JPH0257336B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention provides In ₁ - _x Ga _x As, In ₁ - _x Ga _x
This invention relates to a liquid phase epitaxial (LPE) growth method for obtaining epitaxial crystal layers such as As _y P ₁ - _y and InP.

Multilayer liquid-phase epitaxial growth of compound semiconductors is used in semiconductor lasers (hereinafter referred to as LDs), light emitting diodes (hereinafter referred to as LEDs), and avalanche photodiodes (hereinafter referred to as APDs), which are light-emitting and light-receiving devices for optical communications.
It is an important growth method for obtaining elements such as photodiodes (hereinafter referred to as PD) and photodiodes (hereinafter referred to as PD), and it is desired to establish a high-quality growth method with fewer defects, and research and development is actively progressing. ing. For example, the oscillation wavelength of a semiconductor laser is from 0.8 μm to 1.6 μm, such as GaAs-GaAlAs or InP-
Research and development of InGaAsP-based semiconductor lasers is the mainstream. In addition, Si is used as a photodetector for the main oscillation wavelength of 0.8μm to 0.87μm of GaAs-GaAlAs LD.
PDs or APDs using single crystals are widely used in practice, but it is difficult to detect light with a wavelength of 1 μm or more using Si materials due to the small absorption coefficient. μm～
It cannot be used in the 1.6μm wavelength range. Also
Ga-APDs are available for wavelengths over 1.1 μm, but they have large dark currents and excessive noise, so they are not necessarily the best photodetectors for optical communications. For this reason,
- PD or APD using group compound semiconductors, etc. is required, and InGaAs, InGaAsP, GaAlSb,
There are reports of prototype production using GaAlAsSP, GaSp, etc.

In ₁ - _x on the conventional InP substrate
Ga _x As _y P ₁ - _y In liquid phase epitaxial growth, when a thick film is grown, particularly by slow cooling, compositional changes often occur in the direction of the growth thickness. Along with this, the lattice constant also changes, so in extreme cases, on the thick In ₁ - _x Ga _x As _y P ₁ - _y layer that has the above compositional deviation.
InP epitaxial growth is not possible and double
Cannot form a heterostructure. In particular, in LEDs that require In ₁ - _x Ga _x As _y P ₁ - _y with a thickness of about 1 to 2 μm, it has been recognized that the luminous efficiency decreases when the above composition deviation occurs, and it is possible to Establishment of crystal growth technology is desired. Also on In ₁ ― _x Ga _x As
It has been reported that when In ₁ - _x Ga _x As _y P ₁ - _y or InP layers are grown by LPE, meltback development often occurs at the interface with In ₁ - _x Ga _x As, making it impossible to obtain a flat interface. It is desired to establish a growth method that allows for growth.

The purpose of the present invention is to provide the above-mentioned LD, LED,
By devising a multilayer liquid-phase epitaxial growth method for compound semiconductors that require particularly thick films for APD, PD, etc. wafers and accelerating the growth rate, we can produce high-quality epitaxial growth layers with fewer defects and good uniformity. It is something that forms.

The liquid phase epitaxial growth method of the present invention involves bringing an InP substrate into contact with a growth solution at a saturated solution temperature,
Next, In ₁ ― _x Ga _x As _y is deposited on the InP substrate while the temperature is lowered.
In the epitaxial growth method of P ₁ - _y (0≦x0.47, 0≦y≦1), the growth temperature is changed from the saturated solution temperature to a temperature 12 to 20°C lower than the saturated solution temperature at a rate of 1°C/min. descend at descending speed, then
It is characterized by epitaxial growth while decreasing the temperature at a rate of 0.5°C/min or less.

Next, the advantages of the present invention will be explained based on one embodiment. FIG. 1 shows an embodiment forming the gist of the present invention. Figure 1 shows that in In solution at 615℃,
It shows the growth rate when growth is performed using this growth solution, changing the quenching temperature and transitioning to slow cooling, including the saturated amounts of Ga, As, and P at this temperature. The growth rate here is the value obtained by dividing the epitaxial growth layer thickness by the square of the growth time.
100 seconds), the difference between the growth layer thickness d and the growth time t is d.
There is a relationship of ∝√, and growth progresses at a rate of diffusion, and represents the growth rate (d/√) per unit time. This figure shows that the growth rate increases by lowering the growth temperature from the saturation temperature, and the temperature difference is 17℃.
It is shown that the growth rate has a local maximum value, and when the growth temperature is increased beyond that, the growth rate decreases, and the region of high growth rate is 12 to
It can be seen that the temperature is in the range of 20℃.

