JPH09167855A - Semiconductor optical device and light emitting diode - Google Patents

Abstract

(57) Abstract: Brightness reduction, brightness variation, and thyristor phenomenon are effectively prevented by using a dopant that does not easily diffuse even if a pn interface is grown at a high temperature. SOLUTION: Mg is used as a p-type dopant of a p-type epitaxial layer forming an AlGaAs red light emitting diode having a double hetero structure. The switching temperature during the pn interface growth from the p-type AlGaAs active layer to the n-type AlGaAs window layer by liquid phase epitaxial growth is set to 840 ° C. or higher and 950 ° C. or lower. Regarding the emission brightness characteristics, when the pn switching temperature is lower than 840 ° C., there is almost no difference in the emission brightness between Zn-doped and Mg-doped, but when it exceeds 840 ° C., the Mg-doped has a larger emission brightness. As the temperature rises, the variation in the in-plane emission brightness increases, but Mg
In the case of, the effect is not so great as Zn doping.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor optical device and a light emitting diode, and more particularly to an improved pn interface.

[0002]

2. Description of the Related Art In recent years, the luminance of red light-emitting diodes using AlGaAs has been improved, and they have been used as display panels and high-mount stop lamps for automobiles. For use in these applications, it is required that the luminance be high enough to be visible even in daylight. In order to meet this demand, a single heterostructure (SH
Structure), double hetero structure (DH structure), back reflection type D
Light emitting diodes (LEDs) having a heterostructure such as an H structure have been developed. In terms of growth conditions, studies are being made to increase the output with respect to the growth temperature and growth rate.

[0003]

The LED emits light near the pn interface. Therefore, if there is a defect near the interface, high luminance cannot be obtained. High brightness LE as described above
The pn interface of D is composed of a heterojunction. This heterojunction has the effect of increasing the carrier density, and also contributes to increasing the luminance by the effect of the window layer. However, there is a lattice constant difference at the hetero interface, which causes defects at the interface.

For example, a GaAs / AlGaAs system having relatively high luminance is used for a compound mixed crystal semiconductor for an LED, and the lattice constant of GaAs and AlGaAs constituting a heterojunction is almost the same, and the defect at the heterointerface is small. It is said that. Certainly, the defect is small compared to other mixed crystal combinations such as GaP, but considering that the theoretical brightness has not yet been obtained, the slight difference in lattice constant affects the LED brightness. it is conceivable that.

Incidentally, in order to reduce defects caused by a difference in lattice constant at the pn interface, ideally, a temperature at which the lattice constants of the p-type layer and the n-type layer become the same or extremely small during the growth of the pn interface. You only need to grow it. However, this temperature is extremely high at about 925 ° C. in the case of AlGaAs, and when grown at such a high temperature, Zn is usually used as a p-type dopant, but the diffusion of the Zn dopant tends to occur. This causes problems such as a decrease in luminance, a variation in luminance, and a thyristor phenomenon (parasitic thyristor). If the growth is performed at a low temperature to avoid this, a satisfactory high luminance cannot be obtained. This problem is not limited to the AlGaAs red LED.
The same applies to an AlGaAs infrared LED and an optical semiconductor element including a light receiving element.

An object of the present invention is to solve the above-mentioned drawbacks of the prior art by introducing an optimum p-type dopant for improving the pn interface, and to provide a semiconductor optical device having good optical characteristics. It is in. Another object of the present invention is to provide an inexpensive LED with high emission brightness, small variation, and high yield without thyristor phenomenon.

[0007]

The semiconductor optical device of the present invention is such that Mg is used as the p-type dopant of the p-type epitaxial layer constituting the device. AlGaAs red LED, GaP red LE
D, a light emitting element such as an AlGaAs infrared LED, and a light receiving element such as an InGaAs photodiode are also included.

[0008] In particular, as the AlGaAs red LED, a DH structure LED formed on a p-type GaAs substrate,
There are an LED having an SH structure and an LED having a back-reflection type DH structure from which a substrate has been removed. At least the active layer of these p-type layers has a structure in which Mg is contained as a p-type dopant. In this case, the carrier concentration of the active layer doped with Mg is preferably 1 × 10 ¹⁷ cm ⁻³ to 1 × 10 ¹⁹ cm ⁻³ . This is for the following reason. That is, the range of the carrier concentration at which the light emission output is highest is 1 × 10
^{It is 17} cm ^-3 to 2 × 10 ¹⁸ cm ^-3 , and in order to increase the response speed, the carrier concentration is 1 × 1 depending on the required value.
From 0 ¹⁸ cm ⁻³ to 1 × 10 ¹⁹ cm ⁻³ . When these are combined, the carrier concentration range is from 1 × 10 ¹⁷ cm ⁻³ to 1 × 1
This is because it becomes 0 ¹⁹ cm ^-3 .

