JP2004022989A - Nitride semiconductor laser and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a gallium-nitride-based compound-semiconductor laser wherein the width of the electrode forming region of its ridge portion is controlled, and at the same time, it has no hysteresis such that its semiconductor laminated structure is covered with at least an inorganic dielectric before forming its upper electrode. <P>SOLUTION: The manufacturing method of the gallium-nitride-based compound-semiconductor laser has a process for forming an upper-electrode layer (10) on a gallium-nitride-based compound-semiconductor laminated structure (100), a process for forming thereon a photoresist (40) for a stripe, a process for removing the upper-electrode layer by dry etching while using this photoresist for the stripe as a mask, and further, a process for removing a portion of the gallium-nitride-based compound-semiconductor laminated structure by dry etching, while using an identical photoresist for the stripe as a mask to form the ridge stripe. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a semiconductor laser device, and more particularly to a gallium nitride compound semiconductor laser device having a ridge stripe structure and a method of manufacturing the same.
[0002]
[Prior art]
In a semiconductor laser using a gallium nitride compound semiconductor, a ridge stripe type waveguide structure is often provided to confine light and current. FIGS. 16A to 16G are schematic cross-sectional views showing a step of forming a ridge stripe type waveguide structure in a conventional ridge stripe type gallium nitride based compound semiconductor laser device.
[0003]
Usually, a photoresist mask 44 for forming a stripe is formed on a gallium nitride-based compound semiconductor multilayer structure 700 formed on a substrate as shown in FIG. 16A, and then a reactive ion etching apparatus, an inductively coupled plasma etching apparatus, or the like is used. Using the dry etching apparatus described above, the surface of the semiconductor laminated structure 700 is etched as shown in FIG. Next, after removing the stripe-forming photoresist mask 44, as shown in FIG. 16C, the surface is covered with a dielectric film 35 of SiO2, SiN or the like, and from thereover, as shown in FIG. 16D. Then, a photoresist film 70 having a stripe-shaped opening 80 is formed.
[0004]
Next, as shown in FIG. 16E, the opening 80 of the photoresist is transferred to the dielectric film 35 by the wet etching method, and the opening 90 is provided. Next, after removing the photoresist film 70, as shown in FIG. 16F, a photoresist film 71 having an opening 81 including a ridge stripe region is formed, and an upper electrode metal layer is deposited on the entire surface, and then lift-off is performed. By the method, an upper electrode 25 is obtained as shown in FIG.
[0005]
Note that the photoresist mask 44 for forming a stripe used here is not a photoresist but a SiO 2₂It is common practice to use an inorganic dielectric film such as the above instead.
[0006]
[Problems to be solved by the invention]
When the ridge stripe and the upper electrode are manufactured by the above-described conventional method, there are the following two problems. Hereinafter, a description will be given based on FIG. 16 used for the description.
[0007]
First, when the opening 90 is provided in the dielectric film 35, the wet etching method in which isotropic etching is performed is used. The point is that the variation of the width becomes large. Since the width of the opening 90 determines the current injection region, the variation is directly linked to variations in the current-voltage characteristics, oscillation threshold current, oscillation mode, and the like of the semiconductor laser device. If the openings 90 are formed by performing anisotropic etching by dry etching instead of wet etching, it is possible to reduce the variation in the width. However, the surface of the semiconductor stacked structure 700 The semiconductor device is exposed to a plasma atmosphere, and the damage causes an increase in operating voltage and a decrease in reliability.
[0008]
The second point is that the stripe forming photoresist mask 44 and the dielectric film 35 are used twice until the upper electrode is formed on the semiconductor laminated structure 700 through the opening 90 of the dielectric film 35. That is, it has gone through the coating history. When the coating histories of the organic and inorganic substances on the semiconductor multilayer structure 700 overlap, even after a process of removing them, residues are generated on the semiconductor multilayer structure 700, and these are caused by current and voltage of the semiconductor laser device. It adversely affects characteristics and reliability. This point is more remarkable especially when the coating with the inorganic dielectric is repeated, and instead of the photoresist mask 44 for forming the stripe, SiO 2 is used.₂In the case where an inorganic dielectric film such as that described above is used as a mask for forming a stripe and the upper electrode 25 is formed through two coating histories with the inorganic dielectric including the coating with the dielectric film 35 in a later step, oscillation occurs. In some cases, the threshold voltage may increase by 1 volt or more.
[0009]
The present invention has been made in view of the above circumstances, and it is an object of the present invention to control the width of an electrode forming region of a ridge portion, and at the same time, at least to form a semiconductor laminated structure by an inorganic dielectric before forming an upper electrode. It is an object of the present invention to provide a method of manufacturing a gallium nitride-based compound semiconductor laser and a structure of the gallium nitride-based compound semiconductor laser, wherein the gallium nitride-based compound semiconductor laser does not have a coating history and desirably does not have any coating history.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, according to the present invention, a substrate, a gallium nitride-based compound semiconductor multilayer structure, and a method of manufacturing a ridge stripe type gallium nitride-based compound semiconductor laser including a pair of electrodes include a stacked structure of one or more layers. A step of forming a first upper electrode layer in contact with an upper surface of the gallium nitride based compound semiconductor stacked structure among the upper electrodes, a step of forming a photoresist for a stripe on the first upper electrode layer, The method includes a step of removing the first upper electrode layer by dry etching using the photoresist for mask as a mask, and a step of forming a ridge stripe by removing a part of the gallium nitride-based compound semiconductor laminated structure also by dry etching.
[0011]
That is, since the first upper electrode layer is patterned in a stripe shape by a dry etching method that is anisotropic etching, the variation in the width of the current injection region is substantially caused by the formation of the photoresist mask for the stripe. It is determined only by the variation of the line width. As described above, in the case of the process according to the related art, the width of the current injection region is determined by the wet etching method in addition to the variation in the line width of the stripe photoresist mask for providing the opening in the dielectric. Variations in the width of the opening that occur when forming the portion also affect variations in the width of the current injection region. Therefore, the manufacturing method according to the present invention can greatly reduce the variation in the width of the current injection region as compared with the conventional method.
[0012]
Further, in the manufacturing method according to the present invention, first, a step of forming the first upper electrode layer on the surface of the gallium nitride-based compound semiconductor multilayer structure is performed. On the other hand, as described above, in the case of the process according to the conventional technique, before the upper electrode layer is formed on the surface of the gallium nitride-based compound semiconductor laminated structure, it is necessary to pass two histories of covering with the dielectric film. Become. Therefore, the manufacturing method according to the present invention is more effective in producing a residue on the semiconductor laminated structure due to the passage of the coating history and the resulting current-voltage characteristics and reliability of the semiconductor laser device, as compared with the conventional method. The negative effect on sex can be greatly reduced.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, some embodiments of the present invention will be described with reference to the drawings.
[0014]
<First embodiment>
FIG. 1 is a schematic sectional view illustrating a method for manufacturing a gallium nitride-based compound semiconductor laser according to the first embodiment of the present invention. An undoped GaN buffer layer formed by low-temperature growth, an n-type GaN contact layer, an n-type Al_0.1Ga_0.9N clad layer, n-type GaN light guide, In_0.05Ga_0.95N barrier layer and In_0.15Ga_{0. 85}An active layer having a quantum well structure in which an N well layer is superposed three times, p-type Al_0.2Ga_0.8N carrier block layer, p-type GaN light guide layer, p-type Al_0.1Ga_0.9As shown in FIG. 1A, the surface of a gallium nitride-based compound semiconductor multilayer structure 100 obtained by sequentially laminating an N clad layer and a p-type GaN contact layer is formed from Pb having a thickness of 150 Å by electron beam evaporation. A first upper electrode layer 10 is formed.
