JPH0257335B2 - - 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 growing multiple epitaxial crystal layers such as AsP _1-y and InP.

Multilayer liquid-phase epitaxial growth of compound semiconductors is used for light-emitting and light-receiving devices for optical communications. Semiconductor laser (hereinafter referred to as LD), light emitting diode (hereinafter referred to as LED), avalanche photodiode (hereinafter referred to as LED),
This is an important growth method for obtaining devices such as APD (hereinafter referred to as APD) and photodiodes (hereinafter referred to as PD), and it is desired to establish a growth method that can obtain high-quality grown crystal layers with few defects.

Currently, GaAs-
Research and development of GaAlAs-based or InP-InGaAsP-based LDs is the mainstream. In addition, GaAs-GaAlAs LD
PDs or APDs using Si single crystals are widely used as photodetectors for the main oscillation wavelength of 0.8 μm to 0.87 μm. However, with Si single crystals, it is practically difficult to detect light with a wavelength of 1 μm or more because the absorption coefficient becomes small, and it cannot be used in the 1.1 μm to 1.6 μm wavelength range where optical fiber has low transmission loss. Also, for wavelengths of 1.1 μm or more,
Ge-APD is available, but it is not necessarily the best photodetector for optical communications because of its large dark current and excessive noise. For this reason, - group compound semiconductors, etc.
PD or APD is required, and InGaAs,
There are reports of trial production using InGaAsP GaA-iSb, GaAlsSb, GaSb, etc.

Figure 1 shows an In _1-x Ga _x As _y P _1-y layer as a light absorption layer.
This is a reported example of a planar APD in which a Pn junction is formed in InP, and is described in detail in Japanese Patent Application No. 54-39169. The shape of a wafer with this structure is n ⁺
An n ⁺ -InP buffer layer 12 is formed on the -InP substrate 11, and then an n-type In _1-x Ga _x As _y P _1-y layer (light absorption layer) is formed.
This is a wafer in which an n-type InP layer 14 is formed after forming 13, and by basically forming a P ⁺ region 15 in the InP layer 14 by selective diffusion, low dark current and high multiplication characteristics are achieved. APD is obtained.

Lattice matching a device structure similar to this with InP
In _1-x corresponds to the longest wavelength composition of In _1- x Ga _x As _y P _1-y
Ga _x As is used as a light absorber when producing APDs, PDs, etc. that detect all wavelengths of light from light sources such as LDs and LEDs that have In _1-x Ga _x As _y P _1-y as the active layer. ,
It is necessary to epitaxially grow an InP layer on the In _1-x Ga _x As. However, in the liquid phase growth method, when trying to grow InP on In _1-x Ga _x As,
Conversely, so-called meltback development occurs in which the In _1-x Ga _x As layer dissolves in the InP growth solution, making it impossible to form a multilayer structure. For this reason, a layered structure is obtained by epitaxially growing a so-called anti-meltback In 1 _{- x} Ga _x As _y P _1-y layer on In 1-x _Ga x As and then growing an InP layer. In this case as well, the wavelength of the anti-meltback layer is about 1.5 μm and In _1-x
Relatively good In _1-x when the composition is close to Ga _x As
Ga _x As―In _1-x Ga _x As _y P _1-y interface is obtained, but
In _1-x Ga _x with a composition close to InP, that is, with a shorter wavelength composition
When the As _y P _1-y layer is used as an anti-meltback layer, a good heterointerface cannot be obtained.

In addition, LD with In _1-x Ga _x As active layer or
When creating multilayer structures for LEDs, anti-meltback In _1-x Ga _x As _y P, which is closer to InP composition with a shorter wavelength, is used to suppress leakage of the injection carrier and increase the light containment effect. _1-y layer is required. Also,
In the case of APDs and PDs that use In _1-x Ga _x As as a light absorption layer, short-wavelength anti-meltback In _{1-x Ga}
As _y P _1-y layer is required.

The purpose of the present invention is to meet the above-mentioned objectives.
For wafers for LDs, LEDs, APDs, PDs, etc., we apply the multilayer liquid phase epitaxial growth method of compound semiconductors to form a good hetero interface and produce high-quality epitaxial growth layers with few defects and good uniformity. It is something that forms.

The liquid phase epitaxial growth method of the present invention epitaxially grows an In _1-x Ga _x As _y P _1-y layer on an In _1-x Ga _x As _y crystal formed by lattice matching on an InP substrate. The growth rate A (μm/sec ^1/2 ) is the value obtained by dividing the growth layer thickness of the In _1-x Ga _x As _y P _1-y layer by the square root of the growth time.
When the wavelength corresponding to the forbidden band width Eg of the In _1-x Ga _x As _y P _1-y layer is λ _Q μm (λ _Q = 1.239 (ey) / Eg (ev)), A≧−λ _Q This is a liquid phase epitaxial growth method characterized by performing liquid phase epitaxial growth under the conditions of +1.4, 1.2λ _Q 1.36.

