JPH06334256A - Method for manufacturing semiconductor light reflecting layer - Google Patents

Abstract

(57) [Summary] [Object] To provide a method capable of producing a semiconductor light-reflecting layer capable of maintaining high reflectance and having low resistance by using the MOCVD method. [Structure] Al _X Ga _1-X As / Al _Y Ga _1-Y As using Zn as a p-type dopant by the MOCVD method.
When the semiconductor light reflection layer composed of (X> Y, 0 ≦ X, Y ≦ 1) is formed, the growth temperature is set to n-type Al _X Ga _{1 -X} As / A.
The temperature is lowered by at least 150 ° C. from the growth temperature when forming the semiconductor light reflecting layer 12 made of l _Y Ga _{1 -Y} As, and
By doping more Zn in Al _X Ga _1-X As than in Al _Y Ga _1-Y As, a semiconductor light-reflecting layer 14 having high reflectance and extremely low resistance is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is based on the MOCVD method.
Al _x Ga _1-x As / using n as a p-type dopant
The present invention relates to a method for producing a semiconductor light reflection layer made of Al _Y Ga _{1 -Y} As.

[0002]

2. Description of the Related Art A surface emitting laser is one in which an optical resonator is formed perpendicularly to the main surface of a substrate by a technique such as crystal growth, and laser light is extracted in a direction perpendicular to the main surface of the substrate. Therefore, it is possible to easily perform high-density two-dimensional integration on the substrate due to the structure. Recently, the surface emitting laser has been tried with various material systems corresponding to the oscillation wavelength from 0.78 μm to 1.55 μm, and its volume is smaller than that of a normal laser, so that the threshold value is extremely low below 1 mA. Lasers with an electric current have become feasible.

In order to oscillate the surface emitting laser, the Q of the etalon that constitutes the surface emitting laser is used.
The value, that is, the reflectance of the first and second semiconductor light-reflecting layers must be extremely high. Therefore, in the semiconductor light reflecting layer, normally, a semiconductor having a _first refractive index n ₁ and a second refractive index n ₂ (n ₁ > n ₂ ) is ¼ of the oscillation wavelength under the condition that the lattice constants are matched. It is configured such that the film thicknesses of the optical wavelengths are alternately distributed. Specifically, for example, Al _0.2 Ga _0.8
In a surface emission laser with an oscillation wavelength of 0.85 μm, which has an As / GaAs quantum well layer (QWs) as an active layer, a high reflectance (99% or more) is realized. Al _0.15 Ga _0.85 As (refractive index 3.58) and Al with a large refractive index difference
And As (refractive index 2.98).

[0004]

By the way, when a current is injected through the semiconductor light reflecting layer, the forbidden band widths of the first and second semiconductors constituting the semiconductor light reflecting layer are largely different (ΔEg to 0.7 eV). Since it is formed by 20 to 30 pairs of heterojunctions, it is known that the p-type has a very high resistance of several kΩ at a mesa diameter of 20 to 30 μm due to band discontinuity. For this reason, in the case of manufacturing by the MBE method, the resistance is reduced by introducing an Al composition intermediate layer or an Al composition gradient layer between the first and second semiconductors.

However, the MOCVD method, which is more producible in mass production than the MBE method, has a different growth mechanism (or growth condition) from the MBE method, and the commonly used dopant species are relatively diffused. Since Zn is easy to perform, there has been a problem that even if the structure of the semiconductor light reflection layer is changed, the resistance cannot be lowered almost.

In view of the above conventional problems, the present invention provides an MOC.
It is an object of the present invention to provide a method capable of maintaining a high reflectance and manufacturing a semiconductor light reflection layer having a low resistance by using the VD method.

[0007]

In order to achieve the above object, the present invention uses Al _x Ga ₁ -x As / Al _y Ga ₁ -y As as a p-type dopant using Zn by the MOCVD method.
In a method of manufacturing a semiconductor light-reflecting layer for forming a semiconductor light-reflecting layer consisting of (X> Y, 0 ≦ X, Y ≦ 1), a growth temperature is n type Al _X Ga _1-X As / Al _Y Ga _{1- At} least 150 ° C. lower than the growth temperature at the time of forming the semiconductor light reflection layer made of _Y As, and more Zn is doped in Al _X Ga _1-X As than Al _Y Ga _1-Y As. A method of manufacturing the semiconductor light reflection layer is proposed.

