JP4056717B2 - Semiconductor laser and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor laser, and more particularly to a semiconductor laser used as a light source for an optical disc system, information processing, or optical communication.
[0002]
[Prior art]
In the conventional manufacturing process of a semiconductor laser device, a first crystal growth is performed in which at least a first conductivity type cladding layer, an active layer, and a second conductivity type cladding layer are formed on a first conductivity type semiconductor substrate. Through a stripe formation process for forming a region where current is injected, epitaxial growth is performed to embed the stripe portion, thereby forming a device.
[0003]
For example, the manufacturing process of the ridge type semiconductor laser device as shown in FIG. 4 generally includes three crystal growth steps (double hetero structure formation, current block layer formation, buried layer formation). First, as shown in FIG. 4A, the n-type cladding layer 2, the active layer 3, and the p-type cladding layer 4 are sequentially deposited and grown on the n-type substrate 1 by the first crystal growth. Next, as shown in FIG. 4B, the p-type cladding layer 4 is etched using a photolithographic technique to form a ridge portion 4a. Next, as shown in FIG. 4C, the n-type current blocking layer 8 is formed by the second crystal growth. Next, as shown in FIG. 4D, the p-type buried layer 16 is formed by the third crystal growth, and the p-type contact layer 7 is further formed. Finally, as shown in FIG. 4E, the p-side ohmic contact electrode 13 is formed on the p-type contact layer 7, and the n-side ohmic contact electrode 12 is formed on the bottom surface of the n-type substrate 1.
[0004]
Even in the case of the groove type semiconductor laser device shown in FIG. 5, it is necessary to perform crystal growth twice (double heterostructure formation, buried layer formation). First, as shown in FIG. 5A, the n-type cladding layer 2, the active layer 3, the p-type cladding layer 4, and the n-type current blocking layer 8 are sequentially formed on the n-type substrate 1 by the first crystal growth. Deposit growth. Next, as shown in FIG. 5B, the n-type current blocking layer 8 is etched using a photolithographic technique to form a groove 8a. Next, as shown in FIG. 5C, the p-type buried layer 16 is formed by the second crystal growth, and the p-type contact layer 7 is further formed. Finally, as shown in FIG. 5D, the p-side ohmic contact electrode 13 and the n-side ohmic contact electrode 12 are formed.
[0005]
Such multiple crystal growth has been a major obstacle to reducing the manufacturing cost of the laser chip. Therefore, as a method of manufacturing a semiconductor laser device by omitting embedded crystal growth and performing single crystal growth, a ridge-type waveguide structure is formed, and current confinement and light are generated by a dielectric film such as SiO ₂ or Si ₃ N _4. Devices that perform confinement have been developed and produced (see, for example, J. Hashimoto et. Al., IEEE J. Quantum Electron, vol. 33, pp. 66-70, 1997). An example is shown in FIG. First, as shown in FIG. 6A, an n-type cladding layer 2, an active layer 3, a p-type cladding layer 4, and a p-type contact layer 7 are sequentially deposited on the n-type substrate 1 by the first crystal growth. Grows and forms a double heterostructure. Next, as shown in FIG. 6B, the ridge portion 4b is formed by etching the p-type contact layer 7 and the p-type cladding layer 4 using a photolithographic technique. Next, as shown in FIG. 6C, an insulating film (dielectric film) 11 is formed, and a resist mask 11a is formed by patterning. Next, as shown in FIG. 6D, the insulating film (dielectric film) 11 is etched using the resist mask 11a to expose the p-type contact layer 7. Finally, as shown in FIG. 6E, a p-side ohmic contact electrode 13 and an n-side ohmic contact electrode 12 are formed.
[0006]
Similar ridge type semiconductor lasers are disclosed in JP-A-63-90879, JP-A-5-327113, and JP-A-12-164986. Most of them employ a ridge formation method by re-growth (selective growth), and the production cost is expected to be higher than that shown in FIG. On the other hand, as a common point of these structures, in addition to the fact that the ridge type semiconductor laser can omit the buried growth, a contact layer is formed on the uppermost layer of the ridge portion, and an electrode is directly formed without forming an insulating film on the contact layer. The contact is formed by doing this. Therefore, the contact layer is limited to a narrow region above the ridge, and the contact area becomes narrow, so that an increase in device resistance becomes a big problem. As shown in FIGS. 4 and 5, in the semiconductor laser having the conventional structure in which the buried growth is performed, since the contact layer can be formed in a wide area on the element surface, the contact area with the electrode can be widened, and there is little problem of increasing the contact resistance. .
