JP5204170B2 - Gallium nitride semiconductor laser and manufacturing method thereof - Google Patents

Description

  The present invention relates to a semiconductor laser device, in particular, a gallium nitride compound semiconductor laser device having a ridge stripe structure, and a method for manufacturing the same.

  In a semiconductor laser using a gallium nitride compound semiconductor, in order to confine light and current, for example, as shown in Japanese Patent Application Laid-Open Nos. 11-340573 and 2002-43692, a ridge stripe type semiconductor laser is used. A waveguide structure is often provided.

JP 11-340573 A JP 2002-43692 A

FIG. 5 shows a schematic diagram of a conventional ridge stripe type gallium nitride compound semiconductor laser device. The gallium nitride compound semiconductor multilayer structure 500 formed on the substrate has a ridge stripe 98, and the gallium nitride compound semiconductor multilayer structure 500 is formed of SiO ₂ , SiN except for the opening 88 provided on the upper surface of the ridge stripe 98. Etc., which are covered with a dielectric layer 48. Further, the upper electrode layer 18 is formed so as to cover the entire surface of the ridge stripe 98.

  The conventional structure described above has the following problems. This will be described with reference to FIG. A dielectric layer 48 having an opening 88 is provided between the upper electrode 18 and the gallium nitride compound semiconductor multilayer structure 500 so as to selectively inject current through the ridge stripe 98 to narrow the current. ing. The opening 88 is generally provided on the upper surface of the ridge stripe 98 with a width narrower than the width of the upper surface of the ridge stripe 98. In order to obtain the opening 88, it is necessary to form a photomask for providing the opening on the upper surface of the ridge stripe 98.

However, when forming a photomask for providing an opening having a width narrower than the width of the ridge stripe 98 by 1.0 micron (1 micron = 10 ⁻⁶ m), for example, on the upper surface of the ridge stripe 98, Assuming that the center and the center of the opening on the photomask are perfectly matched, the clearance from the end of the ridge stripe 98 to the end of the opening is only 0.5 microns on the left and right. On the other hand, an exposure apparatus used for forming a photomask is generally said to have an alignment accuracy of about plus or minus 0.3 microns. That is, in the above case, the left and right clearances vary between 0.2 microns and 0.8 microns, which means that the opening is formed on either side of the ridge. It means you need to be patient.

  However, in this way, when the design clearance is as small as 0.5 microns, if the opening is formed on either side of the ridge, the symmetry of the horizontal far-field image of the semiconductor laser is lost. When used as a light source for reading and writing on a recording disk medium, there has been a problem in that the beam condensing characteristics are deteriorated, leading to deterioration in reading and writing quality. This problem is particularly noticeable in a gallium nitride compound semiconductor laser in which the p-type gallium nitride compound semiconductor layer has a relatively high electrical resistance and a very small current spread in the lateral direction.

  In order to solve the above problems, in the method of manufacturing a ridge stripe type gallium nitride compound semiconductor laser according to the present invention, a step of providing a first upper electrode layer on the upper surface of the gallium nitride compound semiconductor multilayer structure, A step of providing a striped mask layer on the upper surface of the upper electrode layer, a step of removing a part of the first upper electrode layer by selective etching using the mask layer as a mask, and the mask layer as a mask Removing a part of the gallium nitride compound semiconductor multilayer structure by selective etching to form a ridge on the gallium nitride compound semiconductor multilayer structure; and an upper surface of the mask layer and the gallium nitride compound semiconductor multilayer structure A step of providing a first dielectric layer on the upper surface of the substrate and a portion of the mask layer and the first dielectric layer on the mask layer. Removing the first dielectric layer by an off method to provide an opening in the first dielectric layer and exposing the first upper electrode layer from the opening; and the first upper electrode exposed from the opening in the first dielectric layer Providing an intermediate electrode layer over the entire upper surface of the layer; providing a second dielectric layer on the upper surface of the intermediate electrode layer and the upper surface of the first dielectric layer; and an intermediate electrode of the second dielectric layer Providing an opening at a position on the layer to expose the intermediate electrode layer from the opening; an upper surface of the intermediate electrode layer exposed from the opening of the second dielectric layer; and an upper surface of the second dielectric layer And a step of providing a second upper electrode layer.

