JPH058155B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a gallium arsenide-aluminum mixed crystal epitaxial wafer suitable for manufacturing high-power light emitting diodes, and a method for manufacturing the same.

"Conventional technology" Gallium aluminum arsenide (Ga _1-x Al _x As)
The mixed crystal has a direct transition type energy structure in the infrared to visible region (950 to 650 nm), and
Since the lattice constant is almost the same as that of gallium arsenide (GaAs), it has the characteristic that there is no need to gradually change the mixed crystal ratio to avoid lattice-missmatch.

Epitaxial wafers for manufacturing light-emitting diodes using gallium arsenide/aluminum mixed crystal are usually manufactured by liquid phase epitaxial growth (LPE) using a gallium arsenide single crystal substrate.
In this case, since the segregation coefficient of aluminum is large, the content of aluminum, that is, the mixed crystal ratio, decreases as the crystal grows. In gallium arsenide/aluminum arsenide mixed crystal, the band spacing decreases as the mixed crystal percentage decreases, so if a light emitting diode is manufactured using such an epitaxial wafer,
The problem was that light and internal absorption were large, making it impossible to obtain a high-output light emitting diode. In order to avoid such problems, conventionally, a p-type GaAs substrate with a band spacing corresponding to the desired emission wavelength was fabricated on a p-type GaAs substrate.
Epitaxially grow a Ga _1-x Al _x As mixed crystal layer,
Next, an n-type Ga _{1- y} Al _y As _mixed crystal layer (x<
y), that is, it has been proposed to manufacture light emitting diodes using an epitaxial wafer on which a layer having a larger band spacing than the p-type layer is grown. During operation of a light emitting diode, light emission mainly occurs on the p-type layer side of the p-n junction, and therefore, the emission wavelength is determined by the band spacing of the p-type layer. The generated light has a larger band spacing n
High light output can be obtained because the light is emitted to the outside without being absorbed by the mold layer.

“Problems to be solved by the invention” However, Ga1− _x Al _x having the above structure
When manufacturing light emitting diodes using As epitaxial wafers, it has been difficult to form good electrodes with low electrical resistance on the n-type layer side. As a result, there was a problem in that the forward voltage (Vf) of the light emitting diode became high and sufficient output could not be obtained.

The present inventors have conducted intensive research aimed at obtaining a Ga _1-x Al _x As mixed crystal epitaxial wafer that does not have such problems and can easily form electrodes with low electrical resistance, and as a result, the present invention has been developed. has been reached.

"Means for Solving the Problems" The above object of the present invention is to provide a p-type GaAs single crystal substrate,
The mixed crystal ratio formed on the above single crystal substrate is 0.05~
0.4 p-type Ga _1-X AlxAs mixed crystal layer and the above p
an _n -type Ga _1-x Al
In the Ga _1-x Al _x As mixed crystal epitaxial wafer comprising a mixed crystal layer, the n-type mixed crystal layer has a thickness of at least 20 μm and a mixed crystal ratio of less than 0.7,
Further, the n-type carrier concentration is 5×10 ¹⁶ to 3×10 17 cm −3 near the interface with the p-type layer, and at least 5×10 ¹⁷ cm ⁻³ near the surface.
×10 ¹⁷ cm ⁻³ . Further, the Ga _1-x Al _x As mixed crystal epixial wafer has a p-type Ga _1-x Al _x As mixed crystal layer with a mixed crystal ratio of 0.05 to 0.4 formed on a p-type GaAs single crystal substrate. , Subsequently, in a method for forming an n-type Ga _1-x Al _x As mixed crystal layer whose mixed crystal percentage is higher than that of the p-type mixed crystal layer, the p-type GaAs single crystal substrate is
Contact with a melt for growing a p-type mixed crystal layer at a temperature of 920 to 850°C, and cool to a temperature in the range of 870 to 820°C, lower than the contact temperature to form the p-type mixed crystal layer. , and then brought into contact with the above melt for growing an n-type mixed crystal layer and cooled at a cooling rate of 760 to 700°C at a cooling rate of 0.2 to 0.7°C/min.
After cooling to a temperature of 600 to 500 °C at a cooling rate of 1 to 3 °C/min, the substrate was separated from the melt for growing an n-type mixed crystal layer and allowed to cool naturally. The obtained substrate on which the p- and n-type mixed crystal layers are formed is treated with a 0.1 to 10N caustic alkali aqueous solution to form an n-type Ga _1-x Al _x As having a mixed crystal ratio of greater than 0.7.
It is obtained by a method characterized by removing the mixed crystal layer.

