JP4826019B2 - Manufacturing method of semiconductor laser device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a semiconductor laser device having a semiconductor layer made of p-type and n-type compound semiconductors, and more particularly to a method for manufacturing a semiconductor laser device having a buried structure.
[0002]
[Prior art]
III-V group nitride semiconductors such as GaN, AlGaN, GaInN or AlGaInN all have a direct transition band structure, and the band gap ranges from 1.9 eV to 6.2 eV at room temperature. Therefore, light emission is possible in a wide wavelength range from the ultraviolet region to the entire visible light region, and in recent years, it has attracted attention as a material for a light emitting element. In particular, a laser capable of emitting light in a short wavelength range from blue to ultraviolet is attracting attention as a light source for a high-density optical disc, and development is actively promoted. When writing an optical disk, the laser is required to have a high output and a low driving current, a stable transverse mode oscillation, and a long life. It is effective to make the structure embedded.
[0003]
The buried type refers to a structure in which buried layers are provided up to both sides of the semiconductor layer constituting the laser or even above the semiconductor layer, and a part of the semiconductor layer is buried in the buried layer, and the current confinement depends on the material of the buried layer. And transverse mode confinement. For example, a buried heterostructure (BH) is a well-known buried laser having a refractive index waveguide structure, in which buried layers are formed of a low refractive index material on both sides of an active region of a double heterostructure, and are parallel to each other. This improves the stability of the transverse mode of direction. In manufacturing such a laser, a semiconductor layer is stacked, and once a double heterostructure is formed, this is etched and processed into a striped convex shape having a width of several μm, and this convex portion is embedded. Thus, a method of forming buried layers on both side surfaces is generally used. Accordingly, the convex portion includes the p-type layer above the active region, but may also be configured to include the n-type layer below the active region. Further, the buried layer may be configured to be n-type for the p-type layer and active region and p-type for the n-type layer.
[0004]
In the ridge embedded type, a part of the p-type layer in the upper layer of the active region is formed as a convex portion (ridge) and both sides thereof are embedded. Incidentally, the ridge structure is a typical structure for a gain-guided laser in which the current is confined. If the ridge-embedded structure is used, both the gain-guided and refractive-index-guided characteristics can be realized. .
[0005]
[Problems to be solved by the invention]
The formation of such a nitride semiconductor layer of a laser is usually performed by vapor phase epitaxial growth by MOCVD (Metal Organic Chemical Vapor Deposition) method using hydrogen gas as a carrier gas. However, when a semiconductor layer is grown in a hydrogen atmosphere, hydrogen penetrates into the layer, causing cracks and inactivating p-type impurities such as magnesium (Mg) doped in the p-type layer. I was doing. These cause increases in the laser drive current and drive voltage. Thus, conventionally, in order to obtain a fully activated p-type layer, reactivation by heat treatment in an inert gas atmosphere has been performed after the growth of each layer.
[0006]
In general, the buried layer is grown laterally from the side surface of the ridge. However, in the hydrogen atmosphere, the growth rate is slow, and the time required for the growth process becomes long. During this time, the active layer may be thermally deteriorated. .
[0007]
The present invention has been made in view of such problems, and an object of the present invention is to provide a method of manufacturing a semiconductor laser device that can easily obtain a semiconductor laser device having a small driving current and a long lifetime.
[0008]
The method for manufacturing a semiconductor laser device of the present invention includes a step of forming an n-type semiconductor layer, a step of forming a p-type semiconductor layer using hydrogen (H ₂ ) as a carrier gas, an n-type semiconductor layer, and a p-type semiconductor. and forming a buried layer on at least a portion of the stack of layers, and the buried layer, it is shall be formed by growing using a carrier gas to the inert gas or nitrogen (N _2).
