrowth) can be used as the underlayer, and thus a nitride semiconductor with better crystallinity can be grown. ELOG growth is a general term for growth methods involving lateral growth. For example, after a nitride semiconductor layer is grown on a heterogeneous substrate, a protective film on which the nitride semiconductor is difficult to grow is formed on the surface. In this growth method, a nitride semiconductor is newly grown from the surface of a nitride semiconductor that is formed in stripes at regular intervals and exposed between the protective films, thereby covering the entire substrate with the nitride semiconductor. That is, when the mask region where the mask is formed and the non-mask region where the nitride semiconductor is exposed are alternately formed and the nitride semiconductor is grown again from the surface of the nitride semiconductor exposed in the non-mask region, What has been grown in the thickness direction grows in the lateral direction to cover the entire substrate so as to cover the mask region as the growth proceeds.

  In addition, as an ELOG growth, in the nitride semiconductor layer first grown on a different substrate, an opening is provided so that the substrate surface is exposed, and the nitride semiconductor laterally extends from the nitride semiconductor located on the side surface of the opening. There is also a method of forming a film by growing the film.

  In the present invention, these various types of ELOG growth can be used. When a nitride semiconductor is grown by using these ELOG growth methods, the nitride semiconductor formed by lateral growth has good crystallinity. Therefore, there is an advantage that a nitride semiconductor layer having good crystallinity as a whole can be obtained.

  Next, the following layers constituting the element structure are stacked on the base layer made of a nitride semiconductor.

(N-type contact layer 104)
First, an n-type contact layer 104 made of GaN doped with 1 × 10 ¹⁸ / cm ³ of Si at 1050 ° C. using TMG, ammonia, and silane gas as an impurity gas on the obtained nitride semiconductor substrate (underlayer) 103. The film is grown with a thickness of 4.5 μm.

(Crack Prevention Layer 105) Next, using TMG, TMI (trimethylindium), and ammonia, the temperature is set to 800 ° C., and the crack prevention layer 105 made of In _0.06 Ga _0.94 N is grown to a thickness of 0.15 μm. This crack prevention layer can be omitted.

(N-type cladding layer 106) Next, the temperature is set to 1050 ° C., and TMA (trimethylaluminum), TMG and ammonia are used as source gases, and an A layer made of undoped AlGaN is grown to a thickness of 25 mm, , TMA is stopped, silane gas is used as an impurity gas, and a B layer made of GaN doped with Si at 5 × 10 ¹⁸ / cm ³ is grown to a thickness of 25 mm. Then, this operation is repeated 160 times to laminate the A layer and the B layer, and the n-type cladding layer 106 made of a multilayer film (superlattice structure) having a total film thickness of 8000 mm is grown. At this time, if the Al mixed crystal ratio of undoped AlGaN is in the range of 0.05 or more and 0.3 or less, a difference in refractive index that sufficiently functions as a cladding layer can be provided.

(N-type light guide layer 107) Next, at the same temperature, TMG and ammonia are used as source gases, and an n-type light guide layer 107 made of undoped GaN is grown to a thickness of 0.1 μm. The n-type light guide layer 107 may be doped with n-type impurities.

(Active layer 108) Next, the temperature was set to 800 ° C., TMI (trimethylindium), TMG, and ammonia were used as source gases, silane gas was used as an impurity gas, and In _0.05 doped with Si at 5 × 10 ¹⁸ / cm ^3. A barrier layer made of Ga _0.95 N is grown to a thickness of 100 mm. Subsequently, silane gas is stopped and a well layer made of undoped In _0.1 Ga _0.9 N is grown to a thickness of 50 mm. This operation is repeated three times to grow a multiquantum well structure (MQW) active layer 108 having a total film thickness of 550 し た which is laminated so that the last is a barrier layer.

(P-type electron confinement layer 109) Next, TMA, TMG, and ammonia are used as source gases at the same temperature, Cp ₂ Mg (cyclopentadienyl magnesium) is used as an impurity gas, and Mg is 1 × 10 ¹⁹ / the p-type electron confinement layer 109 made of cm ³ doped with AlGaN is grown to the thickness of 100 Å. Although this layer is not necessarily provided, it functions as electron confinement and contributes to lowering the threshold.

(P-type light guide layer 110) Next, the temperature is set to 1050 ° C., TMG and ammonia are used as source gases, and the p-type light guide layer 110 made of undoped GaN is grown to a thickness of 750 mm.

The p-type light guide layer 110 is grown as undoped, but due to the diffusion of Mg from the p-type electron confinement layer 109, the Mg concentration becomes 5 × 10 ¹⁶ / cm ³ and exhibits p-type. This layer may be intentionally doped with Mg during growth.

(P-type cladding layer 111) Subsequently, a layer made of undoped Al _0.16 Ga _0.84 N is grown at 1050 ° C. to a thickness of 25 mm, and then TMA is stopped, and a layer made of Mg-doped GaN using Cp ₂ Mg. By repeating this process, a p-side cladding layer 111 made of a superlattice layer having a total film thickness of 0.6 μm is grown. When the p-side cladding layer is made of a superlattice in which at least one nitride semiconductor layer containing Al is included and nitride semiconductor layers having different band gap energies are stacked, impurities are doped in a large amount in either one of the layers. The so-called modulation doping tends to improve the crystallinity. However, in the present invention, both may be similarly doped. The cladding layer 111 preferably has a nitride semiconductor layer containing Al, preferably a superlattice structure containing Al _x Ga _1-X N (0 <X <1), and more preferably GaN and AlGaN are stacked. A superlattice structure is adopted. By making the p-side cladding layer 111 a superlattice structure, the Al mixed crystal ratio as the entire cladding layer can be increased, so that the refractive index of the cladding layer itself can be decreased, and further the band gap energy can be increased. This is very effective in reducing the threshold. Furthermore, since the superlattice is used, the number of pits generated in the cladding layer itself can be reduced as compared with the case where the superlattice is not used.

(P-type contact layer 112) Finally, the p-side contact layer 112 made of p-type GaN doped with 1 × 10 ²⁰ / cm ^{3 of} Mg on the p-side cladding layer 111 at 1050 ° C. with a thickness of 150 mm. Grow. The p-side contact layer can be composed of p-type In _X Al _Y Ga _1-XY N (0 ≦ X, 0 ≦ Y, X + Y ≦ 1), and preferably a p electrode if Mg-doped GaN is used. The most preferred ohmic contact with 20 is obtained. Since the contact layer 112 is a layer for forming an electrode, a high carrier concentration of 1 × 10 ¹⁷ / cm ³ or more is desirable. If it is lower than 1 × 10 ¹⁷ / cm ^3, it tends to be difficult to obtain a preferable ohmic with the electrode. Furthermore, when the composition of the contact layer is GaN, a preferable ohmic with the electrode material is easily obtained. After the completion of the reaction, the wafer is annealed in a reaction vessel at 700 ° C. in a nitrogen atmosphere to further reduce the resistance of the p-type layer.