[0008]

According to the present invention, it is possible to obtain a semiconductor light-reflecting layer which can maintain a high reflectance and has an extremely low resistance as compared with the conventional one by the MOCVD method suitable for mass production.

[0009]

EXAMPLE As an example using the semiconductor light reflecting layer according to the present invention, a case of an oscillation wavelength 0.85 μm surface emitting laser using an AlGaAs / GaAs superlattice as an active layer will be described below. Needless to say, the embodiment is merely an example, and various modifications and improvements can be made without departing from the spirit of the present invention.

FIG. 1 shows an example of an element for checking the resistance dependence of the p-type semiconductor light reflection layer on the growth temperature. A p-type Al _0.15 Ga _{0.85 is formed} on a p-type GaAs substrate 1.
A semiconductor light reflection layer 2 made of As / AlAs10 pairs is formed, and then the GaAs substrate 1 is etched off, and ohmic electrodes 3 and 4 made of AuZnNi / Au are formed on the front and back surfaces of the structure, respectively.

FIG. 2 shows the dependence of the resistance of the device of FIG. 1 on the growth temperature, which was evaluated by IV measurement.
The horizontal axis is the mesa radius of the element, and the vertical axis is the resistance value. From the figure, when the growth temperature was 750 ° C, the resistance value was too high to measure, but as the growth temperature was lowered, the device resistance was
You can see that it goes down on the og scale. Then, when the growth temperature was lowered by 120 ° C (630 ° C) from the temperature at which the n-type semiconductor light-reflecting layer was formed (750 ° C), it was almost equal to the value reported by the MBE method, and the element resistance saturated. did. In addition, "Graded" in the figure means Al _0.15 Ga _0.85 As
The case where the composition change between the layer and the AlAs layer is gentle, and "Abrupt" indicates the case where the composition change is abrupt.

At this time, the doping concentration of Al _0.15 Ga _0.85 As becomes 1 × 10 ¹⁹ cm ⁻³ or more, and the oscillation wavelength is 850 n.
Since the free carrier absorption at m was about 1000 cm ⁻³ , the reflectance was reduced by about 1%. Therefore, the growth temperature is lowered by 150 ° C. (600 ° C.) from the temperature (750 ° C.) at the time of forming the n-type semiconductor light reflection layer, and Al _0.15 G
When modulation doping was performed to introduce more Zn into AlAs than with a _0.85 As, the same resistance value was obtained.

As is clear from the above, at least the growth temperature at the time of forming the p-type semiconductor light reflecting layer is lowered by 150 ° C. from the temperature at the time of forming the n-type semiconductor light reflecting layer, and
It is necessary to dope more Zn in AlAs than in Al _0.15 Ga _0.85 As.

FIG. 3 shows an embodiment of a surface emitting laser provided with a semiconductor light reflecting layer manufactured by the method of the present invention.

In order to manufacture this, first, the thickness is 350 μm.
An n-type GaAs buffer layer is grown on the n-type GaAs crystal substrate 11 by a low pressure MOCVD method at a growth temperature of 750 ° C. Next, at the same growth temperature, the film thickness of each layer is λ / 4n.
(N is the refractive index) Doping concentration 1 × 10 ¹⁸ cm
^-3 n-type Al _0.15 Ga _0.85 As / AlAs 34.5 pair is formed to form the first semiconductor light reflection layer 12.

Next, an Al _0.3 Ga _0.7 As layer 13a and 6 pairs of Al _0.2 Ga _0.8 As / GaA as active layers are formed.
The cavity layer 13 composed of the s superlattice layer 13b and the Al _0.3 Ga _0.7 As layer 13c is an optical film having an oscillation wavelength. Thereafter, the growth temperature is lowered to 600 ° C., and similarly, the thickness of each layer is p-type Al _0.15 consisting of λ / 4n.
Ga _0.85 As (p to 10 ¹⁸ cm ^-3 ) / AlAs (p to 1)
0 ¹⁹ cm ⁻³ ) 27 second semiconductor light reflecting layer 14
Is formed by modulating the flow rate of DEZ, and is p ^{+ +} type Al that also functions as a phase matching with metal (Au) and a contact layer.
_The matching layer 15 made of _0.15 Ga _0.85 As is formed.