Next, a comparison with a conventional method will be explained using a multilayer structure liquid phase epitaxial growth to form an LED with a wavelength of 1.3 μm as an example. Using a 615℃ saturated solution in Figure 2,
A schematic cross-section of a wafer grown at a cooling rate of 0.2°C/min is shown. The growth board is a horizontal slide board containing at least three growth solutions. In the conventional method, after holding the saturation temperature at 615°C for about 1 hour, cooling is started at 0.2°C/min, and once the temperature reaches 613°C, the n ⁺ -InP substrate 11 is immediately moved under the InP buffer layer growth solution. By doing n ⁺
-Grow the InP buffer layer 12. Next 610℃
Ga, As, and P are added to the In solution at 615℃.
The growth of the n ⁺ -InP buffer layer 12 is stopped by moving the InP substrate 11 under a solution containing a certain saturation amount of InP, and the growth of the n + -InP buffer layer 12 is then continued, and n-type In ₁ - _x Ga _x As _y with a wavelength of 1.3 μm is subsequently transferred. P ₁ - Grow _{the y} layer 13. By growing for about 5 minutes here, the size of about 1 to 2 μm
After growing the In ₁ - _x Ga _x As _y P ₁ - _y layer 13, the InP substrate is moved under the P ⁺ -InP growth solution, and the P ⁺ -InP layer is grown.
In ₁ ― _x Ga _x As _y P ₁ ― Hold on _{the y} layer 13 for a predetermined time.
A P ⁺ -nP layer 14 of about 2 μm is formed. FIG. 3 shows the results of measuring the so-called X-ray Lockkin curve of the lattice constant of the wafer produced as described above using (004) reflected X-rays. In Fig. 3, the horizontal axis is the rotation angle θ of the sample prepared as described above, the vertical axis is the relative strength, Si is the lattice constant of InP, and S ₂ is the above In ₁ - _x Ga _x As _y P ₁ - corresponds to the lattice constant of _{the y} layer 13, and the difference between S ₁ and S ₂ corresponds to the shift in the lattice constant.

Figure 4 shows a 1.3 μm wavelength grown by the growth method of the present invention.
The results of measuring the X-ray Lockkin curve of a multilayer liquid-phase epitaxially grown sample for LED use are shown. The growth method involves rapid cooling using a saturated solution at 615°C.
After the start of rapid cooling, if an n ⁺ InP buffer layer is grown on the n ⁺ -InP substrate and the temperature reaches 600℃, the temperature drop will be 0.2
℃/min, at this time In ₁ ― _x Ga _x As _y P ₁ ― _y
By growing the layer for about 40 seconds, a layer of about 1.5 μm is formed.
In ₁ ― _x Ga _x As _y P ₁ ― obtains _{the y} layer, followed by P ⁺ ―InP
This is a sample in which a layer of approximately 2 μm is grown over a predetermined period of time. The structure is similar to that shown in FIG. In Figure 4
S ₁ and S ₂ are InP and In ₁ - _x Ga _x As _y P ₁ - _y as in Fig. 3
This corresponds to the lattice constant of the layer, and when comparing Figures 3 and 4, the shape of S ₂ shows that the half width of the relative intensity is narrower in the sample prepared by the method of the present invention than in the conventional method. I understand that. This is because compared to the conventional method, which requires a long growth time and growth temperature changes, the method of the present invention allows for growth in a short time of about 40 seconds and with little temperature change.
Because thick film growth of about 2 μm is now possible,
This shows that a uniformly grown layer with little compositional variation in the In ₁ - _x Ga _x As _y P ₁ - _y layer was obtained, and a high-quality crystal layer was obtained.

