JP2007142227A - Semiconductor laser device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor laser device the high output of which can be achieved without changing a resonator length of the semiconductor laser device. <P>SOLUTION: The semiconductor laser device can increase an optical output limited by thermal saturation by extending the effective resonator length of a waveguide path, while suppressing increase in the resonator length as a distance between reflection mirrors (corner mirrors 201) formed by cleaved faces through the formation of a refracted waveguide path in a way of propagating light reflected in the corner mirrors 201 or the like. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical disc apparatus such as DVD-RAM, DVD-R, DVD-RW, DVD + R, DVD + RW, CD-R, CD-RW, DVD-ROM, CD-ROM, DVD-Video, CD-DA, VCD, Or it is related with the semiconductor laser apparatus used as light sources, such as optical information processing, optical communication, and optical measurement.

Since semiconductor lasers have advantages such as small size, low power consumption, low cost, and high reliability, they are widely used as lasers for optical disks such as CDs and DVDs.
9A and 9B are diagrams showing the structure of a conventional semiconductor laser device. FIG. 9A is a cross-sectional view, and FIG. 9B is a plan view seen from above.

  In FIG. 9, an active layer 103 sandwiched between cladding layers 102 and 104 is provided on a substrate 101, and a part of the cladding layer 104 has a ridge waveguide structure including a ridge stripe region 105 formed in a stripe shape. ing. In general, the substrate 101 and the clad layer 102 are n-type, the active layer 103 is non-doped, the clad layer 104, and the ridge stripe region 105 are p-type semiconductors composed of p-type semiconductors. A p-side electrode 106 and an n-side electrode 107 are provided in each part. The resonator end face 108 is formed with a reflecting mirror by cleavage, and is further coated with a dielectric film as a control film for the reflectance and transmittance and as an end face protective film. A ridge waveguide structure is linearly formed between the two reflecting mirrors formed on the resonator end face 108.

  In particular, red lasers having an oscillation wavelength band of 650 nm used for DVDs are often Si-doped GaAs on the substrate, AlGaInP doped with Si or Se on the n-type cladding layer, and Zn or Mg on the p-type cladding layer. Is used, and a quantum well made of GaInP and AlGaInP is used for the active layer (see, for example, Patent Document 1).

FIG. 10 is a diagram showing a structure of a conventional dual wavelength semiconductor laser device, and FIG. 11 is a diagram showing current-light output characteristics of the conventional dual wavelength laser device.
As shown in FIG. 10, for example, an infrared semiconductor laser and a red semiconductor laser are monolithically formed on one substrate. As shown in FIG. 11, the current-light output characteristics of this two-wavelength semiconductor laser device are such that, even if the current increases, the light output of the red laser decreases due to thermal saturation, and the red laser emits less light than the infrared laser. The maximum light output is reduced.

Optical disc lasers are required to have various characteristics such as optical output, operating current / voltage, oscillation wavelength, and outgoing light divergence angle. In particular, since the writing speed to the optical disk depends on the light output, higher output of laser light is required year by year in order to write data at a higher speed.
JP 2001-57462 A

  As the output increases, the injection current required for operation increases. As a result, the heat generated from the element also increases, and the element temperature rises. An increase in device temperature increases the proportion of non-radiative recombination of injected electrons. The feedback as described above causes a phenomenon that the optical output is saturated even when current is injected. In order to achieve higher output of the laser, it is necessary to increase this thermal saturation level.

  Therefore, it is known that increasing the resonator length to easily release the generated heat is effective for increasing the output. In “IEEE Journal of Selected Topics in Quantum Electron, vol. 9, No. 5, pp. 1260-1264, Sep / Oct 2003”, the cavity length is increased from 100 μm to 100 μm. As a result, it was reported that the maximum light output was improved from 245 mW to 290 mW.

However, the following matters can be cited as problems caused by increasing the resonator length.
(1) Since the chip area increases, the number of chips that can be taken from the wafer decreases, and the cost increases.

  (2) When the chip is bonded to the submount by soldering, the residual strain due to the force applied to the chip from the jig and the difference between the thermal expansion coefficients of the chip and the solder becomes large, which can be a cause of deterioration in reliability.