[0015]
Next, as shown in FIG. 2B, a stripe photoresist mask 40 having a line width of 1.5 μm is formed by photolithography, and further, as shown in FIG. 2C, the formed stripe photoresist mask 40 is formed. Is used as a mask, the first upper electrode layer 10 is etched by reactive ion etching until the surface of the gallium nitride-based compound semiconductor multilayer structure 100 is exposed.
[0016]
As the process gas in this case, Ar or Ar is Cl₂, SiCl₄, BCl₃A chlorine-based gas such as 0% to 50% by volume is used. The addition of these chlorine-based gases has the effect of suppressing the re-adhesion of Pb sputtered from the surface by Ar to the etched surface. However, when the addition is 50% or more, the selectivity to the gallium nitride-based compound semiconductor is greatly reduced, and the etching is substantially stopped when the surface of the gallium nitride-based compound semiconductor laminated structure 100 is exposed. It is difficult to obtain the cross-sectional shape as shown in FIG.
[0017]
Subsequent to the etching of the first upper electrode layer 10, the gallium nitride-based compound semiconductor multilayer structure 100 is also etched to the middle of the upper clad layer by the reactive ion etching method to form a ridge stripe as shown in FIG. I do. In this case, Cl₂, SiCl₄, BCl₃By using a process gas containing a chlorine-based gas in a volume ratio of 50% or more, the gallium nitride-based compound semiconductor multilayer structure 100 can be etched using the stripe photoresist mask 40 as a mask. Then, the photoresist mask 40 for stripes is removed with an organic solvent or the like to obtain the gallium nitride-based compound semiconductor laser according to the first embodiment.
[0018]
According to the method shown in the present embodiment, a ridge stripe type semiconductor laser having a ridge width obtained by accurately transferring the line width of the stripe photoresist mask 40 can be obtained. Variations in the current-voltage characteristics, oscillation threshold current, oscillation mode, etc. of the semiconductor laser device were reduced to less than half. Further, the method described in the present embodiment does not include a step of coating the gallium nitride-based compound semiconductor laminated structure at all before forming the first upper electrode layer 10, and therefore, the conventional technique Operating voltage about 0.5 volts lower than that of the gallium nitride-based compound semiconductor laser device fabricated by the method described above.
[0019]
In the first embodiment shown in FIG. 1, the first upper electrode layer is formed over the entire surface of the gallium nitride-based compound semiconductor multilayer structure. In this case, in the later step of etching the first upper electrode layer by the reactive ion etching method, depending on the etching conditions, the electrode metal detached from the surface is re-adhered to the etched surface, causing roughness on the etched surface. Sometimes. This phenomenon becomes more remarkable as the region to be etched becomes larger than the region covered with the mask material.
[0020]
For example, in the above example, the area covered with the mask material is a part covered with a stripe photoresist mask having a line width of 1.5 microns. Assuming that the stripe photoresist mask is formed at a repetitive pitch of 400 microns, the first upper electrode layer is etched in a 398.5-micron wide region up to the next stripe photoresist mask. The ratio of the region where the electrode metal is etched to the region where the electrode metal is not etched because it is covered with the mask material is about 266.
[0021]
As described above, the danger of etching surface roughness that occurs depending on the etching conditions is almost problematic when the ratio of the region where the electrode metal is etched to the region where the electrode metal is not etched is set to, for example, 1 or less. It can be reduced to a level without any. The specific method will be described below.
[0022]
<Second embodiment>
FIG. 2 is a schematic sectional view illustrating a method for manufacturing a gallium nitride-based compound semiconductor laser according to a second embodiment of the present invention. As shown in FIG. 2A, the surface of a gallium nitride-based compound semiconductor laminated structure 200 obtained by sequentially laminating the same structure as that of the first embodiment of the present invention on a substrate such as sapphire, as shown in FIG. To form a first upper electrode layer 11 made of Pb having a thickness of 150 Å. At this time, as in the first embodiment, the first upper electrode layer is formed not on the entire surface of the gallium nitride-based compound semiconductor laminated structure, but only in a region having a width of 40 μm. deep.
[0023]
Next, as shown in FIG. 3B, a stripe photoresist mask 41 having a line width of 1.5 μm is formed on the upper center of the first upper electrode layer 11 by photolithography. As shown in c), the first upper electrode layer 11 is etched by reactive ion etching using the formed photoresist mask 41 for a stripe until the surface of the gallium nitride-based compound semiconductor multilayer structure 200 is exposed. At this time, even on the surface of the gallium nitride-based compound semiconductor multilayer structure 200, a step 91 is formed between a region covered with the first upper electrode layer 11 before etching and a region not covered with the first upper electrode layer 11. The height of the step 91 is mainly determined by the thickness of the first upper electrode layer 11 and the addition ratio of the chlorine-based gas to Ar in the process gas. In the case of the present embodiment, the height is about 500 Å. is there.
[0024]
Subsequently, the gallium nitride-based compound semiconductor multilayer structure 200 is also etched to the middle of the upper clad layer by the reactive ion etching method to form a ridge stripe as shown in FIG. After that, the photoresist mask 41 for stripes is removed with an organic solvent or the like to obtain a gallium nitride-based compound semiconductor laser according to the second embodiment.
[0025]
According to the method described in the present embodiment, the region where the electrode metal is etched is covered with the stripe photoresist mask 41 having a line width of 1.5 μm in the first upper electrode layer 11 having a width of 40 μm. Only the area corresponding to a width of 38.5 microns. On the other hand, the region where the electrode metal is not etched is, as in the first embodiment, the region corresponding to a width of 361.5 μm if the stripe photoresist mask is formed at a repetition pitch of 400 μm. It is.
[0026]
Therefore, the ratio of the region where the electrode metal is etched to the region where the electrode metal is not etched is about 0.1, which is significantly smaller than that of about 266 in the first embodiment. The danger of etching surface roughness that occurs depending on the etching conditions could be reduced to a level that would cause almost no problem on an industrial level.
[0027]
Further, the method of the present embodiment for reducing the region where the electrode metal is etched includes a step of etching the first upper electrode layer by a reactive ion etching method, in which the electrode metal is And the amount of the reaction product can be greatly reduced, so that the second effect that etching with higher reproducibility can be repeatedly performed can be obtained.
[0028]
These effects are more effective as the width of the first upper electrode layer 11 formed in the step shown in FIG. 2A is smaller, but as shown in FIG. In the process, care must be taken because the step 91 generated when the first upper electrode layer 11 is removed by the reactive ion etching method becomes too close to the ridge to be formed. That is, as described above, in the step of forming a ridge, the semiconductor multilayer structure is etched to a point in the middle of the upper clad layer, and the remaining film thickness of the upper clad layer in controlling the light confinement in the horizontal direction. It is an important parameter.
[0029]
However, in the present manufacturing method, even if the optimum remaining film thickness of the upper cladding layer is obtained in a portion closer to the ridge than the step 91, in the portion farther from the ridge than the step 91, the optimum remaining film thickness is smaller. Will also be thin. For this reason, if the step 91 approaches the ridge too much, more specifically, if the step 91 approaches a distance less than twice the width of the ridge, its influence on the light confinement in the horizontal direction cannot be ignored. Therefore, in the example of the present embodiment, since the width of the ridge is 1.5 μm, the first upper electrode layer 11 is desirably 6.0 μm or more.
[0030]
In the present embodiment, as shown in FIG. 2B, the stripe photoresist mask 41 having a line width of 1.5 μm is provided at the upper center of the first upper electrode layer 11, but it is not necessarily the first upper electrode layer. It is not necessary to be provided at the center of the layer 11, and for the above-described reason, it is only required that the distance from the left and right ends of the first upper electrode layer 11 is at least 3 microns, which is twice the width of the ridge, closer to the center. good.
