JPS6041454B2 - Multilayer epitaxial growth method including thick films - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thick film multilayer epitaxial growth method for epitaxially growing a compound semiconductor crystal layer so that its composition is always homogeneous.

BACKGROUND OF THE INVENTION Compound semiconductors, particularly crystals of m-V group compound semiconductors, are widely used as materials for photoelectric devices such as semiconductor lasers and light emitting diodes (LEDs).

The crystals are produced using two types of techniques: liquid phase epitaxial growth and vapor phase epitaxial growth.

Among these, the liquid phase epitaxial growth method is, for example, Ga
It is said to be superior to the vapor phase epitaxial growth method in that it is relatively easy to realize epitaxial growth layers with a high-quality multilayer structure, as typified by semiconductor lasers and LEDs using As-AI ship moat crystals. It is considered. However, when such a mixed crystal as described above is grown by a normal liquid phase epitaxial growth method, it is inevitable that compositional fluctuations occur in the growth direction within the film. For example, if the film is a thin film with a thickness of several micrometers or less, this can be ignored because the absolute value of the composition variation within the film is small, but it becomes a problem in the case of a thick film. Conventionally, a technique called a temperature difference method has been developed as a method for suppressing compositional fluctuations that occur during epitaxial growth of thick films, and LEDs using thick films formed using this method have also been announced. However, this temperature difference method has the following drawbacks.

Namely, 1. Since the growth rate is extremely slow, it takes a long time to obtain the required film thickness.

2 Poor reproducibility, especially difficult to control thickness.

3. It is difficult to create a multilayer structure.

etc.

In general, when looking at the photoelectric elements, such as LEDs, it is essential to have a multi-channel structure from the viewpoint of performance improvement, and the above-mentioned drawback 3 is serious. In an attempt to overcome this drawback, we first grew a thick film using the temperature difference method, then removed it from the growth furnace, subjected it to surface treatment, and then grew the required number of crystal layers on top of it using the usual method. It is also being considered to create a multilayer structure by adding layers, but this method requires many steps and
The cost becomes high, and furthermore, the above-mentioned two disadvantages inherent to the temperature difference method are also compounded, and the yield is also deteriorated. The present invention makes it possible to obtain a compound semiconductor wafer with a thick film multilayer structure by using a normal liquid phase epitaxial growth method without using a temperature difference method, and will be described in detail below.

Now, in general, for example, the relationship between the solution composition and the epitaxial growth layer composition when growing a mixed crystal of an m-V group compound by the liquid phase epitaxial growth method, and the composition fluctuation during growth, can be explained using a regular solution. Based on theoretical calculations based on theory and numerical calculations assuming thermal equilibrium during growth,
It is possible to predict accurately.

Figure 1 shows the case where the growth starts at 900 [〇C].
The figure shows how the composition of the epitaxial growth layer changes when the epitaxial growth layer is gradually cooled and the growth continues, using numerical calculations and graphing the results.

For example, when growing at a temperature of 900 [°C] and a molar ratio x = 0.3 of AlAS in the epitaxial growth layer, the molar ratio x decreases as the growth progresses due to precipitation, and the molar ratio x decreases to 840 [°C]. In [℃], x = 0.09800 [〇C]
So xto. 0 (GaAs).

Therefore, once the reduction width ΔT of the growth temperature is determined, what is the composition of the epitaxial growth layer at the growth start temperature? .

The difference Δx=xo-x between the composition 3A of the epitaxially grown layer at the temperature To-ΔT at the end of growth can be determined by numerical calculation. Therefore, conversely, in order to obtain a thick film whose composition at the end of growth (temperature To - △T) is x, growth should be started from a composition larger by △x determined as described above. I understand that. Further developing this idea, for example, the first layer is a thick film and the composition on the surface side is x, and the layer after the second eyebrow is, for example, several thin films and the composition on the surface side is uniform, so... In order to obtain a wafer having a multilayer structure, the amount of compositional variation △average, △... of each layer with respect to the width of further temperature reduction is determined by numerical calculation, and the epitaxial growth layer at the first layer growth start temperature To is determined by numerical calculation. So that the composition is uniformly 10△&, x30△x3...
By setting the composition of the solution corresponding to each layer, a multilayer thick film can be grown in one step without having to perform multiple growths. Based on such knowledge, a case will be described in which a double-layer thick film substrate used for light emitting diodes for optical communication is manufactured by a liquid phase epitaxial growth method called a sliding method.