[0007]
A manufacturing method for forming the ridge portion by selective growth using the insulating film as a mask is shown in FIG. First, as shown in FIG. 7A, the n-type cladding layer 2, the active layer 3, and the p-type cladding layer 4 are sequentially deposited and grown on the n-type substrate 1 by the first crystal growth, and the antioxidant layer 70 is further grown. Are laminated. Next, as shown in FIG. 7B, a protective film 71 which is an insulating layer is deposited, the protective film 71 in the outer portion region is removed by using a photolithographic technique, and then the first selection is made in that region. An n-type current blocking layer 8 is formed by growth. Further, as shown in FIG. 7C, a ridge forming opening is formed in the central portion of the protective film 71 using a photolithographic technique, and then the p-type second cladding layer 72 is formed by the second selective growth. A p-type contact layer 73 is sequentially deposited and grown. Finally, as shown in FIG. 7D, a p-side ohmic contact electrode 13 and an n-side ohmic contact electrode 12 are formed.
[0008]
In this method, since there is no insulating film near the contact layer, a contact can be formed by performing direct electrode formation after selective growth (contact layer formation) as shown in FIG. However, as shown in FIGS. 7A to 7D, a plurality of times of crystal growth are required, and thus there is a problem that the manufacturing cost is increased.
[0009]
On the other hand, when the ridge portion is formed by selective etching as shown in FIG. 6, since the insulating film is formed after the ridge is formed, it is necessary to open the insulating film on the contact layer.
[0010]
Japanese Patent Laid-Open No. 4-329688 discloses an example of forming an insulating film pattern by lift-off in a ridge type semiconductor laser in which embedded crystal growth is omitted in order to manufacture a ridge type semiconductor laser in which current is confined by a dielectric film. Is disclosed. An example of this is shown in FIG. First, as shown in FIG. 8A, after forming a double heterostructure, a resist mask 80 is formed and etched to form a ridge portion as shown in FIG. 8B. Next, the insulating film (dielectric film) 11 is formed by sputtering as shown in FIG. 8C, leaving the resist mask 80 having ridges. Next, as shown in FIG. 8D, the current injection portion of the ridge portion is formed by lifting off the insulating film 11 on the ridge together with the resist mask 80. Finally, electrodes are formed as shown in FIG.
[0011]
This method has a problem that the shape of the insulating film on the slope of the ridge is greatly affected by the size of the ridges of the resist mask 80. When the wrinkles are large, it is difficult to form an insulating film on the slope of the ridge portion. Therefore, it is desirable that no wrinkles be formed in the contact layer after the ridge portion is formed. Accordingly, as shown in FIG. 9A, the ridge shape is the same as that produced by selective growth, and it is difficult in principle to increase the surface area of the contact layer by forming the ridges.
[0012]
Further, as a known method for selectively removing the insulating film on the ridge, there is an etch back method by dry etching. For example, after forming the ridge portion, an insulating film was formed on the entire surface, and the resist was applied so that the uppermost portion of the ridge was thinned, the resist was etched by O ₂ plasma treatment, and the thinnest resist on the upper surface of the ridge portion was completely etched. Thereafter, the insulating film is selectively etched. In this case, the insulating film on the ridge portion can be selectively removed, but it is considered that there are problems in process complexity, cost increase, and stability of in-plane distribution. In principle, this method only removes the insulating film on the surface of the contact layer as shown in FIG. 9B, so that a sufficient contact area cannot be obtained, and it is considered difficult to significantly reduce the element resistance. .
[0013]
[Problems to be solved by the invention]
As described above, in the ridge type semiconductor laser in which the buried growth is omitted, a contact is formed directly with the electrode at a part of the ridge portion regardless of whether the ridge formation method is the selective growth method or the selective etching method. It becomes composition. In particular, in the selective etching method, since it is not easy to accurately manufacture the size and position of the contact window portion, the contact resistance and thus the increase and variation of the element resistance become problems.
