JP2000299528A - Semiconductor laser and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ridge waveguide type semiconductor laser of a constitution, wherein an electrode can be formed at a prescribed position with good accuracy even in the case where a deviation is generated in the electrode formation position, a good current constriction can be realized and the adhesion of a semiconductor layer to an insulating film is good. SOLUTION: A P-type contact layer 101 and a first electrode layer 113 are formed on a ridge part 120 provided in a P-type clad layer 112. The layer 113 is formed in a two-layer structure consisting of a first layer Ni layer and a second layer Pt layer. A silicon oxide film 102 and a second electrode layer 114 are formed on the layers 113 and 112 in the order of the film 102 and the layer 114. The layer 114 is formed in a three-layer structure consisting of a first layer Ti layer, a second layer Pt layer and a third layer Au layer. A connection hole to reach the layer 13 is provided in the film 102, and the layers 114 and 113 are connected with each other via this connection hole.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode structure and a method for forming a ridge waveguide type semiconductor laser, and more particularly, to forming a ridge (convex portion) in a cladding layer or the like to reduce current confinement and confinement of light. The present invention relates to a technique for forming an electrode of a semiconductor laser.

[0002]

2. Description of the Related Art It is effective to employ a refractive index waveguide structure as a method for controlling a horizontal / lateral mode in a semiconductor laser. The refractive index waveguide structure is roughly divided into a rib waveguide type,
It is divided into a ridge waveguide type and a buried waveguide type. Among these, the ridge waveguide type semiconductor laser can simultaneously realize current confinement and light confinement, so that a stable horizontal transverse mode can be obtained, and excellent device characteristics such as a low oscillation threshold can be realized. Since the ridge waveguide structure does not require exposing the active layer to air in the manufacturing process, it is particularly effective when a material whose luminous efficiency is significantly reduced by contact with air is used for the active layer.

However, when an attempt is made to apply the ridge waveguide structure to a semiconductor laser using a specific semiconductor material, various restrictions are imposed on the structure of the electrode provided on the ridge portion and the method of forming the ridge portion due to device characteristics or a manufacturing process. May be added. For example, when a ridge waveguide structure is applied to a gallium nitride based semiconductor laser, various restrictions are added to the structure and the formation method of the p-electrode. That is, it is necessary to realize good ohmic contact of the electrode and to improve the adhesion between the electrode and the semiconductor layer while forming the p-electrode at a desired position with high accuracy. Hereinafter, a prior art in which a ridge waveguide structure is applied to a gallium nitride laser will be described.

FIG. 10 is a diagram showing a cross-sectional structure of a typical gallium nitride-based semiconductor laser (Proceedings of The S).
econd International Conference on Nitride Semicond
uctors, S-3). In this nitride semiconductor laser, an n-type Al _0.09 Ga _0.91 N layer 60 is formed on an n-type SiC substrate 601.
2. n-type GaN layer 603, n-type Al _0.09 Ga _0.91 N cladding layer 604, n-type GaN light confinement layer 605, multiple quantum well structure active layer 606, p-type Al _0.18 Ga _0.82 N layer 60
7, p-type GaN light confinement layer 608, p-type Al _0.09 Ga _0.91
An N cladding layer 609 and a p-type GaN contact layer 610 are formed. A p-electrode 612 is formed on a silicon oxide film 611 provided with a stripe-shaped connection hole.
An n-electrode 613 is formed on the back surface of the iC substrate 601. The first layer of the p-electrode 612 is Ni, the second layer is Ti,
The layer is Au. The first layer of the n-electrode 613 is Ni, the second layer is Ti, and the third layer is Au.

This semiconductor laser has a p-type Al _0.09 Ga
_{Since the} ridge portion 620 is provided in the _0.91 N cladding layer 609, the cladding layer is thicker in a region immediately below the ridge portion 620 than in other regions. Therefore, the real part of the effective refractive index is larger in the region immediately below the ridge portion than in the other regions, and confinement of light is realized by the effective refractive index distribution in the horizontal direction. Also, regarding the current, the ridge portion 620
The current flows only through the path passing through, so that the spread in the horizontal direction is suppressed.

[0006]

However, the above prior art has the following problems.