In general, for example, near-infrared light-emitting diodes for high-output optical communication using (Ga, AI)As, it is important to increase the brightness of the light-emitting part, and for this purpose, a heterojunction structure is adopted. , and it is necessary to minimize the thermal resistance.

Therefore, for such LEDs, we usually seek a structure called an up-side-down type, in which the light-emitting part is placed as close to the surface as possible, and bonded so that the surface side is close to the heat sink. and explore structures that extract light from the surface. However, (Ga, AI)A
As a substrate for forming the epitaxial growth layer of s, a Ga carrier having a smaller band gap than the (Ga, N) pseudo band gap Eg is used, so that the GaA
If the s-substrate (Ga, AI) remains present, it is not possible to efficiently extract light from the light-emitting portion, which is the epitaxial growth layer.

Therefore, after forming the CanAs epitaxial growth layer, it is necessary to remove the Ga* substrate, and for this purpose, the epitaxial growth layer alone must be thick enough to have sufficient mechanical strength. Usually its thickness is 40-50
It is said to be [A's]. Figure 2A shows a two-layer single heterostructure LED constructed with the above points in mind.
FIG.

That is, the illustrated waveform is, for example, a G having a [100] plane.
aAs substrate 1 with a thickness of 50 [rm] or more, final value of composition x
, is 0.09, the first epitaxial growth layer 2 of n(Te)-Ga(,)NX melon is grown, and on top of that,
It has a structure in which a second layer epitaxially grown layer (hetero layer) 3 of Ga, -xA1xAs is grown with a thickness of 1.8 [mountain surface] and a final composition value x2 of 0.34, p.n.
The junction is obtained by diffusing zinc (Zn) from the surface to form a p-type region 4.

The opening in FIG. 2 is a bran diagram showing the composition distribution in the wafer shown in FIG. In order to satisfy the condition of the growth starting temperature To=900 [OC] in a wafer having the structure as shown in FIG. Width 4T must be determined.

Therefore, "Cooling rate 0.2 [OC/mjn], x = 0.0
The experimental growth rate for 9 hills is 0.8 to 0.9.
[um/qC]. ” Therefore, 4T=60 [℃]
It was found that the first epitaxially grown layer 5 had a thickness of 50 m or more. Furthermore, x at △T=60 [OC]:
When the composition sea at 900 [° C.], which is 0.09, was determined by the numerical calculation described above, xo = 0.32. Similarly, regarding the second epitaxial growth layer 3, ΔT=60
To obtain an average of 0.34 at [°C], 0.34 at 900 [°C].
It was found that a composition of 50 was sufficient. Based on such analysis results, the wafer was manufactured using a liquid phase epitaxial growth apparatus shown in FIG.

In FIG. 3, 11 is a carbon slider, 12 is a carbon base, 13 is a first layer solution, 14 is a second layer solution, 15 is a dummy GaAs plate, and 16 is formed on the base 12. 17 and 18 indicate solution reservoirs, respectively.

The compositions of the first layer solution 13 and the second layer solution 14 are determined as follows using the above analysis results and the Ga-AI-As ternary system equilibrium phase diagram.

That is, solution 13Ga: 10.6 [evening], AI: 13.
0 [guy], Ga ship: 1.0 [evening] solution 14Ga: 10
．． 6 [no], AI: 26.5 [glue], Ga$: 0.
77 [Evening] Also, in the solution 13, 300% tellurium (Te) was added so that the n-type impurity concentration in the first epitaxial growth layer would be 2 to 3 × 1 and 7 [number of atoms/clump]. Rita] It's in.