[0014]
In a low-cost ridge-type semiconductor laser element (hereinafter, low-cost laser) having a single crystal growth as shown in FIG. 6D, a selective etching method is essential for forming the ridge portion, and an insulating film is formed. The structure requires a step of selectively removing the contact layer surface of the ridge portion. In addition to reducing the surface area of the contact layer, since the buried growth is not performed, the size and position accuracy of the contact window is generally not sufficiently high as described above, so that the contact area with the electrode cannot be increased. For this reason, it was more difficult to reduce the contact resistance than in the case of the selective growth method.
[0015]
SUMMARY OF THE INVENTION An object of the present invention is to provide a structure of a semiconductor laser capable of reducing contact resistance and, as a result, reducing element resistance in a ridge type semiconductor laser that can be manufactured at a low cost by a single crystal growth, and a method for manufacturing the same. .
[0016]
[Means for Solving the Problems]
The semiconductor laser of the present invention is a semiconductor laser having a refractive index guided ridge structure including a stacked body of a plurality of compound semiconductor layers, an upper electrode, and a lower electrode. The uppermost layer of the ridge portion is a contact layer made of a highly doped compound semiconductor layer, and the second semiconductor layer located below the contact layer and in contact with the contact layer has an upper surface width of the contact layer. Narrower than the bottom width. Upper surface of the contact layer in the ridge portion, the entire side surfaces and a bottom surface, wherein the upper electrode is in direct contact, the top surface of the contact layer, the entire side surfaces, and the surface of the ridge portion other than the bottom surface insulating film Covered with.
[0017]
With the above configuration, the upper electrode is contacted not only on the surface of the contact layer but also on both side surfaces or the bottom surface thereof, so that the contact area is increased and the contact resistance is reduced. In addition, since the electrode is not in direct contact with the second semiconductor layer (cladding layer) generally having a high Al composition, problems such as electrode peeling do not occur. The contact layer is preferably a semiconductor layer having a low Al composition (Al composition <20%), such as GaAs, in order to suppress electrode peeling.
[0018]
Further, as described above, by reducing the width of the lower layer of the contact layer so that the contact layer becomes a ridge, the surface area of the contact layer is increased, the contact area with the upper electrode is further increased, and the contact resistance is increased. Can be further reduced.
[0019]
However, if the wrinkles are too large, damage to the wrinkles occurs during the diffusion process. Therefore, the thickness of the contact layer is d, the bottom width in the direction perpendicular to the stripe direction of the contact layer is A, and the second semiconductor layer is When the upper surface width in the direction perpendicular to the stripe direction is B, it is desirable that 0.1 <d <1.0 μm, (A−B) / B <2, 0.5 μm <A <10 μm.
[0021]
The method of manufacturing a semiconductor laser according to the present invention includes a double hetero structure in which an active layer is sandwiched between clad layers having a larger forbidden band than the active layer, an n-type semiconductor substrate, a highly doped p-type contact layer, and a step of laminating n-type or undoped semiconductor layers in this order; a step of removing a part or all of the n-type or undoped semiconductor layer; and a portion of the p-type contact layer and the cladding layer as p-type contacts. a step of the layer is selectively removed so that the eaves, a step of covering the wafer surface with an insulating film, and forming to have an opening of the resist to the p-type contact layer, using the resist as a mask A step of selectively removing the insulating film; and a step of covering the wafer surface with a metal electrode to form an electrode.
[0022]
The wrinkle of the contact layer (high concentration layer) can be easily realized by forming the ridge portion by etching as in this method, and is difficult to realize by the selective growth method.
[0023]
As a method for reducing the element resistance, activation of Zn dopant in the p-type semiconductor layer is effective. This phenomenon is particularly remarkable in a P-based semiconductor layer used in an AlGaInP-based red semiconductor laser or the like. For the activation of the Zn dopant, heat treatment is performed after the formation of the p-type semiconductor layer, or after the growth of the heavily doped p-type contact layer as in the method of the present invention, an n-type or undoped semiconductor layer is formed with a specific film thickness. It is effective to form (about 0.3 μm or more).