  In order to solve the above-described problem, a ridge stripe-type gallium nitride compound semiconductor laser according to the present invention has the same width as the upper surface of the ridge, and a first upper electrode layer covering the entire upper surface of the ridge; A first dielectric layer that covers a portion of the upper surface of the gallium nitride compound semiconductor multilayer structure that is not covered by the first upper electrode layer; and a width that is wider than the first upper electrode layer; An intermediate electrode layer covering the entire upper electrode layer, and a second dielectric layer having an opening narrower than the intermediate electrode layer, covering the intermediate electrode layer and exposing a part thereof from the opening; A structure obtained by sequentially laminating a second upper electrode layer that has a width wider than the opening of the second dielectric layer and covers the intermediate electrode layer exposed from the opening of the second dielectric layer. It is characterized by that.

  In the ridge stripe type gallium nitride semiconductor laser of the present invention, the first upper electrode layer having the same width as the upper surface of the ridge and covering the entire upper surface of the ridge is present, and the opening provided in the dielectric is And provided on the upper portion of the first upper electrode layer. Therefore, even if the center of the opening and the center of the ridge do not coincide with each other, current injection occurs in a region equivalent to the entire width of the ridge stripe, so that the symmetry of the horizontal far-field image of the semiconductor laser is lost. For example, when the recording disk medium is used as a light source for reading and writing, there is no case where the beam condensing characteristic deteriorates and the reading and writing quality deteriorates.

Sectional drawing which shows typically the gallium nitride type compound semiconductor laser in the middle of manufacture by the manufacturing method of 1st embodiment. Sectional drawing which shows typically the gallium nitride type compound semiconductor laser in the middle of manufacture by the manufacturing method of 2nd embodiment. Sectional drawing which shows typically the gallium nitride type compound semiconductor laser in the middle of manufacture by the manufacturing method of 3rd embodiment. Sectional drawing which shows typically the gallium nitride type compound semiconductor laser in the middle of manufacture by the manufacturing method of 4th embodiment. Sectional drawing which shows typically the gallium nitride type compound semiconductor laser manufactured by the prior art.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

<First embodiment>
FIG. 1 is a schematic cross-sectional view showing a method for manufacturing a gallium nitride-based compound semiconductor laser according to the first embodiment of the present invention. As shown in FIG. 1A, the surface of a gallium nitride compound semiconductor stacked structure 100 obtained by sequentially stacking an n-type gallium nitride compound semiconductor layer and a p-type gallium nitride compound semiconductor layer on a substrate such as sapphire is as shown in FIG. Then, the first upper electrode layer 10 made of Pd having a thickness of 150 mm (1 mm = 10 ⁻¹⁰ m) is formed by electron beam evaporation.

  Next, as shown in FIG. 6B, a stripe photoresist mask 60 having a line width of 1.8 microns is formed by photolithography. Further, as shown in FIG. 5C, the formed stripe photoresist mask 60 is formed. As a mask, the first upper electrode layer 10 is etched by reactive ion etching until the surface of the gallium nitride compound semiconductor multilayer structure 100 is exposed.

As a process gas in this case, Ar or a gas obtained by adding a chlorine-based gas such as Cl ₂ , SiCl ₄ , BCl ₃ or the like to Ar in a volume ratio of 0% to 50% is used. The addition of these chlorine-based gases has the effect of suppressing the reattachment of Pd sputtered from the surface by Ar onto the etched surface. However, if it is added in an amount of 50% or more, the selectivity to the gallium nitride compound semiconductor is greatly reduced, and the etching cannot be substantially stopped when the surface of the gallium nitride compound semiconductor multilayer structure 100 is exposed. It becomes difficult to obtain a cross-sectional shape as shown in FIG.

Following the etching of the first upper electrode layer 10, the gallium nitride-based compound semiconductor multilayer structure 100 is etched partway through the upper cladding layer by reactive ion etching to form a ridge stripe 90 as shown in FIG. To do. In this case, by using a process gas containing 50% or more of a chlorine-based gas such as Cl ₂ , SiCl ₄ , and BCl ₃ by volume, the gallium nitride-based compound semiconductor stack is formed using the striped photoresist mask 60 as a mask. The structure 100 can be etched.

Next, by cleaning the wafer with an organic solvent, after removing the stripe photoresist mask 60, as in FIG. (E), by an electron beam evaporation method, on the entire surface, from SiO ₂ having a thickness of 2000Å A dielectric layer 40 is formed.