[0009]
In this semiconductor laser device manufacturing method, the use of an inert gas or nitrogen as the carrier gas increases the lateral growth of the crystal, and the buried layer is formed in a short time. Also, the p-type layer is activated during the growth of the buried layer, eliminating the need for a heat treatment step.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0011]
FIG. 1 shows a schematic configuration of a semiconductor laser 1 manufactured based on a semiconductor laser device manufacturing method according to an embodiment of the present invention. That is, the buffer layer 12, the n-side contact layer 13, the n-type cladding layer 14, the n-type light guide layer 15, the active layer 16, the p-type light guide layer 17, the p-type cladding layer 18 and the p-side contact are formed on the substrate 11. The layers 19 are sequentially laminated, and the upper layer of the n-side contact layer 13 is a convex portion (mesa) extending in a stripe shape in a direction perpendicular to the paper surface. Further, the upper portion of the p-type cladding layer 18 and the p-side contact layer 19 are stripe-shaped protrusions (ridges) having a narrower width than the mesa portion, and buried layers 20 are formed on both side surfaces thereof. Is provided. Further, a striped p-side electrode 22 is provided on the p-side contact layer 19 so as to overhang the buried layer 20, and a part of one n-side contact layer 13 is A stripe-shaped n-side electrode 23 is provided. The surface of the semiconductor laser 1 is covered with an insulating layer 21 except for the upper portions of the electrodes 22 and 23 and the buried layer 20.
[0012]
Next, a method for manufacturing such a semiconductor laser 1 will be described.
[0013]
First, as shown in FIG. 2A, a buffer layer 12 made of a nitride III-V compound semiconductor, an n-side contact layer 13, an n-type cladding layer 14, and an n-side light guide layer are formed on a substrate 11. 15, the active layer 16, the p-side light guide layer 17, the p-type cladding layer 18 and the p-side contact layer 19 are grown sequentially. Here, crystal growth is performed using the MOCVD method.
[0014]
Specifically, for example, a substrate 11 made of sapphire having a thickness of 400 μm is placed in an MOCVD apparatus, and a buffer layer 12 made of GaN is added to the substrate 11 with 30 nm, and silicon (Si) is added as an n-type impurity. n-type contact layer 13 (thickness 5.0 μm) made of n-type GaN, n-type cladding layer 14 (thickness 1.0 μm) made of n-type AlGaN doped with silicon as an impurity, and silicon added as n-type impurity An n-side light guide layer 15 (thickness: 0.1 μm) made of n-type GaN is grown in order. Subsequently, an active layer 16 (thickness 40 nm) having a multiple quantum well structure made of, for example, Ga _1-x In _x N and Ga _1-y In _y N is grown, and further magnesium (Mg) as a p-type impurity thereon. P-side light guide layer 17 (thickness 0.1 μm) made of p-type GaN with addition of p), p-type cladding layer 18 (thickness 0.7 μm) made of p-type AlGaN with addition of magnesium as p-type impurities, impurities Then, a p-side contact layer 19 (thickness: 0.1 μm) made of p-type GaN doped with magnesium is sequentially grown.
[0015]
At that time, for example, ammonia (NH ₃ ) is used as a raw material for nitrogen (N), trimethylaluminum ((CH ₃ ) ₃ Al) is used as a raw material for aluminum (Al), and trimethylgallium (Ga) is used as a raw material for gallium (Ga). (CH ₃ ) ₃ Ga) or triethylgallium ((C ₂ H ₅ ) ₃ Ga), trimethylindium ((CH ₃ ) ₃ In) as a raw material for indium (In), and monosilane (SiH as a raw material for silicon) ₄ ) and bis = methylcyclopentadienylmagnesium (MeCp ₂ Mg) or bis = cyclopentadienylmagnesium (Cp ₂ Mg), respectively, as raw materials for magnesium.
[0016]
Further, hydrogen (H ₂ ) is used as the carrier gas. Accordingly, in the p-type semiconductor layers 17 to 19, hydrogen is taken into the layers during the growth, and the p-type impurities are inactivated by receiving charge donation to hydrogen.