[0031]
As shown in FIG. 1A, in order to form the first upper electrode layer 11 only in a region having a width of 40 μm, a photoresist film having an opening having a width of 40 μm must be formed by stacking a gallium nitride-based compound semiconductor layer. A first upper electrode layer is formed on the structure 200 by a photolithography method, subsequently, a first upper electrode layer is formed by an electron beam evaporation method, and the photoresist film and the first upper electrode layer thereover are formed of an organic material such as acetone. There is a method of removing by a lift-off method in a solvent.
[0032]
However, in this case, before the first upper electrode layer 11 is formed, a step of covering the gallium nitride-based compound semiconductor laminated structure with a photoresist is included once. However, even so, compared to the conventional technology, which requires two coating histories of a stripe-forming photoresist mask and a dielectric film, or a dielectric film and a dielectric film, the semiconductor stacked structure has It is possible to greatly reduce the generation of the residue and the resulting adverse effect on the current-voltage characteristics and reliability of the semiconductor laser device.
[0033]
As shown in FIG. 2A, as a second technique for forming the first upper electrode layer 11 only in a region having a width of 40 μm, the first upper electrode layer 11 is formed on the entire upper surface of the gallium nitride-based compound semiconductor multilayer structure 200. Forming a first upper electrode layer by an electron beam evaporation method, and subsequently forming a striped photoresist film having a width of 40 μm on the first upper electrode layer by a photolithography method, followed by a wet etching method. There is a method of removing the first upper electrode layer formed in a region not covered with the photoresist film, and then removing the photoresist film with an organic solvent or the like.
[0034]
According to this method, as in the first embodiment of the present invention, before forming the first upper electrode layer, any step of covering the gallium nitride-based compound semiconductor multilayer structure is included. In addition, at the same time, the ratio of the region where the electrode metal is etched to the region where the electrode metal is not etched can be made smaller than in the case of the first embodiment of the present invention. In this method, since the first upper electrode layer is etched by the wet etching method, the width of the first upper electrode layer is relatively difficult to control, and a variation of several microns occurs. This is not a problem as long as it is formed at a distance of twice or more the width.
[0035]
In this example, even if the dispersion during wet etching is several microns with respect to the design value of the width of 40 microns, the width after etching can be formed with sufficient reproducibility to be 6.0 microns or more as described above. . For the etching of the first upper electrode layer 11 made of Pb, for example, a mixed solution of hydrochloric acid, nitric acid and water may be used.
[0036]
Further, as shown in FIG. 2A, as a third method for forming the first upper electrode layer 11 only in a region having a width of 40 μm, a metal mask having an opening having a width of 40 μm is used. A first upper electrode layer is formed by an electron beam evaporation method while being placed on the gallium nitride-based compound semiconductor multilayer structure 200, and after deposition, a metal mask is placed on the gallium nitride-based compound semiconductor multilayer structure 200 from above. There is a way to get rid of it. According to this method, as in the first embodiment of the present invention, before forming the first upper electrode layer, any step of covering the gallium nitride-based compound semiconductor multilayer structure is included. In addition, at the same time, the ratio of the region where the electrode metal is etched to the region where the electrode metal is not etched can be made smaller than in the case of the first embodiment of the present invention.
[0037]
In the first and second embodiments described above, the upper electrode layer is formed only on the ridge. However, in practice, the width of the upper part of the ridge is very narrow, 1.5 microns, and it is difficult to arrange a gold wire or the like for applying a voltage from the outside on the ridge.
[0038]
Therefore, an embodiment in which a second upper electrode is formed to solve this problem will be described below.
[0039]
<Third embodiment>
FIG. 3 is a schematic sectional view illustrating a method for manufacturing a gallium nitride-based compound semiconductor laser according to a third embodiment of the present invention. First, a gallium nitride-based compound semiconductor multilayer structure 300, a first upper electrode layer 12 made of Pb having a thickness of 150 Å, and a stripe photo having a line width of 1.5 μm are formed by the method described in detail in the first embodiment. The structure shown in FIG. 3A having the resist mask 42 is obtained.
[0040]
Next, as shown in FIG. 3B, a 2000-Å-thick SiO 2 film is formed on the entire surface by electron beam evaporation.₂The film 30 is formed. Next, a photoresist mask 42 for stripes and SiO 2₂A part of the film 30 is removed by a lift-off method in an organic solvent such as acetone to obtain a structure as shown in FIG.
[0041]
Thereafter, as shown in FIG. 3D, Au is formed on the first upper electrode layer 12 as the second upper electrode layer 20 having a width of 150 μm to a thickness of 2500 Å. In order to selectively form the second upper electrode layer only in the region having a width of 150 microns, a top electrode metal is formed by electron beam evaporation from a photoresist film having an opening having a width of 150 microns formed thereon. After the formation, the photoresist and the upper electrode metal deposited thereon can be easily formed by a lift-off method in an organic solvent.
[0042]
According to this method, the second upper electrode layer 20 has a width of 150 μm and a width sufficient to arrange a gold wire or the like for applying a voltage from the outside thereon, and The effect of the present invention on the width of the current injection region and the covering history of the gallium nitride based compound semiconductor laminated structure described in the method described in the first embodiment or the method in the second embodiment is maintained as it is. I have.
[0043]
Here, in order to obtain the structure shown in FIG. 3A, the method detailed in the first embodiment is used, but the method detailed in the second embodiment may be used instead. It is possible. However, in this case, similarly to the case of the second embodiment, even on the surface of the gallium nitride-based compound semiconductor multilayer structure 300, the region covered with the first upper electrode layer 12 before etching and the region not covered were not covered. A step is formed in the area.
[0044]
Here, in the gallium nitride based compound semiconductor laser according to the third embodiment described in FIG. 3, the direction (ridge) of the second upper electrode layer 20 shown in FIG. (Direction along the stripe) was not specified. However, in this direction, in particular, by forming the gallium nitride-based compound semiconductor laser so as not to be directly above the cavity facet, it is possible to produce a higher-quality gallium nitride-based compound semiconductor laser with higher yield. Become. Next, the case will be described.
[0045]
<Fourth embodiment>
FIG. 4 is a schematic diagram showing a structure of a gallium nitride-based compound semiconductor laser according to a fourth embodiment of the present invention. The shape of the gallium nitride based compound semiconductor laser shown in the figure is basically the same as that of the third embodiment, and the difference is that the second upper electrode layer 20 shown in FIG. 3 showing the third embodiment. In the present embodiment, the length of the second upper electrode layer 21 in the direction parallel to the stripe is 200 microns as shown in FIG. 4, the cavity length is 500 microns, and It is only a point defined to a finite length.
[0046]
The first upper electrode layer 13 formed on the gallium nitride-based compound semiconductor laminated structure 400 has a thickness of 150 Å of Pd, and the dielectric layer 31 has a thickness of 2000 Å of SiO.₂The film and the second upper electrode layer 21 are made of Au having a thickness of 2500 Å.
[0047]
As shown in FIG. 4, the length of the second upper electrode 21 in the direction parallel to the stripe is made shorter than the resonator length so that the second upper electrode is not formed immediately above the resonator end face. The following advantages are newly obtained. In other words, the thicker the electrode metal layer immediately above the cavity end face, the more the electrode metal layer is turned up from the cleavage plane as a starting point when forming the cavity end face by cleavage, so that a region where current is not injected is formed. In addition, the possibility that a problem such as blocking the optical path of the laser light emitted from the turned-up electrode metal increases. Such a danger is more remarkable when, for example, the thickness of the electrode metal layer immediately above the cavity end face exceeds 1,000 Å.