  (3) In a two-wavelength laser in which an infrared laser for CD and a red laser for DVD are monolithically integrated, when the resonator length, which is the distance between the cleavage planes of the red semiconductor laser, is increased for higher output, the infrared semiconductor The operating current of the laser will increase. This is because the infrared laser has a longer wavelength than the red laser and the spatial spread of the light is large. In the case of a high-power laser, the output is not only within the cladding layer but also to the GaAs contact layer and other layers that absorb light. This is because the waveguide loss increases because light spreads.

  In order to solve these problems, it is an object of the semiconductor laser device of the present invention to increase the output of the semiconductor laser device without changing the resonator length of the semiconductor laser device.

  The semiconductor laser device according to claim 1 of the present invention is formed by laminating a first conduction type cladding layer, an active layer, and a second conduction type cladding layer on a substrate, and having two parallel resonator end faces. A semiconductor laser device that is formed by a cleaved surface and emits light from at least one of the cavity end faces. The effective resonator length, which is a one-way distance propagating between the two resonator end faces, is longer.

  The semiconductor laser device according to claim 2 is the semiconductor laser device according to claim 1, wherein the effective resonator length is changed by changing a traveling direction of light propagating between the two resonator end faces in the active layer. A waveguide structure that is longer than the resonator length is provided in the resonator.

According to a third aspect of the present invention, in the semiconductor laser device according to the first or second aspect, the waveguide has a ridge waveguide structure.
According to a fourth aspect of the present invention, there is provided the semiconductor laser device according to the third aspect, wherein the width of the ridge upper portion of the waveguide is a waveguide in a direction perpendicular to the cleavage plane and a waveguide in a horizontal direction. It is characterized by being different.

  The semiconductor laser device according to claim 5 is the semiconductor laser device according to claim 2, wherein the waveguide structure is a corner mirror.

A semiconductor laser device according to a sixth aspect is the semiconductor laser device according to the fifth aspect, wherein the corner mirror changes the traveling direction of light to a right angle.
The semiconductor laser device according to claim 7 is the semiconductor laser device according to claim 2, wherein the waveguide structure is a defect waveguide using a photonic crystal. Features.

  The semiconductor laser device according to claim 8 is a two-wavelength semiconductor laser device in which a red semiconductor laser device and an infrared semiconductor laser device are monolithically formed, and the red semiconductor laser is claimed in claim 1, claim 2, or claim 2. A semiconductor laser device according to claim 3, claim 4, claim 5, claim 6, or claim 7.

  The semiconductor laser device according to claim 9 is a multi-wavelength semiconductor laser device including a plurality of semiconductor laser devices, and the one or more semiconductor laser devices are the above-mentioned claim 1, claim 2, claim 3, or claim 4. Alternatively, it is a semiconductor laser device according to any one of claims 5, 6, and 7.

  As described above, high output of the semiconductor laser device can be realized without changing the resonator length of the semiconductor laser device.

  According to the present invention, by forming a waveguide refracted so that light is reflected and propagated by a plurality of corner mirrors or the like, an increase in the resonator length, which is the distance between the reflecting mirrors formed by cleavage, is suppressed. However, the effective resonator length, which is the effective waveguide length, can be extended to increase the optical output limited by thermal saturation. In monolithic two-wavelength semiconductor laser devices, the effective cavity length of the red semiconductor laser can be increased while suppressing an increase in the cavity length of the infrared semiconductor laser, thereby suppressing the infrared laser and increasing the output of the red laser. It is possible to achieve both.

  The present invention provides a semiconductor laser without changing the resonator length of the semiconductor laser device by making the effective resonator length, which is the length of the waveguide for propagating light, longer than the resonator length, which is the distance between the cleavage planes. High output of the apparatus can be realized. For example, this is realized by providing a refracted waveguide and adjusting the traveling direction of light in accordance with the refracted waveguide.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(Embodiment 1)
First, the semiconductor laser device according to the first embodiment will be described with reference to FIG. 1, FIG. 2, FIG. 3, FIG.