[0017]
Next, the substrate 11 is once taken out from the MOCVD apparatus, and a silicon dioxide (SiO ₂ ) film (not shown) having a predetermined shape is formed using, for example, a CVD method, a vacuum evaporation method, a sputtering method, or the like. Next, as shown in FIG. 2B, the n-side contact layer 13 is etched by using the SiO ₂ film as a mask until the n-side contact layer 13 is exposed by, for example, RIE (Reactive Ion Etching). The upper layer, that is, the n-type cladding layer 14, the n-side light guide layer 15, the active layer 16, the p-side light guide layer 17, the p-type cladding layer 18 and the p-side contact layer 19 are patterned in a mesa shape. After patterning, the SiO ₂ film is etched away.
[0018]
Next, as shown in FIG. 3A, a mask (not shown) is partially formed on the p-side contact layer 19, and etching is performed, for example, by the RIE method using this mask. As a result, the upper portion of the p-type cladding layer 18 and the p-side contact layer 19 are formed into a thin strip-shaped ridge.
[0019]
Next, as shown in FIG. 3B, the substrate 11 is placed in the MOCVD apparatus again, and the buried layers 20 are formed on both side surfaces of the ridge composed of the p-type cladding layer 18 and the p-side contact layer 19. Here, unlike the other semiconductor layers 12 to 19, nitrogen (N ₂ ) gas is used as the carrier gas. In addition, an inert gas such as Ar may be used as the carrier gas. For example, Al _x Ga _1-x N (0 ≦ x ≦ 1) is used as the material of the buried layer 20, and if the composition is selected so that the amount of Al is larger than that of the p-type cladding layer 18, the p-type cladding is used. The refractive index is relatively lower than that of the layer 18, which is preferable. Further, it is preferable to add an impurity such as Si to make the buried layer 20 an n-type because the current can be more strongly confined as will be described later. Such a buried layer 20 is formed by, for example, crystal growth accompanied by lateral growth.
[0020]
The lateral growth in this case proceeds in a direction parallel to the layer surface of the p-type cladding layer 18 from the ridge side surface. At the same time, growth in the direction perpendicular to the layer surface of the p-type cladding layer 18 is also promoted in the region where the lateral growth is performed. Here, the growth conditions are set so that the lateral growth becomes dominant. Are formed by substantially lateral growth. In this case, since nitrogen gas is used as the carrier gas here, the lateral growth rate is faster than when the carrier gas is hydrogen. Therefore, the growth rate ratio between the crystal growing laterally from the side surface of the ridge and the crystal growing vertically in the exposed surface of the p-type cladding layer 18 is expanded, and the buried layer 20 has a dome shape as shown in the figure. It becomes. The buried layer 20 does not need to be grown until the upper surface is completely flat, and may be substantially in contact with the side surface of the ridge and the remaining bottom surface of the p-type cladding layer 18. By forming a dome shape by stopping the process, it can be easily and quickly formed without deteriorating element characteristics.
[0021]
In general, in the lateral growth region, dislocations are not easily propagated from the lower layer or a crystal serving as a growth seed, and the crystallinity is improved. Therefore, in this case, the buried layer 20 has a low dislocation density and excellent crystallinity.
[0022]
During the growth of the buried layer 20, nitrogen (N ₂ ) gas is continuously supplied to the surface of the substrate 11. Therefore, in this step, hydrogen existing inside the previously formed p-type semiconductor layers 17 to 19 is released. In addition, if the buried layer 20 formed here is n-type, hydrogen is more easily separated. As a result, the p-type semiconductor layers 17 to 19 are activated, and the buried layer 20 is formed in a carrier gas not containing hydrogen and has few cracks.
[0023]
Next, as shown in FIG. 1, for example, an insulating layer 21 such as SiO ₂ is formed on the entire surface of the substrate 11 excluding the upper part of the mesa by vapor deposition and patterning. Next, RIE is performed at a predetermined position on the insulating layer 21 on the n-side contact layer 13 to expose the n-side contact layer 13. Further, a predetermined resist pattern (not shown) is formed on the surface of the p-side contact layer 19 by, for example, lithography. Using this resist pattern as a mask, a Pd film, a pt film, and an Au film are sequentially formed using, for example, a vacuum deposition method, and a p-side electrode 22 is formed at a predetermined position on the p-side contact layer 19. Here, the p-side electrode 22 is formed with a large surface area so as to cover a part of the buried layer 20. Further, a resist pattern (not shown) having a predetermined shape is formed on the substrate surface, and a Ti film, an Al film, a pt film, and an Au film are sequentially formed by a vacuum vapor deposition method or the like as in the case of the p-side electrode 22. . As a result, the n-side electrode 23 is formed on the exposed portion of the n-side contact layer 13.