[0048]
The first upper electrode layer 13 shown in the figure has a thickness of at most 150 Å, whereas the second upper electrode layer 21 has a practical problem when bonding a gold wire thereon. In order to secure a bonding strength of a level that does not have any, a thickness of several thousand angstroms is required as in this embodiment. Therefore, if the second upper electrode layer 21 is arranged so as not to cover the resonator end face as shown in the figure, the electrode metal layer immediately above the resonator end face is only Pd having a thickness of 150 Å. Therefore, the risk described above is so small that it can be ignored. Moreover, at the same time, since the first upper electrode layer has a structure that covers the top of the ridge stripe including directly above the cavity end face, there is no region in which current is not injected.
[0049]
As shown in the figure, in order to form a second upper electrode having a length of 200 microns in the direction parallel to the stripe, a photoresist film having an opening having a length of 200 microns in the direction parallel to the stripe is formed. After the upper electrode metal is formed by electron beam evaporation from above, the photoresist and the upper electrode metal deposited thereon can be easily formed by a lift-off method in an organic solvent.
[0050]
Here, in the gallium nitride-based compound semiconductor laser according to the fourth embodiment described with reference to FIG. 4, it is assumed that the cavity surface is formed by cleavage. However, depending on the combination of the substrate to be used and the compound semiconductor laminated structure thereon, a plane having good cleavage properties cannot be obtained on both of them, and accordingly, a high quality end face may not be obtained depending on the cleavage. In such a case, the cavity end face is formed by a dry etching method. In this case, the present invention also provides a suitable manufacturing method which is not included in the conventional manufacturing method.
[0051]
That is, in a conventional gallium nitride-based compound semiconductor laser having a cavity facet formed by a dry etching method, in order to form an upper electrode after the cavity facet is formed, a few microns from the cavity facet of the laser element. An electrode can be formed only in a region inside the recessed portion, and there is a problem that the region where the electrode is not formed functions as an absorption layer.
[0052]
On the other hand, according to the manufacturing method of the present invention, it is possible to obtain a gallium nitride-based compound semiconductor laser having an upper electrode formed up to the end face of the resonator formed by dry etching. Hereinafter, the method will be described in detail.
[0053]
<Fifth embodiment>
FIG. 5 is a schematic diagram showing a structure of a gallium nitride-based compound semiconductor laser according to a fifth embodiment of the present invention. FIG. 6 is a schematic view showing the manufacturing method. The gallium nitride-based compound semiconductor laser shown in FIG. 5 has a 2000-Å-thick SiO 2 film on a gallium nitride-based compound semiconductor laminated structure 500 having a ridge stripe structure.₂A first upper electrode layer 14 made of Pb and having a thickness of 150 Å and a second upper electrode layer 22 made of Au and having a thickness of 2500 Å are formed via the film 32. This is the same as that of the gallium nitride based compound semiconductor laser according to the fourth embodiment shown in FIG.
[0054]
The difference is that the gallium nitride-based compound semiconductor laser according to the fourth embodiment is based on the premise that the resonator surface is formed by cleavage, whereas the gallium nitride-based compound semiconductor laser according to the present embodiment is: As shown in FIG. 5, the resonator end face 60 is formed by a dry etching method. A method for manufacturing a gallium nitride-based compound semiconductor laser having such a structure will be described below.
[0055]
The same structure as that according to the fourth embodiment, that is, a gallium nitride-based compound semiconductor laminated structure 500, a first upper electrode layer 14 made of Pb having a thickness of 150 angstroms, and a SiO 2 having a thickness of 2000 angstroms.₂As shown in FIG. 6B, a photomask for forming an end face of the resonator is formed on the structure shown in FIG. 6A comprising the film 32 and the second upper electrode 22 made of Au having a thickness of 2500 angstroms. 50 is formed. Next, by the reactive ion etching method, the SiO 2 in the region not covered with the cavity end face forming photomask 50 is removed.₂The film 32 is removed to obtain the shape shown in FIG.
[0056]
In this case, the process gas used for the reactive ion etching method is CF.₄, CHF₃According to these gases, the first upper electrode layer 14 in a region not covered with the cavity end face forming photomask 50 is hardly etched as shown in FIG. Remaining, SiO₂Only the membrane 32 is removed.
[0057]
Thereafter, as described in the first to fourth embodiments, as the process gas, Ar or Ar to Cl₂, SiCl₄, BCl₃The first upper portion of the region not covered with the cavity end face forming photomask 50 by the reactive ion etching method using a chlorine-based gas such as 0% to 50% added by volume ratio. The electrode layer 14 is etched until the surface of the gallium nitride-based compound semiconductor multilayer structure 500 is exposed to obtain the structure shown in FIG.
[0058]
Next, the gallium nitride-based compound semiconductor multilayer structure 500 is also etched by the reactive ion etching method, and the resonator end face 60 is formed as shown in FIG. In this case, Cl₂, SiCl₄, BCl₃By using a chlorine-based gas such as a main etching gas, the gallium nitride-based compound semiconductor multilayer structure 500 can be etched using the photomask 50 for cavity facet formation as a mask. After that, the photomask 50 for cavity end face formation is removed to obtain the gallium nitride compound semiconductor laser shown in FIG.
[0059]
According to the manufacturing method described in the present embodiment, the first upper electrode layer 14 and the gallium nitride-based compound semiconductor multilayer structure 500 thereunder are continuously etched using the photomask 50 for cavity facet formation as a mask. As a result, the first upper electrode layer 14 can be formed up to the end face of the resonator, and the conventional gallium nitride-based compound semiconductor laser having the end face of the resonator formed by the dry etching method poses a problem. There is no problem that a region where an electrode is not formed is formed, and that portion functions as an absorption layer.
[0060]
In the first to fifth embodiments described so far, the gallium nitride-based compound semiconductor multilayer structure is etched by the dry etching method, leaving only the ridge portion, but it is not necessary to etch all except the ridge portion. Alternatively, only the vicinity thereof may be etched.
[0061]
When etching is performed while leaving only the ridge portion, there is a risk that the ridge portion protruding from the surface may be damaged in a later process. On the other hand, when only the vicinity of the ridge is etched, only the ridge portion does not protrude, so that the risk of damage in such a post-process can be greatly reduced. Therefore, next, a case where only the vicinity of the ridge is etched will be described.
[0062]
<Sixth embodiment>
FIG. 7 is a schematic diagram showing a structure of a gallium nitride-based compound semiconductor laser according to a sixth embodiment of the present invention. FIG. 8 is a schematic view showing the manufacturing method. The gallium nitride based compound semiconductor laser shown in FIG. 7 has a 1000 angstrom thick SiO 2 on a gallium nitride based compound semiconductor laminated structure 600 having a ridge stripe structure.₂Film 33 and 1500 angstrom thick SiO₂A first upper electrode layer 15 made of Pb having a thickness of 150 Å and a second upper electrode layer 23 made of Au having a thickness of 2500 Å are formed via a film 34. This is the same as that of the gallium nitride based compound semiconductor laser according to the fourth embodiment shown in FIG.
[0063]
The difference is that in the gallium nitride-based compound semiconductor laser according to the fourth embodiment, the entire surface of the gallium nitride-based compound semiconductor laminated structure 600 except for the ridge stripe portion is dug down by the dry etching method. In the gallium nitride based compound semiconductor laser according to the embodiment, only the portions having a width of 25 μm on each side on both sides of the ridge are dug down. A method for manufacturing a gallium nitride-based compound semiconductor laser having such a structure will be described below.
[0064]
First, on the surface of a gallium nitride-based compound semiconductor laminated structure 600 obtained by sequentially laminating an n-type gallium nitride-based compound semiconductor layer and a p-type gallium nitride-based compound semiconductor layer on a substrate such as sapphire, FIG. As described above, the first upper electrode layer 15 made of Pb having a thickness of 150 angstroms is formed by the electron beam evaporation method. At this time, the first upper electrode 15 is formed only in a region having a width of 40 microns by the same method as that described in detail in the description of the second embodiment.