[0024]
FIG. 10 shows the relationship between the n-type or undoped semiconductor layer thickness d and the Zn dopant activation rate in an AlGaInP-based red semiconductor laser. In the layer structure shown in FIG. 10B, when the thickness of the n-type (or undoped) semiconductor layer is d, as shown in FIG. 10A, d> 3000 mm (0.3 μm) and p-type cladding It can be seen that the activation rate of the Zn dopant in the layer is sufficiently high.
[0025]
In a semiconductor laser that performs buried growth, Zn can be activated during the buried growth. However, since the low-cost laser of the present invention does not perform buried growth, the above-described method is effective for activating Zn. Since semiconductor lasers generally employ n-type substrates, the contact layer becomes a p-type layer, and the above contents can be applied. That is, an n-type or undoped semiconductor layer is formed in advance on the contact layer during crystal growth, and selectively removed, so that contact resistance and device resistance can be reduced.
[0026]
On the other hand, even if the method of forming the ridge portion by selective growth is employed, there are many problems in the following points. (1) Since the contact layer is crystal-grown following the lower layer, the contact layer has a shape with no wrinkles as shown in FIG. 9A, and the contact surface with the electrode is limited only to the upper surface and the side surface of the contact layer. Is done. (2) Since the electrode is in contact with the cladding layer having a high Al composition in the lower layer of the contact layer (Al composition> 0.5), the electrode may be peeled off. (3) When a semiconductor layer is further formed on the contact layer, the selective removal thereof is very difficult, and it is difficult to activate the Zn dopant as in the present invention.
[0027]
The doping concentration of the contact layer (high concentration layer) is preferably 5 × 10 ¹⁸ cm ⁻³ or more and 5 × 10 ¹⁹ cm ⁻³ or less. Although a higher doping concentration is desirable, a high concentration doping requires a decrease in crystal growth temperature, and crystallinity decreases due to a decrease in crystal growth temperature.
[0028]
Further, it is desirable that the contact layer is thicker because the surface area of the contact layer increases and the contact area can be expanded. However, if it is too thick, the height of the ridge portion becomes high, and the ridge portion is easily subjected to stress during assembly with the ridge portion side as a joint surface, which may lead to deterioration of element characteristics. Further, if the contact layer is thin, the surface area of the high-concentration layer is reduced, and if the contact layer has a large wrinkle, the wrinkle may be broken during the process to reduce the contact layer area. This is greatly influenced by the setting of the stripe width of the element. Considering the above reasons, the thickness of the contact layer is preferably 0.3 to 1.0 μm.
[0029]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to FIG.
[0030]
(Embodiment 1)
FIG. 1 shows a structure of a semiconductor laser device and a manufacturing method thereof in the first embodiment. The first embodiment is an example in which the present invention is applied to a ridge type semiconductor laser element using an AlGaAs-based material.
[0031]
First, as shown in FIG. 1A, an n-GaAs substrate 101 is placed in a crystal growth apparatus (not shown), and an n-AlGaAs cladding layer is formed on the n-GaAs substrate 101 by the first crystal growth. 102 (n-Al _0.5 Ga _0.5 As, carrier concentration 1E18 cm ⁻³ , thickness 1.0 μm), non-doped quantum well active layer 103, p-AlGaAs first cladding layer 104 (p-Al _0.5 Ga _0.5 As, carrier concentration 1E18 cm) ^-3 , thickness 0.2 μm), p-AlGaAs etching stop layer 105 (p-Al _0.20 Ga _0.80 As, carrier concentration 1E18 cm ⁻³ , thickness 100 mm), p-AlGaAs second cladding layer 106 (p-Al _0.5 Ga _0.5 As, carrier concentration 1E18 cm ⁻³ , thickness 1 μm), p-GaAs contact layer 107 (p-GaAs, carrier concentration 2E) 19 cm ⁻³ , thickness 0.4 μm), n-AlGaAs current blocking layer 108 (n-Al _0.5 Ga _0.5 As, carrier concentration 1E18 cm ⁻³ , thickness 0.1 μm) and n-GaAs protective layer 109 (carrier concentration 1E18 cm). ^-3 and a thickness of 0.4 μm) are sequentially deposited and grown.
[0032]
The active layer 103 has a triple quantum well structure including an Al _0.07 Ga _0.93 As well layer (thickness 65 mm), an Al _0.3 Ga _0.7 As barrier layer (thickness 50 mm), and a guide layer (thickness 550 mm) having the same composition.