  Next, as shown in FIG. 5F, a resist mask 70 having an opening 80 having a width of 1.2 microns is formed, and the dielectric layer 40 whose surface is exposed at the opening 80 by hydrofluoric acid or the like. Is removed until the underlying first upper electrode layer 10 is exposed, thereby obtaining an opening 81 as shown in FIG. As another means for obtaining the opening 81, a dielectric layer 40 is formed on the entire surface of the first upper electrode layer 10 after a resist mask having a width of 1.2 microns is formed on the upper surface of the first upper electrode layer 10, and lift-off is used. A method of obtaining the opening 81 may be used.

  Finally, the second upper electrode layer 20 made of Au having a thickness of 2500 mm and a width of 250 microns is formed on the upper surface of the first upper electrode layer 10 and a part of the upper surface of the dielectric layer 40. A gallium nitride compound semiconductor laser having the structure shown in FIG.

The structure of the obtained gallium nitride compound semiconductor laser will be described in detail here again. It is obtained by sequentially laminating an n-type gallium nitride compound semiconductor layer and a p-type gallium nitride compound semiconductor layer on a substrate such as sapphire. A ridge stripe 90 is formed on the surface of the gallium nitride compound semiconductor multilayer structure 100, and the first ridge stripe 90 is made of Pd having the same width as the ridge stripe 90 and having a thickness of 150 mm. The upper electrode layer 10 is formed. The surface of the gallium nitride compound semiconductor multilayer structure 100 is covered with a dielectric layer 40 made of SiO ₂ having a thickness of 2000 mm except for the upper surface portion of the ridge stripe 90.

  A second upper electrode layer 20 made of Au having a thickness of 2500 mm is formed on a part of the upper surface of the first upper electrode layer 10 and a part of the upper surface of the dielectric layer 40. The widths of the first and second upper electrode layers 10 and 20 are 1.8 microns and 250 microns, respectively.

  Each of the first and second upper electrode layers 10 and 20 has a purpose of obtaining ohmic contact with the gallium nitride-based compound semiconductor multilayer structure 100 and a bonding region such as a gold wire for electrical connection to an external circuit. It is formed for the purpose of obtaining.

  In the structure of this embodiment, the first upper electrode layer 10 having the same width as the upper surface of the ridge stripe 90 and covering the entire upper surface of the ridge stripe 90 exists, and the opening provided in the dielectric is Provided on top of the first upper electrode layer. Therefore, even if the center of the opening and the center of the ridge do not coincide with each other, current injection occurs in a region equivalent to the entire width of the ridge stripe 90, so that the symmetry of the horizontal far-field image of the semiconductor laser is lost. In the case of using as a light source for reading and writing of a recording disk medium, the beam condensing characteristics are not deteriorated, and the reading and writing quality is not deteriorated.

  In the first embodiment, as a method for obtaining the opening 81 in the dielectric layer 40, the resist mask 70 having the opening 80 having a width of 1.2 microns is formed, and the opening is formed using hydrofluoric acid or the like. The method of removing the dielectric layer 40 whose surface was exposed until the underlying first upper electrode layer 10 was exposed was used.

  However, in this case, when the dielectric layer 40 is etched with hydrofluoric acid, the etching proceeds not only in the depth direction but also in the lateral direction. Is formed wider than the first upper electrode layer 10, and there is a risk that the structure of this embodiment cannot be obtained. If the dry etching method is used, the progress of the etching in the lateral direction can be suppressed, but on the other hand, the upper electrode layer 10 may be damaged.

  As another means for obtaining the opening 81, a dielectric layer 40 is formed on the entire surface of the first upper electrode layer 10 after a resist mask having a width of 1.2 microns is formed on the upper surface of the first upper electrode layer 10, and lift-off is used. Although the method of obtaining the opening 81 may be used, in this case as well, when the thickness of the dielectric layer 40 is thicker than that in the present embodiment, for example, 4500 mm is required, the lift-off method is used. It will be subject to process restrictions that make it difficult.

  However, these problems can be solved by forming the dielectric layer in two steps. The specific method is illustrated below.

<Second Embodiment>
FIG. 2 is a schematic cross-sectional view showing a method for manufacturing a gallium nitride-based compound semiconductor laser according to the second embodiment of the present invention.