Further, a p-type GaAs substrate may be doped with Mg, and a substrate having a carrier concentration of 1 × 10 ¹⁸ cm ⁻³ or more may be used. Mg can be used as a substrate dopant for the following reasons. That is, the dopant of the substrate also diffuses and affects the epitaxial layer. In this regard, Mg is less likely to diffuse than Zn, and can be said to be a suitable substrate dopant for growing a high-quality epitaxial layer.

The method for manufacturing the AlGaAs red LED is based on p-type AlGa by liquid phase epitaxial growth.
Pn from As active layer to n-type AlGaAs window layer
The switching temperature during interface growth is set to 840 ° C or higher and 950 ° C or lower.

Here, a red LED having a DH structure which can obtain particularly high brightness among hetero structures will be described.
p-type AlGaAs clad layer on p-type GaAs substrate, p
In order to form an epitaxial wafer by liquid phase epitaxial growth of the n-type AlGaAs active layer and the n-type AlGaAs window layer, a slow cooling method is generally used, but a temperature difference method may also be used. If they are the same, the same effect can be expected. The switching temperature of the pn interface required for both methods is 840 ° C or more and 950 ° C or less. The temperature range was limited to 840 ° C.
If it is lower, there is not much difference from conventional Zn doping, and it is 950
This is because if the temperature exceeds ° C, the variation in the emission brightness becomes large, which is not preferable. When the pn interface is grown in this temperature range, the lattice constant of the p-layer and the n-layer becomes the same or very small, so that the diffusion of the Mg dopant hardly occurs, and the brightness reduction, the brightness variation, and the thyristor phenomenon can be effectively prevented. .

Although Mg is used as a dopant in a plurality of p-type epitaxial layers such as a p-type AlGaAs active layer and a p-type AlGaAs cladding layer, Mg is used only in the active layer playing the most important role in photoelectric conversion. May be used. Even with this structure, the emission luminance is significantly improved as compared with the conventional Zn doping alone.
In addition, as a p-type dopant, both Zn and Mg may be added and grown together.
The emission luminance is higher than that of a red LED using only n as a dopant. Of course, if the mixing ratio of Zn and Mg is increased so that Mg becomes large, the emission luminance becomes Mg
Only approaching the case. Further, it is also possible to mix a small amount of one or a plurality of dopants other than Mg and use them as a p-type dopant. Thus, AlG
By using Mg as the dopant for the p-layer at the pn interface of the aAs-based red LED, an LED with high emission luminance can be obtained.

In the above description, the LED having the DH structure has been described. However, the same effect can be expected with an AlGaAs-based LED having another structure. Good characteristics can also be expected for the light receiving element. In the case of a light receiving element, it is known that the shape of the pn interface greatly affects the light receiving characteristics. However, if the growth method of the present invention is used, a light receiving element with few defects and a clean pn interface shape can be manufactured. . Further, excellent characteristics can be obtained as a p-type dopant for GaP grown by the liquid phase epitaxial method.

[0014]

Embodiments of the present invention will be described below. FIG. 2 shows the red LE of the AlGaAs type DH structure of this embodiment.
The structure of D is shown. This LED is 0.3mm × 0.3mm
The size is 0.3 mm. On the p-type GaAs substrate 3, three epitaxial layers of a p-type AlGaAs clad layer 7, a p-type AlGaAs active layer 6, and an n-type AlGaAs window layer 1, and n formed on the front surface and the back surface, respectively.
It is composed of the side surface electrode 4 and the p-side back surface electrode 5. The p-type GaAs substrate 3 has a thickness of 250 μm and a carrier concentration of 1 ×
It is 10 ¹⁹ cm ^-3 . p-type AlGaAs layer clad layer 7
Has a film thickness of 30 μm, an AlAs mixed crystal ratio of 0.65, and is doped with Mg as a p-type dopant. p-type AlGaA
The s active layer 6 has a film thickness of 1 μm and an AlAs mixed crystal ratio of 0.35.
Mg is doped as a p-type dopant. In a Mg-doped liquid phase epitaxial wafer, the relationship between the amount of Mg added to the solvent used for growth and the carrier concentration differs depending on the growth temperature, but the carrier concentration in the active layer of the LED is generally 1 × 10 ¹⁷ cm ^−. Since it is in the range of ³ to 1 × 10 ¹⁹ cm ⁻³ , the doping amount of Mg should be in this range. The n-type AlGaAs window layer 1 has a thickness of 40 μm.
m, AlAs mixed crystal ratio 0.65, T as n-type dopant
e is doped and the carrier concentration is 1 × 10 ¹⁸ cm on the surface.
It is ^-3 .

