JPH05267779A - Method for manufacturing planar light emitting device - Google Patents

Abstract

(57) [Summary] [Purpose] To realize a very low resistance element while maintaining high reflection. [Structure] Al _x Ga ₁ -x on n-type GaAs crystal substrate 11
The light-reflecting layer 12 is used when manufacturing a planar light-emitting device in which the active layer (13, 14, 15) is sandwiched by the n-type light-reflecting layer 12 and the p-type reflecting layer 16 made of As / Al _Y Ga _{1 -Y} As. , 1
The composition ratios X and Y in 6 are 0.6 ≦ X ≦ 0.7 for the p-type reflective layer 16 and 0.7 for the n-type light reflective layer 12 by the metal organic chemical vapor deposition method. It is formed in the range of ≦ X ≦ 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is directed to Al _X Ga _1-X As / Al _Y Ga _1-Y As (X> Y, 0 <X) on the main surface of a semiconductor substrate.
The present invention relates to a method of manufacturing a surface emitting device applied to a surface emitting laser that oscillates with an optical resonator formed of a semiconductor light reflecting layer of ≦ 1).

[0002]

2. Description of the Related Art Generally, a III-V compound semiconductor laser typified by GaAs or InGaAs has a Fabry-Perot resonator or DB in a direction parallel to a substrate.
F is formed, and the laser light is extracted from the cleaved end face of the semiconductor crystal.

[0003]

However, it is extremely difficult to two-dimensionally integrate the laser on the wafer surface at a high density in the semiconductor laser having such a structure because of its structural problem. That is, each laser must individually form an emission end face, and the length of the optical resonator is 100
Since it is as long as ~ 800 μm, there is a limit to the number of lasers that can be integrated in a wafer per unit area, and since laser light is emitted parallel to the substrate, it is necessary to extract light in a direction perpendicular to the substrate. However, for that purpose, there is a problem that a 45-degree high-reflection mirror must be formed by etching separately from the laser portion.

On the other hand, a so-called surface emitting laser, in which an optical resonator is formed perpendicularly to the main surface of the substrate by crystal growth or the like and laser light is taken out perpendicularly to the main surface of the substrate, is easy because of its structure. It is possible to realize high-density two-dimensional integration on a substrate. That is, a semiconductor substrate is provided with a first light reflecting layer, a cavity including an active layer, and a second light reflecting layer in this order, and oscillation is performed perpendicularly to the substrate. Recently, the oscillation wavelengths are 0.85μm, 0.98μm, 1.55μ
Various surface materials such as m have been tried, and the surface emitting laser has a threshold current of 1 mA as compared with a normal laser.
Lasers with very low thresholds below 1% have become feasible.

In the above-mentioned surface emitting laser, in order to oscillate the laser, the Q value of the etalon constituting the surface emitting laser is increased, that is, the first light reflecting layer and the second light reflecting layer are extremely high. I have to For this reason, the semiconductor or the dielectric having the first refractive index n ₁ and the second refractive index n ₂ (n ₁ > n ₂ ) of the normal light reflection layer is alternated with the film thickness of ¼ optical wavelength of the oscillation wavelength. It is distributed and constructed. For example, In _0.2 Ga _0.8 As /
In a surface emitting laser having GaAs as an active layer, in order to achieve a high reflectance (99% or more), the reflection layer has no absorption at the oscillation wavelength (0.98 μm) and the lattice constant is almost matched, which is possible. GaAs (refractive index 3.58) and AlAs (refractive index 2.
98) and.

However, when a current is injected through the light reflection layer, the forbidden band widths of the first semiconductor and the second semiconductor forming the light reflection layer are significantly different (ΔEg.
It is known that since it is formed by 20 to 30 pairs of heterojunctions, it has a very high resistance of several kΩ in a size of 20 to 30 μm due to band discontinuity. This tendency is particularly remarkable in the p-type. Therefore, the second light reflecting layer is formed of TiO ₂ (refractive index 2.19), Si
0 ₂ (refractive index 1.44) is used as the light reflection layer made of a dielectric material, and the current is injected from another location, or Zn is diffused only on the side surface of the second light reflection layer, and the current is injected here. Although a structure has been attempted, it is known that the process steps are complicated and the yield is extremely low.