The method of manufacturing the gallium nitride compound semiconductor laser according to the first embodiment has been described, and an n-type gallium nitride compound semiconductor is formed on a substrate such as sapphire by the same method as shown in FIGS. And a first upper portion made of Pd having a thickness of 150 mm and a width of 1.8 microns on the surface of the gallium nitride compound semiconductor multilayer structure 200 obtained by sequentially laminating a p-type gallium nitride compound semiconductor layer. A ridge stripe 91 having the electrode layer 11 is formed. Thereafter, a first dielectric layer 41 made of SiO ₂ having a thickness of 1500 mm is formed on the entire surface of the wafer by an electron beam evaporation method, and a stripe photoresist mask used when forming the ridge stripe 91 by a lift-off method. Then, the structure shown in FIG. 2A is obtained by removing the first dielectric layer 41 on the upper portion thereof.

Next, as shown in FIG. 2B, a second dielectric layer 51 made of TiO ₂ having a thickness of 2000 mm is formed on the entire surface of the wafer by an electron beam evaporation method. One of the two methods used to obtain 81 is also used here to obtain an opening 82 above the first upper electrode layer 11 as shown in FIG.

  Finally, the second upper electrode layer 21 made of Au having a thickness of 2500 mm and a width of 250 microns is formed on the upper surface of the first upper electrode layer 11 and a part of the upper surface of the second dielectric layer 51. Thus, the gallium nitride compound semiconductor laser having the structure shown in FIG.

The structure of the obtained gallium nitride compound semiconductor laser will be described in detail here again. It is obtained by sequentially laminating an n-type gallium nitride compound semiconductor layer and a p-type gallium nitride compound semiconductor layer on a substrate such as sapphire. A ridge stripe 91 is formed on the surface of the gallium nitride compound semiconductor multilayer structure 200, and a first surface made of Pd having the same width as the ridge stripe 91 and a thickness of 150 mm is formed on the upper surface of the ridge stripe 91. The upper electrode layer 11 is formed. The surface of the gallium nitride compound semiconductor multilayer structure 200 is covered with a first dielectric layer 41 made of SiO ₂ having a thickness of 1500 mm except for the upper surface portion of the ridge stripe 91.

A second dielectric layer 51 made of TiO ₂ having a thickness of 2000 mm is formed on the upper surface of the first dielectric layer 41 and part of the upper surface of the first upper electrode layer 11. Further, a part of the second dielectric layer 51 and a part of the first upper electrode layer 11 are covered with a second upper electrode layer 21 made of Au having a thickness of 2500 mm. The widths of the first and second upper electrode layers 11 and 21 are 1.8 microns and 250 microns, respectively.

  The first and second upper electrode layers 11 and 21 each have an object of obtaining an ohmic contact with the gallium nitride compound semiconductor multilayer structure 200 and a bonding region such as a gold wire for electrical connection to an external circuit. It is formed for the purpose of obtaining.

  In the structure of the present embodiment, since current injection occurs in a region equivalent to the entire width of the ridge stripe 91, the symmetry of the horizontal far-field image of the semiconductor laser is not lost. In addition, since the dielectric layer has a first and second two-layer structure, the total thickness of the dielectric layer can be increased compared to the structure of the first embodiment. it can. That is, in the case of the first embodiment, the thickness of the dielectric layer 40 was 2000 mm, but in the present embodiment, the first dielectric layer 41 is 1500 mm and the second dielectric layer 51 is 2000 mm. The total is 3500cm. For this reason, for example, when bonding a gold wire on the second upper electrode layer 21, it is possible to reduce the risk of the dielectric layer being cracked by the impact and causing current leakage from the cracked portion. .

  2D showing the final form of the gallium nitride-based compound semiconductor laser according to the present embodiment, the second upper electrode 21 is directly formed on the surface of the first dielectric layer 41 except for the second dielectric layer 51. Let us consider the case where a structure having a shape is adopted. Even in this case, since current injection occurs in a region equivalent to the entire width of the ridge stripe 91, the symmetry of the horizontal far-field image of the semiconductor laser is the same as when the second dielectric layer 51 is present. The effect that it does not collapse can be secured. However, in this structure, since the opening is provided by the lift-off method using the stripe photoresist mask used when forming the ridge stripe 91 after the formation of the first dielectric layer 41, the first dielectric layer When the thickness of the layer 41 is relatively thick, for example, exceeding 3500 mm, there is a problem that it cannot be applied, which is not desirable.

  In the case of providing the second upper electrode layer in the gallium nitride compound semiconductor laser having the structure shown in FIGS. 1 (h) and 2 (d), for example, it may be avoided to form directly above the pair of resonator end faces. is there. This is because when the resonator is formed by cleaving the gallium nitride compound semiconductor multilayer structure, the risk that the relatively thick second upper electrode layer becomes a burr or turns up just above the resonator end face is avoided. In such a case, the first upper electrode is exposed in the region where the second upper electrode layer is not formed.