  1 is a perspective view showing the structure of a semiconductor laser according to the first embodiment of the present invention, FIG. 2 is a diagram showing a ridge stripe forming process in the semiconductor laser device according to the first embodiment, and FIG. 3 is a semiconductor laser according to the first embodiment. It is a figure which shows the corner mirror formation process in an apparatus. 2 and 3, FIGS. 2 (b), 2 (d), 2 (f), 3 (b), 3 (d), and 3 (f) are plan views. 2 (a), FIG. 2 (c), FIG. 2 (e), FIG. 3 (a), FIG. 3 (c), and FIG. 4A and 4B are views showing the shape of the ridge stripe in the semiconductor laser device of the present invention. FIG. 4A is a plan view showing the shape of the ridge stripe, and FIG. 4B is an AA view of FIG. It is sectional drawing between "between and BB". FIG. 5 is a diagram comparing the current-light output characteristics of the red semiconductor laser device according to the first embodiment with a conventional infrared semiconductor laser device, and FIG. 6 is a diagram illustrating a ridge stripe configuration example of the semiconductor laser device according to the first embodiment. It is.

  Here, the red semiconductor laser device will be described along the manufacturing steps shown in FIGS. Note that the MOCVD crystal growth technique, photolithography technique, semiconductor etching technique, CVD dielectric film deposition technique, etc. in each process are all based on known techniques. In the actual manufacturing process, the process is performed in units of wafers. However, in the schematic diagrams showing the manufacturing process in FIGS. 2 and 3, for convenience of explanation, one chip is illustrated.

  First, as shown in FIGS. 2A and 2B, an n-type cladding layer 102, an active layer 103, and a p-type cladding layer 104 are sequentially stacked on an n-type GaAs substrate 101. The active layer 103 has a quantum well structure, and the oscillation wavelength is set between 655 and 665 nm.

  Next, as shown in FIGS. 2C and 2D, a resist mask 301 having a waveguide pattern is formed in order to form a ridge waveguide structure. The waveguide pattern is provided with patterns that are bent at four angles at right angles.

  Next, as shown in FIGS. 2E and 2F, a part of the p-type cladding layer 104 is selectively removed by dry etching using the resist mask 301 as a mask to form a stripe region 105. A ridge structure is produced. The top widths of the stripe pattern in the direction perpendicular to the cleavage plane and in the horizontal direction are 1.5 μm and 2.0 μm, respectively. Also in ridge formation by dry etching, due to the influence of chemical reaction during etching, the cross-sectional shapes are different from each other in the directions perpendicular and horizontal to the cleavage plane as shown in FIG. The reason why the stripe widths are different from each other in the direction perpendicular to and horizontal to the cleavage plane is to compensate for this difference in shape and stabilize the light propagation mode by making the bottom widths equal.

Next, as shown in FIGS. 3A and 3B, the resist mask 301 is removed to expose the stripe region 105.
Next, as shown in FIGS. 3C and 3D, a resist mask 302 is formed in a region excluding the corner mirror formation region in order to produce a corner mirror for bending light in the resonator.

Next, as shown in FIGS. 3E and 3F, a resist mask 302 is used so that light is totally reflected at the mirror portion by changing the direction by 90 degrees due to the difference in refractive index between the semiconductor and air. A corner mirror 201 is formed by dry etching, and the resist mask 302 is removed. Etching is performed halfway through the n-type cladding layer 102 so that the etched surface of the active layer is in contact with air. A substance having a refractive index smaller than that of the semiconductor constituting the active layer, such as a SiO ₂ dielectric film, may be formed on the etched surface of the active layer. Note that in order to reduce the scattering loss of propagating light as much as possible, the etching is performed as perpendicular to the substrate as possible and the etching surface becomes smooth.

また、本実施の形態における実効共振器長（リッジ導波路の合計距離）は１５００μｍ、チップ長さである共振器長（劈開面間の距離）は９００μｍ、チップ幅は３５０μｍである。 In the subsequent steps, although not shown, an electrode is formed in the lower part of the element, element separation and end face reflection mirror formation are performed by cleavage, and an end face dielectric film is formed on the end face to complete the element.
Examples of the material, conductivity type, film thickness, and carrier concentration of each layer are shown in the following table.

In this embodiment, the effective resonator length (total distance of the ridge waveguide) is 1500 μm, the resonator length (distance between the cleavage planes) is 900 μm, and the chip width is 350 μm.