After growing the nitride semiconductor and laminating the layers as described above, the wafer is taken out from the reaction vessel, and a protective film made of SiO ₂ is formed on the surface of the uppermost p-type contact layer, and RIE (reactive ions) is formed. It etched with SiCl ₄ gas using the etching), as shown in FIG. 8, to expose the surface of the n-type contact layer 104 for forming the n electrode. Thus, SiO ₂ is optimal as a protective film for deep etching of the nitride semiconductor. Further, the n-type contact layer 104 may be exposed, and at the same time, the active layer end face serving as the resonator face may be exposed, and the etching end face may be used as the resonator face.

Next, a method for forming the _first waveguide region C ₁ and the second waveguide region C ₂ as the above-described stripe-shaped waveguide regions will be described in detail. First, a first protective film made of Si oxide (mainly SiO ₂ ) having a thickness of 0.5 μm was formed on almost the entire surface of the uppermost p-type contact layer (upper contact layer) 8 by a PVD apparatus. Thereafter, patterning is performed to form a first protective film 161 (see FIG. 5A used in the description of the embodiment). Here, the patterning of the first protective film 161 is performed by a photolithography technique and an RIE (reactive ion etching) apparatus using CF ₄ gas. Next, using the first protective film 161 as a mask, the p-type contact layer 112 and a part of the p-type cladding layer 111 are removed so that the p-type cladding layer 111 remains thin on both sides of the mask. A stripe-shaped convex portion is formed above the layer 3 (see FIG. 5B used in the description of the embodiment). As a result, the second ridge 202 for forming the second waveguide region C ₂ is formed. At this time, the second ridge is etched to a depth at which the thickness of the p-type cladding layer 111 is 0.01 μm by etching a part of the p-side contact layer 112 and the p-side cladding layer 111. Is formed.

  Next, after the stripe-shaped second ridge is formed, a photoresist film is formed as the third protective film 163 except for a part of the second ridge (the portion constituting the first waveguide region). (See FIG. 5C used in the description of the embodiment). Note that the first protective film 161 remains formed on the upper surface of the convex portion of the portion forming the second waveguide region and the upper surface of the convex portion located in the portion constituting the first waveguide region. ing.

Subsequently, the wafer is transferred to an RIE (reactive ion etching) apparatus, and the third protective film 163 and the first protective film 161 are used as a mask to form the first waveguide region in the portion where the first waveguide region is formed using SiCl ₄ gas. By etching the both sides of one protective film 161 at a depth at which the n-type clad layer 106 is exposed, a stripe-shaped first ridge constituting the _first waveguide region C ₁ is formed. At this time, the formed striped first ridge is formed by etching to a depth at which the film thickness of the n-type cladding layer 106 on both sides of the first ridge is 0.2 μm.

  Next, the third protective film 163 is removed.

Further, the wafer on which the _first waveguide region C ₁ and the second waveguide region C ₂ are formed is transferred to a PVD apparatus, and a second protective film 162 made of Zr oxide (mainly ZrO ₂ ) is formed on the second protective film 162. On the first protective film 161, on the side surfaces of the first and second ridges, and on the p-type cladding layer 111 and the n-type cladding layer 106 exposed by etching, a thickness of 0.5 μm is continuously formed ( FIG. 7A used in the description of the embodiment).

After the formation of the second protective film 162, the wafer is heat-treated at 600 ° C. When the second protective film is formed of a material other than SiO _{2 in} this way, after the formation of the second protective film, it is 300 ° C. or higher, preferably 400 ° C. or higher, and below the decomposition temperature of the nitride semiconductor (1200 The second protective film can be hardly dissolved in the material (hydrofluoric acid) that dissolves the first protective film by performing the heat treatment at a temperature of ° C. Therefore, it is desirable to add this heat treatment step.

Next, the wafer is immersed in hydrofluoric acid to remove the first protective film 161 (lift-off method). As a result, the first protective film 161 provided on the p-type contact layer 112 is removed, and the p-type contact layer 112 is exposed. As described above, the side surfaces of the stripe-shaped first and second ridges (projections) 201 and 202 provided in the _first waveguide region C ₁ and the second waveguide region C ₂ , and continuous thereto. The second protective film 162 is formed on the planes on both sides of the ridge (the surface of the p-type cladding layer 111 located on both sides of the second ridge and the surface of the n-type cladding layer located on both sides of the first ridge). (See FIGS. 7B and 7C used in the description of the embodiment). Subsequently, in a region where the n-electrode 121 is formed, etching is performed at a depth reaching the n-type contact layer 104 to expose the surface of the n-type contact layer 104 for forming the n-type electrode 121 (in the embodiment). FIG. 7C used in the description).

Thus, after the first protective film 161 provided on the p-type contact layer 112 is removed, as shown in FIG. 8, the Ni / A p-electrode 120 made of Au is formed. However, the p-electrode 120 has a stripe width of 100 μm and is formed over the second protective film 162 as shown in FIG. At this time, the p-electrode 120 is formed only in the _second waveguide region C2 in the first embodiment in the stripe direction. Further, in the first embodiment, the p-electrode 120 is formed with a length that does not reach both ends of the _second waveguide region C2. After the formation of the second protective film 162, an n electrode 21 made of Ti / Al is formed in a direction parallel to the stripes on the surface of the n-side contact layer 104 that has already been exposed.

Next, a region for providing the extraction electrode on the p and n electrodes is masked to form a dielectric multilayer film 164 made of SiO ₂ and TiO ₂ . Then, by removing the mask, an opening for opening the p and n electrodes is formed in the dielectric multilayer film 164, and Ni—Ti—Au (1000Å) is formed on the p and n electrodes through the opening. Extraction (pad) electrodes 122 and 123 made of −1000 Å−8000 Å are formed. In Example 1, the width of the active layer 108 in the _second waveguide region C2 is 200 μm (width in the direction perpendicular to the resonator direction). The guide layer is also formed with the same width.

After forming the n-electrode and the p-electrode, etching is further performed until the substrate is exposed, and a resonator surface is provided at the ends of the _first waveguide region C ₁ and the second waveguide region C ₂ .