  In this case, since the exposed first upper electrode layer is as thin as 150 microns in the above two embodiments, migration occurs during energization, and in the worst case, disconnection occurs. For this reason, it is desirable to coat with a metal having excellent conductivity so that such a problem does not occur. In the present invention, while maintaining the effects of the invention introduced in the above two embodiments, the risk of occurrence of migration or the like is greatly increased by adding a method of covering with the metal having excellent conductivity. It is possible to reduce to The specific method is illustrated below.

<Third embodiment>
FIG. 3 is a schematic sectional view showing a method for manufacturing a gallium nitride-based compound semiconductor laser according to the third embodiment of the present invention.

An n-type gallium nitride compound semiconductor is formed on a substrate such as sapphire by the same method as shown in FIGS. 2A to 2C, which explains the method for manufacturing a gallium nitride compound semiconductor laser according to the second embodiment. And a first upper portion made of Pd having a thickness of 150 mm and a width of 1.8 microns on the surface of the gallium nitride compound semiconductor laminated structure 300 obtained by sequentially laminating a layer and a p-type gallium nitride compound semiconductor layer. A ridge stripe 92 having the electrode layer 12 is formed. Thereafter, a first dielectric layer 42 made of SiO ₂ having a thickness of 1500 mm is formed on the entire surface of the wafer by an electron beam evaporation method, and a stripe photoresist mask used when forming the ridge stripe 92 by a lift-off method. And the first dielectric layer 42 thereon is removed. Next, a second dielectric layer 52 made of TiO ₂ having a thickness of 2000 mm is formed on the entire surface of the wafer by electron beam evaporation, and an opening is obtained above the first upper electrode layer 12.

  Next, as shown in FIG. 3A, an intermediate electrode layer 32 made of Au having a thickness of 500 mm and a width of 10 microns is formed on the upper surface of the first upper electrode layer 12 and a part of the upper surface of the second dielectric layer 52. Further, a part of the second dielectric layer 52 and the intermediate electrode layer 32 are covered with a second upper electrode layer 22 made of Au having a thickness of 2500 mm and a width of 250 microns. The structure shown in b) is obtained. At this time, the second upper electrode layer 22 is not formed for the portion corresponding to the resonator end face.

The structure of the obtained gallium nitride compound semiconductor laser will be described in detail here again. It is obtained by sequentially laminating an n-type gallium nitride compound semiconductor layer and a p-type gallium nitride compound semiconductor layer on a substrate such as sapphire. A ridge stripe 92 is formed on the surface of the gallium nitride-based compound semiconductor multilayer structure 300, and a first surface made of Pd having the same width as the ridge stripe 92 and a thickness of 150 mm is formed on the upper surface of the ridge stripe 92. The upper electrode layer 12 is formed. The surface of the gallium nitride compound semiconductor multilayer structure 300 is covered with a first dielectric layer 42 made of SiO ₂ having a thickness of 1500 mm except for the upper surface portion of the ridge stripe 92.

A second dielectric layer 52 made of TiO ₂ having a thickness of 2000 mm is formed on the upper surface of the first dielectric layer 42 and the upper surface of the first upper electrode layer 12. Further, an intermediate electrode layer 32 made of Au having a thickness of 500 mm is formed on a part of the upper surface of the first upper electrode layer 12 and a part of the upper surface of the second dielectric layer 52. Further, a part of the second dielectric layer 52 and the intermediate electrode layer 32 are covered with a second upper electrode layer 22 made of Au having a thickness of 2500 mm. However, the intermediate electrode layer 32 is exposed without being covered with the second upper electrode layer 22 in the vicinity of the resonator end face. The widths of the first, second, and intermediate electrode layers 12, 22, and 32 are 1.8 microns, 250 microns, and 10 microns, respectively.

  The first, second, and intermediate electrode layers 12, 22, and 32 are respectively for the purpose of obtaining ohmic contact with the gallium nitride compound semiconductor multilayer structure 300, and bonding regions such as gold wires for electrical connection to an external circuit. And for the purpose of protecting the first upper electrode layer.