  FIG. 5 shows current-light output characteristics according to this embodiment. For comparison, the current-light output characteristics of a high-power red semiconductor laser device having a conventional ridge structure with a resonator length of 1500 μm and a chip width of 300 μm are shown in FIG. Although the chip area of the present embodiment is 70% of the conventional one, the effective resonator length is equivalent, so that the thermal saturation level is also equivalent. Therefore, the number of chips with the same performance from the same size wafer can be increased by about 1.4 times compared to the conventional size, and the cost can be reduced. Further, the reduction of the chip length also reduces the residual strain after assembly, which contributes to the reduction of risks such as deterioration of reliability caused by the strain.

  In the present embodiment, the effective resonator length is made larger than the chip length by four corner mirrors. However, it may be refracted by two corner mirrors as shown in the top view of FIG. As shown in FIG. 6B, the positions of the four corner mirrors may be adjusted so that the effective resonator length becomes longer. As described above, even if the corner mirrors have different positions and numbers than those of the present embodiment, the effect of the present invention is expected by installing the corner mirrors so that the light is reflected and propagates in the refracted waveguide. it can.

  Further, although a corner mirror is used as a method of bending light in the present embodiment, the present invention can be applied to a structure using a bent waveguide bent in an arc shape or a bent waveguide using a defect waveguide using a photonic crystal. The effect by can be expected.

In addition, the figure shows the case where light is bent at a right angle, but the waveguide mechanism that refracts light may be bent at a right angle, may be bent at other angles, or may be bent in an arc shape. .
In the above description, the red semiconductor laser device has been described as an example. However, the constituent material, the film thickness, the carrier concentration, the size of the component, etc. are arbitrary, and may be used for semiconductor laser devices having other oscillation wavelengths.

As described above, by forming a waveguide refracted so that light is reflected and propagated by a plurality of corner mirrors, the effective resonator length can be increased without increasing the resonator length. High output can be achieved by increasing the saturation level.
(Embodiment 2)
First, the semiconductor laser device according to the second embodiment will be described with reference to FIGS.

FIG. 7 is a perspective view showing the structure of the semiconductor laser device according to the second embodiment of the present invention, and FIG. 8 is a diagram showing the current-light output characteristics of the dual wavelength semiconductor laser device according to the second embodiment.
The major feature of the present embodiment is that the substrate 101 has a two-wavelength integrated monolithically with an infrared semiconductor laser whose active layer 403 is made of GaAs / AlGaAs and a red laser whose active layer 103 is made of GaInP / AlGaInP. In contrast to the conventional ridge stripe structure, the infrared semiconductor laser has a structure including a waveguide stripe region 105 in which the red semiconductor laser is refracted by the corner mirror 201. is there.

  The manufacturing method of the present embodiment is similar to the manufacturing method of a monolithic two-wavelength semiconductor laser device currently in practical use as shown in FIG. 10, and first, after forming an infrared semiconductor laser structure, a red semiconductor laser is formed. The infrared semiconductor laser structure in the region to be etched is removed to the substrate, and a red semiconductor laser is formed in the etched region. The formation of the red semiconductor laser is the same as in the first embodiment.

また、本実施の形態における赤色半導体レーザの実効共振器長（リッジ導波路の合計距離）は２２００μｍ、チップ長さである共振器長（劈開面間の距離＝赤外レーザの共振器長）は１５００μｍ、チップ幅は４００μｍである。 The following table shows Example 2 of the material, conductivity type, film thickness, and carrier concentration of each layer.

The effective cavity length (total distance of the ridge waveguide) of the red semiconductor laser in the present embodiment is 2200 μm, and the cavity length (distance between the cleavage planes = the cavity length of the infrared laser) is the chip length. 1500 μm and the chip width are 400 μm.

  FIG. 8 shows the current-light output characteristics of the dual wavelength laser apparatus according to the present embodiment, which is compared with the current-light output characteristics of the conventional dual wavelength laser apparatus of FIG. In conventional dual-wavelength laser devices, red semiconductor lasers are more strongly affected by thermal saturation, so the maximum optical output of red semiconductor lasers is higher than that of infrared semiconductor lasers in dual-wavelength semiconductor laser devices with the same cavity length. However, in this embodiment, only the red semiconductor laser is effective only by using a waveguide refracted using a corner mirror or the like. Since the cavity length can be extended and the thermal saturation level of the red semiconductor laser can be increased, high output of both the infrared and red semiconductor lasers can be realized.

  In the present embodiment, the structure in which the effective resonator length is made larger than the chip length by four corner mirrors in the red semiconductor laser is shown. However, the position and number of corner mirrors are the same as in the first embodiment. The effects of the present invention can be expected even with a structure other than the form.