[0033]
Next, the n-GaAs substrate 101 on which the semiconductor layer is formed is taken out from the growth apparatus and reaches the p-GaAs contact layer 107 as shown in FIG. 1B by using a known selective etching technique. In this way, the n-AlGaAs current blocking layer 108 and the n-GaAs protective layer 109 are etched. FIG. 1B shows an example in which the n-AlGaAs current blocking layer 108 and the n-GaAs protective layer 109 are all removed.
[0034]
Next, as shown in FIG. 1B, a striped SiO ₂ mask 110 is formed on the p-GaAs contact layer 107 by using a known photolithography technique. Using this SiO ₂ mask 110 as an etching mask, using a known selective etching technique, as shown in FIG. 1C, the p-GaAs contact layer 107 and the p− GaAs layer until the p−AlGaAs etching stop layer 105 is reached. The AlGaAs second cladding layer 106 is processed into a ridge shape.
[0035]
In this embodiment, hydrofluoric acid is used as the selective etching solution for the AlGaAs layer, and a solution obtained by adding hydrogen peroxide to ammonia water is used as the selective etching solution for the GaAs layer. The width of the bottom of the ridge (stripe width) was 1 to 4 μm.
[0036]
Thereafter, as shown in FIG. 1D, a SiO ₂ insulating film 111 is formed on the wafer surface, and a stepper exposure method, which is a well-known high-precision photolithography technique, is used to connect the opening of the resist mask 114 to a p-type contact. Formed on layer 107. Next, as shown in FIG. 1E, the SiO ₂ insulating film 111 (thickness 0.1 to 0.3 μm) on the p-GaAs contact layer 107 is removed by wet etching with hydrofluoric acid. Finally, as shown in FIG. 1F, a p-side ohmic electrode 113 is formed on the upper surface on the p-GaAs contact layer 107 side, and an n-side ohmic electrode 112 is formed on the lower surface of the n-GaAs substrate 101. The length of the device is adjusted to 200 μm, and a coating film having a reflectance of 30% is formed on the output side end face and a reflectance of 50% is formed on the opposite end face (not shown).
[0037]
2B and 2C show enlarged cross sections of the ridge portion in the ridge type semiconductor laser device manufactured as described above. 2B and 2C are enlarged views of the region of the ridge portion A indicated by a circle in FIG.
[0038]
In the case of the element according to the present embodiment, when forming the ridge portion, an AlGaAs layer formed on a GaAs substrate having a (100) plane as a main surface is formed using a hydrofluoric acid-based anisotropic etching solution. By etching in the <011> direction in a stripe shape, the forward mesa structure shown in FIG. 2C is obtained. Further, by rotating the stripe direction by 90 °, the inverted mesa structure shown in FIG. 2B is obtained. In the hydrofluoric acid-based etching solution, the etching rate of the (111) crystal plane is sufficiently smaller than that of the (100) plane, so that the side surface of the ridge portion is formed with the (111) crystal plane.
[0039]
In the conventional example shown in FIG. 9B, that is, in the case of a ridge type semiconductor laser in which only the surface of the high concentration layer is opened and the doping concentration of the p type contact layer 7 is 5E18 cm ⁻³ , the p side ohmic electrode 13 is bonded. The element resistance when assembled to a SiC submount as a surface was about 30Ω. On the other hand, in the case of the ridge type semiconductor laser according to the present embodiment shown in FIG. 2, in addition to the surface of the high concentration layer, the side SiO ₂ insulating film 111 is also removed to increase the contact area with the electrode. The doping concentration of the type contact layer 107 is 2E19 cm ⁻³ . As a result, when the ridge type semiconductor laser element having the forward mesa structure shown in FIG. 2C was assembled in the same manner as described above, the element resistance was about 8Ω. In this case, the width of the upper surface of the high concentration layer of the element was about 1 μm.
[0040]
Further, as a method of reducing the element resistance value, as shown in FIG. 2B, the ridge portion A may be formed in an inverted mesa shape. From the geometric calculation, the area of the upper part of the ridge A is about 2-3 times that of the reverse mesa structure in the reverse mesa structure (when the ridge height = 1.0 μm and the stripe width = 3-5 μm). Since the mesa structure increases the contact area with the electrode, the contact resistance is reduced, and as a result, the series resistance value of the element can be reduced.
