JP2666525B2 - GaAs light emitting diode and method of manufacturing the same - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a GaAlAs light-emitting diode, and in particular, to a high-power GaAlAs.
The present invention relates to a light emitting diode and a method for manufacturing the same.

[Background Art] Light emitting diodes (hereinafter, referred to as LEDs) are used in devices in all fields as display elements and communication elements. Among them, an LED used for a remote controller (remote controller) is an LED for infrared light emission, and an LED having a shorter wavelength and a higher output has been required.

The infrared high-power LED for this remote control is usually Si
Doped GaAs is widely used. The emission wavelength of this GaAs-LED is from 930nm to 960nm, and shorter wavelength LED
Is used, Si-doped GaAlAs is used.

[Problem to be Solved by the Invention] In the above Si-doped GaAlAs, the AlAs mixed crystal ratio at the pn interface is reduced.
The emission wavelength is controlled by changing the amount of Al added. However, in an LED whose emission wavelength is controlled by the AlAs mixed crystal ratio, n
Although the AlAs mixed crystal ratio of the layer is higher than the AlAs mixed crystal ratio of the pn interface,
The AlAs mixed crystal ratio of the p layer is lower than the AlAs mixed crystal ratio of the pn interface. This is because, since the emission wavelength is controlled by changing the AlAs mixed crystal ratio, one of the mixed crystal ratios must be lowered.

In the conventional Si-doped GaAlAs, a steep heterojunction is formed at the pn interface. This is so due to constraints coming from the manufacturing method. That is, the conventional liquid-phase epitaxial manufacturing method for an LED epitaxial wafer having a pn interface has two types of growth solutions for the first layer growth and the second layer growth solution having different AlAs mixed crystal ratios on the substrate. The solution is prepared separately, and after the first layer is grown, the second layer is grown. For this reason, a steep heterojunction is formed near the pn interface.

As described above, when the AlAs mixed crystal ratio of the p layer is lower than the AlAs mixed crystal ratio of the pn interface, the energy gap of the p layer is the smallest, so that the wavelength is shorter than that of the n layer or the pn interface. Light will be absorbed. Therefore, although the light emitted at the pn interface is extracted through the n-layer, the light directed to the p-layer is absorbed, and there is a drawback that a high emission output cannot be obtained.

In addition, when a steep heterojunction is formed near the pn interface, defects due to lattice mismatch peculiar to the heterointerface occur, and high light emission output cannot be obtained due to the existence of the heterojunction.

An object of the present invention is to eliminate the above-mentioned disadvantages of the prior art,
New GaAlAs that can greatly increase light output
-To provide an LED.

Further, an object of the present invention is to solve the above-mentioned drawbacks of the prior art, to have no steep heterojunction, and to provide either a p-layer or an n-layer.
An object of the present invention is to provide a novel method for manufacturing a GaAlAs-LED having a high AlAs mixed crystal ratio.

Means for Solving the Problems The gist of the present invention is to provide a GaAlAs in which an n-type layer and a p-type layer are formed by pn inversion of added Si from n-type to p-type dopant in the thickness direction of the crystal. In a GaAlAs-LED having a layer and electrodes formed on both sides of the GaAlAs layer, a p-type dopant other than Si is added to the p-type layer of the GaAlAs layer together with the Si, and the AlAs mixture of the GaAlAs layer is mixed. Crystal ratio is above pn
This is a GaAlAs-LED having the lowest value near the interface, thereby greatly improving the light emission output.

Further, in order to obtain a longer life with higher output, it is desirable not to have a steep heterojunction near the pn interface of the GaAlAs layer.

And, as p-type dopants other than Si, C, Zn,
One or several of Ge or Mg can be used.

On the other hand, in the method for manufacturing a GaAlAs-LED of the present invention, the SiAl-added GaAlAs growth solution is brought into contact with the substrate surface and gradually cooled, and during the slow cooling, the Si is pn-inverted from n-type to p-type and n After growing a GaAlAs layer having a p-type layer and a p-type layer,
In the method of manufacturing a GaAlAs light-emitting diode in which the substrate is removed and electrodes are formed on both surfaces of the GaAlAs layer, an additional solution in which a p-type dopant other than GaAs, Al and Si is dissolved is prepared in advance, and the n-type At a pn inversion temperature after the GaAlAs layer was grown, the growth solution was brought into contact with the growth solution for a certain period of time, and then the growth solution was separated from the growth solution and the growth solution was gradually cooled to form a p-type GaAlAs layer. It is grown to obtain a high-power GaAlAs-LED.