In the present invention, "mixed crystal ratio" refers to the value of x when the gallium arsenide/aluminum mixed crystal is expressed as Ga _1-x Al _x As. Note that 1≧x≧0.
As the single crystal substrate used in the present invention, p-type
A GaAs single crystal substrate is suitable. When a GaAs single crystal substrate is used, there is no need to provide a layer for adjusting the difference in lattice constant from the Ga _1-x Al _x As mixed crystal. Group b atoms, particularly zinc (Zn), are used as the p-type impurity. The plane of a single crystal substrate is usually (100)
Although a plane is used, a (111) plane or the like may also be used. Also,
The method for producing a single crystal may be a boat growth method or a Czyochralski method.

P-type formed on the above p-type GaAs single crystal substrate
A suitable mixed crystal ratio of the Ga _1-x Al _x As mixed crystal is 0.05 to 0.4, preferably 0.25 to 0.35, which is a region having a direct transition type energy structure. Below 0.05,
Since it has the same emission wavelength as GaAs,
There is no particular need to use Ga _1-x Al _x As, and if it exceeds 0.4, it becomes an indirect transition type and the luminous efficiency decreases, which is not preferable. Note that it is sufficient that the above-mentioned mixed crystal ratio is achieved in a region at least 10 μm from the interface (pn junction) with the n-type mixed crystal layer. The thickness of the p-type mixed crystal layer is preferably 20 to 40 μm. Further, as the p-type impurity, group b elements, particularly Zn, are used.

Formation of the p-type mixed crystal layer is performed by a liquid phase growth method. In this case, metal Ga is used as the solvent,
In addition, GaAs polycrystal or single crystal, metal Al and
A melt for growing a p-type mixed crystal layer is prepared in which Zn and other necessary additives are dissolved, and this melt is brought into contact with the substrate. The above melt contains 3 to 15% by weight of GaAs.
It is preferable that it contains.

The temperature of the melt and the substrate is 920-850℃, preferably
Contact is carried out at a temperature of 910-890°C and cooled to a temperature in the range of 870-820°C, which is lower than the contact temperature. The cooling temperature range may be 50°C or higher.
If the contact temperature exceeds 920℃, problems such as Zn evaporation from the growth melt and melting of the substrate will occur.
If the temperature is less than 0.degree. C., it is not suitable because a sufficient cooling temperature range cannot be obtained and, therefore, the thickness of the mixed crystal layer cannot be grown sufficiently. Furthermore, if the lower limit of the cooling temperature is higher than 870°C, the cooling temperature range will be insufficient and the p-type mixed crystal layer will not be able to grow sufficiently. ,
This is not preferable because the next n-type mixed crystal layer cannot be grown sufficiently.

As the cooling rate increases, the amount of Al segregation tends to increase, so it is preferable to set the cooling rate to about 0.1 to 0.8°C/min. The p-type carrier concentration of the p-type mixed crystal is preferably 5×10 ¹⁶ to 1×10 ¹⁸ cm ^-3 , and 2×
Particularly preferred is 10 ¹⁷ to 6×10 ¹⁷ cm ⁻³ .

When the growth of the p-type mixed crystal layer is completed, the substrate is
The substrate is separated from the melt for growing an n-type mixed crystal layer and brought into contact with the melt for growing an n-type mixed crystal layer.