[0041]
In the first embodiment, the case where the present invention is applied to a low-power semiconductor laser element used for reading a CD or the like has been described. However, the present invention relates to an AlGaInP-based red semiconductor laser and a high-power used for recording and reproduction. The present invention can be similarly applied to a semiconductor laser element and a self-excited oscillation type semiconductor laser.
[0042]
Further, in the conventional structure shown in FIG. 6, the p-type contact layer 7 is the final layer of crystal growth, and the Zn dopant is deactivated by atomic hydrogen (Akazaki Isao, III-
Group V compound semiconductors, Bafukan, pp. 312-313) were generated, and there was a problem that the device resistance was increased. On the other hand, the structure of the present embodiment shown in FIG. 1 has an advantage that the inactivation by hydrogen can be suppressed because the n-type semiconductor layer is grown on the p-type contact layer 107. The activation of Zn is not remarkable in the AlGaAs semiconductor laser, but is particularly remarkable in the case of the AlGaInP red semiconductor laser.
[0043]
(Embodiment 2)
The structure of the semiconductor laser device in the second embodiment is shown in FIG. FIG. 3B is an enlarged view of the region of the ridge portion B indicated by a circle in FIG. In the second embodiment, the etching of the ridge portion is not a solution in which hydrogen peroxide is added to hydrofluoric acid and ammonia water, but a solution in which hydrogen peroxide is added to tartaric acid (the mixing ratio is tartaric acid: peroxide). Hydrogen water = 5: 1 (volume ratio)). Other than that, the configuration is the same as in the first embodiment. The etching stop layer 105 is desirably a high Al composition AlGaAs layer (Al composition> 0.7) or a P-based semiconductor layer.
[0044]
By the above etching, as shown in FIG. 3B, the high-concentration contact layer has no wrinkles in the ridge portion, which is similar to the ridge shape formed by selective growth. This is because a solution obtained by adding hydrogen peroxide to tartaric acid has no selectivity between the GaAs layer and the AlGaAs layer (Al composition <0.6), and both are etched.
[0045]
Also in the second embodiment, the shape of the SiO ₂ insulating film 111 similar to that of the first embodiment as shown in FIG. 3 is obtained by high-precision mask alignment (pattern alignment accuracy of 0.1 μm or less) and selective etching using a stepper. . Thereby, the electrode is not brought into contact with the surface of the p-type second clad layer 106 having a high Al composition, and the electrode is brought into contact with the surface and the side surface of the heavily doped p-type contact layer 107, so that there is no electrode peeling. The effect of reducing contact resistance can be obtained.
[0046]
【The invention's effect】
The ridge type semiconductor laser of the present invention can be manufactured at a low cost by a single crystal growth, and the contact resistance is reduced. As a result, the element resistance is reduced.
[0047]
Further, according to the manufacturing method of the present invention, Zn, which is a p-type impurity, can be sufficiently activated by one crystal growth, and a reduction in device resistance can be easily realized without performing embedded growth. In addition, the activation of Zn by the manufacturing method of the present invention is more remarkable in a P-based semiconductor material typified by a red semiconductor laser.