Next, the advantages of the present invention will be explained based on one embodiment. FIG. 2 shows an embodiment of the invention. In Figure 2, the horizontal axis is the growth rate A, and the vertical axis is the unevenness of the hetero interface when growing an In _1-x Ga _x As _y P _1-y layer on In _1-x Ga _x As, such as angle polishing. This corresponds to the melt back measured by In this experiment, various compositions and growth rates A were used.
Growth temperature of In _1-x Ga _x As _y P _1-y layer on In _1-x Ga _x As
This is the result of liquid phase epitaxy at 600°C.

In addition, in this experiment, InP−In _1-x Ga _x As−
In _1-x Ga _x As _y P _1-y wafer InP and In _1-x Ga _x As
When In _1-x Ga _x As _y P _1-y growth initiation surface is observed after selective removal of In 1-x Ga It was confirmed that there was no significant difference from the single layer epitaxial growth surface. In Fig. 2, even if the growth rate A is the same, the unevenness of the hetero interface is the wavelength λ _Q of In _1-x Ga _x As _y P _1-y (the gap between the forbidden band width Eg and the wavelength λ _Q is approximately Eg = 1.239 (ev)/λ _Q (μm)) is strongly dependent on the long wavelength composition In _1-x Ga _x
It was shown that As _y P _1-y had less unevenness, and even at the same wavelength (composition), as the growth rate increased, the unevenness decreased. Figure 3 shows In _1-x Ga _x As based on these experimental results.
When an In _1-x Ga _x As _y P _1-y layer is grown on top of the In 1-x Ga x As y P 1-y layer by liquid phase epitaxial growth, the In _1-x Ga _x As _y P _1-y is necessary for the hetero interface to exhibit an extremely good mirror surface. The relationship between the wavelength (composition) and growth rate () and the In _1-x Ga _x As _y required for the mirror surface limit (roughness of 500 to 600 Å) that does not exhibit white turbidity.
The relationship between the wavelength (composition) and growth rate of P _1-y () is shown. This figure 3 shows the gist of the present invention.
When an In 1 _{- x} Ga _x As _y P _1-y layer is liquid-phase epitaxially grown on In ₁ -x Ga x As, at a wavelength composition of 1.2λ _Q 1.36, the white-mirror boundary () is It was shown that the growth rate can be approximated by A=-λ _Q +1.4, and by having a growth rate higher than this, a heterointerface with a mirror surface and less unevenness can be obtained. Figure 4 shows APD and PD.
A schematic cross section of a manufactured wafer is shown. The growth method uses a horizontal sliding boat with at least 4 solution baths, and a predetermined amount of Ga, As, and P are charged into each growth solution bath along with In as necessary to lattice match the InP substrate. After that, the temperature of the growth furnace was raised to about 640°C and held for about 1 hour to mix the solution thoroughly, and then the temperature was lowered to 615°C for 1 hour.
Stabilize the solution by keeping it constant for a certain amount of time,
Start rapid cooling at about 2°C/min. Following the start of this rapid cooling, the n ⁺ -InP substrate 21 is moved under the n ⁺ -InP buffer layer growth solution to grow the n-InP buffer layer 22 . Next, when the temperature of the furnace reaches 600℃, it immediately shifts to slow cooling at a rate of about 0.2℃/min. At the same time as this gradual cooling process, the InP substrate ^is
By moving from under the -InP buffer layer wavelength solution to under the In _1-x Ga _x As wavelength solution, the growth of the n ⁺ -InP buffer layer 22 is stopped, and the n-type In _1-x Ga _x As layer 2 is
3 starts growing. After obtaining an n-type In _1-x Ga _x As layer 24 with a thickness of 3 to 4 μm by growing for about 50 seconds, the InP substrate is moved under the In _1-x Ga _x As _y P _1-y growth solution. With a growth time of about 4 seconds, the growth time is about 0.5 μm.
An In _1-x Ga _x As _y P _1-y layer 24 is obtained.

Here, the composition of the In _1-x Ga _x As _y P _1-y layer is at a wavelength of 1.3 μm.
The growth rate using the equivalent is 0.25μm/sec ^1/2 . Next, move the InP substrate under the n-type InP growth solution.
An n-type InP layer 25 with a thickness of 3 to 4 μm is obtained by a growth time of about 40 minutes. The hetero-interface of the wafer produced in this way is extremely good, and high-quality APD and PD can be produced by a process similar to that shown in FIG. In comparison, Fig. 5 shows an example of the conventional method, in which the saturation temperature of the growth solution is set at 615°C.
From 610℃ using a gradual cooling method of 0.2℃/min.
An example is shown in which growth with the same basic layer structure as in Figure 4 was performed during a temperature drop of 600°C. The growth is performed by slow cooling at 0.2°C/min, and after reaching 610°C, the n ⁺ -InP substrate 31 is moved under the growth melt ^.
Buffer layer 32, n-type In _1-x Ga _x As layer 33, n-type In _1-x Ga _x As _y P _1-y layer 34 equivalent to a wavelength of 1.3 μm, n
The type InP layer 35 is sequentially grown for a predetermined period of time to form a fourth layer.
The thickness of each layer was approximately the same as shown in the figure.