The melt for growing an n-type Ga _1-x Al _x As mixed crystal layer uses metallic gallium as a solvent, and GaAs polycrystal or single crystal, metallic Al, and other necessary impurities are dissolved therein. n
Group elements are used as type impurities, especially
Te is preferred. When using Te, pre-prepared
It is preferable to add Te in the form of GaAs single crystal or polycrystal (carrier concentration 10 ¹⁷ to 10 ¹⁹ cm ^-3 ).

The concentration of the melt for growing the n-type mixed crystal layer is GaAs,
1 to 5% by weight is preferred.

After bringing the substrate into contact with the melt for growing an n-type mixed crystal layer,
From 760 to 700°C, it is cooled at a cooling rate of 0.2 to 0.7°C/min. If it is less than 0.2°C/min, it will take a long time to grow, and if it exceeds 0.7°C/min, uniform distribution of Al will occur, which is not preferable.

In addition, the n-type carrier concentration is 1×10 ¹⁷ to 3×10 ¹⁷
cm ^-3 is appropriate; outside this range, sufficient luminous output cannot be obtained.

In addition, when the temperature of the substrate and melt exceeds 760 to 700℃, the cooling rate is increased to 1 to 3℃/min.
Cool to a temperature of ~500°C.

If the cooling rate is less than 1° C./min, the n-type carrier concentration will not exceed 5×10 ¹⁷ cm ^-3 , which is suitable for forming an electrode. On the other hand, if it exceeds 3° C./min, the amount of Al segregation increases, and as a result, a layer with a mixed crystal ratio of 0.07 or more is formed on the surface, which is undesirable because it becomes easily oxidized by air. The appropriate temperature for increasing the cooling rate is 760 to 700°C, and if it is outside this temperature range, the thickness of the n-type mixed crystal layer with a low carrier concentration or the n-type mixed crystal layer with a high carrier concentration may decrease. I don't like it because it's inappropriate. The thickness of the n-type mixed crystal layer is
It is necessary that the layer is at least 20 μm, and a layer near the surface, that is, within a range of 1 to 5 μm from the surface, has a high carrier concentration, that is, the carrier concentration is at least 5×10 ¹⁷ cm ⁻³ , preferably 8×
It is necessary that the layer is 10 ¹⁷ to 5×10 ¹⁸ cm ⁻³ . If the thickness of the n-type mixed crystal layer is less than 20 μm, the light emitting output of the light emitting diode will decrease, which is not preferable.

When the temperature of the substrate and melt reaches 600-500℃,
After the substrate and melt are separated, they are allowed to cool naturally. If the temperature at which the substrate and melt are separated exceeds 600°C, the thickness of the n-type mixed crystal layer with a high carrier concentration will not be sufficient, and if it is less than 500°C, the surface of the substrate will be contaminated, so it is preferable. do not have.

As already explained, the carrier concentration of the n-type mixed crystal layer needs to be at least 5×10 ¹⁷ cm ^-3 near the surface, that is, in the range of 1 to 5 μm from the surface, and is 5×10 ^{17 .} If it is less than cm ^-3 , it is not possible to form a good ohmic contact with the electrode material. Furthermore, since the layer with a high carrier concentration is provided in order to obtain a good electrode, it is sufficient that the layer has a thickness near the surface, that is, 1 to 5 μm from the surface.

Further, the carrier concentration in the vicinity of the interface between the n-type mixed crystal layer and the p-type mixed crystal layer, that is, at least 5 μm from the interface, and preferably in the portion of the n-type mixed crystal layer excluding the above-mentioned high carrier concentration layer, is 5×. 10 ¹⁶ ~ 3×10 ¹⁷ cm
Must be in the range ^-3 . 5×10 ¹⁶ cm ^-3
If it is less than 3×10 ^{17 cm −3, the internal resistance increases, and if it exceeds 3×10 17} cm ⁻³ , the crystallinity of the n-type mixed crystal layer decreases, which is not preferable.