[Action] When the AlAs mixed crystal ratio is the lowest near the pn interface, the energy gap of both the n-layer and the p-layer is larger than that of the pn interface serving as the light-emitting portion. Unlike the case where the mixed crystal ratio of one layer is small, light of short wavelength emitted at the pn interface is not particularly easily absorbed by either layer. Therefore, light emitted at the pn interface is extracted to the outside through both the n-layer and the p-layer, so that a high emission output can be obtained.

Further, when a heterojunction that is not steep but slow is formed near the pn interface, defects due to lattice mismatch unique to the heterointerface do not occur, so that a higher emission output is obtained and the life is prolonged.

On the other hand, according to the method of manufacturing a GaAlAs-LED of the present invention, if the second layer is grown after the first layer is grown, the first and second layers are grown discontinuously. From the fact that a steep heterojunction occurs,
The growth condition of the second layer is adjusted without waiting for the growth of the layer,
Thereafter, the first layer and the second layer are continuously grown.

When the high-temperature growth solution stored in the growth solution holder is brought into contact with the substrate and gradually cooled, the p-type conduction type at a relatively high growth temperature and the n-type conduction type epitaxial layer at a relatively low temperature are formed. This leads to a pn inversion temperature at which p-type is converted to n-type. When the temperature reaches the pn inversion temperature, when the additive solution stored in the additive solution holder is kept in contact with the growth solution for a certain period of time, the additive solution diffuses into the growth solution and is deposited on the upper layer of the growth solution for the first layer growth. A second growth solution layer is formed. Since the diffusion in the growth solution is slow, the boundaries of the layers are also composed of slow changes.

After that, when the added solution is separated from the growth solution and cooled, the first and second epitaxial layers grow continuously, and the AlAs mixed crystal ratio becomes the lowest near the pn interface,
A gentle heterojunction is formed near the interface.

Embodiment An embodiment of the present invention will be described below with reference to FIGS.

 FIG. 2 shows a GaAlAs-LED structure according to the present embodiment.

The LED is mounted on an n-type GaAs substrate
It has a heterostructure in which a 100 μm n-type GaAlAs layer 2 and a 100 μm p-type GaAlAs layer 3 having a mixed crystal ratio profile are sequentially grown in a epitaxial manner, and the n-type GaAs substrate is removed later. N-type epitaxial wafer with substrate removed
On the surface of the GaAlAs layer 2, a circular n-side electrode 1 having a diameter of 150 μm
A p-side partial electrode having a diameter of 30 μm is formed on the back surface of the p-type GaAlAs layer 3.

When a current is applied to this LED, light emission recombination occurs at the pn interface 5. p
Light traveling from the n interface 5 to the front surface through the n-type GaAlAs layer 2 is directly extracted to the outside, and light traveling to the rear surface through the p-type GaAlAs layer 3 is reflected by the rear surface without being absorbed. Can be taken out.

FIG. 1 shows the AlAs mixed crystal ratio profile of this LED.
In the n layer, the surface mixed crystal ratio is 0.30 and descends almost linearly toward the pn interface, and the AlAs mixed crystal ratio at the pn interface is 0.07. From the pn interface toward the p-layer, the AlAs mixed crystal ratio gradually increases, and at about 20 μm, the AlAs mixed crystal ratio reaches a maximum of 0.48, and then the mixed crystal ratio decreases linearly toward the back surface, The AlAs mixed crystal ratio is 0.19.

As described above, the GaAlAs-LED has a profile in which the AlAs mixed crystal ratio is lowest near the pn interface and has no sharp heterojunction near the pn interface.

Next, a method for manufacturing a GaAlAs-LED having an AlAs mixed crystal ratio profile as described above will be described. FIG. 3 shows a slide type liquid phase epitaxial growth jig for manufacturing an epitaxial wafer for LED, and a series of steps from setting a raw material to the growth jig to manufacturing an epitaxial wafer.