In the laser element of Example 1, the total length of the resonator was 650 μm, and the first waveguide region C ₁ was formed so as to include one resonance end face and to have a total length of 5 μm. Accordingly, the second waveguide region C ₂ includes the other end face and has a total length of 645 μm. Then, a dielectric multilayer film made of SiO ₂ and TiO ₂ was formed on the cavity end face as an etching surface. After that, the sapphire substrate of the wafer is polished to 70 μm, divided into bars from the substrate side in the direction perpendicular to the stripe-shaped electrodes, and the bar-shaped wafer is further divided into individual elements. obtain.

  In Example 1, the resonator surface was formed by forming a dielectric multilayer film on the etching surface. However, as a method for forming the resonance surface, the (1 1-0 0) M plane, which is a GaN cleavage plane, is used. Alternatively, a method may be used in which the wafer is divided into bars and its surface is used as a resonator surface.

In the laser device of Example 1 fabricated as described above, continuous oscillation with an oscillation wavelength of 405 nm was confirmed at room temperature at a threshold of 2.0 kA / cm ² and an output of 30 mW. F. In P, a good beam can be obtained, and the aspect ratio is 1.5, which is sufficiently satisfactory as a light source for an optical disc system. Such an excellent characteristic is that the width of the convex portion of the _first waveguide region C1 on the emission side is appropriately adjusted regardless of the stripe width of the _second waveguide region C2 that mainly functions as a gain region. This is because of the characteristic action of the present invention that the laser beam having desired optical characteristics can be extracted. In addition, the laser element of Example 1 has characteristics suitable as a reading / writing light source for an optical disc system without moving in a transverse mode in an optical output range of 5 to 30 mW. In addition, when driving at 30 mW, an excellent laser element can be obtained in the same manner as a conventional refractive index guided laser element.

Further, in the first embodiment, as shown in FIG. 7C, the p-electrode may be provided with a length covering (covering) the _first waveguide region C 1. The laser device has excellent beam characteristics, and has a long device life.

[Example 2]
In Example 1, a laser element is obtained in the same manner as in Example 1 except that the length of the _first waveguide region C ₁ is set to 1 μm. In order to form the _first waveguide region C ₁ as short as described above, in the first embodiment, the stripe-shaped first ridge is longer than the actually obtained resonator length (for example, several tens μm to After the formation, a resonator surface is formed by etching or dividing the substrate at a position where the _first waveguide region C ₁ has a desired length. For this reason, it is difficult to stably form the shape of the second ridge 201 as compared with the first embodiment, but it is possible to control the transverse mode satisfactorily even with this length, and the first waveguide. Since the region becomes shorter, the device life is slightly better than that of the first embodiment.

[Example 3]
The semiconductor laser device of Example 3 is configured in the same manner as Example 1 except that the _first waveguide region C ₁ having a length of 5 μm is formed at both ends (see FIG. 4B). That is, in the laser device of the third embodiment, the second waveguide region C ₂ is arranged in the central portion, the first waveguide region C ₁ is disposed on both sides of the first waveguide region C ₁ Each resonator includes a resonance end face. The laser element of Example 3 configured as described above has an F.F. F. P. The aspect ratio is almost the same as that of the first embodiment.

[Example 4]
In the first embodiment, the second ridge (projection) 202 for forming the _second waveguide region C ₂ is left on the both sides of the second ridge so that a p-type guide layer having a thickness of 500 mm remains. The structure is the same as in Example 1 except that it is formed by etching. The obtained laser element tends to have a lower threshold current than that of the first embodiment, but a beam characteristic that is almost as good as that of the first embodiment can be obtained.

[Example 5]
The semiconductor laser device of Example 5 is the same as Example 1 except that an inclined surface is provided between the _first waveguide region C ₁ and the second waveguide region C _{2 in} Example 1. Configure (see FIG. 4A).

That is, in Example 5, at the boundary between the _first waveguide region C ₁ and the second waveguide region C ₂ , the surface of the n-type cladding layer 106 positioned on both sides of the first ridge and the second The etching cross section formed between the surface of the p-type cladding layer 111 located on both sides of the ridge is inclined so as to be 90 ° or more with respect to the surface of the n-type cladding layer 106.

  The laser device manufactured in this way may have variations in device characteristics as compared with the first embodiment, but the effect of the present invention that a good FFP can be obtained and the reliability can be improved is obtained. It is done.

[Example 6]
As shown in FIG. 13, the semiconductor laser device of Example 6 is provided with a _third waveguide region C ₃ provided between the _first waveguide region C ₁ and the second waveguide region C _2. It is produced in the same manner as in Example 1. That is, in the laser element of Example 6, after forming the second ridge (projection) 202 at a depth reaching the second conductivity type layer (p-type cladding layer 111), the first conductivity type layer is formed. when in (n-type cladding layer 106) etched until formation of a first ridge, forms the third waveguide region C ₃ in which α angle formed between the resonator direction has a side surface 204 which is 20 ° at the same time . In this manner, the laser device of Example 6 having the _third waveguide region C ₃ in addition to the _first waveguide region C ₁ and the second waveguide region C ₂ is manufactured. In the laser device of Example 6 configured as described above, the light that is spread and guided in the active layer plane in the _second waveguide region C ₂ is reflected by the side surface 204 of the _third waveguide region C _3. Then, since it is guided to the _first waveguide region C ₁ , smooth waveguide is possible. That is, the light guided in the direction of the resonator is incident on the side surface 204 at an incident angle (90 ° −α), so that it is totally reflected on the side surface 204 and is not lost in the stripe-shaped waveguide region. Because it can lead. In the second waveguide region C ₂ and the third waveguide region C ₃ , effective refraction is performed by the second ridge (convex portion) 202 provided in the second conductivity type layer (p-type cladding layer 111). A rate difference is provided in the active layer surface to form a stripe-shaped waveguide region. In the third waveguide region C ₃ , the light guided out of the region immediately below the second ridge is guided by It can be suitably guided into the _first waveguide region C1.

As described above, in Example 6, the side surface 204 is provided so as to be inclined with respect to the side surface of the first ridge (convex portion) 201 in the first waveguide region C ₁ , thereby allowing smooth light guiding. Wave can be realized. Further, as shown in FIG. 13, the boundary portion between the side surface 204 and the second waveguide region C ₂ may be directly connected to the side surface of the _second waveguide region C ₂ without bending.