Next, with respect to the crystal thus obtained, first, the back surface of the substrate 11 is polished with brommethanol. Then, the back surface of the substrate 11 is coated with Si.
The Au layer is formed by the AR layer 16 made of O ₂ and the vapor deposition sinter.
An n-electrode 17 made of eNi / Au is formed, and then a p-electrode 18 made of semitransparent Au having a thickness of 10 nm and a diameter of 5 to 40 μm, which also serves as an auxiliary reflection mirror, is formed on the upper part of the crystal by lift-off.

Finally, a mask is formed on the p-electrode 18 by resist patterning, and the unmasked portion is dry-etched to the middle of the first semiconductor light reflection layer 12 by ECR etching with chlorine gas, and further dry-etched. Sulfuric acid-based slight etching is performed to remove the damage due to the above, and the manufacturing is completed.

The reason why the etching is performed halfway through the first semiconductor light reflecting layer 12 is to avoid an increase in resistance value without increasing optical waveguide loss.

A current was injected into the above-mentioned surface emitting laser and the IL characteristics were examined. As a result, IL was observed at a low threshold value of 2 to 10 mA, which is similar to the conventionally reported value.
It was confirmed that the curve rose and laser oscillation occurred. Further, the voltage in the vicinity of the threshold value is 2 to 2.5 V, which is improved by two digits or more as compared with the voltage produced by the conventional MOCVD method.

FIG. 4 shows the resistance value of the surface emitting laser of FIG.
It is evaluated by V measurement and shows the dependence on the growth temperature. The horizontal axis is the mesa radius of the device, and the vertical axis is the resistance value.
From the figure, it can be seen that according to this example, a semiconductor light reflection layer having a higher reflectance and a lower resistance than that of the conventional MBE method can be obtained. Note that “Modulated A” and “Modulated B” in the figure both indicate that the DEZ flow rate is modulated as described above.
The amount of modulation is different for each.

[0022]

As described above, according to the present invention, it is possible to obtain a semiconductor light-reflecting layer which can maintain a high reflectance and has an extremely low resistance as compared with the conventional one by the MOCVD method suitable for mass production. , It is possible to provide an optical device such as a surface emitting laser using a semiconductor light reflecting layer at a low cost, and it is very economical to realize optical switching, optical neural network, optical information processing that requires a large number of lasers and other light sources. The effect can be obtained.

[Brief description of drawings]

FIG. 1 is a structural diagram showing an example of an element for checking the resistance dependence of a p-type semiconductor light reflecting layer on the growth temperature.

FIG. 2 is a diagram showing the dependence of the resistance value on the growth temperature of the device of FIG.

FIG. 3 is a structural diagram showing an embodiment of a surface emitting laser having a semiconductor light reflecting layer manufactured by the method of the present invention.

4 is a diagram showing the dependence of the resistance value on the growth temperature of the device of FIG.

[Explanation of symbols]

1 ... p-type GaAs substrate, 2 ... semiconductor light reflecting layer, 3, 4 ...
Ohmic electrode, 11 ... N-type GaAs substrate, 12 ... First
Semiconductor light reflecting layer, 13 ... Cavity layer, 14 ... Second
Semiconductor light reflecting layer, 15 ... Matching layer, 16 ... AR
Layer, 17 ... N electrode, 18 ... P electrode.

Claims (1)

[Claims] 1. An Al _X Ga _1-X As / Al _Y Ga _1-YA using Zn as a p-type dopant by the MOCVD method.
In the method for manufacturing a semiconductor light-reflecting layer for forming a semiconductor light-reflecting layer made of s (X> Y, 0 ≦ X, Y ≦ 1), a growth temperature is n type Al _X Ga _1-X As / Al _Y Ga _{1 -Y}
The growth temperature at the time of forming the semiconductor light-reflecting layer made of As is lowered by at least 150 ° C., and more Zn is doped into Al _X Ga _1-X As than Al _Y Ga _1-Y As. A method for producing a semiconductor light-reflecting layer, characterized in that.