[0007] The first problem is that it is difficult to perform positioning when forming electrodes. When the ridge waveguide type is adopted,
It is necessary to form the p-electrode in the ridge with high accuracy. However, this ridge needs to be formed with a narrow width in order to achieve good current confinement and optical confinement. For example, a gallium nitride based semiconductor laser usually has a thickness of 2 to 3 μm.
Degree. When the ridge width is reduced as described above, it is difficult to form the p-electrode in the ridge portion with high accuracy. This will be described with reference to FIG. The ridge waveguide type semiconductor laser generally has a structure in which an insulating film 611 having a connection hole is formed and an electrode layer 612 is formed thereon as shown in FIG. As a result, current flows only through the ridge portion, and good current confinement is realized. Here, when forming the connection hole, it is necessary to align the pattern formed in the semiconductor layer with the exposure mask. However, this alignment is difficult as the width of the connection hole becomes narrower than the width of the ridge. , Relaxed. However, in the prior art shown in FIG. 10, when the width of the connection hole is reduced, the contact area between the electrode layer and the GaN semiconductor layer decreases, and the contact resistance increases. Therefore, in the prior art, it has been difficult to form the electrode at a predetermined position with high accuracy while facilitating the alignment while reducing the contact resistance.

In the case of a nitride-based semiconductor laser, a sapphire substrate is often used as a substrate material.
There is a large difference in thermal expansion coefficient between the nitride-based semiconductor layer and the sapphire substrate. For this reason, a sapphire substrate having a nitride-based semiconductor formed on its surface is likely to be warped, and this warpage is particularly remarkable when the nitride-based semiconductor layer is thicker than about 10 μm. When the warpage of the substrate is increased as described above, the alignment at the time of forming the p-electrode becomes more difficult.

A second problem is that when the position of the electrode is displaced, current confinement is not performed well and the laser efficiency is reduced. For example, in the conventional semiconductor laser of FIG. 10, the connection hole of the insulating film 611 is provided only above the p-type GaN contact layer 610, and the p-electrode 612 directly contacts the p-type cladding layer 609 in a region other than the ridge portion 620. Is preventing. As a result, the region where the current flows is limited only to the ridge portion, and good current confinement is realized. However, when the connection hole of the silicon oxide film 611 is displaced, the result is as shown in FIG. In this case, current flows from the p-electrode 612 to the p-type cladding layer 609 through the path indicated by the arrow in the figure, and the current spreads in the horizontal direction. Here, since the lowermost layer of the p-electrode 612 is usually made of a material such as Ni having a low contact resistance with the gallium nitride semiconductor layer, the current passing through the above-mentioned path has a certain magnitude. Therefore, the current confinement becomes defective and the threshold current increases, thereby deteriorating the device characteristics.

[0010] A third problem is that the electrode is apt to peel off. In a laser using a specific semiconductor material, it is necessary to appropriately select the constituent material of the lowermost layer of the electrode layer in order to reduce the contact resistance between the semiconductor layer and the electrode layer. However, the electrode material selected from such a viewpoint may have poor adhesion to the semiconductor layer, and the electrode may be easily peeled off. For example, in a nitride-based semiconductor laser, Ni is generally used as a material of the first layer of the p-electrode.
A metal with a large work function, such as Pd or Pt, is used. Thereby, the contact resistance between the nitride-based semiconductor layer and the p-electrode can be reduced. However, these metals have poor adhesion to the semiconductor layer and the insulating film, and may cause peeling of the p-electrode.

The problem has been described above with reference to a gallium nitride-based laser as an example, but the above-mentioned problem is common to not only the gallium nitride-based laser but also the ridge waveguide type semiconductor laser.

[0012] Of the above-mentioned problems, the first and second problems are problems peculiar to the case where the ridge waveguide structure is employed, and do not cause much problems in the case of the non-ridge waveguide structure. For example, FIGS. 12A and 12B show a typical example of a gallium nitride semiconductor laser having a non-ridged waveguide structure. In such a structure, positional deviation in forming an electrode does not cause much problem. There is no problem even if the position of the connection hole of the film 302 is slightly shifted. However, when this structure is employed, current confinement is not sufficiently performed, and it is difficult to realize a high level laser characteristic as desired at present.

The present invention has been made in view of the above circumstances, and when the ridge waveguide structure is employed to achieve good current confinement and light confinement, it is possible to accurately form electrodes at predetermined positions. It is an object of the present invention to provide a semiconductor laser capable of achieving good current confinement even when a shift occurs in an electrode formation position and having good adhesion to a semiconductor layer or an insulating film. .

[0014]

According to the present invention for solving the above-mentioned problems, according to the present invention, an active layer and a semiconductor layer having a ridge portion and provided on the active layer are provided. One electrode layer is formed, an insulating film provided with a connection hole reaching the first electrode layer is formed on the first electrode layer and the semiconductor layer, and the connection film is formed on the insulating film. A semiconductor laser is provided, wherein a second electrode layer connected to the first electrode layer through a hole is formed.