As described above, in the laser device of Example 6, the light guided in the second waveguide region C ₂ in the stripe-shaped waveguide region in the active layer surface or off the first waveguide is transmitted. since it can be guided efficiently into waveguide region C _1, thereby improving the device characteristics. In the laser device of the sixth embodiment, in particular, the threshold current density can be reduced, and the slope efficiency can be improved.

[Example 7]
The laser device of Example 7, the first waveguide region C ₁ different points constituted by two-stage ridges sides becomes two stages as in Example 1, as other portions of Example 1 Composed.

  That is, in Example 7, after forming a striped ridge by etching so as not to reach the active layer, a ridge wider than the stripe width of the ridge is formed in a portion where the first waveguide region is formed. Etching up to the mold cladding layer 106 forms a two-step ridge.

Here, FIG. 14A is a perspective view for explaining the laser element structure of the seventh embodiment, FIG. 14C is a cross-sectional view in the _first waveguide region C ₁ , and FIG. b) is a cross-sectional view of the _second waveguide region C2. In the laser device of Example 7, as shown in FIG. 14A, the first waveguide region C _{2 includes} an upper ridge (convex portion) having a width S _{w1 and} a lower ridge (convex portion) having a width S _w2. Are formed by a two-stage ridge consisting of Guide in the first waveguide region C _1, the active layer is located in the lower ridge, the width of the active layer 3 is determined by the width S _w2 of the lower ridge, by the substantially lower bridge It can be considered that a waveguide is formed. With the structure of the seventh embodiment, it becomes easier to control the width _Rw2 of the lower ridge as compared with the case where the first ridge is formed in the first embodiment. The width of the active layer can be formed with high accuracy. This is because, when the first ridge 201 for forming the first waveguide region C ₁ is formed by the method shown in FIG. 5, etching is performed in two stages using one mask. When etching to a depth that reaches the first conductivity type layer 1 by etching, a step is formed on the side surface at the boundary between the first ridge formed in common with the portion that is common to the first ridge, and the portion below it. This is because the width in the portion may not be accurately controlled.

  However, in the seventh embodiment, after forming the upper ridge in the same etching process as the second ridge, a mask different from the mask used when forming the upper ridge is formed to form the lower ridge. Since the lower ridge is formed by etching using the other mask, the width of the lower ridge can be formed with high accuracy, and the width of the active layer 3 positioned in the lower ridge can be formed with high accuracy. .

  Therefore, according to the present embodiment, it is possible to provide a laser element having characteristics equivalent to those of the first embodiment and having little manufacturing variation. That is, the laser device of Example 7 is advantageous in manufacturing.

[Example 8]
The laser device according to the eighth embodiment is a laser device in which a third waveguide region is formed between the first waveguide region and the second waveguide region, and the third waveguide region is used in the embodiment. 6 is an example configured in a different form.

Specifically, in the laser device of the present embodiment 8, the third waveguide region C _3, as shown in FIG. 15 (a), first provided in the p-type cladding layer 111 and p-type contact layer 112 The third ridge is formed so that the width becomes narrower as it approaches the first waveguide region.

  That is, in the eighth embodiment, by forming the third waveguide region, the first waveguide region and the second waveguide region having different waveguide widths are discontinuous, and the waveguide width is discontinuous. You can connect without changing to.

Here, FIG. 15A is a perspective view for explaining the laser element structure of Example 8, and FIG. 15B is a cross-sectional view of the active layer. In FIG. 15B, the width indicated by S _w1 is the width at the bottom of the second ridge, and the width indicated by S _w2 is the width of the active layer portion in the first ridge.

  Here, the imaginary line (two-dot chain line) in FIG. 15B is a line obtained by projecting the second ridge and the third ridge onto the cross section of the active layer. Each of the waveguides in the waveguide region is formed by forming an effective refractive index difference in the active layer corresponding to the second ridge and the third ridge. The chain line) can be considered to substantially indicate the waveguides in the second waveguide region and the third waveguide region.

  As in Example 1, the laser element of Example 8 manufactured as described above has excellent characteristics.

[Example 9]
The ninth embodiment is an example in which a laser element configured in the same manner as the first embodiment is manufactured by a method different from the first embodiment.

  That is, in Example 9, the second ridge is formed after the first ridge is formed.

  Specifically, the respective layers are stacked in the same manner as in Example 1, and then, a stripe-shaped first protective film 161 is formed on the surface of the stacked body as shown in FIG. Then, as shown in FIG. 6A, a third protective film 163 is formed except for a part of the first protective film 161 (a portion for forming the first waveguide region), and FIG. As shown in b), the first ridge 201 is formed by etching both sides of the first protective film 161 to such a depth that the lower cladding layer 5 (n-type cladding layer 106) is exposed. Subsequently, after removing the third protective film 163, a third protective film 163 is formed so as to cover the first ridge 201 as shown in FIG. 6C. In this state, the portions forming the second waveguide region are covered with at least one of the first protective film 161 and the third protective film 163 except for both sides of the first protective film 161. Will be. After this state, the second ridge is formed by etching so that the region not covered with the first protective film 161 and the third protective film 163 does not reach the active layer.

At this time, the ridge width and ridge height of each ridge constituting the _first waveguide region C ₁ and the second waveguide region C ₂ are the same as those in the first embodiment. Subsequently, the third protective film 163 on the _first waveguide region C1 is removed so that only the first protective film that is a striped mask is used, and the subsequent steps are the same as in the first embodiment. The protective film (buried layer) is formed on the stripe side surface and the nitride semiconductor layer plane continuous therewith. Thereafter, in the same manner as in Example 1, a laser element is obtained. According to the method of Example 9 described above, the number of steps is increased compared to the method described in Example 1, but a laser element similar to that of Example 1 can be manufactured.

[Example 10]
Example 10 is an example of fabricating a laser device using a nitride semiconductor substrate. The basic device structure is the second waveguide region C ₂ having the structure shown in FIG. in one waveguide region C ₁ has a structure shown in FIG.

(Substrate 101) In Example 10, a nitride semiconductor substrate made of GaN having a thickness of 80 μm manufactured as follows is used.