  In addition, in the present embodiment, a structure using a corner mirror is shown as a method of bending the red semiconductor laser beam. However, a structure using a curved waveguide bent by an arc and a defect waveguide using a photonic crystal is used. Even if is used, the effect of the present invention can be expected.

In addition, the figure shows the case where light is bent at a right angle, but the waveguide mechanism that refracts light may be bent at a right angle, may be bent at other angles, or may be bent in an arc shape. .
Further, the present invention can be applied not only to the two-wavelength laser as in the present embodiment but also to an integrated laser such as a three-wavelength laser or a laser array.

  As described above, even in a multi-wavelength semiconductor laser device, by forming a waveguide that is refracted so that light is emitted and propagated by a plurality of corner mirrors, a necessary effective resonator length can be obtained without increasing the resonator length. Since it can be ensured, it is possible to increase the thermal saturation level and achieve high output.

  The present invention can achieve high output of a semiconductor laser device without changing the resonator length of the semiconductor laser device, and can be used as a light source for an optical disk device or optical information processing, optical communication, optical measurement, etc. Useful for laser devices and the like.

The perspective view which shows the structure of the semiconductor laser in Embodiment 1 of this invention The figure which shows the ridge stripe formation process in the semiconductor laser apparatus of Embodiment 1. The figure which shows the corner mirror formation process in the semiconductor laser apparatus of Embodiment 1. The figure which shows the shape of the ridge stripe in the semiconductor laser apparatus of this invention The figure which compared the current-light output characteristic of the red semiconductor laser device in Embodiment 1 with the conventional infrared semiconductor laser device FIG. 5 is a diagram showing a ridge stripe configuration example of the semiconductor laser device in the first embodiment. The perspective view which shows the structure of the semiconductor laser apparatus in Embodiment 2 of this invention. The figure which shows the electric current-light output characteristic of the two wavelength semiconductor laser apparatus in Embodiment 2 The figure which shows the structure of the conventional semiconductor laser device Diagram showing the structure of a conventional dual wavelength semiconductor laser device The figure which shows the electric current-light output characteristic of the conventional dual wavelength laser apparatus

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Substrate 102 Clad layer 103 Active layer 104 Clad layer 105 Stripe region 106 P-side electrode 107 N-side electrode 108 Resonator end face 201 Corner mirror 301 Resist mask 302 Resist mask 403 Active layer

Claims (9)

On the substrate, a clad layer of the first conductivity type, an active layer, and a clad layer of the second conductivity type are stacked, and the resonator end face is formed by two parallel cleaved faces, and at least one resonator end face A semiconductor laser device that emits more light,
The effective resonator length, which is a one-way distance in which light propagates between the two resonator end surfaces in the active layer, is longer than the resonator length that is the distance between the resonator end surfaces. Semiconductor laser device.   A waveguide structure is provided in the resonator to change the traveling direction of light propagating between the two resonator end faces in the active layer so that the effective resonator length is longer than the resonator length. The semiconductor laser device according to claim 1.   The semiconductor laser device according to claim 1, wherein the waveguide has a ridge waveguide structure.   4. The semiconductor laser device according to claim 3, wherein a width of an upper portion of the ridge of the waveguide is different between a waveguide in a direction perpendicular to the cleavage plane and a waveguide in a horizontal direction.   The semiconductor laser device according to claim 2, wherein the waveguide structure is a corner mirror.   6. The semiconductor laser device according to claim 5, wherein the corner mirror changes the traveling direction of light to a right angle.   5. The semiconductor laser device according to claim 2, wherein the waveguide structure is a defect waveguide using a photonic crystal. A two-wavelength semiconductor laser device in which a red semiconductor laser device and an infrared semiconductor laser device are monolithically formed,
The semiconductor laser device according to claim 1, wherein the red semiconductor laser is the semiconductor laser device according to claim 1, claim 2, claim 3, claim 4, claim 5, claim 6, or claim 7. apparatus. A multi-wavelength semiconductor laser device comprising a plurality of semiconductor laser devices,
One or a plurality of semiconductor laser devices are the semiconductor laser devices according to claim 1, claim 2, claim 3, claim 4, claim 5, claim 6, or claim 7. A semiconductor laser device.

Images