According to this manufacturing method, since the dielectric layer is a total of 3500 mm, the first dielectric layer 42 having a thickness of 1500 mm and the second dielectric layer 52 made of TiO ₂ having a thickness of 2000 mm. In addition, since the intermediate electrode layer 32 covers the first upper electrode 12, the second upper electrode layer 22 covers the ridge stripe 92 even in the vicinity of the resonator end face. Even if not, the risk of migration is significantly less.

  In the present embodiment, the width of the intermediate electrode layer is made narrower than that of the second upper electrode layer, but conversely, the width of the intermediate electrode layer can be made wider. For example, the intermediate electrode layer has a two-layer structure of Mo having a thickness of 100 mm on the side in contact with the second dielectric layer and Au having a thickness of 350 mm on the upper side, and the width of the second upper electrode is, for example, 270 microns. If it is wider than that of the gallium nitride compound semiconductor laser having the structure shown in FIG. 3, the adhesiveness at the interface between the second dielectric layer and the second upper electrode layer is increased, and the second upper electrode layer When bonding a gold wire to the upper part, it is possible to give a new effect that the wire peeling is less likely to occur.

  In the first, second, and third embodiments described so far, the dielectric layer is provided with an opening on the upper surface of the ridge, and the first upper electrode layer and the second electrode are formed through the opening. The upper electrode layer of was electrically connected. However, in this case, when the width of the ridge stripe is extremely narrow, for example, 1.2 microns, the process for forming a narrower opening on the ridge stripe becomes very difficult. Therefore, current injection cannot be generated in a region equivalent to the full width of the ridge stripe, which is the object of the present invention.

  However, as described in the second embodiment, it is possible to cope with the case where the dielectric layer needs to be thickened, and the first upper electrode as described in the third embodiment. There is a technique for solving the above problem while substantially maintaining the effects of both techniques of coating the layer with a metal having excellent conductivity. The specific method is illustrated below.

<Fourth embodiment>
FIG. 4 is a schematic sectional view showing a method for manufacturing a gallium nitride compound semiconductor laser according to the fourth embodiment of the present invention.

The method of manufacturing the gallium nitride compound semiconductor laser according to the first embodiment has been described, and an n-type gallium nitride compound semiconductor is formed on a substrate such as sapphire by the same method as shown in FIGS. A first upper portion made of Pd having a thickness of 150 mm and a width of 1.4 microns on the surface of a gallium nitride compound semiconductor multilayer structure 400 obtained by sequentially laminating a layer and a p-type gallium nitride compound semiconductor layer. A ridge stripe 93 having the electrode layer 13 is formed. Thereafter, a first dielectric layer 43 made of SiO ₂ having a thickness of 1500 mm is formed on the entire surface of the wafer by an electron beam evaporation method, and a stripe photoresist mask used when forming the ridge stripe 93 by a lift-off method. Then, the structure shown in FIG. 4A is obtained by removing the first dielectric layer 43 thereon.

  Next, as shown in FIG. 2B, an intermediate electrode layer 33 made of Au having a thickness of 500 mm and a width of 10 microns is formed on a part of the upper surface of the first dielectric layer 43 and the upper surface of the upper electrode layer 13. To do.

Further, the manufacturing method of the gallium nitride-based compound semiconductor laser according to the second embodiment is described, and an opening 83 having a width of 1.0 μm is provided by the same method as that shown in FIGS. 2B to 2C. A second dielectric layer 53 made of TiO ₂ having a thickness of 2000 mm and a second upper electrode layer 23 made of Au having a thickness of 2500 mm and a width of 250 microns are formed, as shown in FIG. Thus, a gallium nitride compound semiconductor laser having the above structure can be obtained.

The structure of the obtained gallium nitride compound semiconductor laser will be described in detail here again. It is obtained by sequentially laminating an n-type gallium nitride compound semiconductor layer and a p-type gallium nitride compound semiconductor layer on a substrate such as sapphire. A ridge stripe 93 is formed on the surface of the gallium nitride-based compound semiconductor multilayer structure 400, and a first surface made of Pd having the same width as the ridge stripe 93 and having a thickness of 150 mm is formed on the upper surface of the ridge stripe 93. The upper electrode layer 13 is formed. The surface of the gallium nitride compound semiconductor multilayer structure 400 is covered with a first dielectric layer 43 made of SiO ₂ having a thickness of 1500 mm except for the upper surface portion of the ridge stripe 93.