Here, first, a sapphire substrate having a thickness of 425 μm, 2 inches φ, a C-plane main surface, and an A-plane orientation flat surface (hereinafter referred to as an orientation flat surface) is prepared as a heterogeneous substrate for growing a nitride semiconductor. Then, the wafer is set in a MOCVD reaction vessel. Next, the temperature is set to 510 ° C., hydrogen is used as the carrier gas, ammonia and TMG (trimethyl gallium) are used as the source gas, and a low-temperature growth buffer layer made of GaN is formed on the sapphire substrate with a film thickness of about 200 Å. Then, the temperature is set to 1050 ° C., TMG and ammonia are used as source gases, and an underlayer made of undoped GaN is grown to a thickness of 2.5 μm. Subsequently, a plurality of masks made of striped SiO ₂ each having a width of 6 μm in a direction tilted by θ = 0.3 ° from a direction perpendicular to the orientation flat surface (A surface) of the sapphire substrate are arranged between the masks. They are formed in parallel so that the interval (mask opening) is 14 μm. Then, returning to the MOCVD apparatus, undoped GaN is grown to a thickness of 15 μm. In this way, GaN selectively grown from the mask opening grows mainly in the vertical direction (thickness direction) in the mask opening, and grows laterally on the mask to cover the mask and the mask opening. Are formed (ELOG growth). In the underlying layer grown in this way, the laterally grown nitride semiconductor layer can reduce threading dislocations. Specifically, the threading dislocations have a dislocation density as high as about 10 ¹⁰ / cm ² above the mask opening and near the center of the mask where the nitride semiconductor grown laterally from both sides of the mask joins. On the mask excluding the central portion of the mask, the dislocation density is as low as about 10 ⁸ / cm ² .

  Next, the wafer is placed on the HVPE apparatus, and undoped GaN is further grown on the underlayer to a thickness of about 100 μm (the layer grown to a thickness of about 100 μm is referred to as a thick film layer). . Subsequently, the heterogeneous substrate, the low-temperature growth buffer layer, the base layer, and the thick film layer are partially removed to form only the thick film layer (single unit) to obtain a GaN substrate having a thickness of 80 μm. Here, the nitride film other than GaN may be used for the HVPE thick film layer. However, in the present invention, GaN or AlN that has good crystallinity and can easily grow a thick nitride semiconductor is used. It is preferable to use it. Further, the removal of the heterogeneous substrate or the like may be performed at any stage after the element structure shown below is formed, after the waveguide is formed, and after the electrode is formed. Further, by removing the heterogeneous substrate or the like before cutting the wafer into bars or chips, the nitride semiconductor cleavage plane (approximate in the hexagonal system {1 1-0 0 } M plane, {1010} A plane, (0001) C plane).

(Underlayer 102)
By growing a nitride semiconductor on the nitride semiconductor substrate 101 so as to be accompanied by lateral growth using a striped SiO ₂ mask in the same manner as the underlying layer used when producing the nitride semiconductor substrate, the underlying layer is obtained. 102 is formed with a film thickness of 15 μm.

(Buffer layer 103)
Next, a buffer layer 103 made of undoped AlGaN having an Al mixed crystal ratio of 0.01 is formed on the base layer 102. This buffer layer 103 can be omitted, but when the substrate using lateral growth is GaN, or when the underlying layer formed by lateral growth is GaN, nitriding with a smaller thermal expansion coefficient than that is performed. By using the buffer layer 103 made of _a physical semiconductor, that is, Al _a Ga _1-a N (0 <a ≦ 1) or the like, pits can be reduced, and thus the buffer layer 103 is preferably formed. That is, when another nitride semiconductor is grown on a nitride semiconductor layer formed with lateral growth as in the base layer 102, pits are likely to be generated. There is an effect to prevent.

  Further, the Al mixed crystal ratio a of the buffer layer 103 is preferably 0 <a <0.3, whereby a buffer layer with good crystallinity can be formed. In addition, this buffer layer may be formed as a layer that also functions as an n-side contact layer, or after forming the buffer layer 103, an n-side contact layer represented by the same composition formula as the buffer layer is formed. Then, the n-side contact layer 104 may also have a buffer effect. That is, the buffer layer 103 is between the lateral growth layer (GaN substrate) and the nitride semiconductor layer constituting the device structure, or between the active layer in the device structure and the lateral growth layer (GaN substrate). More preferably, by providing at least one layer between the substrate side in the device structure, the lower cladding layer and the lateral growth layer (GaN substrate), pits can be reduced and device characteristics can be improved. it can. Further, when the buffer layer having the function of the n-side contact layer is used, the Al mixed crystal ratio a is preferably 0.1 or less so that a good ohmic contact with the electrode can be obtained. The buffer layer formed on the base layer 102 may be grown at a low temperature of 300 ° C. or more and 900 ° C. or less, like the buffer layer provided on the above-described different substrate, but preferably 800 ° C. or more and 1200 ° C. or less. When the single crystal is grown at a temperature, the above-described pit reduction effect tends to be obtained more effectively. Further, the buffer layer 103 may be doped with n-type and p-type impurities, or may be undoped, but is preferably formed undoped to improve the crystallinity. Furthermore, when two or more buffer layers are provided, the n-type, p-type impurity concentration, and Al mixed crystal ratio can be changed.

(N-side contact layer 104)
On the buffer layer 103, an n-side contact layer 104 made of Al _0.01 Ga _0.99 N doped with 4 μm thick and 3 × 10 ¹⁸ / cm ^{3 of} Si is formed.

(Crack prevention layer 105)
A crack prevention layer 105 made of In _0.06 Ga _0.94 N having a thickness of 0.15 μm is formed on the n-side contact layer 104.

(N-side cladding layer 106)
An n-side cladding layer 106 having a superlattice structure with a total film thickness of 1.2 μm is formed on the crack prevention layer 105.

Specifically, an n-doped Al _0.05 Ga _0.95 N layer having a thickness of 25 mm and a GaN layer having a thickness of 25 mm and doped with 1 × 10 ¹⁹ / cm ^{3 of} Si are alternately stacked to form n A side cladding layer 106 is formed.

(N-side light guide layer 107)
An n-side light guide layer 107 made of undoped GaN having a thickness of 0.15 μm is formed on the n-side cladding layer 106.

(Active layer 108)
On the n-side light guide layer 107, an active layer 108 having a total quantum thickness of 550 mm and having a multiple quantum well structure is formed.

Specifically, a barrier layer (B) made of Si-doped In _0.05 Ga _0.95 N with a thickness of 140 mm doped with 5 × 10 ¹⁸ / cm ³ of Si, and an undoped In _0.13 Ga film with a thickness of 50 mm. _The active layer 108 is formed by stacking the well layer (W) made of _0.87 N in the order of (B)-(W)-(B)-(W)-(B).

(P-side electron confinement layer 109)
On the active layer 108, a p-side electron confinement layer 109 made of p-type Al _0.3 Ga _0.7 N doped with 100 μm thick and 1 × 10 ²⁰ / cm ³ Mg is formed.