Further, according to the present invention, a step of forming a semiconductor multilayer film including an active layer and a semiconductor layer provided on the active layer on a substrate; Forming a first electrode layer via
After forming a mask at a predetermined position on the first electrode layer, an etching process is performed on a region where the mask is not formed so as to leave a part of the semiconductor layer, and a ridge portion is formed in the semiconductor layer. Step and after removing the mask,
Forming an insulating film on the first electrode layer, providing a connection hole in the insulating film to reach the first electrode layer, and forming a connection hole on the insulating film to bury the connection hole. Forming a second electrode layer.

Further, according to the present invention, a step of forming a semiconductor multilayer film including an active layer and a semiconductor layer provided on the active layer on a substrate, and forming an opening on the semiconductor layer Forming a mask provided, further growing the semiconductor layer in the opening and forming a ridge, and forming a first electrode layer directly or via a contact layer on the semiconductor layer. A step of forming an insulating film on the first electrode layer, a step of providing a connection hole reaching the first electrode layer in the insulating film,
Forming a second electrode layer so as to bury the connection hole.

The semiconductor laser of the present invention has a ridge waveguide structure in which a semiconductor layer having a ridge portion is formed on an active layer, a stable horizontal transverse mode can be obtained, and good current confinement and light Confinement is achieved. In addition, since the electrode structure is as described above, the following various effects can be obtained.

First, it is possible to obtain a semiconductor laser excellent in manufacturing stability, in which electrodes can be accurately formed at predetermined positions. As described above, in the related art, the width of the connection hole in the insulating film must be increased to a certain degree from the viewpoint of reducing the electrode resistance.
It has been difficult to align the pattern formed on the semiconductor layer with the exposure mask. On the other hand, in the present invention, even if the width of the connection hole in the insulating film is reduced, the above problem can be solved without increasing the contact resistance. This will be described with reference to FIG. FIG. 1 is a diagram showing a schematic structure of a gallium nitride based semiconductor laser which is an example of the semiconductor laser of the present invention. As shown, the first electrode layer 1
13 is a p-type contact layer 101 provided in the ridge portion.
Is formed on. Then, the second electrode layer 114 and the first electrode layer 113 are connected via a connection hole 121 provided in the silicon oxide film 102. The resistance of the electrode is particularly G
The contact resistance between the aN-based semiconductor layer and the metal electrode layer, that is, the contact area between these layers, is governed by the contact resistance between the first electrode layer 113 and the p-type contact layer 101 in the above electrode structure. Extends over the entire ridge width, and a sufficiently low contact resistance can be obtained. On the other hand, since the connection hole 121 is a connection point between the metal layers,
Even if the width of this portion is reduced, the increase width of the electrode resistance is small.
Therefore, in the semiconductor laser according to the present invention, the width of the connection hole 121 can be narrowed and the alignment can be facilitated while preventing the electrode resistance from increasing. Further, in the present invention, since the electrode portion has a specific structure, the connection hole 121 can be formed in a self-aligned manner by using an etch-back method. When such a method is adopted, it becomes possible to form the electrode at a predetermined position with higher accuracy. This point will be described later in the section of Examples (Example 2).

Second, it is possible to obtain a semiconductor laser excellent in manufacturing stability, which can maintain good current confinement even when the position of the electrode is shifted. As described above, in the semiconductor laser of the related art shown in FIG. 10, when the connection hole of the silicon oxide film 611 is displaced, FIG.
Thus, there has been a problem that the device characteristics are deteriorated, for example, the current constriction becomes defective and the threshold current increases.
On the other hand, according to the present invention, good current constriction is realized even if the connection holes are displaced. In the semiconductor laser of the present invention shown in FIG. 9A, a current flows in a path indicated by a solid arrow. When the position of the connection hole provided in the silicon oxide film 102 is shifted in this semiconductor laser, the structure becomes as shown in FIG. 9B. Here, in this semiconductor laser, although the lowermost layer of the first electrode layer 102 needs to be made of a material such as Ni having a low contact resistance with the gallium nitride semiconductor layer, the lowermost layer of the second electrode layer 114 Does not have such a restriction. Therefore, by appropriately selecting a material having a high contact resistance as the material of the lowermost layer of the second electrode layer 114, it is possible to reduce the current passing through the path indicated by the dotted arrow in FIG. 9B. There are many materials that can be selected from such a viewpoint. If a material other than the above-described specific material such as Ni is used, a certain current reduction effect can be obtained. However, when the adhesiveness of the electrode layer described later is intended to be improved, it is desirable to select a material in consideration of such a viewpoint.

As described above, in the present invention, since the restriction on the material of the lowermost layer of the second electrode layer is removed, a semiconductor laser capable of maintaining a good current confinement even when a connection hole is displaced. Can be obtained.