Next, this DH structure AlGaAs red L
A method for manufacturing an ED will be described. First, an epitaxial layer is grown by a slow cooling method by a slide boat method which is one of the liquid phase epitaxial methods. A GaAs substrate and raw materials are set on a three-layer growth slide boat. The raw materials are Ga, Al, GaAs polycrystal, Mg for the first layer.
Is used. Ga, Al, GaAs polycrystal, and Mg are used for the second layer. Ga, Al, GaAs for the third layer
Use s polycrystal and Te. The slide boat is set in the reaction tube, and after exhausting the air in the reaction tube, hydrogen gas is introduced. In this state, the temperature of the epitaxial furnace is raised to the cooling start temperature. After the temperature is raised, the temperature is maintained, and Al, GaAs polycrystal, dopant Mg or Te are dissolved in the Ga solution to form a solution. When the composition becomes uniform, start lowering the temperature of the epitaxial furnace. By moving the substrate holder of the slide boat and bringing the GaAs substrate into contact with the first layer solution, the second layer solution and the third layer solution sequentially, the DH
Form an epitaxial layer of the structure. When the epitaxial growth is completed, the heater of the epitaxial furnace is turned off to lower the temperature. Electrodes are formed on the front and back surfaces of the obtained epitaxial wafer by vapor deposition and photolithography. After forming an electrode with a diameter of 150 μm in the center of the front surface and an entire surface electrode on the back surface, an LE of 0.3 mm × 0.3 mm × 0.3 mm is formed.
Cut out from the wafer as D chips.

In preparing such a wafer, the switching temperature of the pn interface from the second layer to the third layer was changed from 800 ° C. to 940 ° C. in steps of 20 ° C., and eight kinds of DH structure wafers were grown. . For comparison, a DH structure wafer using a conventional p-type dopant Zn was grown under the same growth conditions. LED chips with a DH structure were manufactured from a total of 16 types of epitaxial wafers, and the emission luminance was measured. FIG. 1 shows the measurement results. The emission luminance characteristics
When the pn switching temperature is lower than 840 ° C., there is almost no difference in light emission luminance between Zn-doped and Mg-doped.
When the value exceeds the threshold value, the emission luminance greatly differs between Zn-doped and Mg-doped. In addition, as the temperature becomes higher, the variation of the emission luminance in the plane becomes larger, and the influence of Zn doping is more significant. As for the electrical characteristics, the LED chips exhibiting the thyristor phenomenon increase as the variation in the emission luminance increases. Experiments have confirmed that an LED with high light emission luminance can be manufactured when the pn switching temperature is higher than 840 ° C. using Mg as a dopant.

As described above, according to this embodiment, a red LED having a DH structure with high emission luminance can be grown by changing the temperature condition and the dopant. This luminance is about 50% higher than the conventional red LED of the same structure,
This structure has a value close to the theoretical limit. Further, since the diffusion of the Mg dopant is effectively suppressed, the variation in the luminance of the LED is small, the product yield can be increased, and the occurrence rate of the thyristor characteristics is reduced, so that the electrical characteristics are also excellent. In order to grow the epitaxial wafer of the present embodiment, the temperature conditions and the compounding conditions of the material for the epitaxial growth layer are different from those of the conventional method using a Zn dopant. However, since the conventional liquid phase epitaxial growth apparatus and growth jig can be used, the capital investment is small, the product cost is not so high, and a high-brightness epitaxial wafer can be grown at low cost.