(P-side light guide layer 110)
On the p-side electron confinement layer 109, a p-side light guide layer 110 made of p-type GaN doped with Mg having a thickness of 0.15 μm is formed at 1 × 10 ¹⁸ / cm ³ .

(P-side cladding layer 111)
A p-side cladding layer 111 having a superlattice structure with a total film thickness of 0.45 μm is formed on the p-side light guide layer 110.

Specifically, by alternately laminating undoped Al _0.05 Ga _0.95 N with a film thickness of 25 mm and p-type GaN doped with 1 × 10 ²⁰ / cm ³ of Mg with a film thickness of 25 mm, A p-side cladding layer 111 is formed.

(P-side contact layer 112)
On the p-side cladding layer 111, a p-side contact layer 112 made of p-type GaN doped with 150 mm thick and 2 × 10 ²⁰ / cm ³ Mg is formed.

As described above, after the element structure from the n-side contact layer 104 to the p-side contact layer 112 is formed, the n-side contact layer 104 is exposed in the same manner as in Example 1, and the first waveguide region C ₁ is exposed. , the second waveguide region C ₂ formed by etching, forming a second protective film 162 (buried layer) on each side and the nitride semiconductor layer plane continuous with that of the first ridge and the second ridge To do. At this time, the second ridge for forming the _second waveguide region C2 is etched to such a depth that the thickness of the p-side light guide layer 110 on both sides of the second ridge is 0.1 μm. To form.

  Next, a method for forming the resonance end face of each laser element in Example 10 will be described.

  In the tenth embodiment, by arranging two laser elements as a pair and facing each other so that the two elements are symmetrical with respect to one surface (opposing surface), each resonance end face is efficiently formed. Forming.

Specifically, a length of 645 μm on each side of the first waveguide region C _{1 having} a length of 10 μm (with the first waveguide regions of one set of laser elements connected) second to form a waveguide region _{C 2} (see part of IIIb and IVb of FIG. 17 (b)).

The outer end faces of the _second waveguide regions C2 on both sides are simultaneously formed by etching when exposing the n-side contact layer.

  Subsequently, similarly to Example 1, an n-electrode 121 and a p-electrode 120 are formed on the surfaces of the n-side contact layer 104 and the p-side contact layer 112.

  Next, an insulating film (reflection film) 164 made of a dielectric multilayer film is formed on all exposed surfaces including the end face of the second waveguide region and the side surfaces of the ridges for constituting the waveguide region.

As a result, an insulating film 164 that functions as a reflective film at the end face of the _second waveguide region C2 and functions as an insulating film at other portions (particularly, a function of preventing a short circuit between the pn electrodes) is formed. In Example 10, unlike in FIGS. 8 and 9, the p-electrode 120 is formed on a part of the surface of the p-side contact layer 112 with a width smaller than the stripe width of the p-side contact layer 112. In the 120 stripe direction, it is formed only on the _second waveguide region C2. The p-electrode 120 is formed slightly apart from the end of the _second waveguide region C2.

Then, a part of the insulating film 164 on the n-electrode and the p-electrode is removed to expose each electrode, and pad electrodes 122 and 123 to be electrically connected are formed on each electrode surface. Next, in a substantially central portion of the _first waveguide region C1 having a length of 10 μm (see the EE line in FIG. 17B), the nitride semiconductor is cleaved at the M-plane to form a bar shape. Further, the bar is cleaved in parallel with the cavity direction on the A plane perpendicular to the M plane cleaved between the respective elements to obtain a laser chip.

The laser chip obtained as described above has a first waveguide region C ₁ having a length of about 5 μm and a second waveguide region C ₂ having a length of 645 μm, as in the first embodiment. The end face of the _first waveguide region C1 is the emission side.

The obtained laser element has a threshold current density of 2.5 kA / cm ² at room temperature, a threshold voltage of 4.5 V, an oscillation wavelength of 405 nm, and an aspect ratio of the emitted laser beam of 1.5. In addition, a high-power laser element having a long lifetime of 1000 hours or longer with a continuous oscillation of 30 mW can be obtained. The laser element can continuously oscillate in an output range of 5 mW to 80 mW, and has a beam characteristic suitable as a light source for an optical disc system in the output range.

[Example 11]
The laser element of Example 11 is configured using n-type GaN doped with Si with a thickness of 80 μm as the substrate 101 instead of the substrate made of undoped GaN with a thickness of 80 μm in Example 10. The substrate 101 made of n-type GaN doped with Si is formed by forming a low-temperature growth buffer layer on a heterogeneous substrate and growing the underlayer with lateral growth in the same manner as in Example 10. After the formation, a thick film of Si-doped GaN is grown at 100 μm by HVPE, and the heterogeneous substrate is removed.

In Example 11, a buffer layer 102 made of Si-doped Al _0.01 Ga _0.99 N is formed on an n-type GaN substrate 101, and an element structure is formed on the buffer layer 102 in the same manner as in Example 1. The side contact layer 104 to the p-side contact layer 112 are stacked.

  Subsequently, in order to define a region for forming a waveguide region of each element, etching is performed so that the surface of the n-side contact layer 112 is exposed to form a separation groove. In Example 11, unlike Example 10, a pair of positive and negative electrodes are not formed on the same surface side, and the electrodes are arranged opposite to each other with the substrate interposed therebetween, so that an n electrode is provided on the exposed surface of the n-side contact layer. There is no need to provide space. Therefore, the adjacent elements can be arranged closer to each other than the tenth embodiment.

  In Example 11, each region is defined by exposing the n-side contact layer by etching. However, in this configuration, the following steps may be performed without etching because the electrodes are arranged opposite to each other. . In the case of forming the separation groove, the layer between the n-side contact layer and the substrate may be exposed, or the separation groove may be formed so as to expose the substrate. Further, when the separation groove is formed by exposing the substrate, the substrate may be exposed by etching partway through the substrate.

Note that the area defined for constituting each element does not necessarily need to be formed for each element, and the area for constituting two elements may be integrally formed as described in the tenth embodiment. Further, a region for forming three or more elements may be integrally formed (for example, the portions shown in FIGS. 17A and 17B, III and IV are integrally formed).
Similarly, in a direction perpendicular to the light guiding direction, a plurality of regions may be continuously formed without forming separation grooves between elements.

  It should be noted that after forming the groove by etching deeper than the active layer at the portion where the substrate is divided, the substrate is divided at the portion of the groove (for example, A− in FIGS. 17A and 17B). A portion indicated by A), and cracking and chipping in the active layer portion due to impact of splitting can be avoided.