Another example is an example in which a double heterostructure is desirable for an In ₁ - _x Ga _x As photodetector in terms of high quantum efficiency, etc., and multilayer liquid phase growth is performed to achieve this. FIG. 5 shows that by the method of the present invention, that is,
This figure shows a cross section of a sample grown in liquid phase using a saturated solution at 615°C, rapidly cooled to 15°C, and then slowly cooled down at a rate of about 0.2°C/min. As for the growth procedure, after growing an n ⁺ -InP buffer layer 22 on an n ⁺ -InP substrate 21 by the same method as described above, an In ₁ - _x Ga _x As layer 23 is grown for a predetermined period of time to a layer thickness of about 3 μm. After obtaining the wavelength
N-type In ₁ - _x Ga _x As _y P ₁ - _y layer 24 with a composition equivalent to 1.3 μm
was grown for a specified period of time to obtain a thickness of about 0.5 μm, and then an n-type
By growing the InP layer 25 for a predetermined time,
About 4 μm was obtained. In this example
The In ₁ - _x Ga _x As and In ₁ - _x Ga _x As _y P ₁ - _y interfaces are extremely flat. On the other hand, In ₁ ― _x Ga _x As by conventional method
1.3μm wavelength equivalent In ₁ ― _x Ga _x As _y P ₁ ― _y to LPE
As shown in FIG. 6, the grown example had irregularities of about 0.2 to 0.6 μm. The layer structure in Figure 6 is the same as that in Figure 5, and the growth method is the same as in Figure 5.
By a program similar to the example shown in the figure,
n ⁺ -InP buffer layer 32 on n ⁺ -InP substrate 31
After growing, an n-type In ₁ - _x Ga _x As layer is grown by LPE for a predetermined time to obtain a thickness of about 3 μm, and then an n-type In ₁ - _x Ga _x As _y P ₁ - _y layer with a composition corresponding to a wavelength of 1.3 μm is grown. Approximately 1μm
After LPE growth, an n-type InP layer with a thickness of about 3 to 4 μm was obtained.

As explained above, according to the growth method of the present invention, since the growth rate is fast, less perturbation acts on the growth layer during growth. Therefore, on InP substrates, especially
It is possible to obtain a flat, high-quality epitaxial layer with little compositional variation in the In ₁ - _x Ga _x As _y P ₁ - _y layer, and it is possible to achieve high-quality liquid phase epitaxial growth of a multilayer structure.

[Brief explanation of drawings]

FIG. 1 shows an embodiment that constitutes the gist of the present invention, where the horizontal axis shows the difference in quenching temperature from the saturation temperature, and the vertical axis shows the growth of the growth layer epitaxially grown when gradual cooling is started at that quenching temperature. Represents speed. Figure 2 shows an example of a prototype wafer for LEDs, where 11 is n ⁺
-InP substrate 12 is an n ⁺ -InP buffer layer, 13 is an n-type In ₁ - _x Ga _x As ₁ - _y P ₁ - _y layer, and 14 is a P ⁺ -InP layer. Figure 3 shows the X-ray Rockkin curve obtained by the conventional method, Si is InP, S ₂ is
This is a signal corresponding to the lattice constant of In ₁ - _x Ga _x As _y P ₁ - _y , and FIG. 4 shows the X-ray Lockkin curve obtained by the present invention. S ₁ and S ₂ are the same as in FIG. FIG. 5 shows an example of a prototype wafer for APD and PD, where 21 is an n ⁺ -InP substrate, 22 is an n ⁺ -InP buffer layer, 23 is an n-type In ₁ - _x Ga _x As layer, and 24
represents an n-type In ₁ - _x Ga _x As _y P ₁ - _y layer, and 25 represents a p ⁺ type InP layer. Figure 6 shows an example of a prototype wafer for APD and PD manufactured using the conventional method, and 31 is an n ⁺ -InP wafer.
Substrate, 32 is n ⁺ -InP buffer layer, 33 is n-type
In ₁ - _x GaAs layer, 34 is n-type In ₁ - _x Ga _x As _y P ₁ - _y
Layer 35 represents an n-type InP layer.

Claims (1)

[Claims] 1 In ₁ - _x Ga _x As _y P ₁ - _y (0≦x0.47, 0≦y
≦) The InP substrate is brought into contact with the growth solution.
In a method of liquid phase epitaxial growth of In ₁ - _x Ga _x As _y P ₁ - _y on an InP substrate, the growth temperature is varied by 1°C/1°C from the saturated solution temperature to a temperature 12 to 20°C lower than the saturated solution temperature. then descend at a speed of 0.5 min
A liquid phase epitaxial growth method characterized by performing epitaxial growth while lowering the temperature at a temperature lowering rate of ℃/min or less.