Third, the adhesion of the electrode layer to the semiconductor layer can be improved. In the semiconductor laser of the present invention shown in FIG. 1, the first electrode layer 113 and the p-type contact layer 1
In the case of a value between 01 and 01, sufficient adhesion cannot always be obtained as in the prior art. This is because the lowermost layer of the first electrode layer 113 needs to be made of a material having low contact resistance with the gallium nitride based semiconductor. However, there is no such restriction on the lowermost layer of the second electrode layer 114 in the present invention. Therefore, by appropriately selecting the material of the lowermost layer of the second electrode layer 114,
And the silicon oxide film 102 can have sufficiently high adhesion. The first electrode layer has a structure that is covered with the silicon oxide film 102 and the second electrode layer 114. Therefore, the first electrode layer 113 and the p-type contact layer 1
Even if the adhesiveness with No. 01 is not good, sufficiently high adhesiveness is realized as the whole electrode. Further, the area where the silicon oxide film 102 and the second electrode layer 114 are in contact with each other can be made sufficiently large as shown in the figure, and sufficient electrode adhesion can be obtained even when a ridge structure having a narrow stripe width is employed. is there.

In the present invention, a first electrode layer for contacting the gallium nitride based semiconductor layer and realizing a low contact resistance, and a second electrode layer for disposing the electrode layer on the semiconductor laser body with good adhesion. And Thus, in the present invention, by providing two electrode layers having different functions, it is possible to achieve both low electrode resistance and good electrode adhesion.

A semiconductor laser having the advantages described above is
The semiconductor laser can be suitably manufactured by the above-described semiconductor laser manufacturing method of the present invention. According to the production method of the present invention,
The electrode can be formed at a predetermined position with high accuracy by a relatively simple process. In addition, the semiconductor laser manufactured by this manufacturing method can achieve good current confinement even when a shift occurs in the electrode formation position, and further, has good adhesion to the semiconductor layer and the insulating film. is there.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, a ridge portion is formed in a semiconductor layer provided on an active layer, and horizontal current confinement and light confinement are realized by the ridge portion. This semiconductor layer can be a semiconductor layer having a function of confining light in the optical waveguide layer, such as a cladding layer or an optical confinement layer. Note that another semiconductor layer may be interposed between the semiconductor layer and the active layer.

In the semiconductor laser of the present invention, the ridge portion is formed by partially etching the semiconductor layer provided on the active layer, or by growing the semiconductor layer constituting the ridge portion by selective growth. Will be

In the semiconductor laser of the present invention, the first electrode layer is formed directly on the ridge portion or via the contact layer. The first electrode layer is preferably formed only on the ridge. In the case where the contact layer is formed via the contact layer, the contact layer is preferably formed only on the ridge portion. In this way, it is possible to suppress the spread of the current in the horizontal direction and to realize a good current constriction.

In the semiconductor laser of the present invention, it is preferable that the second electrode layer has a structure formed over a ridge portion and a region other than the ridge portion. Here, the insulating film is preferably formed so as to cover the entire surface of the semiconductor layer. This prevents unnecessary current from flowing through the semiconductor layer, and realizes good current confinement. In addition, if the second electrode layer is formed over the ridge portion and the region other than the ridge portion, a large electrode area is secured, and it is difficult to perform positioning when bonding a wire or bringing a current probe into contact. Can be reduced.

In the semiconductor laser of the present invention, the connection hole is preferably connected only to the first electrode layer. With this configuration, the second electrode layer does not come into contact with the semiconductor layer, and the formation of the alloy between the second electrode layer and the semiconductor layer can be prevented.

In the present invention, the semiconductor layer provided on the active layer has a ridge. There is no particular limitation on the shape of the ridge portion, but from the viewpoint of forming a low-resistance electrode by a simple method, the ridge portion preferably has a shape extending in a stripe shape in the plane direction. In this case, the width of the ridge portion is appropriately determined according to the emission wavelength of the semiconductor laser. From the viewpoint of realizing high-efficiency and high-output laser characteristics, the width is preferably 5 μm or less, and more preferably 0.3 μm or less.
4 μm. The width of the ridge means the width at the bottom of the ridge. In the case of such a ridge width, in the related art, problems such as displacement of the electrode formation position and poor adhesion of the electrodes are likely to occur. According to the present invention, the ridge width can be reduced while solving such a problem,
A laser structure advantageous for realizing high-efficiency and high-output laser characteristics can be realized. In the present invention, the first electrode layer is composed of one or more layers. The lowermost layer of the first electrode layer is preferably made of Ni, Pd, Pt or an alloy containing these, particularly preferably Ni. By selecting such a material, the contact resistance between the first electrode layer and the semiconductor layer can be further reduced.