[0065]
Next, as shown in FIG. 2B, a thickness of 1000 gm is formed on the entire surface of the gallium nitride-based compound semiconductor stacked structure 600 except for a region having a width of 5 μm on one side on both sides of the first upper electrode 15. Angstrom SiO₂The film 33 is formed by an electron beam evaporation method.
[0066]
Next, as shown in FIG. 2C, a stripe photoresist mask 43 having a line width of 1.5 μm is formed on the first upper electrode layer 15 by photolithography. As described in (1), the first upper electrode layer 15 is etched by the reactive ion etching method using the formed photoresist mask for stripes 43 until the surface of the gallium nitride-based compound semiconductor multilayer structure 600 is exposed. At this time, even on the surface of the gallium nitride-based compound semiconductor laminated structure 600, a step 92 is formed between a region covered with the first upper electrode layer 15 before etching and a region not covered with the first upper electrode layer 15.
[0067]
Subsequently, as shown in FIG. 3E, the gallium nitride-based compound semiconductor multilayer structure 600 is also etched to the middle of the upper clad layer by the reactive ion etching method to form a ridge stripe. The two dry etching steps by the reactive ion etching method can be performed by the same method as that in the method of manufacturing the gallium nitride-based compound semiconductor laser according to the first embodiment, and thus the details are omitted here.
[0068]
Next, a 1500 angstrom thick SiO₂A film 34 is formed by an electron beam evaporation method, and thereafter, by a lift-off method, a photoresist mask 43 for a stripe and a SiO 2₂By removing the film 34, the structure shown in FIG.
[0069]
Thereafter, Au is formed on the first upper electrode layer 15 as the second upper electrode layer 23 having a width of 150 μm to a thickness of 2500 Å, and the gallium nitride-based compound semiconductor laser shown in FIG. obtain. The second upper electrode layer 23 having a width of 150 μm can be formed by the same method as that in the method of manufacturing the gallium nitride-based compound semiconductor laser according to the third embodiment, and thus the details thereof are omitted here.
[0070]
According to the manufacturing method shown in the present embodiment, only the region having a width of 30 μm on one side near the ridge is dug down by dry etching, so that the entire surface of the wafer is etched while leaving only the ridge portion. There is no danger that the ridge protruding from the surface will be damaged in a later process.
[0071]
In the present embodiment, a portion having a width of 25 μm on each side is dug down on both sides of the ridge, so that a pair of grooves having a width of 25 μm is formed on the left and right sides of the ridge. However, this groove is provided only on one of the left and right sides of the ridge, that is, on the side where the groove is not provided, only the ridge portion does not protrude even if the entire upper surface is etched to the middle of the upper cladding layer. The same effects as those of the present embodiment can be obtained. Also, when grooves are provided on both sides of the ridge, their widths do not necessarily have to be symmetrical. Further, in FIG. 7 showing the present embodiment, the second upper electrode layer is drawn so as to be symmetrical with respect to the ridge. However, even if the left and right widths are asymmetrical, the second upper electrode layer is provided only on one side. If there is, there is no problem.
[0072]
As described above, the present invention has been described in detail based on some embodiments. However, the contents of the present invention are not limited to the contents of the embodiments described here. Next, modifications based on the technical idea of the present invention will be described.
[0073]
The “gallium nitride-based compound semiconductor” in the present invention includes, in addition to gallium nitride (GaN), a semiconductor in which Ga is partially replaced by another group III element, for example, Ga_sAl_tIn_1-stN (0 <s ≦ 1, 0 ≦ t <1, 0 <s + t ≦ 1), and a semiconductor in which some of the constituent atoms are replaced with impurity atoms or the like, or other impurities are added. Semiconductors are also included.
[0074]
The dry etching method used in each of the above-described embodiments was a reactive ion etching method. Etching similar to that described above is possible.
[0075]
In each embodiment, as the process gas in the dry etching method for the first upper electrode, Ar or Cl is added to Ar.₂, SiCl₄, BCl₃Although a chlorine-based gas such as 0% to 50% added by volume ratio was used, another inert gas such as He or Ne may be used instead of Ar.
[0076]
In each embodiment, Pb was used as the first upper electrode. However, even if Ni, Ti, or the like, or a structure in which another metal such as Au, Mo, etc. is laminated thereon, A similar gallium nitride-based compound semiconductor laser can be produced by a manufacturing method. However, as a result of the examination, when Ni or Ti is used, the optimum thickness for minimizing the contact resistance is about 65% thicker than when Pb is used. Therefore, the etching time in the step of removing the first upper electrode layer by dry etching using the photoresist for stripes as a mask becomes longer, and the amount of film reduction of the photoresist for stripes increases. This stripe photoresist is also used as a mask in a step of forming a ridge stripe by removing a part of the gallium nitride-based compound semiconductor laminated structure. Attention must be paid to the possibility that a necessary resist film thickness cannot be ensured in the process.
[0077]
Further, in each embodiment, the thickness of the first upper electrode is set to 150 Å, but the layer thickness is not limited to 150 Å. However, in the case where the layer thickness is a structure in which a plurality of metals are laminated, if the total thickness exceeds 1000 angstroms, the electrode metal layer may be cleaved when forming the cavity end face by cleavage. Care must be taken because there is a high possibility that there will be problems such as turning up from the starting point, creating an area where current is not injected, and blocking the optical path of the laser light emitted by the electrode metal that has been turned up. is there. Further, as described above, the thicker the film, the longer the etching time in the step of removing the first upper electrode layer by dry etching using the photoresist for the stripe as a mask, and thus the film of the photoresist for the stripe. Attention must also be paid to the fact that the weight loss increases.
[0078]
Although the second upper electrode formed in the third to sixth embodiments was Au, a gold wire can be bonded to electrically connect the prepared gallium nitride based compound semiconductor laser device to the outside, or As long as it can be welded to an external electrode pad, a metal such as Al can be used, and there is no problem with a structure in which a plurality of metals are stacked instead of a single metal. Also, there is no problem with the thickness as long as it is thick enough for external electrical connection.
[0079]
In addition, the SiO used in the third to sixth embodiments₂Is ZrO₂And TiO₂, SiO, Ta₂O₅There is no problem even if it is replaced with another inorganic dielectric such as GaN, SiN, or the like, or a gallium nitride compound such as AlGaN, and the thickness is not limited to the thickness exemplified in the description of the embodiment. Also, the formation method may be a sputtering method, a plasma CVD method, or the like, instead of the electron beam evaporation method exemplified in the description of the embodiment.
[0080]
As described above, the active layers in the gallium nitride-based compound semiconductor multilayer structures 100 to 600 in the first to sixth embodiments have In as described at the beginning of the first embodiment._0.05Ga_0.95N barrier layer and In_0.15Ga_0.85An active layer having a quantum well structure in which an N well layer is superposed three times has been employed. However, it is also possible to use two or three barrier layers. The case will be described below.
[0081]
<Seventh embodiment>
FIG. 9 shows a detailed laminated structure in the vicinity of the active layer in the present embodiment. 4 nm thick In_0.15Ga_0.85N well layer 803 and 4 nm thick GaN, (801, 805) and 4 nm thick In_0.05Ga_0.95An active layer having a multiple quantum well structure composed of N (802, 804) barrier layers is grown in the order of barrier layer / well layer / barrier layer / well layer / barrier layer / well layer / barrier layer. The number of well layers was three. At this time, the well layer was grown without doping with impurities.