An intermediate electrode layer 33 made of Au having a thickness of 500 mm is formed on a part of the upper surface of the first dielectric layer 43 and the upper surface of the upper electrode layer 13. Further, a second dielectric layer 53 made of TiO ₂ having a thickness of 2000 mm is formed on the upper surface of the first dielectric layer 43 and the upper surface of the intermediate electrode layer 33. The second dielectric layer 53 is provided with an opening 83 having a width of 1.0 μm, and a part of the intermediate electrode layer 33 is exposed through the opening 83. Further, a part of the second dielectric layer 53 and the opening 83 are covered with a second upper electrode layer 23 made of Au having a thickness of 2500 mm. The widths of the first, second, and intermediate electrode layers 13, 23, and 33 are 1.4 microns, 250 microns, and 10 microns, respectively.

  The first, second, and intermediate electrode layers 13, 23, and 33 are respectively for the purpose of obtaining ohmic contact with the gallium nitride compound semiconductor multilayer structure 400, and bonding regions such as gold wires for electrical connection to an external circuit. And for the purpose of protecting the first upper electrode layer.

  In the structure of this embodiment, since current injection occurs in a region equivalent to the entire width of the ridge stripe 93, the effect that the symmetry of the horizontal far-field image of the semiconductor laser is not lost, and the two layers By being able to form a dielectric film having a structure, both of the effects of being able to form a dielectric layer that is relatively thicker than when a single-layer structure is employed are provided. On the other hand, if the opening 83 is shifted from just above the first upper electrode layer 13 having a width of 1.4 microns, the current injection is still performed as long as it is on the intermediate electrode layer 33 having a width of 10 microns. Since it occurs in a region equivalent to the entire width of the ridge stripe 93, a new effect is obtained that the symmetry of the horizontal far-field image of the semiconductor laser is not lost.

  Although the present invention has been described in detail based on the embodiments, the content of the present invention is not limited to the description of the embodiments given here. Next, modifications based on the technical idea of the present invention will be exemplified.

In the present invention, the “gallium nitride-based compound semiconductor” refers to a semiconductor in which Ga of gallium nitride (GaN) is partially replaced with another group III element, for example, Ga _s Al _t In _1-st N (0 < s.ltoreq.1, 0.ltoreq.t <1, 0 <s + t.ltoreq.1), including a semiconductor in which a part of each constituent atom is replaced by an impurity atom or the like, or a semiconductor to which another impurity is added.

  In addition, the dry etching method used in each embodiment is a reactive ion etching method. However, the inductively coupled plasma etching method, the ECR plasma etching method, and the like are shown in each embodiment by using the same process gas. Etching similar to that of the above can be performed.

The process gas used in the dry etching method of the first upper electrode layers 10, 11, 12, and 13 used in each embodiment is Ar or a chlorine-based gas such as Cl ₂ , SiCl ₄ , or BCl ₃ in Ar. However, it is also possible to use other inert gas such as He or Ne instead of Ar.

  In addition, the first upper electrode layers 10, 11, 12, and 13 used in each embodiment were Pd. However, Ni, Ti, and the like, and another metal such as Mo is laminated thereon. Even with such a structure, a similar gallium nitride-based compound semiconductor laser can be manufactured by the manufacturing method shown in each embodiment.

  Moreover, although the thickness of the 1st upper electrode layer 10, 11, 12, 13 used in each embodiment was 150 mm, the layer thickness is not limited to 150 mm. However, when the first upper electrode layer has a structure in which a plurality of metals are laminated, the first upper electrode layer, the intermediate electrode layer, and the second upper electrode layer are portions corresponding to the resonator end faces. When the total thickness exceeds 1000 mm, when the resonator end face is formed by cleavage, the electrode metal layer turns up starting from the cleavage plane, thereby creating a region where no current is injected, or the electrode that has been turned up. Care should be taken because the possibility of problems such as blocking the optical path of the laser beam emitted by the metal increases.

  Moreover, although the intermediate electrode layers 32 and 33 used in each embodiment are Au, Al, Pt, Mo, or a laminated structure of these metals may be used. Although the thickness was 500 mm, even if the thickness is less than 500 mm, the operation current of the manufactured gallium nitride-based compound semiconductor laser element can be applied if the above-described migration does not occur. There is no problem if the total thickness of the first upper electrode layer, the intermediate electrode layer, and the second upper electrode layer is 1000 mm or less at the portion corresponding to the end face. Further, the width of the intermediate electrode layer used in each embodiment is 10 microns, but it may be the same width as the first upper electrode layer or wider than the width of the first upper electrode layer.