In the present invention, the second electrode layer is composed of one or more layers. The lowermost layer of the second electrode layer is preferably made of Cr, Al, Ti or an alloy containing these, particularly preferably Ti. By selecting such a material, the contact resistance between the first electrode layer and the semiconductor layer can be further reduced.

The insulating film in the present invention is not particularly limited as long as it has good insulating properties. For example, a silicon oxide film, a silicon nitride film, or a multilayer film thereof can be used.

In the present invention, there is no particular limitation on the semiconductor material, and the present invention can be applied to III-V group semiconductor lasers, II-VI group semiconductor lasers, and the like. It is a target. In a gallium nitride based semiconductor laser, when the active layer material is exposed to air, the luminous efficiency is significantly reduced. Therefore, the horizontal current confinement and light emission in the horizontal direction are performed while keeping the horizontal width of the semiconductor layer including the active layer at a certain value or more. It is desirable to perform confinement. Therefore, in a gallium nitride based semiconductor laser, it is effective to adopt a ridge waveguide structure, and the application of the present invention is particularly effective. In addition, the use of an electrode material having a low contact resistance with a gallium nitride-based semiconductor causes a problem of electrode adhesion, so that the application of the present invention is effective from this point. When the present invention is applied to a gallium nitride-based semiconductor, the first electrode layer has a structure formed in contact with the upper surface of the gallium nitride-based semiconductor layer. In this case, it was difficult to achieve both low contact resistance and good electrode adhesion.However, according to the present invention, the first electrode layer for achieving low contact resistance in contact with the gallium nitride based semiconductor layer was used. By providing the second electrode layer for disposing the electrode layer on the semiconductor laser body with good adhesion, the above problem can be effectively solved. Note that a gallium nitride-based semiconductor refers to a semiconductor containing nitrogen and gallium as constituent elements.

As described above, when the structure in which the first electrode layer is formed in contact with the upper surface of the gallium nitride-based semiconductor layer is employed, the material of the substrate is preferably a gallium nitride-based semiconductor layer thereon. It is desirable to select a material that can be grown. Such materials include sapphire,
GaN, Si, SiC and the like can be mentioned. When sapphire is selected among them, in the related art, there is a problem that the electrode forming position is easily shifted due to the warpage of the substrate. According to the present invention, such a problem can be effectively solved.

In the method of manufacturing a semiconductor laser according to the present invention, the step of providing a connection hole reaching the first electrode layer in the insulating film is preferably performed by the following steps (a) to (c). (A) a step of forming a mask layer on the entire surface of the insulating film; (b) a step of exposing the insulating film located on the first electrode layer by etching back the mask layer; Step of providing a connection hole for removing and exposing the first electrode layer This method forms a connection hole using an etch-back technique. According to this method, the connection hole connected only to the first electrode layer can be formed in a self-aligned manner, and the electrode can be formed more accurately.

The reason why the connection hole can be formed by the above method is that the semiconductor laser of the present invention has a specific structure. This will be described with reference to FIGS.

FIG. 4 is a process sectional view showing a process of the present invention to which the above method is applied. First, resist 10
3 (FIG. 4A), the silicon oxide film 102 is exposed by etch back (FIG. 4B). Next, using the remaining resist 103 as a mask, the silicon oxide film 102
An opening is formed in the substrate (FIG. 4C). By such a method, the connection holes can be formed in a self-aligned manner.

The above method cannot be suitably implemented unless the height of the projections including the first electrode layer is sufficient. FIG.
FIG. 3 is an assumption diagram when a conventional semiconductor laser is manufactured by applying the above method. In this structure, the height of the projection is not sufficient, so that when the mask layer is etched back, the etching residue 340 of the mask layer easily occurs on the silicon oxide film 302 (FIG. 13B). For this reason, it is difficult to suitably form the connection hole in a subsequent step. On the other hand, in the semiconductor laser of the present invention, the thickness of the first electrode layer can be freely set, so that the first electrode layer can be formed in a thick film to increase the height of the projection. Therefore, as shown in FIG. 4B, no etching residue remains in the mask layer, and the connection hole can be suitably formed by the above method.

In the method of manufacturing a semiconductor laser according to the present invention, the substrate may be removed after forming the electrodes.