[0082]
Further, the thickness of the well layer is preferably in the range of 2 to 7 nm. If the thickness is smaller than 2 nm, interface scattering increases and the threshold current increases, which is not preferable. If the thickness is larger than 7 nm, electrons and holes are formed in the well layer. Spatial separation occurs, and the threshold current is increased in order to lower the recombination probability. In other words, the thickness of the well layer is preferably 2 nm or more and 7 nm or less, and the thickness of the well layer is 4 nm in the present embodiment.
[0083]
The barrier layer had a two-layer structure. Of the two layers, the layer on the n-type GaN light guide layer 104 side is the first layer 801 or the p-type Al_0.2Ga_0.8The layer on the N carrier block layer 106 side is referred to as a second layer 802. In addition, as shown in FIG. 9, a first layer in contact with the n-type GaN light guide layer 104 is a third layer 805 and a p-type Al layer._{0. 2}Ga_0.8A layer in contact with the N carrier block layer 106 will be referred to as a fourth layer 804. Since the third layer and the fourth layer are not in direct contact with the well layer, the situation is different from the other first layer and the second layer, and the third layer and the fourth layer are referred to as the third and fourth layers to distinguish them. It was to be. That is, the first and third layers are GaN, the second and fourth layers are In._0.05Ga_{0. 95}N.
[0084]
In this embodiment, the thickness of the first, second, third, and fourth layers is 4 nm, the thickness of the entire barrier layer is 8 nm, and the first and third layers are doped with n-type impurities such as Si. I do. With respect to the second and fourth layers, n-type impurities such as Si were not added intentionally and were made non-doped. The Si concentration at this time is 5 × 10^Fifteencm^-3~ 1 × 10²⁰cm^-3Is good, this time 1 × 10¹⁸cm^-3I went in. Si concentration is 1 × 10²⁰cm^-3In the above case, excessive doping of Si deteriorates the crystallinity of the active layer and causes an increase in threshold current density, which is not good. Also, 5 × 10^Fifteencm^-3If the value is below, generation of carriers does not occur, causing an increase in threshold current density. Further, within the above range, there is no problem even if the Si concentrations of the first and third layers are different. This Si concentration is measured using a measuring method such as SIMS. FIG. 10 shows a band diagram of the active layer shown in FIG.
[0085]
In this embodiment, Mg doped as an impurity is doped as a p-type impurity.¹⁹/ Cm³~ 2 × 10²⁰/ Cm³It is added at a concentration of
[0086]
In this way, a gallium nitride-based compound semiconductor multilayer structure is formed on the n-type GaN substrate, and thereafter, the Mg-doped layer is made into a low-resistance p-type by heat treatment or the like, and then the same as in the third embodiment of the present invention. A semiconductor laser device was manufactured by the manufacturing method described above. The semiconductor laser device was mounted on a stem using solder or the like, and was electrically connected by wire bonding. A semiconductor laser device was assembled, and the characteristic yield was evaluated. As a result, good characteristics were obtained.
[0087]
The threshold current density of the semiconductor laser device thus obtained is 2.5 kA / cm²Met. FIG. 11 shows that the thickness of the entire barrier layer is constant at 8 nm, the first layer and the third layer, the second layer and the fourth layer have the same thickness, and the first layer thickness is the X-axis. Is plotted. That is, when the first layer is 1 nm, the second layer is 7 nm, when the first layer is 2 nm, the second layer is 6 nm, and when the first layer is 4 nm, the second layer is 7 nm. The layer thickness of the second layer is determined so that the layer is 4 nm and the overall thickness of the barrier layer is 8 nm. FIG. 11 shows the result of an experiment performed with the layer thickness determined as described above. The effect of reducing the threshold current density was observed when the first layer and the third layer were 4 nm or less.
[0088]
Regarding the above results, the increase in the threshold current density where the first layer and the third layer are thicker than 4 nm is due to the fact that even if the first layer and the third layer are further thickened, the injection into the well layer is not performed. It is considered that the amount of carriers to be doped does not increase and the amount of Si doped in the barrier layer increases, so that the free carrier scattering in the active layer increases and the internal loss increases, so that the threshold current density increases. However, by reducing the thickness of the first layer and the third layer to 4 nm or less, an increase in internal loss due to free carrier scattering is suppressed, and the first layer and the third layer are doped with Si. Thus, it is considered that an element having a low threshold current density was realized by efficiently supplying carriers to the well layer.
[0089]
However, if the thicknesses of the first layer and the third layer are 0.3 nm or less, a sufficient number of carriers cannot be injected into the well layer, so that the threshold current density increases again. Further, in the present embodiment, the third layer was doped with Si, but the result of the third layer was the same as that shown in FIG. 11 whether or not Si was doped.
[0090]
The above experiment was performed with the well layer thickness in the range of 2 nm or more and 7 nm or less and the barrier layer thickness in the range of 7 nm to 12 nm. When the thickness of the barrier layer was less than 7 nm, the threshold current density increased. This is probably because the thickness of the active layer was reduced and the light confinement was weakened. Further, when the thickness was 12 nm or more, the wells were too far apart, and holes with low mobility were not uniformly injected into each well layer, causing a decrease in gain and an increase in threshold current density.
[0091]
In summary, when the number of regions in the barrier layer doped with impurities such as Si increases, the free carrier scattering in the active layer increases and the internal loss increases, so that the threshold current density increases. In addition, it has been found that when the first layer and the third layer are doped with Si, the threshold current density decreases because carriers are efficiently injected into the well layer.
[0092]
That is, when the thickness of the well layer is in the range of 2 to 7 nm and the thickness of the barrier layer is in the range of 7 nm to 12 nm, the doping of the barrier layer is preferably performed on the first layer and the third layer. Carriers can be well injected into the well layer. When the thickness of the first and third layers is 0.3 nm or more and 4 nm or less, increase in internal loss due to free carrier scattering is suppressed, and carriers can be efficiently injected into the well layer, so that the threshold current density is reduced. can do. However, a region thicker than 4 nm is not preferable because the effect of carrier injection into the well layer causes an increase in internal loss due to free carrier scattering.
[0093]
In the present embodiment, the second layer and the fourth layer are made of In._0.05Ga_0.95Although it is assumed to be N, even if this layer is GaN, almost the same result can be obtained without any problem.
[0094]
<Eighth embodiment>
In this embodiment, the first layer and the third layer are made of In._0.05Ga_0.95This is exactly the same as the seventh embodiment, except that N is non-doped, the second layer and the fourth layer are GaN and Si-doped. When the thicknesses of the second and fourth layers were plotted on the X-axis with the same thickness of the second and fourth layers, almost the same results as in FIG. 11 were obtained. When the thickness of the well layer is in the range of 2 nm to 7 nm and the thickness of the barrier layer is in the range of 7 nm to 12 nm, the barrier layer is preferably doped into the second layer and the fourth layer. Carriers can be well injected into the well layer.
[0095]
When the thickness of the second layer and the fourth layer is not less than 0.3 nm and not more than 4 nm, an increase in internal loss due to free carrier scattering is suppressed, and carriers can be efficiently injected into the well layer. can do. However, in a region thicker than 4 nm, the effect of carrier injection undesirably causes an increase in internal loss due to free carrier scattering. In the present embodiment, the first layer and the third layer are made of In._0.05Ga_0.95Although it is assumed to be N, even if this layer is GaN, almost the same result can be obtained without any problem.
[0096]
<Ninth embodiment>
In the present embodiment, the barrier layer of the active layer is composed of three layers. The active layer is formed as follows, and a detailed laminated structure near the active layer is shown in FIG. 4 nm thick In_0.15Ga_0.85N well layer 604, 9 nm thick GaN (602) and In_0.05Ga_0.95An active layer having a multiple quantum well structure composed of barrier layers made of N (601, 603, 606, 607) is formed in the order of barrier layer / well layer / barrier layer / well layer / barrier layer / well layer / barrier layer. Grew up. At this time, the well layer was grown without doping with impurities.