In Example 11, each element is manufactured by separating a region for each element. Subsequently, as in the tenth embodiment, in order to configure each waveguide region, a striped ridge is formed, and the first waveguide region C ₁ , the _first waveguide region C ₁ , second waveguide region C ₂ to form, respectively. At this time, the first waveguide region _{C 1} is formed with stripe length 10 [mu] m.

Subsequently, as in Example 10, a striped p-electrode having a narrower width than the surface is formed on the surface of the p-side contact layer only in the _second waveguide region C2. Here, the striped p-electrode is formed with a length that does not reach the end so as to be slightly away from the end face of the second ridge for constituting the _second waveguide region C2.

  Next, an n-electrode is formed on the back side of the substrate (the surface facing the substrate surface on which the element structure is formed), and the p-electrode and the n-electrode are arranged opposite to each other with the substrate and the element structure interposed therebetween. Subsequently, as in Example 10, an insulating film (reflective film) 164 made of a dielectric multilayer film is formed on almost the entire surface of the substrate where the element structure is formed, and a part of the p-electrode is exposed. Then, a pad electrode electrically connected to the exposed p-electrode is formed.

Finally, as indicated by II in FIG. 17 (b), as a cutting direction perpendicular to the resonator, the DD cutting position at the substantially central portion in the _first waveguide region C1 and the A between the elements. Cleave at the M-plane of the substrate at the A cutting position to form a bar, and then cleave between the elements at the A-plane perpendicular to the cleavage plane to obtain a chip-shaped laser element.

The laser element thus obtained has a cleaved surface provided at the end of the _first waveguide region C1 and an etching end surface provided at the end of the _second waveguide region C2 and provided with a reflective film. And can be used for laser oscillation. The laser element thus obtained has excellent laser characteristics as in Example 10.

[Example 12]
In the laser element of Example 12, a resonator end face is formed at the same time as etching to the n-type contact layer in Example 10, and etching is performed to the substrate before dividing the substrate between the resonator end faces. 1) and 2) are divided at the AA cut plane. At this time, the portion protruding from the resonator end face was 3 μm. The characteristics of the laser element thus obtained have excellent element characteristics and optical characteristics as in Example 10.

[Comparative Example 1]
As Comparative Example 1, in Example 1, a laser element in which the second waveguide region is formed over the entire length without forming the first waveguide region is manufactured.

  In the first comparative example, as in the first embodiment, the layers that form the element structure are stacked. Thereafter, as shown in FIG. 5B, a stripe-shaped second ridge is formed from one end face to the other end face of the element using the first protective film 161 as a mask.

Next, a protective film made of ZrO ₂ is formed on the side surface of the first ridge formed over the entire length and on the etching exposed surfaces on both sides of the first ridge, and the wafer is immersed in hydrofluoric acid. 161 is removed by a lift-off method. Subsequently, similarly to Example 1, the resonator surface and each electrode are formed, and the laser element of Comparative Example 1 having only the second ridge for forming the _second waveguide region C ₂ is obtained. .

  In the laser device of Comparative Example 1 manufactured as described above, it is difficult to effectively suppress unnecessary transverse modes, the stability of the transverse modes is poor, and kinks are frequently generated in the current-light output characteristics. It becomes a laser element.

  In particular, movement in the transverse mode is likely to occur under conditions such as a high output range with a large optical output, for example, an output of 30 mW necessary for writing data in an optical disc system. In addition, since the element characteristics react sensitively to the dimensional accuracy of the stripe-shaped second ridge, as shown in FIG. 10, it is difficult to improve the manufacturing yield because of large variations among elements. Further, the aspect ratio of the obtained laser beam spot is mostly located between 2.5 and 3.0, and when the acceptable line of the aspect ratio is 2.0 or less, the production yield is greatly reduced.

  Hereinafter, the results of studies conducted to confirm the effects (laser element lifetime, drive current, lateral mode controllability) obtained by the configuration of the laser element according to the present invention will be described.

  In this study, laser elements having different ridge heights are manufactured by sequentially changing the etching depth using the same element structure (semiconductor laminated structure) as in Example 1, and each laser element is divided into laser elements. Lifetime, drive current, and lateral mode controllability were evaluated.

  FIG. 12 shows the laser lifetime versus optical depth (tested with an optical output of 30 mW).

  As shown in FIG. 12, when the etching depth is in the vicinity of the boundary between the p-type cladding layer and the p-type light guide layer, the lifetime of the element is the longest, and the lifetime is shortened whether it is shallower or deeper. Further, when etching is performed up to the vicinity of the boundary between the p-type light guide layer and the p-type electron confinement layer, the laser lifetime decreases rapidly, and when the stripe-shaped waveguide region is formed at a depth reaching the active layer, the device lifetime It has a great adverse effect on Therefore, in consideration of the device lifetime, it is better to perform the etching at a depth that does not reach the p-type electron confinement layer. Further, it can be understood that a very good lifetime can be obtained by forming a ridge by etching from the boundary between the p-type cladding layer and the p-type light guide layer to a depth of about 0.1 μm above and below. In consideration of confinement of light in the thickness direction, it is preferable to perform etching so as not to reach the p-type guide layer. Including this point, the boundary from the vicinity of the interface between the p-type light guide layer and the p-type cladding layer It is more preferable to etch to a depth reaching between 0.1 μm above.

  FIG. 10 is a graph showing the non-defective rate with respect to the etching depth. FIG. 10 shows that a high yield rate can be obtained by etching deeper than 0.1 μm above the boundary between the p-type cladding layer and the p-type light guide layer. Here, the non-defective product rate in FIG. 10 indicates the ratio of elements that can oscillate in a basic single transverse mode at 5 mW among the elements that have been confirmed to oscillate. The stripe width of the waveguide region at this time is 1 .8 μm.

  Further, if the etching depth is such that the p-type cladding layer remains at 0.1 μm or more on both sides of the ridge, kinks are rapidly generated and the yield rate is greatly reduced.

  FIG. 11 shows the drive current (at an optical output of 30 mW) with respect to the etching depth. In this study, the waveguide region was set to a width of 1.8 μm. As is apparent from FIG. 11, when etching is performed deeper than the intermediate point (intermediate point in the thickness direction) of the p-type light guide layer (on the active layer side), it becomes constant at 50 mA regardless of the etching depth. Further, when the etching depth is gradually reduced from the middle point of the p-type light guide layer, the current value gradually increases up to 0.1 μm above the boundary between the p-type cladding layer and the p-type light guide layer, When the etching depth is shallower than 0.1 μm above the boundary between the p-type cladding layer and the p-type light guide layer (the etching depth in which the p-type cladding layer remains at a thickness of 0.1 μm or more on both sides of the ridge) The current value increases. Furthermore, if the p-type cladding layer is etched so as to remain with a thickness of 0.25 μm or more, a light output of 30 mW cannot be obtained.