[0039]

(Embodiment 1) FIG. 1 shows the structure of a gallium nitride based semiconductor laser according to this embodiment. In the figure, only the main layers are shown except for the electrodes. This semiconductor laser has an n-type cladding layer 151 on a sapphire substrate 150,
The active layer 152 and the p-type cladding layer 112 have a structure in which they are stacked in this order. Each of these layers is made of a GaN-based semiconductor material. p-type cladding layer 11
2 has a ridge portion 120, whereby horizontal light confinement and current confinement are achieved. Ridge part 12
On p, a p-type contact layer 101 made of a GaN-based semiconductor material and a first electrode layer 113 are stacked. The first electrode layer 113 has a two-layer structure in which the first layer is made of Ni and the second layer is made of Pt. First electrode layer 1
13 and the silicon oxide film 1 on the p-type cladding layer 112.
02 and the second electrode layer 114 are stacked. The second electrode layer 114 has a first layer of Ti, a second layer of Pt,
The third layer has a three-layer structure made of Au. Silicon oxide film 1
02 is provided with a connection hole reaching the first electrode layer 113, and the second electrode layer 114 and the first electrode layer 113 are connected via this connection hole. Note that an n-electrode 160 is provided on the n-type cladding layer 151.

In this semiconductor laser, the silicon oxide film 102
Is in contact only with a Ti film having good adhesion to the silicon oxide film 102, and a wide contact area is secured. For this reason, the structure has excellent electrode adhesion. Also,
Since the connection hole is formed in the silicon oxide film 102, the connection hole can be easily provided by etching or the like. Therefore, a connection hole having a desired size can be formed with good controllability.

On the other hand, since it is possible to increase the electrode area of the second electrode layer 114, it is possible to reduce the difficulty in positioning when bonding a wire or bringing a current probe into contact. Further, wire bonding or the like can be performed in a region other than the upper portion of the ridge, and the risk of damaging the active layer is reduced.

The second electrode layer 114 is not in contact with the p-type contact layer 101. If they touch, p
In the electrode alloying step or the like, the second electrode layer 114 and p
In some cases, the alloy of the mold contact layer progresses and the p-contact resistance of the device deteriorates. However, such a problem is solved in the semiconductor laser of this embodiment.

Hereinafter, a method of manufacturing the semiconductor laser shown in FIG. 1 will be described with reference to FIGS. Here, FIGS. 2 and 3 show a process subsequent to the formation of the active layer 152, and show only a portion above the active layer 152.

First, as shown in FIG. 2A, a p-type cladding layer 112 and a p-type cladding layer 112 are formed on an active layer 152 made of a nitride semiconductor.
The mold contact layer 101 and the first electrode layer 113 were formed in this order, and a resist 103 was applied thereon. Next, the resist 103 was patterned into a stripe shape by exposure, development, and the like (FIG. 2B). Next, etching was performed using the stripe-shaped resist 103 as a mask by a reactive ion beam etching method using chlorine gas so as to leave a part of the p-type cladding layer 112 (FIG. 2C).

After the resist 103 is removed by organic cleaning, a silicon oxide film 102 is formed on the entire surface by thermal chemical vapor deposition.
Was formed, and a resist 103 was applied to the surface thereof (FIG. 3A). Next, an opening was formed in the resist 103 by exposure and development (FIG. 3B). Subsequently, using the resist 103 in which the opening was formed as a mask, an opening was formed in the silicon oxide film 102 by wet etching using buffered hydrofluoric acid (FIG. 3C). After removing the resist 103 by organic washing, a second first electrode layer 114 was formed on the entire surface by vapor deposition.

Thereafter, the n-electrode 160 is formed using a known method.
After that, the semiconductor laser shown in FIG. 1 was completed. In the obtained semiconductor laser, the electrodes were accurately formed at predetermined positions, and the adhesion of the electrodes was also good.

(Embodiment 2) A method of manufacturing a semiconductor laser according to this embodiment will be described with reference to the drawings. First, FIG.
After performing the same steps as in (a) to (c), the mask 103
Was removed. Subsequently, as shown in FIG. 4A, a resist 103 was applied to the entire surface. Next, the resist 103 was etched by a reactive ion beam etching method using an oxygen gas until the silicon oxide film 102 on the first p-electrode 113 was exposed (FIG. 4B). The remaining resist 10
3 was used as a mask to form an opening in the silicon oxide film 102 by wet etching using buffered hydrofluoric acid (FIG. 4C). After removing the resist 103 by organic cleaning (FIG. 4D), a second electrode layer 114 was formed on the entire surface by vapor deposition. Here, the second electrode layer 114 has a three-layer structure in which the first layer is made of Ti, the second layer is made of Pt, and the third layer is made of Au.

Thereafter, an n-electrode and the like were formed by using a known method to complete a semiconductor laser. In the obtained semiconductor laser, the electrode position was accurately formed at a predetermined position, and the adhesion of the electrode was good.

In the manufacturing method of this embodiment, the first p
When the silicon oxide film 102 on the electrode 113 is exposed, a so-called etch-back method is used, so that there is no need to align a pattern formed in the semiconductor layer with an exposure mask, and a connection hole is formed in a self-aligned manner. Can be formed. Therefore, the electrodes could be formed more accurately. (Embodiment 3) The semiconductor laser of this embodiment has a structure as shown in FIG. Hereinafter, a method of manufacturing the semiconductor laser will be described with reference to FIGS. Here, FIGS. 5 to 7 show steps subsequent to the formation of the active layer 152, and show only a portion above the active layer 152.