Further, there is a method of using a molecular beam epitaxy (MBE) growth method as a method for obtaining a semiconductor reflection layer having high reflection and low resistance, but the MBE method requires an ultra-high vacuum, so that there is a problem in maintaining the device. There is. Further, since the growth rate is slow, when the semiconductor layers are used for both the first reflection layer and the second reflection layer like the surface laser, the film thickness of all the epitaxial layers becomes 10 μm or more, and the growth time becomes long. .. Therefore, there are problems in maintaining growth conditions and productivity. Further, the MBE method has a defect called oval defect, which has been a major obstacle in forming a two-dimensional array, which is the greatest feature of the surface laser.

Therefore, the present invention has been made in order to solve the above-mentioned conventional problems, and an object of the invention is to manufacture a surface-type light emitting device capable of maintaining a high reflection and realizing an extremely low resistance device. To provide a method.

[0009]

Means for Solving the Problems In order to achieve such an object, the present inventors have conducted various experiments, and as a result,
The composition ratios X and Y in the semiconductor light reflecting layer are 0.6 ≦ X ≦ 0.7 and Y = 0 for the p-type semiconductor light reflecting layer, and X = for the n-type semiconductor light reflecting layer. By setting 1 and Y = 0, it has succeeded in obtaining a semiconductor reflection layer which maintains a high reflectance and has an extremely low resistance. Therefore, the present invention is directed to Al _X Ga _1-X As / Al _Y Ga _1-Y As on the main surface of the semiconductor substrate.
The composition ratios X and Y in the semiconductor light reflection layer are organic with respect to the surface emitting laser that oscillates by the optical resonator formed of the semiconductor light reflection layer of (X> Y, 0 <X ≦ 1). By the metal vapor deposition method (MOCVD method), 0.6 ≦ X ≦ 0.7 for the p-type semiconductor light reflecting layer and 0.7 ≦ X ≦ 1 for the n-type semiconductor light reflecting layer. It is formed in the range.

[0010]

In the present invention, by setting the ranges of the composition ratios X and Y with respect to the p-type semiconductor light-reflecting layer and the n-type semiconductor light-reflecting layer, a semiconductor reflection layer having a high reflectance and an extremely low resistance can be obtained. Be done.

[0011]

Embodiments of the present invention will be described in detail below with reference to the drawings. As an example using the semiconductor light reflecting layer according to the present invention, a case of an oscillation wavelength 0.98 μm surface emitting laser using an In _0.2 Ga _0.8 As / GaAs strained superlattice as an active layer will be described. Needless to say, this embodiment is merely an example, and various modifications and improvements can be made without departing from the spirit of the present invention.

First, a structure as shown in the sectional view of FIG. 1 was prepared, and the characteristics of the element resistance with respect to the composition ratio X in the p-type semiconductor light reflecting layer were compared. Sample is n-type G
A semiconductor light reflection layer consisting of a pair of n-AlAs / GaAs layers 2 on aAs substrate 1, and undoped Al _0.3 Ga on both sides.
Undoped In _0.2 Ga ₀ centered with _0.7 As layers 3 and 5
_.8 a cavity layer having an As / GaAs strained superlattice layer 4 as an active layer, a pair of p-Al _1-x Ga _x As / GaAs (where X = 0, 0.6, 0.7, 1. 0) a semiconductor light-reflecting layer composed of a layer 6 in this order, and the Au electrode 7 and AuG are formed on the front and back surfaces of the pin structure, respectively.
The ohmic electrode of the eNi / Au electrode 8 is formed and IV
It was evaluated by measurement.

FIG. 2 shows the results of measurement of the differential resistance obtained from the vicinity of the rising in the forward direction with respect to the composition ratio X of the element diameter 110 μmφ. As is clear from this figure, it was found that the differential resistance equal to that of bulk was obtained only at X = 0.6. From this, in the p-type semiconductor light reflecting layer, the composition ratio of 0.6 ≦ X ≦ 0.7 is optimal in order to make the difference in refractive index as large as possible and the device resistance as low as possible.

Next, a method of manufacturing a surface emitting device using a semiconductor reflection layer according to an embodiment of the present invention will be described with reference to FIG. First, n-GaAs is first formed on a 350 μm thick n-type GaAs crystal substrate 11 by a low pressure MOCVD method.
Grow the buffer layer. Then, the film thickness of each layer is λ / 4n
(N is the refractive index) doping concentration 1 × 10 ¹⁸ cm
^-3 , the first consisting of 29.5 pairs of n-AlAs / GaAs
The light reflection layer 12 of was formed. This first light reflection layer 12
In general, since the resistance value is smaller than that of the p-type and there is no problem, it is set under an optically advantageous condition. For that purpose, it is preferable that X is as large as possible, and considering the chemical stability of the material, X ≧ 0.7 is desirable, but here X = 1.0.