  The second upper electrode layers 20, 21, 22, and 23 used in each embodiment were Au, but a gold wire was used to electrically connect the manufactured gallium nitride compound semiconductor laser device to the outside. As long as it can be bonded or can be welded to an external electrode pad, for example, a metal such as Al can be used, and there is no problem with a structure in which a plurality of metals are laminated instead of a single metal. Also, regarding the thickness, there is no problem as long as it is thick enough for electrical connection to the outside. Also, the width is not a problem as long as it is wide enough for electrical connection to the outside.

In addition, SiO ₂ and TiO ₂ used in each embodiment have no problem even if they are replaced with other inorganic dielectrics such as SiO, Ta ₂ O ₅ , SiN, or gallium nitride compound semiconductors such as AlGaN, The thickness is not limited to the thickness exemplified in the description of the embodiment. Also, the formation method may be based on the sputtering method, the plasma CDV method, or the like, instead of the electron beam evaporation method exemplified in the description of the embodiment.

  In addition, the effect of providing the intermediate electrode layer described in the third and fourth embodiments is the case where the dielectric layer having the first and second two-layer structures as in the case of these embodiments is employed. Of course, the present invention is effective even when the dielectric layer is composed of one layer as shown in FIG.

  In addition, a gallium nitride compound semiconductor laser having a loss guide structure can be formed by employing a layer having an effect of absorbing light generated in the active layer as at least a part of the dielectric layer shown in each embodiment. Is also possible.

10, 11, 12, 13 First upper electrode layer 20, 21, 22, 23 Second upper electrode layer 32, 33 Intermediate electrode layer 18 Upper electrode layer 100, 200, 300, 400, 500 Gallium nitride based semiconductor multilayer Structure 60 Photoresist mask for stripe formation 70 Photoresist mask for opening formation 40, 41, 42, 43 First dielectric layer 51, 52, 53 Second dielectric layer 48 Dielectric layer 80, 81, 82, 83, 88 Opening 90, 91, 92, 93, 98 Ridge stripe

Claims (2)

In a manufacturing method of a ridge stripe type gallium nitride semiconductor laser having a striped ridge on an upper part of a gallium nitride compound semiconductor multilayer structure,
Providing a first upper electrode layer on the upper surface of the gallium nitride compound semiconductor multilayer structure;
Providing a striped mask layer on the upper surface of the first upper electrode layer;
Removing a part of the first upper electrode layer by selective etching using the mask layer as a mask;
A step of removing a part of the gallium nitride compound semiconductor multilayer structure by selective etching using the mask layer as a mask to form a ridge on the gallium nitride compound semiconductor multilayer structure;
Providing a first dielectric layer on the top surface of the mask layer and the top surface of the gallium nitride compound semiconductor multilayer structure;
The mask layer and the portion of the first dielectric layer on the mask layer are removed by a lift-off method to provide an opening in the first dielectric layer, and the first upper electrode layer is exposed from the opening. A process of
Providing an intermediate electrode layer over the entire top surface of the first upper electrode layer exposed from the opening of the first dielectric layer;
Providing a second dielectric layer on the upper surface of the intermediate electrode layer and the upper surface of the first dielectric layer;
Providing an opening in a portion of the second dielectric layer on the intermediate electrode layer, exposing the intermediate electrode layer from the opening; and
A ridge stripe gallium nitride comprising: an upper surface of the intermediate electrode layer exposed from the opening of the second dielectric layer; and a step of providing a second upper electrode layer on the upper surface of the second dielectric layer. For manufacturing a semiconductor compound semiconductor laser. In a ridge stripe type gallium nitride semiconductor laser having a stripe ridge on top of a gallium nitride compound semiconductor multilayer structure,
A first upper electrode layer having the same width as the top surface of the ridge and covering the entire top surface of the ridge;
A first dielectric layer covering a portion of the upper surface of the gallium nitride compound semiconductor multilayer structure that is not covered by the first upper electrode layer;
An intermediate electrode layer having a width wider than the first upper electrode layer and covering the entire first upper electrode layer;
A second dielectric layer having an opening narrower than the intermediate electrode layer, covering the intermediate electrode layer and exposing a part thereof from the opening;
A structure obtained by sequentially laminating a second upper electrode layer that has a width wider than the opening of the second dielectric layer and covers the intermediate electrode layer exposed from the opening of the second dielectric layer. A ridge stripe type gallium nitride semiconductor laser characterized by the above.

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