In order to prevent internal absorption of generated light, the n-type mixed crystal layer should have a higher mixed crystal ratio than the p-type mixed crystal layer, preferably within a range that exhibits an indirect transition type energy structure. It needs to be larger than a certain 0.4, more preferably between 0.5 and 0.68. Further, if the mixed crystal ratio exceeds 0.7, it is not preferable because it will be oxidized in the air, making it difficult to form an electrode.

When forming a layer with a high carrier concentration, if the cooling rate is set to 1 to 3 degrees Celsius per minute and the temperature is cooled to 600 to 500 degrees Celsius, a layer with a mixed crystal ratio exceeding 0.7 will be formed on the surface, especially at the end of growth. For the purpose of removing this layer, the substrate after epitaxial growth is
Etching treatment is preferably carried out using a 0.5 to 3N aqueous caustic alkali solution. As the caustic alkali, sodium hydroxide or potassium hydroxide is suitable. A suitable concentration is 0.1 to 10 normal. If it is less than 0.1 normal, the ability to etch and remove the high mixed crystal content layer will not be sufficient, and if it exceeds 10 normal, it will be difficult to handle the liquid, which is not preferable.

The treatment temperature is not particularly limited, but preferably,
It is appropriate to process at 30-80°C. The treatment time is preferably 5 to 15 minutes.

The etching solution used in the method of the present invention has a characteristic that the etching speed is very slow when the mixed crystal ratio is 0.7 or less, so there is no particular problem even if the etching process is performed for a long time, but the etching process can be completed within 15 minutes. It is efficient to do so.

"Effects of the Invention" When light emitting diodes are manufactured using the Ga _1-x Al _x As mixed crystal epitaxial wafer according to the present invention, good electrodes can be formed, so that the forward voltage (Vf) of the light emitting diodes is reduced. , hence the output,
The efficiency is improved, and the yield (rate of non-defective products) is also improved.

"Example" Example A two-tank sliding boat was used as the boat for liquid phase growth, and this boat was housed in an open-tube quartz reaction tube and heated in an electric furnace in a hydrogen stream. As a substrate, a p-type GaAs (100)-plane substrate doped with Zn having a carrier concentration of 1.5×10 ¹⁹ cm ⁻³ was used.

A melt for growing a p-type Ga _1-x Al _x As mixed crystal layer was prepared by dissolving 6.0 g of undoped GaAs polycrystal, 2.1 g of metal Al, and 0.25 g of metal Zn in 100 g of metal Ga.

As a melt for growing an n-type Ga _1-x Al _x As mixed crystal layer, 1.8 g of undoped GaAs polycrystal and 0.43 g of metal A doped with Te with a carrier concentration of 1×10 ¹⁹ cm ^-3 in 100 g of metal Ga.
A solution was prepared in which 0.8 g of GaAs polycrystal was dissolved.

The above-mentioned substrate was stored in the substrate storage section of the boat, and each of the above-mentioned melts was stored in each tank of the boat. The temperature was raised to 900℃ without contact between the melt and the substrate, and after confirming that the temperature of the substrate and melt had stabilized at 900℃,
The substrate was brought into contact with the melt for growing a p-type mixed crystal layer and cooled to 860°C at a cooling rate of 0.5°C/min.

Subsequently, the boat was operated to bring the substrate into contact with the melt for growing an n-type mixed crystal layer, and the substrate was cooled to 750°C at a cooling rate of 0.5°C/min. Thereafter, the cooling rate was changed to 2°C/min to cool to 540°C. The substrate and melt were separated at 540°C and allowed to cool naturally.

The obtained epitaxial wafer had a p-type mixed crystal layer with a thickness of 35 μm, a carrier concentration of 4.2×10 ¹⁷ cm ^-3 ,
Further, the mixed crystal ratio was 0.35. The n-type mixed crystal layer has a thickness of 40 μm, and the carrier concentration is 1.2×10 ¹⁸ cm ^-3 from the surface to a depth of 6 μm, and 2.5×10 ¹⁷ at a position 3.2 μm from the interface with the p-type mixed crystal layer. It was warm at cm ^-3 . The mixed crystal ratio was 0.66 to 0.68 from a position 3 μm from the surface to the above interface, and increased from a position 3 μm from the surface to 0.72 at the surface.