[0024]
After that, the laser structure is cleaved horizontally with respect to the paper surface of FIG. 1 to form the resonator end face. In this way, the semiconductor laser 1 is completed. In addition, you may make it give the coating for controlling a reflectance to both end surfaces as needed.
[0025]
In the semiconductor laser 1 manufactured in this way, the p-type cladding layer 18 and the p-side contact layer 19 have a ridge shape, and embedded layers 20 are provided on both sides thereof. Therefore, the drive current flowing from the p-side electrode 22 toward the active layer 16 is confined in this ridge portion. Further, when the buried layer 20 is made of Al _x Ga _1-x N (0 ≦ x ≦ 1) having a larger amount of Al than the p-type cladding layer 18, its refractive index is lower than that of the ridge portion. In addition, a refractive index guided laser can be used. Furthermore, at this time, if the buried layer 20 is made n-type by adding an impurity such as Si, current confinement can be more strongly performed.
[0026]
Here, since the p-side electrode 22 has a large surface area so as to extend not only on the p-side contact layer 19 but also to the buried layer 20, the heat dissipation of the semiconductor laser 1 is improved.
[0027]
According to the present embodiment, since the buried layer 20 is formed by vapor phase growth using nitrogen as a carrier gas, the previously formed p-type layers 17 to 19 are reactivated in the formation process. be able to. Therefore, the heat treatment process conventionally required for activating the p-type layer becomes unnecessary. At the same time, since the speed of the lateral growth of the buried layer 20 is improved, there is no possibility that the crystallinity of the active layer 16 is thermally deteriorated during the growth.
[0028]
Here, since each of the semiconductor layers 12 to 19 is grown using hydrogen as a carrier gas and only the buried layer 20 is grown using nitrogen as a carrier gas, the semiconductor layers 12 to 19 are formed at the time of formation. Although there is a possibility that cracks may occur due to the presence of hydrogen, the crystallinity is good. Incidentally, when these are grown in a nitrogen atmosphere, a good surface state and crystallinity cannot be obtained. On the other hand, the buried layer 20 is improved in crystallinity by lateral growth and becomes a crystal layer that is not damaged by cracks or the like (see Example 2).
[0029]
【Example】
Furthermore, the present invention will be described with specific examples.
[0030]
Example 1
As shown in FIG. 4, on the sapphire substrate 111, an unope-GaN layer 112 having a thickness of 2 μm, a Mg-doped GaN layer 113 having a thickness of 0.7 μm, and a Si-added AlN layer 114 having a thickness of 0.1 μm. Were formed in order. At this time, the unope-GaN layer 112 and the Mg-added GaN layer 113 were grown at a growth temperature of 1000 ° C. using hydrogen as a carrier gas, and the Si-added AlN layer 114 was grown at a growth temperature of 770 ° C. and nitrogen as a carrier gas. . After that, the Si-added AlN layer 114 was etched, and the Hall constant of the Mg-added GaN layer 113 was measured.
[0031]
As a result, the carrier concentration of the Mg-added GaN layer 113 was 2.6 × 10 ¹⁷ cm ⁻³ . This means that the carrier is fully activated. Normally, the Si-added AlN layer 114 is also grown in a hydrogen gas atmosphere, and the carrier concentration of the Mg-added GaN layer 113 in that case is not so high. Therefore, it is considered that when the Si-added AlN layer 114 is grown in a nitrogen gas atmosphere, hydrogen is released from the Mg-added GaN layer 113 and the carriers are activated.