[0097]
Further, the thickness of the well layer is preferably in the range of 2 to 7 nm. If the thickness is smaller than 2 nm, interface scattering increases and the threshold current increases, which is not preferable. If the thickness is larger than 7 nm, electrons and holes are formed in the well layer. Spatial separation occurs, and the threshold current is increased in order to lower the recombination probability. In other words, the thickness of the well layer is preferably 2 nm or more and 7 nm or less, and the thickness of the well layer is 4 nm in the present embodiment.
[0098]
As for the barrier layer, the layer on the side of the n-type GaN light guide layer 104 among the −3 layers having the −3 layer structure is a first layer (In layer)._0.05Ga_0.95N) 601 and p-type Al_0.2Ga_0.8The layer on the N carrier block layer 106 side is changed to a third layer (In_0.05Ga_0.95N) 603, and the middle layer is referred to as a second layer (GaN) 602. As shown in FIG. 12, the first layer in contact with the n-type GaN light guide layer 104 is a fourth layer 606 and a p-type Al layer._0.2Ga_0.8The third layer that is in contact with the N carrier block layer 106 will be particularly referred to as a fifth layer 607. Since the fourth layer and the fifth layer are not in direct contact with the well layer, the situation is different from the other first layer and the second layer, and the fourth layer and the fifth layer are referred to as the fourth and fifth layers to distinguish them. It was to be.
[0099]
In the present embodiment, the thicknesses of the first, second, third, fourth, and fifth layers are each 3 nm, and the second layer is doped with an n-type impurity such as Si. The Si concentration at this time is 5 × 10^Fifteencm^-3~ 1 × 10²⁰cm^-3Is good, this time 1 × 10¹⁸cm^-3I went in. Si concentration is 1 × 10²⁰cm^-3In the above case, excessive doping of Si deteriorates the crystallinity of the active layer and causes an increase in threshold current density, which is not good. Also, 5 × 10^Fifteencm^-3If the value is below, generation of carriers does not occur, causing an increase in threshold current density. This Si concentration is measured using a measuring method such as SIMS. FIG. 13 shows a band diagram of the active layer shown in FIG.
[0100]
In this embodiment, Mg doped as an impurity is doped as a p-type impurity.¹⁹/ Cm³~ 2 × 10²⁰/ Cm³It is added at a concentration of
[0101]
In this way, a gallium nitride-based compound semiconductor multilayer structure is formed on the n-type GaN substrate, and thereafter, the Mg-doped layer is made into a low-resistance p-type by heat treatment or the like, and then the same as in the third embodiment of the present invention. A semiconductor laser device was manufactured by the manufacturing method described above. The semiconductor laser device was mounted on a stem using solder or the like, and was electrically connected by wire bonding. A semiconductor laser device was assembled, and the characteristic yield was evaluated. As a result, good characteristics were obtained.
[0102]
The threshold current density of the semiconductor laser device thus obtained is 3.0 kA / cm.²Was a low value. FIG. 14 shows the first layer and the third layer having the same thickness with the thickness of the entire barrier layer 205 being constant at 9 nm, and plotting the layer thickness on the X-axis. That is, when the first layer and the third layer are 1 nm, the second layer is 7 nm. When the first layer and the third layer are 2 nm, the second layer is 5 nm. When the thickness of the second layer is 3 nm, the thickness of the second layer is 3 nm, and the thickness of the second layer is determined so that the entire thickness of the barrier layer 205 is 9 nm.
[0103]
FIG. 14 shows the result of an experiment performed with the layer thickness determined as described above. The effect of reducing the threshold current density was observed when the first layer and the third layer were 3 nm or less. The reason why the threshold current density decreases in the region where the first layer and the third layer are thinner than 3 nm is considered as follows.
[0104]
In the present embodiment, the region of the barrier layer in contact with the well layer is non-doped. Therefore, carriers generated in the barrier layer are not effectively injected into the well layer. However, in the present embodiment, the region of the barrier layer in contact with the well layer is made of In having a smaller energy gap than GaN in the Si-doped region at the center of the barrier layer._0.05Ga_0.95N is used. Therefore, carriers generated in the center of the barrier layer are injected into the well layer without being hindered. Therefore, it is considered that the threshold density can be reduced.
[0105]
Further, the threshold current density increases when the first layer and the third layer are thicker than 3 nm. This is because when the first layer and the third layer are further thickened, the well layer and the Si-doped Because the two layers are separated, the thick In_0.05Ga_0.95It is considered that the N layer is consumed by traps such as light emission and non-light emission, so that carriers are not effectively injected into the well layer, the amount of injected carriers is reduced, and the threshold current density is increased.
[0106]
【The invention's effect】
According to the present invention, since the first upper electrode layer is patterned in a stripe shape by the dry etching method which is anisotropic etching, the variation of the width of the current injection region is substantially reduced by the stripe photo. It is determined only by the variation in the line width of the resist mask. As described above, in the case of the process according to the conventional technique, in addition to the variation in the line width of the photoresist mask for the stripe for providing the opening in the dielectric, the opening generated when the opening is formed by the wet etching method. Variations in section width also affect variations in the width of the current injection region. Therefore, the manufacturing method according to the present invention can greatly reduce the variation in the width of the current injection region as compared with the conventional method.
[0107]
Further, in the manufacturing method according to the present invention, first, a step of forming the first upper electrode layer on the surface of the gallium nitride-based compound semiconductor multilayer structure is performed. On the other hand, as described above, in the case of the process according to the conventional technology, a stripe-forming photoresist mask and a dielectric film, or a dielectric film, are formed on the surface of the gallium nitride-based compound semiconductor laminated structure before the upper electrode layer is formed. Two coating histories of the body film and the dielectric film will be passed. Therefore, the manufacturing method according to the present invention is more effective in producing a residue on the semiconductor laminated structure due to the passage of the coating history and the resulting current-voltage characteristics and reliability of the semiconductor laser device, as compared with the conventional method. The negative effect on sex can be greatly reduced.
[0108]
FIG. 15 is a plan view of the vicinity of the ridge immediately before the formation of the upper electrode layer in the process according to the conventional technique, when the area is observed by micro Auger electron spectroscopy. The state shown in the figure is described in detail. FIG. 16B in the ridge stripe forming step of the conventional gallium nitride-based compound semiconductor laser device described above with reference to FIG. After the formation, the surface of the semiconductor multilayer structure is etched using a dry etching apparatus, which corresponds to a schematic cross-sectional view after forming a ridge stripe. The removed state corresponds to a case when viewed from above the plane of FIG. 16B.
[0109]
FIG. 15A is a plan view showing the distribution of the signal intensity of Auger electrons originating from carbon atoms, and FIG. 15B is a position where a ridge stripe corresponding to the emission intensity distribution shown in FIG. FIG. The signal intensity distribution in FIG. 3A indicates that the closer to white, the stronger the Auger electrons originating from carbon atoms are detected. In correspondence with FIG. It can be seen that the carbon atoms are localized on the side surface 901 and the upper surface 902 of the ridge.
[0110]
In the process, the most likely cause of the localization of carbon atoms on the upper surface 902 of the ridge is carbon contained in the stripe-forming photoresist mask formed on the upper surface 902 of the ridge. After the dry etching process for forming the ridge stripe is completed, the photoresist itself is removed by cleaning with an organic solvent such as acetone. It is presumed that the photomask is deteriorated, and in fact, after forming a photoresist mask for forming a stripe and performing cleaning with acetone as it is without performing dry etching, it is observed by the same micro Auger electron spectroscopy. Auger electrons originating from carbon atoms were not detected in the portion where the resist mask was formed and other portions.
[0111]
On the other hand, the side surface 901 of the ridge has no history of coating with such a resist mask, but in the dry etching step for forming the ridge stripe, the sputtered photoresist mask for forming the stripe scatters, and the side surface of the ridge is scattered. Suspected to have re-attached to the surface.