First, as shown in FIG. 5A, a p-type cladding layer 112 and a p-type contact layer 101 are formed on an active layer 152 made of a nitride semiconductor, and then silicon oxide is formed by a thermal chemical vapor deposition method. The film 130 was formed. Next, a resist 103 was applied to the surface (FIG. 5A). Next, an opening was formed in the resist 103 by exposure and development (FIG. 5B). Subsequently, using the resist 103 in which the opening was formed as a mask, an opening was formed in the silicon oxide film 130 by wet etching using buffered hydrofluoric acid (FIG. 5C).

After removing the resist 103 by organic cleaning, a p-type cladding layer 112 and a p-type contact layer 101 are selectively formed only in the opening of the silicon oxide film 102 by an organic chemical vapor deposition method. First electrode layer 1
13 was formed (FIG. 6A). First electrode layer 113
Has a two-layer structure in which the first layer is made of Ni and the second layer is made of Pt.

Next, by removing the silicon oxide film 130 by wet etching using hydrofluoric acid, the first first electrode layer 113 on the silicon oxide film 130 was also removed and selectively formed. The first electrode layer 113 was left only on the p-type cladding layer 112 and the p-type contact layer 101 (FIG. 6B). Subsequently, a silicon oxide film 102 was formed on the entire surface by thermal chemical vapor deposition, and a resist 103 was applied on the surface of the silicon oxide film 102 (FIG. 6).
(C)).

After an opening is formed in the resist 103 by exposure and development (FIG. 7A), the resist 10
Using the mask 3 as a mask, an opening was formed in the silicon oxide film 102 by wet etching using buffered hydrofluoric acid (FIG. 7B). After removing the resist 103 by organic cleaning, a second electrode layer 114 was formed on the entire surface by vapor deposition (FIG. 7C). The second electrode layer 114 includes a first layer made of Ti, a second layer made of Pt, and a third layer made of Au.
A layer structure was adopted.

Thereafter, the n-electrode 160 is formed using a known method.
After that, the semiconductor laser shown in FIG. 8 was completed. In the obtained semiconductor laser, the electrodes were accurately formed at predetermined positions, and the adhesion of the electrodes was also good.

[0055]

As described above, according to the semiconductor laser of the present invention, in a ridge waveguide type laser, a first electrode layer is formed on a ridge portion, and a connection hole reaching the first electrode layer is formed thereon. The provided insulating film is formed, and a second electrode layer is further formed thereon. The first electrode layer and the second electrode layer are connected through the connection hole. For this reason, the electrodes can be formed at predetermined positions with high accuracy, good current confinement can be achieved even when the electrode formation positions are shifted, and adhesion to the semiconductor layer or insulating film can be achieved. A semiconductor laser having good properties can be obtained.

The method of manufacturing a semiconductor laser according to the present invention
Since the ridge portion is formed by etching or selective growth, a semiconductor laser having the above advantages can be manufactured by a simple process with a high yield. In particular, if a method using an etch-back method is adopted, the connection holes provided in the electrodes can be formed in a self-aligned manner, and the electrode portion can be formed with higher accuracy.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing an example of a semiconductor laser of the present invention.

FIG. 2 is a process sectional view illustrating a method for manufacturing a semiconductor laser according to the present invention.

FIG. 3 is a process cross-sectional view illustrating a method for manufacturing a semiconductor laser of the present invention.

FIG. 4 is a process cross-sectional view illustrating a method for manufacturing a semiconductor laser of the present invention.

FIG. 5 is a process sectional view illustrating the method for manufacturing a semiconductor laser according to the present invention.

FIG. 6 is a process sectional view illustrating the method for manufacturing the semiconductor laser of the present invention.

FIG. 7 is a process sectional view illustrating the method for manufacturing the semiconductor laser of the present invention.

FIG. 8 is a schematic sectional view showing an example of the semiconductor laser of the present invention.

FIG. 9 is a diagram illustrating the operation of the semiconductor laser of the present invention.

FIG. 10 is a diagram showing a typical example of a conventional semiconductor laser.

FIG. 11 is a diagram for explaining a problem of a conventional semiconductor laser.

FIG. 12 is a schematic sectional view of a non-ridge waveguide type semiconductor laser according to the related art.

FIG. 13 is a diagram showing a state when an etch-back method is applied to a conventional semiconductor laser.