Then, undoped Al _0.3 Ga _0.7 As layer 1
3, an undoped In _{0. 2} Ga _0.8 As / Ga as an active layer
After forming a cavity layer having an optical thickness of the oscillation wavelength, which is composed of the As strained superlattice layer 14 and the undoped Al _0.3 Ga _0.7 As layer 15, each layer is similarly doped with a doping concentration of λ / 4n. p-Al _{0. 6} at × 10 ¹⁸ cm ^-3
A second light reflecting layer 16 consisting of 15 pairs of Ga _0.4 As / GaAs was formed, and finally a p-GaAs matching layer and a p ⁺⁺ -GaAs contact layer 17 were formed.

The crystal thus obtained is first of all n
The back surface of the type GaAs crystal substrate 11 is polished with brommethanol. Then, an AR coat 18 made of SiO ₂ and AuGeNi / Au as an n electrode 19 are deposited on the back surface of the n-type GaAs crystal substrate 11 by vapor deposition sintering, and the upper portion of the n-type GaAs crystal substrate 11 is lifted off to a thickness of 5 to 40 μmφ. The Au electrode 20 is formed. After that, a mask is formed on the Au electrode 20 by resist patterning, and the outside of the mask is dry-etched up to the middle of the first light-reflecting layer 12 by ECR etching with chlorine gas to remove damage due to dry-etching. Slight etching with sulfuric acid is performed to complete the process. Here, the reason why the etching is performed halfway through the first light reflection layer 12 is to avoid an increase in the resistance value without increasing the loss of the optical waveguide.

A current is injected into the light emitting laser constructed by using the surface emitting element thus formed, and I-
When the L characteristic was examined, it was confirmed that the IL curve rises and laser oscillation occurs at a low threshold value of 2 to 3 mA, which is similar to the value reported conventionally. Further, the voltage in the vicinity of the threshold value is 2 to 2.5 V, which is improved by two digits as compared with the conventional one.

[0018]

As described above, according to the present invention, Al _X Ga _1-X As / Al _Y Ga _1-Y As is formed on the main surface of the semiconductor substrate.
In a method of manufacturing a surface-type light emitting device in which an active layer is sandwiched by p-type and n-type semiconductor light reflecting layers made of (X> Y, 0 <X ≦ 1), composition ratios X and Y in the semiconductor light reflecting layer are provided.
Is in the range of 0.6 ≦ X ≦ 0.7 for the p-type semiconductor light reflecting layer and 0.7 ≦ X ≦ 1 for the n-type semiconductor light reflecting layer by metalorganic vapor phase epitaxy. By forming it, it is possible to maintain a high reflectance and to realize an extremely low resistance element compared to the conventional one. Therefore, it is necessary to improve devices such as surface emitting lasers using this semiconductor light reflecting layer, and to use this device. It can be used as a light source for optical switching, optical neural networks, and optical information processing, and has extremely excellent effects.

[Brief description of drawings]

FIG. 1 is a cross-sectional view illustrating a structure of a surface emitting laser using a surface emitting element according to the present invention.

FIG. 2 is an Al _X Ga _1-X A of a surface light emitting device according to the present invention.
It is a figure which shows the differential resistance measurement result with respect to the composition ratio X in s.

FIG. 3 is a cross-sectional view illustrating an example of a method for manufacturing a surface light emitting device according to the present invention.

[Explanation of symbols]

11 n-type GaAs crystal substrate 12 first light reflection layer 13 undoped Al _0.3 Ga _0.7 As layer 14 undoped In _0.2 Ga _0.8 As / GaAs strained superlattice layer 15 undoped Al _0.3 Ga _0.7 As layer 16 second light reflection layer 17 p ^++- GaAs contact layer 18 AR coat 19 n electrode 20 Au electrode

Claims (1)

[Claims] 1. An Al _X Ga _1-X As layer on a main surface of a semiconductor substrate.
/ Al _Y Ga _1-Y As (X> Y, 0 <X ≦ 1) p
In a method for manufacturing a surface-type light emitting device in which an active layer is sandwiched between a n-type semiconductor light reflection layer and an n-type semiconductor light reflection layer, the composition ratios X and Y in the semiconductor light reflection layer are p-type semiconductor light reflection layer by metal organic chemical vapor deposition. For 0.6 ≦
A method for manufacturing a surface-type light emitting device, characterized in that X ≦ 0.7 and that the range is 0.7 ≦ X ≦ 1 for the n-type semiconductor light reflecting layer.