In this case, In _1-x Ga _x with the same composition as in Figure 4
Even though the _{As y} P 1 _{- y} layer is grown _by LPE on In _{1-x Ga x As} , there is _a In this case, unevenness of about 0.2 to 0.6 μm occurs and a good heterointerface cannot be obtained.

Note that the limited range of λ _Q in the claims is λ _Q <
In the range of 1.2 μm, it is actually difficult to increase the growth rate to more than 0.25 μm/sec ^1/2 with LPE growth, and the approximate expression of the empirical formula A = λ _Q + 1.4 cannot be specified. Excluded because of. In addition, as mentioned above, In _1-x of λ _Q ~1.5 μm is deposited on In _1-x Ga _x As.
LPE growth of the Ga _x As _y P _1-y layer is often carried out, and the basis for this is clear from the experiments shown in Figures 2 and 3, but empirically
It has been reported that the In _1-x Ga _x As _y P _1-y layer with a composition of 1.35 to 1.5 μm is a difficult region for LPE growth, and that when λ _Q > 1.4 μm, the empirical formula A = −λ _Q This region was excluded because it cannot be defined by the approximation formula of +1.4.

The embodiments, APD, and PD that constitute the gist of the present invention have been described above.
Although we have described an example of manufacturing a wafer for In _{1-x Ga}
The In _1-x Ga _x As _y P _1-y layer, which has a large bandgap difference with the In _{1-x Ga} x As bandgap on As, can be well liquid-phase epitaxially produced, and is suitable for LDs and LEDs. In the case of APD and PD, it is possible to obtain a light-emitting device with excellent properties such as suppressing carrier leakage and having a large light confinement effect, and in the case of APD and PD, it can have a uniform high quantum efficiency over a wide range and a high High-quality multilayer liquid phase epitaxial growth is possible.

[Brief explanation of drawings]

Figure 1 shows a reported example of APD using In _1-x Ga _x As _y P _1-y , 11 is n ⁺ -InP substrate, 12 is n ⁺ -InP
Buffer layer, 13 is n-type In _1-x Ga _x As _y P _1-y layer,
14 is an n-type InP layer, and 15 is a layer in which p-type impurities are formed by selective diffusion technology. Figure 2 shows the gist of the present invention, in which liquid phase epitaxial growth is performed on In _1-x Ga _x As using In _1-x Ga _x As _y P _1-y layers of various compositions and growth rates. The width of the unevenness at the hetero interface between In _1-x Ga _x As and In _1-x Ga _x As _y P _1-y when grown is shown. Figure 3 also forms the gist of the present invention, and shows that In _1-x Ga _x As y is formed on In _1-x Ga _x As _y.
The wavelength (composition) and growth rate of In _1-x Ga _x As _y P _1- y necessary to have an extremely good (roughness < 100 Å) uneven interface when liquid-phase epitaxially forming the P _1-y layer. Relationship (), exhibits a mirror surface (irregularity <600 Å)
The relationship () between the wavelength (composition) and growth rate of In _1-x Ga _x As _y P _1-y required for this is shown. Figure 4 shows an example of wafer production for APD and PD, and 21 is n ⁺ -InP.
Substrate, 22 is n ⁺ -InP buffer layer, 23 is n-type
24 is an n-type In _{1 -x} Ga _x As _y P _1-y anti-meltback layer, and 25 is an n _- type InP layer.
FIG. 5 shows an example using the conventional growth method, and 3
1 is an n ⁺ -InP substrate, 32 is an n ⁺ -InP buffer layer,
33 is an n-type In _1-x Ga _x As layer, 34 is an 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 formed by lattice matching on an InP substrate
When epitaxially growing an In _1-x Ga _x As _y P _1-y layer on an As epitaxial crystal, In _1-x Ga _x As _y
The growth rate A (μm/sec ^1/2 ) is the value obtained by dividing the growth layer thickness of the P _1-y layer by the square root of the growth time, and In _1-x Ga _x AsP _1-y
The wavelength λ _Q μm (λ _Q = 1.239
(ev)/Eg(ev)), A≧−λ _Q +1.4,
A liquid phase epitaxial growth method characterized by performing liquid phase epitaxial growth under the conditions of 1.2λ _Q 1.36.