The growth jig includes a substrate holder 8 for setting a GaAs substrate 11, a growth solution holder 7 for accommodating a growth solution 10 for growing a first layer composed of Ga, GaAs polycrystal, Al, and Si. It is composed of three holders, an additive solution holder 6 for storing an additive solution 9 made of Ga, Al, GaAs polycrystal, and Zn to be added to the growth solution 10 for growing two layers. In addition, 12
Is a lid of the solution reservoir 6a in which the additive solution 9 is stored.

As shown in FIG. 3A, an n-type GaAs substrate 11 doped with Si is set in a substrate holder 8. Growth solution holder 7
In the solution reservoir 7a, 50 g of Ga, 117 mg of Al, 7.0 g of GaAs and 90 mg of Si as an n-type dopant are set. 10 g of Ga, 160 mg of Al, 0.05 g of GaAs, and 100 mg of Zn as a p-type dopant are set in 6 g of the solution reservoir of the additive solution holder 6. In this state, the growth jig is set in a reaction tube (not shown) and replaced with hydrogen gas. After the replacement is completed, the temperature inside the reaction tube is 950 ° C.
And wait until the solute is dissolved in Ga.

As shown in FIG. 3 (b), when the solute is dissolved, the growth solution holder 7 is pushed to bring the growth solution 10 into contact with the GaAs substrate 11,
After contact, slow cooling is started at a cooling rate of 0.2 ° C / min.

As shown in FIG. 3 (c), when the temperature reaches the pn inversion temperature,
The addition solution holder 6 is pulled to bring the growth solution 10 and the addition solution 9 into contact. Hold that state for about 40 minutes.

As shown in FIG. 3 (d), the growth solution 10 and the addition solution 9
After contact, the additive solution holder 6 is pushed back to return to the original position, and the growth solution 10 and the additive solution 9 are separated. Slow cooling is continued as it is to obtain a two-layer epitaxial wafer having a pn interface.

After taking out the obtained epitaxial wafer, GaAs
The substrate 11 is polished and removed.
Polish to 100 μm. After polishing, the mixed crystal ratio profile of the epitaxial wafer was measured.
A profile as shown in FIG. 1 was shown. However, since it takes time for the growth solution 10 in contact with the additive solution 9 in the step of FIG. 3 (c) to be uniform, the manner of rising of the mixed crystal ratio profile at the pn interface differs depending on the location.

An electrode was attached to this epitaxial wafer, and the emission output was measured in a bare chip state. As a result, a value of 6.5 mW or more was obtained at a forward current of 50 mA. This emission output was about 1.9 times the value of the conventional Si-doped GaAlAs-LED. The emission wavelength was 880 nm.

As described above, according to the present embodiment, the mixed crystal ratio of AlAs is the lowest near the pn interface, and since there is no sharp heterojunction near the pn interface, light generated at the pn interface enters the p layer. However, the light is not absorbed, and therefore, the light directed to the p-layer side is reflected on the back surface and can be effectively extracted to the outside from the n-layer surface.

In addition, since the AlAs mixed crystal ratio profile of the present embodiment does not change sharply at the pn interface, there is no defect due to the lattice mismatch peculiar to the hetero interface, and thus a high emission output can be obtained. Furthermore, since the AlAs mixed crystal ratio at the pn interface serving as the light emitting portion is the lowest and the lattice constant is small, a tensile stress acts on the active layer portion, resulting in a long life.

On the other hand, according to the manufacturing method of the present embodiment, before the growth of the first layer is started, the growth solution of the first layer and the second layer are grown using the existing slide type liquid phase epitaxial apparatus. After contacting the growth solution with the additive solution of Example 1 and waiting for the growth solution to become uniform, the first layer and the second layer are continuously grown to obtain an epitaxial wafer having a desired AlAs mixed crystal ratio profile. It can be realized only by changing the conventional operation procedure, and the manufacturing is easy.