[0112]
Also, instead of a photoresist, SiO 2 is used as a mask for forming a stripe.₂In the case where was used, the same observation by micro Auger electron spectroscopy was performed. As a result, residual Si atoms were observed on the upper surface of the ridge. In this case, no Si atom was observed on the side surface of the ridge.
[0113]
On the other hand, in the method of manufacturing a gallium nitride based compound semiconductor laser device according to the present invention, such a resist or SiO 2₂In fact, even if the ridge of the completed laser element was observed by micro Auger electron spectroscopy while sputtering the upper electrode layer, carbon was not present at the interface between the surface of the semiconductor laminated structure and the electrode. No impurity atoms such as Si and Si were detected.
[0114]
Therefore, the effect of the present invention that an operating voltage about 0.5 volt lower than that of the gallium nitride-based compound semiconductor laser device manufactured by the conventional technique described at the end of the description of the first embodiment can be realized. However, it is supported by the absence of impurity atoms at the interface between the surface and the electrode of such a semiconductor multilayer structure, and conversely, the method of manufacturing a gallium nitride-based compound semiconductor laser device according to the present invention is as follows. It can be said that this is a suitable technique for obtaining a structure in which no impurity atoms are present at the interface.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view illustrating a method for manufacturing a gallium nitride-based compound semiconductor laser according to a first embodiment of the present invention.
FIG. 2 is a schematic sectional view illustrating a method for manufacturing a gallium nitride-based compound semiconductor laser according to a second embodiment of the present invention.
FIG. 3 is a schematic sectional view illustrating a method for manufacturing a gallium nitride-based compound semiconductor laser according to a third embodiment of the present invention.
FIG. 4 is a schematic view showing the structure of a gallium nitride based compound semiconductor laser according to a fourth embodiment of the present invention.
FIG. 5 is a schematic view showing the structure of a gallium nitride-based compound semiconductor laser according to a fifth embodiment of the present invention.
FIG. 6 is a schematic sectional view showing a method for manufacturing a gallium nitride-based compound semiconductor laser according to a fifth embodiment of the present invention.
FIG. 7 is a schematic sectional view showing the structure of a gallium nitride based compound semiconductor laser according to a sixth embodiment of the present invention.
FIG. 8 is a schematic sectional view illustrating a method for manufacturing a gallium nitride-based compound semiconductor laser according to a sixth embodiment of the present invention.
FIG. 9 is a schematic sectional view showing the structure of a nitride compound semiconductor laser device according to a seventh embodiment of the present invention.
FIG. 10 is a band diagram showing the energy state of the active layer.
FIG. 11 is a correlation diagram between a thickness of a layer doped with Si in a barrier layer and a threshold current density of an LD.
FIG. 12 is a schematic sectional view showing an active layer structure of a nitride compound semiconductor laser device according to a ninth embodiment of the present invention;
FIG. 13 is a band diagram showing the energy state of the active layer.
FIG. 14 is a correlation diagram between the thickness of the layer doped with Si in the barrier layer and the threshold current density of the LD.
FIG. 15 is a plan view showing a case where a ridge portion in a conventional ridge stripe type semiconductor laser device is observed by micro Auger electron spectroscopy.
FIG. 16 is a schematic cross-sectional view showing a step of forming a ridge stripe type waveguide structure in a conventional ridge stripe type semiconductor laser device.
[Explanation of symbols]
10, 11, 12, 13, 14, 15}... First upper electrode layer
20, 21, 22, 23}... Second upper electrode layer
25: Upper electrode layer
30, 31, 32, 33, 34 {...} SiO₂film
35 ... Dielectric film
40, 41, 42, 43, 44}... Photoresist mask for stripe formation
50 ... Photoresist mask for cavity facet creation
70, 71 ... Photoresist mask
80, 81, 90} ... opening
91, 92 ... Step
100, 200, 300, 400, 500, 600, 700 {...} Gallium nitride based compound semiconductor multilayer structure
104 ... Si-doped n-type GaN optical guide layer
106 ... Mg-doped Al_0.2Ga_0.8N carrier block layer
601 ... First layer
602 ... Second layer
603 ... The third layer
604 Well layer
606 ..4th layer
607 ..5th layer
801 ... First layer
802 ... Second layer
803 Well layer
804… 4th layer
805 ... The third layer
901 ... Side of the ridge
902 ... Top of the ridge

Claims (13)

Forming a first upper electrode layer on the gallium nitride based compound semiconductor laminated structure;
Forming a photoresist for a stripe on the first upper electrode layer;
Removing the first upper electrode layer by dry etching using the photoresist for the stripe as a mask,
A method for manufacturing a ridge stripe type gallium nitride based compound semiconductor laser, comprising forming a ridge stripe by removing a part of the gallium nitride based compound semiconductor laminated structure by dry etching using a stripe photoresist as a mask. . 2. The ridge stripe type gallium nitride based compound semiconductor laser according to claim 1, wherein a process gas containing 50% or more of an inert gas is used in the dry etching in the step of removing the first upper electrode layer. Production method. 2. The method according to claim 1, wherein a process gas containing 50% or more of a chlorine-based gas is used in the dry etching in the step of forming the ridge stripe. 2. The ridge stripe type according to claim 1, wherein, in the step of forming the first upper electrode layer, the first upper electrode layer is formed in a stripe shape, and the width thereof is wider than the width of the stripe photoresist. A method for manufacturing a gallium nitride-based compound semiconductor laser. After forming a first upper electrode layer on the gallium nitride-based compound semiconductor laminated structure, and covering a portion of the first upper electrode layer with a photoresist having a predetermined width, of the first upper electrode layer The method according to claim 4, wherein the first upper electrode layer is striped by removing a portion not covered with the photoresist with an acid-based etching solution, and then removing the photoresist. A method for manufacturing a ridge stripe type gallium nitride compound semiconductor laser. 5. The ridge stripe type gallium nitride-based system according to claim 4, wherein the first upper electrode layer is formed in a stripe shape by forming the first upper electrode layer using a mask having a stripe-shaped opening. A method for manufacturing a compound semiconductor laser. 5. The method according to claim 4, wherein the width of the first upper electrode layer is at least twice the width of the stripe photoresist. After all the above steps,
Forming a dielectric film on the surface including the photoresist for the stripe,
2. The ridge stripe type gallium nitride based compound semiconductor laser according to claim 1, further comprising a step of removing the stripe photoresist and a portion of the dielectric film on the stripe photoresist by a lift-off method. Method. After all the above steps,
9. The method for manufacturing a ridge stripe type gallium nitride based compound semiconductor laser according to claim 8, further comprising a step of forming a second upper electrode layer on a surface including the exposed first upper electrode layer. The method according to claim 9, wherein the second upper electrode layer is not formed immediately above the cavity facet. After all the above steps,
Forming a photoresist for the cavity end face;
Removing the dielectric film by dry etching using the cavity facet photoresist as a mask,
Removing the first upper electrode using the cavity end face photoresist as a mask,
9. The ridge stripe type according to claim 8, further comprising a step of removing a part of the gallium nitride based compound semiconductor laminated structure by dry etching using the cavity facet photoresist as a mask to form a cavity facet. For manufacturing a gallium nitride compound semiconductor laser. A first upper electrode located on the ridge and having substantially the same width as the top of the ridge;
A ridge stripe type gallium nitride-based compound semiconductor laser, comprising a second upper electrode located on the first upper electrode and having a wider width than the first upper electrode. A method for manufacturing a ridge stripe type gallium nitride based compound semiconductor laser, wherein a positional relationship between a ridge top and an upper electrode formed on the ridge top is determined by a self-alignment method.

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