[Explanation of symbols]

Reference Signs List 101 p-type contact layer 102 silicon oxide film 103 resist 112 p-type cladding layer 113 first electrode layer 114 second electrode layer 120 ridge portion 121 connection hole 150 sapphire substrate 151 n-type cladding layer 152 active layer 160 n-electrode 301 p Type contact layer 302 silicon oxide film 312 p-type cladding layer 330 p-electrode 340 remaining etching 350 sapphire substrate 351 n-type cladding layer 352 active layer 360 n-electrode 601 n-type SiC substrate 602 n-type Al _0.09 Ga _0.91 N layer 603 n-type GaN Layer 604 n-type Al _0.09 Ga _0.91 N cladding layer 605 n-type GaN light confinement layer 606 Multiple quantum well structure active layer 607 p-type Al _0.18 Ga _0.82 N electron overflow prevention layer 608 p-type GaN light confinement layer 609 p-type Al _0.09 Ga _0.91 N cladding layer 6 0 p-type GaN contact layer 611 a silicon oxide film 612 p electrode 613 n electrode 620 ridge

Claims (17)

[Claims] An active layer, a semiconductor layer having a ridge portion and provided on the active layer, a first electrode layer is formed on the ridge portion, and the first electrode layer and An insulating film provided with a connection hole reaching the first electrode layer is formed on the semiconductor layer, and a second electrode connected to the first electrode layer through the connection hole on the insulating film. A semiconductor laser having a layer formed. 2. The semiconductor laser according to claim 1, wherein the second electrode layer is formed over the ridge portion and a region other than the ridge portion. 3. The semiconductor laser according to claim 1, wherein the second electrode layer is connected only to the first electrode layer in the connection hole. 4. The semiconductor laser according to claim 1, wherein the ridge has a shape extending in a stripe shape in a plane direction, and the width of the ridge is 5 μm or less. . 5. The lowermost layer of the first electrode layer is made of Ni, P
5. The semiconductor laser according to claim 1, comprising d, Pt, or an alloy containing these. 6. The lowermost layer of the second electrode layer is formed of Cr, A
6. The semiconductor laser according to claim 1, wherein the semiconductor laser is made of l, Ti, or an alloy containing these. 7. The semiconductor laser according to claim 1, wherein the first electrode layer is formed in contact with an upper surface of the gallium nitride based semiconductor layer. 8. The semiconductor laser according to claim 7, wherein said active layer is formed on a sapphire substrate via another layer. 9. A step of forming a semiconductor multilayer film including an active layer and a semiconductor layer provided on the active layer on a substrate, and forming a first semiconductor layer directly on the semiconductor layer or via a contact layer. After forming a mask at a predetermined location on the first electrode layer, performing an etching process to leave a part of the semiconductor layer in a region where the mask is not formed, Forming a ridge portion in the semiconductor layer; forming an insulating film on the first electrode layer after removing the mask; and forming a connection hole in the insulating film to reach the first electrode layer. Providing, and on the insulating film,
Forming a second electrode layer so as to fill the connection hole. 10. A step of forming a semiconductor multilayer film including an active layer and a semiconductor layer provided on the active layer on a substrate, and forming a mask having an opening on the semiconductor layer. Forming a ridge portion, further growing the semiconductor layer in the opening, forming a first electrode layer directly or via a contact layer on the semiconductor layer, A step of forming an insulating film on one electrode layer, a step of providing a connection hole reaching the first electrode layer in the insulating film, and a second step of burying the connection hole on the insulating film. Forming an electrode layer. 11. The semiconductor laser according to claim 9, wherein the step of providing a connection hole reaching the first electrode layer in the insulating film is performed by the following steps (a) to (c). Manufacturing method. (A) a step of forming a mask layer over the entire surface of the insulating film; (b) a step of exposing the insulating film located on the first electrode layer by etching back the mask layer; Removing the exposed portion of the film and providing a connection hole reaching the first electrode layer 12. The method according to claim 9, wherein the second electrode layer is formed over the ridge portion and a region other than the ridge portion. 13. The semiconductor laser according to claim 9, wherein the ridge portion has a shape extending in a stripe shape in a plane direction, and the width of the ridge portion is 5 μm or less. Manufacturing method. 14. The lowermost layer of the first electrode layer is Ni,
14. The method according to claim 9, wherein the semiconductor laser is made of Pd, Pt, or an alloy containing them. 15. The lowermost layer of the second electrode layer may include Cr,
The method according to any one of claims 9 to 14, wherein the method is made of Al, Ti, or an alloy containing these. 16. The method according to claim 9, wherein the first electrode layer is formed in contact with an upper surface of the gallium nitride based semiconductor layer. 17. The method according to claim 16, wherein the substrate is a sapphire substrate.