In particular, in terms of manufacturing cost, a small amount of the second layer growth addition liquid to be added to the first layer growth solution is sufficient.
Most of the raw material cost for the layer growth solution. For this reason, the raw material cost for growing the epitaxial wafer is
It requires less than conventional manufacturing methods that require a separate layer growth solution.

In the above embodiment, Zn was used as the p-type dopant, but C, Ge, or Mg may be used.

Further, in the above example, an LED for infrared light of 880 nm is obtained, but the emission wavelength can be controlled from 600 nm to 940 nm by changing the AlAs mixed crystal ratio, and a red visible LED can be manufactured. It is. Therefore, the present invention is not limited to infrared high-output LEDs for remote control, but can be widely used for display or communication.

[Effects of the Invention] As described above, according to the present invention, the following effects are exhibited.

(1) According to the light emitting diode of the first aspect, the light emitted from the pn interface and directed to either the p layer or the n layer can be extracted outside without being absorbed together. Higher luminous output can be obtained as compared with the related art.

(2) According to the light emitting diode of the second aspect, since the mixed crystal ratio profile does not change sharply at the pn interface,
There is no defect due to lattice mismatch peculiar to the hetero interface, and higher emission output can be obtained.

(3) According to the method for manufacturing a light emitting diode according to the third aspect, the existing growth jig can be used as it is by simply changing the operation procedure, and the second layer growth solution is separately required instead of the additional solution. Compared with the conventional method, the amount of the second layer growth additive solution to be added to the first layer growth solution may be small, so that it can be manufactured inexpensively and easily.

(4) According to the light emitting diode of the fourth aspect, since any dopant can be used, it can be manufactured at lower cost.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an AlAs mixed crystal ratio profile of a GaAlAs-LED according to the present embodiment, and FIG. 2 is a diagram according to an embodiment of the present invention.
FIG. 3 is a cross-sectional view of a GaAlAs-LED structure, FIG. 3 is an explanatory view showing a manufacturing process of a slide type liquid phase epitaxial wafer according to the present embodiment, (a) is an explanatory view at the time of material setting,
(B) is an explanatory diagram during the growth of the first layer, (c) is an explanatory diagram during the addition of the additive solution, and (d) is an explanatory diagram during the growth of the second layer. 1 is an n-side electrode, 2 is an n-type GaAlAs layer, 3 is a p-type GaAlAs layer,
4 is a p-side electrode, 5 is a pn interface, 6 is an additive solution holder, 7 is a growth solution holder, 8 is a substrate holder, 9 is an additive solution, 10 is a growth solution, 11 is an n-type GaAs substrate, and 12 is a lid. .

Claims (4)

(57) [Claims] (1) The added Si is changed from n-type to p-type in the thickness direction of the crystal.
A GaAlAs light-emitting diode having a GaAlAs layer in which an n-type layer and a p-type layer are formed by pn inversion to a dopant of a type, and electrodes formed on both surfaces of the GaAlAs layer, respectively. A GaAlAs light emitting diode, wherein a p-type dopant other than Si is added together with the Si, and the AlAs mixed crystal ratio of the GaAlAs layer is lowest near the pn interface. 2. The GaAl as claimed in claim 1, wherein the GaAlAs layer has no steep heterojunction near the pn interface.
As light emitting diode. 3. A GaAlAs growth solution to which Si is added is brought into contact with the surface of the substrate to be cooled slowly, and the Si is pn inverted from an n-type to a p-type dopant during the slow cooling to have an n-type layer and a p-type layer. Ga
After growing the AlAs layer, the substrate is removed, and then the Ga
In a method for manufacturing a GaAlAs light emitting diode in which electrodes are formed on both surfaces of an AlAs layer, an additional solution in which a p-type dopant other than GaAs, Al and Si is dissolved is prepared in advance, and the pn after the n-type GaAlAs layer is grown is prepared.
Contacting the growth solution with the growth solution at an inversion temperature for a certain period of time; thereafter, growing the p-type GaAlAs layer by separating the growth solution from the growth solution and gradually cooling the growth solution. A method for manufacturing a light emitting diode. 4. C, Zn, Ge as p-type dopants other than Si
4. The method for manufacturing a GaAlAs light emitting diode according to claim 3, wherein one or several kinds of Mg are used.