This wafer was immersed in a 2N NaOH aqueous solution at 50° C. and etched to remove a layer from the surface to a depth of 3.5 μm.

Fifty light emitting diodes were made using the obtained wafer. An-Ge-Ni alloy was used as the electrode material. The peak emission wavelength of the obtained light emitting diode was 660 nm on average, the current density was 8 A/cm ² , and the output measured without epoxy coating was 6.0 mcd on average.
It was hot. Further, the forward voltage (Vf) at a current density of 20 mA/cm ² was 1.7V. This indicates that a low resistance electrode was formed. The yield of the light emitting diode was 98%.

Comparative example: Even after the temperature reached 750°C, the cooling rate was maintained at 0.5°C/min and the temperature was cooled to 540°C.
Liquid phase epitaxial growth was performed in the same manner as in the examples. The carrier concentration of the n-type mixed crystal layer of the obtained epitaxial wafer was 3.2× even on the surface.
10 ¹⁷ cm ⁻³ , and the surface mixed crystal ratio was also 0.68.

Fifty light emitting diodes were produced from this wafer in the same manner as in the example without particularly treating it with a caustic aqueous solution.

The obtained light emitting diode has an average Vf of 2.2V,
The output is an average of 2.5mcd using the same measurement method as in the example.
It was hot. Also, the yield of light emitting diodes is 45%.
It was hot. In other words, a good electrode could not be formed.

Claims (1)

[Scope of Claims] 1. A p-type gallium arsenide single crystal substrate, a p-type gallium arsenide/aluminum mixed crystal layer having a mixed crystal ratio of 0.05 to 0.4 formed on the single crystal substrate, and the above p-type gallium arsenide/aluminum mixed crystal layer having a mixed crystal ratio of 0.05 to 0.4. is formed on the mixed crystal layer, and the mixed crystal ratio is the above p.
The gallium arsenide layer consists of an n-type gallium arsenide/aluminum mixed crystal layer with a higher mixed crystal percentage than the gallium arsenide type mixed crystal layer.
In the aluminum mixed crystal epitaxial wafer, the n-type mixed crystal layer has a thickness of at least 20 μm.
, the mixed crystal ratio is smaller than 0.7, and n
The type carrier concentration is 5×10 ¹⁶ to 3×10 ¹⁷ cm ⁻³ near the interface with the p-type layer, and
Near the surface, at least 5×10 ¹⁷ cm ^-3
A wafer characterized by: 2 On a p-type gallium arsenide single crystal substrate, the mixed crystal percentage is
A p-type gallium arsenide/aluminum mixed crystal layer having a concentration of 0.05 to 0.4 is formed, and then an n-type gallium arsenide/aluminum mixed crystal layer having a mixed crystal ratio higher than that of the p-type mixed crystal layer is formed.
In the method of forming an aluminum mixed crystal layer, the p-type gallium arsenide single crystal substrate is brought into contact with a p-type mixed crystal layer growth melt at a temperature of 920 to 850°C,
The p-type mixed crystal layer is formed by cooling to a temperature in the range of 820°C and lower than the above contact temperature, and then brought into contact with a melt for growing an n-type mixed crystal layer to a temperature of 0.2 to 0.7
Cool to a temperature of 760-700℃ at a cooling rate of ℃/min, then cool to a temperature of 600-500℃ with a cooling rate of 1-3℃/min.
After cooling to a temperature of
and treating the substrate on which the n-type mixed crystal layer is formed with a 0.1 to 10N caustic alkali aqueous solution to remove the n-type gallium arsenide/aluminum mixed crystal layer having a liquid crystal ratio of greater than 0.7. Method.