[Brief description of the drawings]
1 is a cross-sectional view showing a structure of a ridge-type semiconductor laser and a manufacturing method thereof in Embodiment 1 of the present invention. FIG. 2 is an enlarged cross-sectional view showing a ridge portion in the semiconductor laser of FIG. FIG. 4 is a cross-sectional view of a conventional ridge-type semiconductor laser according to Embodiment 2 of the present invention. FIG. 5 is a cross-sectional view showing a structure of a conventional ridge-type semiconductor laser and a manufacturing method thereof. FIG. 6 is a sectional view showing another conventional ridge type semiconductor laser and a sectional view showing the manufacturing method thereof. FIG. 7 is a sectional view showing another conventional ridge type semiconductor laser and a manufacturing method therefor. FIG. 8 is a cross-sectional view showing the structure of another conventional ridge type semiconductor laser and its manufacturing method. FIG. 9 is an enlarged view of the ridge portion of the conventional ridge type semiconductor laser. FIG. 10A is a graph showing the relationship between the n-type or undoped semiconductor layer thickness d and the Zn dopant activation rate in an AlGaInP-based red semiconductor laser, and FIG. Sectional view showing the layer structure of the semiconductor laser used to obtain the graph of a)
1 n-type semiconductor substrate 2 n-type cladding layer 3 active layer 4 p-type first cladding layer 5 p-type etching stop layer 6 p-type second cladding layer 7 p-type contact layer 8 n-type current blocking layer 9 n-type protective layer 10 SiO ₂ mask 11 Insulating film (dielectric film)
12 n-side ohmic contact electrode 13 p-side ohmic contact electrode 101 n-GaAs substrate 102 n-AlGaAs cladding layer 103 active layer 104 p-AlGaAs first cladding layer 105 p-AlGaAs etching stop layer 106 p-AlGaAs second cladding layer 107 p-GaAs contact layer 110 SiO ₂ mask 111 SiO ₂ insulating film 112 n-side ohmic electrode 113 p-side ohmic electrode 114 resist mask

Claims (8)

In a semiconductor laser having a refractive index guided ridge structure including a stack of a plurality of compound semiconductor layers, an upper electrode, and a lower electrode, a contact made of a compound semiconductor layer in which the uppermost layer of the ridge portion is highly doped A second semiconductor layer located below the contact layer and in contact with the contact layer, the width of the upper surface is narrower than the width of the bottom surface of the contact layer, and the upper surface and both sides of the contact layer in the ridge entire surface, and the bottom surface, the semiconductor the and upper electrodes in direct contact, the top surface of the contact layer, the entire side surfaces, and that the surface of the ridge portion other than the bottom surface and being covered with an insulating film laser.   When the thickness of the contact layer is d, the bottom surface width in the direction perpendicular to the stripe direction of the contact layer is A, and the top surface width in the direction perpendicular to the stripe direction of the second semiconductor layer is B, 0.1 < 2. The semiconductor laser according to claim 1, wherein d <1.0 [mu] m, (A-B) / B <2, 0.5 [mu] m <A <10 [mu] m. 3. The semiconductor laser according to claim 1, wherein a doping concentration of the contact layer is 5 × 10 ¹⁸ cm ⁻³ or more and 5 × 10 ¹⁹ cm ⁻³ or less. The insulating _{layer, SiO 2, SiNx, SiON,} Al 2 O 3, ZnO, S
iC, semiconductor laser according to any one of claims 1 to 3, characterized in that it is formed by either a single layer or a plurality of these layers of amorphous Si. 2. A method of manufacturing a semiconductor laser according to claim 1 , wherein a double heterostructure in which an active layer is sandwiched between clad layers having a larger forbidden band width than that of the active layer and a high concentration doping is performed on an n-type semiconductor substrate. a step of laminating a p-type contact layer and an n-type or undoped semiconductor layer in this order; a step of removing a part or all of the n-type or undoped semiconductor layer; and one of the p-type contact layer and the cladding layer Selectively removing the portion so that the p-type contact layer becomes a ridge, covering the surface of the wafer with an insulating film, forming the resist on the p-type contact layer so as to have an opening, And a step of selectively removing the insulating film using the resist as a mask, and a step of covering the wafer surface with a metal electrode to form an electrode. The method of manufacturing a semiconductor laser. When the thickness of the contact layer is d, the bottom surface width in the direction perpendicular to the stripe direction of the contact layer is A, and the top surface width in the direction perpendicular to the stripe direction of the lower layer of the contact layer is B, 0.1 < 6. The method of manufacturing a semiconductor laser according to claim 5 , wherein d <1.0 [mu] m, (A-B) / B <2, 0.5 [mu] m <A <10 [mu] m. Doping concentration of the contact layer, 5 × 10 ¹⁸ cm ^-3 or more 5 × 10 ¹⁹ cm ^-3 semiconductor laser manufacturing method according to claim 5 or 6, characterized in that less. The insulating _{layer, SiO 2, SiNx, SiON,} Al 2 O 3, ZnO,
SiC, a semiconductor laser manufacturing method according to any one of claims 5-7, characterized by being formed by either a single layer or a plurality of these layers of amorphous Si.

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