[0032]
(Example 2)
A semiconductor laser having the same configuration as that of the above embodiment was manufactured by the same method. Further, as a comparative example, a laser having a similar structure was produced by forming the buried layer 20 in a hydrogen atmosphere, and heat treatment was performed at 875 ° C. for 10 minutes.
[0033]
A micrograph (magnification: 200 times) of the laser embedding layer 20 of Example 2 is shown in FIG. 5, and a micrograph (magnification: 500 times) of the laser embedding layer 20 of the comparative example is shown in FIG. Note that the vertical lines in FIGS. 5 and 6 are ELO patterns. As described above, the buried layer 20 grown in the hydrogen atmosphere has cracks running obliquely, but the buried layer 20 grown in the nitrogen atmosphere shows no damage such as cracks. Therefore, it can be seen that crystal growth can be prevented by performing crystal growth in a nitrogen atmosphere.
[0034]
While the present invention has been described with reference to the embodiments and examples, the present invention is not limited to these embodiments and examples, and various modifications can be made. For example, although the sapphire substrate is used as the substrate 11 in the above embodiment, any substrate may be used. For example, the present invention is applied to a SiC substrate, a Si substrate, a GaN substrate, a GaAs substrate, and the like. Can be applied.
[0035]
The semiconductor laser 1 described in the above embodiment is an example of a semiconductor laser element made of a III-V group nitride semiconductor, and the present invention is widely applied to other buried laser structures. can do.
[0036]
【The invention's effect】
As described above, according to the method for manufacturing a semiconductor laser device according to any one of claims 1 to 4, the buried layer is formed by using an inert gas or nitrogen (N ₂ ) as a carrier gas. Therefore, the buried layer is formed in a short time by improving the lateral growth rate, and the active layer is prevented from deteriorating during the lateral growth. Thereby, a long-life semiconductor laser device can be manufactured with high productivity. In addition, since the p-type layer is activated during the growth of the buried layer, the heat treatment step conventionally required for reactivation of the p-type layer becomes unnecessary, and the process can be simplified. At the same time, since an inert gas or nitrogen gas is not used as a carrier gas for the growth of semiconductor layers other than the buried layer, a buried semiconductor laser with less surface roughness of the semiconductor layer and deterioration in crystallinity can be obtained. Therefore, it is possible to easily manufacture a semiconductor laser having a low driving current and voltage, a long life, and high lateral mode stability.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view illustrating a configuration of a semiconductor laser 1 according to an embodiment of the present invention.
FIG. 2 is a cross-sectional view for explaining a manufacturing process of the semiconductor laser 1;
3 is a cross-sectional view for each process following the process of FIG. 2. FIG.
FIG. 4 is a diagram illustrating a configuration of a structure manufactured in Example 1 of the present invention.
5 is a photomicrograph of a buried layer 20 in Example 2. FIG.
FIG. 6 is a micrograph of a buried layer 20 in a comparative example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser, 11 ... Substrate, 12 ... Buffer layer, 13 ... N-side contact layer, 14 ... N-type cladding layer, 15 ... N-side light guide layer, 16 ... Active layer, 17 ... P-side light guide layer, 18 ... p-type cladding layer, 19 ... p-side contact layer, 20 ... buried layer, 21 ... insulating layer, 22 ... p-side electrode, 23 ... n-side electrode

Claims (3)

forming an n-type semiconductor layer ;
Forming a p-type semiconductor layer using hydrogen (H ₂ ) as a carrier gas ;
Forming a buried layer in at least a part of a laminate composed of the n-type semiconductor layer and the p-type semiconductor layer,
Said buried layer, you formed grown with carrier gas an inert gas or nitrogen (N ₂₎
Method of manufacturing a semi-conductor laser element. You formed by said buried layer _{Al x Ga 1-x N (} 0 ≦ x ≦ 1)
The method of manufacturing a semiconductor laser device according to 請 Motomeko 1. Said buried layer, you formed by containing an aluminum (Al) much than the p-type semiconductor layer adjacent thereto
A method for manufacturing a semiconductor laser device according to claim 2 .

Images