[Comparative Example 2]
As Comparative Example 2, a laser element in which the first waveguide region is formed over the entire length without forming the second waveguide region in Example 1 is manufactured.

In the second comparative example, as in the first embodiment, the layers that form the element structure are stacked. Thereafter, as shown in FIG. 5A, a stripe-shaped first protective film 161 is provided, and regions on both sides of the first protective film are etched to a depth reaching the lower clad layer 5, thereby A stripe-shaped ridge for forming the waveguide region C ₁ is formed. Thereafter, a protective film made of ZrO ₂ is formed on the top and side surfaces of the ridge and on the etching exposed surfaces on both sides of the ridge, the wafer is immersed in hydrofluoric acid, and the first protective film 161 is removed by a lift-off method. Subsequently, in the same manner as in Example 1, the resonator surface and each electrode are formed, and a laser element having a cross-sectional structure as shown in FIG. 9 and having only the _first waveguide region C ₁ is obtained. In Comparative Example 2, the striped ridge is etched to a depth at which the film thickness of the n-type cladding layer on both sides of the ridge is 0.2 μm, as in the _first waveguide region C ₁ of Example 1. Is formed.

  Since the obtained laser element is a stripe etched deeper than the active layer, the element life is inferior to that of Example 1, the element life is short as shown in FIG. 12, and the laser element cannot be practically used.

  The present invention relates to a semiconductor laser device provided with a striped ridge (convex portion). In addition, the semiconductor laser device of the present invention has a group III-V nitride semiconductor (InbAldGa1-b-dN, 0 ≦ b, 0 ≦ d, b + d <1) that is GaN, AlN, InN, or a mixed crystal thereof. ).

(A) is a perspective view which shows typically the structure of the laser element of embodiment concerning this invention.

          (B) is sectional drawing in the 2nd waveguide area | region of the laser element of embodiment.

(C) is sectional drawing in the 1st waveguide area | region of the laser element of embodiment.
(A) is a schematic cross section before forming a ridge in the conventional laser element.

          (B) is a schematic cross-sectional view after forming a ridge in a conventional laser element.

(C), (d) is the elements on larger scale of FIG. (B).
(A) is a typical perspective view which shows the layer structure of the laser element of embodiment of this invention, (b) is a side view of Fig.3 (a). (A) is a side view of a laser device according to a modification of the present invention.

(B) is a side view of a laser element of another modification according to the present invention.
(A)-(d) is a perspective view which shows the process of forming the ridge of the laser element of this invention.

          (E) is sectional drawing in the part which forms the 2nd waveguide area | region of FIG.5 (c).

          (F) is sectional drawing in the part which forms the 2nd waveguide area | region of FIG.5 (d).

(A)-(c) is a perspective view which shows the formation process of the ridge of the laser element of this invention by the method different from the method shown to Fig.5 (a)-(d).

(A)-(d) is a perspective view which shows the process of forming the electrode in the laser element of this invention.

It is a schematic cross section in the 2nd waveguide area | region of the laser element of Example 1 which concerns on this invention.

It is a schematic cross section in the 1st waveguide area | region of the laser element of Example 1 which concerns on this invention.

It is a graph which shows the relationship between the etching depth and the yield rate in an effective refractive index type laser element.

It is a graph which shows the relationship between the etching depth and drive current in an effective refractive index type laser element.

It is a graph which shows the relationship between the etching depth and element lifetime in an effective refractive index type laser element.

(A) is a perspective view of the laser element of Example 6 which concerns on this invention.

(B) is a cross-sectional view of the laser device of Example 6 according to the present invention.
(A) is a perspective view of the laser element of Example 7 which concerns on this invention.

            (B) is sectional drawing in the 2nd waveguide area | region of the laser element of Example 7 which concerns on this invention.

            (C) is sectional drawing in the 1st waveguide area | region of the laser element of Example 7 which concerns on this invention.

(A) is a perspective view of the laser element of Example 8 which concerns on this invention.

            (B) is a cross-sectional view of the laser device of Example 8 according to the present invention.

(A)-(d) is a perspective view for demonstrating the manufacturing method of the laser element of this invention using the element formed on a wafer.

(A), (b) is a schematic cross section for demonstrating a cutting position in the manufacturing method of the laser element of this invention.

It is a schematic diagram for demonstrating the process of forming a reflecting film in the manufacturing method of the laser element of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... 1st conductivity type layer, 2 ... 2nd conductivity type layer, 3 ... Active layer, 4 ... Resonator surface, 5 ... Lower clad layer, 6 ... Lower part contact layer, 7 ... upper cladding layer, 8 ... upper contact layer, 9 ... substrate, 10 ... first waveguide region C _1, 11 ... second waveguide region C ₂ 101 ... substrate 102/103 ... buffer layer / underlayer 104 ... n-type contact layer 105 ... crack prevention layer 106 ... n-type cladding layer 107 ... n 20... Active layer, 109... P-side cap layer, 110... P-type light guide layer, 111... P-type cladding layer, 112. , 120 ... p electrode, 21, 121 ... n electrode, 22, 122 ... p pad electrode, 23, 123 ... n pad electrode, 161 ... first protective film, 162 ... second protective film (embedded layer), 163 ... third protective film, 164 ... insulation film

Claims (4)

stacking at least a first conductive type layer made of a nitride semiconductor, an active layer, and a second conductive type layer in order on an n-type GaN substrate;
Forming a separation groove defining the length of the waveguide region on the wafer laminated by the above-described process so that the bottom surface of the groove is deeper than the active layer;
Providing a stripe-shaped convex portion on the second conductivity type layer to form a second waveguide for confining light by an effective refractive index;
Providing a stripe-shaped convex portion including an active layer under the stripe-shaped convex portion to form a first waveguide for confining light by a complete refractive index;
And cleaving the wafer with the separation groove so that the cleaved surface becomes a resonator surface. 2. The method of manufacturing a semiconductor laser device according to claim 1, wherein the separation groove and the waveguide are formed by etching. 3. The method of manufacturing a semiconductor laser device according to claim 1, wherein a bottom surface of the separation groove is formed so that the n-type GaN substrate is exposed. A semiconductor laser device manufactured by the method according to claim 1.

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