FIG. 3 shows a back reflection type AlGaAs having a DH structure.
4 shows an embodiment of a red LED. The three layers of the p-type AlGaAs cladding layer 7, the p-type AlGaAs active layer 6, and the n-type AlGaAs window layer 1 are grown on the GaAs substrate 3 and
An n-junction is formed. The p-type AlGaAs cladding layer 7 is formed thicker than the DH structure of FIG. 2 in order to have a function as a substrate. p-type AlGaAs cladding layer 7, p-type A
Mg is contained in the lGaAs active layer 6 as a p-type dopant, and the p-type AlGaAs active layer 6
The switching temperature at the time of growing the pn interface on the aAs window layer 1 is set to be in a range of 840 ° C. or more and 950 ° C. or less. After growing the three layers, the GaAs substrate 3 is removed, and red light is extracted from the surface opposite to the surface on which the GaAs substrate 3 has been removed. An n-side front surface electrode 4 is provided on the light extraction surface, and a p-side back surface electrode 5 is provided on the substrate removal surface.

FIG. 4 shows an AlGaAs red LE having an SH structure.
D shows an example. p-type AlG on p-type GaAs substrate 3
It has an aAs active layer 2 and an n-type AlGaAs window layer 1. Mg is contained in the p-type AlGaAs active layer 2 as a p-type dopant, and the switching temperature during pn interface growth is within the above-described range. An n-side front surface electrode 4 is provided on the window layer 1 side, and a p-side back surface electrode 5 is provided on the substrate 3 side. The same effect as the DH structure light emitting diode can be obtained by the back reflection type light emitting diode and the SH structure light emitting diode configured as described above. The present invention is also applicable to laser diodes as well as light emitting diodes. .

[0020]

As described above, the present embodiment has the following effects.

(1) According to the optical semiconductor device of the first aspect, since Mg is used as the p-type dopant, the pn interface is improved and good optical characteristics can be obtained.

(2) According to the light emitting diode described in claims 2 to 6, since Mg is used as the p-type dopant,
As compared with the Zn-doped conventional example, it is possible to obtain a high luminance and a luminance close to a theoretical value, and the luminance variation is small, and the occurrence ratio of the thyristor phenomenon can be reduced. Therefore, LE
D can be manufactured with good yield and at low cost.

[Brief description of the drawings]

FIG. 1 is a graph showing light emission luminance characteristics with respect to a pn switching temperature in comparison between an Mg-doped embodiment of the present invention and a Zn-doped conventional example.

FIG. 2 is a sectional view of an AlGaAs-based double hetero red LED structure according to the present embodiment.

FIG. 3 is a cross-sectional view of an AlGaAs-based back reflection type red LED structure according to the present embodiment.

FIG. 4 is a cross-sectional view of an AlGaAs single hetero-type red LED structure according to the present embodiment.

[Explanation of symbols]

 Reference Signs List 1 n-type AlGaAs window layer 3 p-type GaAs substrate 4 n-side front electrode 5 p-side back electrode 6 p-type AlGaAs active layer 7 p-type AlGaAs cladding layer

Claims (6)

[Claims] 1. A semiconductor optical device characterized in that Mg is used as a p-type dopant of a p-type layer constituting the semiconductor optical device. 2. A p-type AlGaAs cladding layer, a p-type AlGaAs active layer, and an n-type AlGaAs on a p-type GaAs substrate.
In a double heterostructure light emitting diode having a window layer, a p-type AlGaAs active layer or a p-type Al
Mg in the GaAs active layer and p-type AlGaAs cladding layer
Is contained as a p-type dopant. 3. The light emitting diode according to claim 2, wherein the p-type GaAs substrate is removed, and a rear surface reflection type structure is provided in which light is extracted from a surface opposite to the surface on which the p-type GaAs substrate is removed. And a light emitting diode. 4. A single heterostructure light emitting diode having a p-type AlGaAs active layer and an n-type AlGaAs window layer on a p-type GaAs substrate, wherein p-type AlGaA is used.
A light emitting diode characterized in that the s active layer contains Mg as a p-type dopant. 5. The light emitting diode according to claim 2, wherein the Mg-doped active layer has a carrier concentration of 1 × 10 ¹⁷ cm ⁻³ to 1 × 10 ¹⁹ cm ^−3. And a light emitting diode. 6. The light-emitting diode according to claim 2, wherein the p-type GaAs substrate is doped with Mg and the carrier concentration is 1 × 10 ¹⁸ cm ⁻³ or more. And a light emitting diode.