A dummy Ga pine substrate 15 is placed on top of the solution 14 so that the solution 14 always remains in equilibrium while growing the first epitaxial growth layer.

Now, the apparatus in the state shown in Figure 3a was set in a reaction tube containing a hydrogen or inert gas atmosphere, inserted into an electric furnace, and the temperature was raised to 900 [°C]. A constant temperature is maintained for about 40 [minutes] to fully saturate solutions 13 and 14. Next, as soon as the temperature begins to decrease at a rate of 0.2 C/min, the slider 11 is moved so that the first layer solution 13 comes into contact with the GaAs substrate 16, as shown in FIG. and start growing the first epitaxial growth layer. 840 [OC] in this state
As the temperature is lowered to (△T=60 [℃]), Ga$
A first layer thick film is grown on the substrate 16 with an initial composition value of xo=0.30 and a final composition value of x,=0.09. 840 [℃]
When the second layer solution 14 reaches the surface of the substrate 16, move the slider 11 so that the second layer solution 14 comes into contact with the substrate 16 as shown in FIG.
Start growing the layer epitaxially.

On top of the thick epitaxial growth layer, Cedar=0.
Growth of 34 second epitaxial growth layers begins. In this state, the temperature was lowered to 8370, and the temperature reached 837 [
OC], the slider is moved as shown in FIG. 3d to remove the solution 14 from the substrate 16 and terminate the growth. When the thickness of the wafer obtained as described above was actually measured, the thickness of the first epitaxially grown layer was 52 m, and the thickness of the second epitaxially grown layer was 1 m.
．． 8 [〆m], and when the composition of each part of the wafer is measured by photoluminescence, it is x.

= 0.30, x, = 0.09 x 2 = 0.34 are obtained,
Both the thickness and composition were as designed. On this wafer,
On the board 16 2.3 [Buddha skin] from the surface, xo = 0.32
n-type (G
a, AI) An epitaxially grown layer of As is formed.

``While growing this first epitaxial growth layer, the dummy Ga$ plate 15 has xo=0.50 ~
GaAIAs whose composition changes continuously up to average = 0.34
An epitaxially grown layer of 14 is formed, thus the solution 14
is always in a state of equilibrium. "Then, 840
When the slider 11 is further moved to bring the solution 14 into contact with the substrate 16 as shown in FIG. Selective diffusion of Zn was carried out to a depth of 35 [one skin] in diameter, and G
After removing the motherboard a, attach n and p electrodes to each side of the wafer, cut out the chip, and perform ponting to form the LE.
Completed D. When the LED emits light, the current is 100
[mA], emission wavelength 8300 [A], output 5-10 [m
w] performance was obtained. In the above description, an example of growing a two-layer wafer having a 50 [mu] thick film (Ga, A) epitaxially grown layer has been described.
Furthermore, even if the wafer has multiple layers, if one layer other than the final layer is a thick film, e.g. 40 mm or more, and the other layer is a thin film, e.g. The composition can also be applied as is. Further, the present invention can also be applied to epitaxial growth of m-V group compound semiconductors other than GaAI or mixed crystals of other compound semiconductors. Furthermore, the growth starting temperature is also 9
The temperature is not limited to 0.00°C, and may be appropriately selected depending on the system to which the present invention is applied. Furthermore, the dummy G
There are no restrictions on the shape or location of the a-trillion plates, as long as they are in contact with a predetermined solution during thick growth.
Strictly speaking, compositional changes that occur during epitaxial growth should exist even if there are only a few (single skin) epitaxial growths, but this does not have a practical effect and can usually be ignored. As can be seen from the above description, according to the present invention, a compound semiconductor wafer having a multilayer structure having a thick film can be easily manufactured with good reproducibility.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the relationship between temperature and composition variation, Fig. 2 (a) is an explanatory diagram of a wafer manufactured according to the present invention-embodiment, and Fig. 2 (a) is a diagram showing the composition distribution in (b). , Figure 3 a~
d is a process explanatory diagram of an embodiment of the present invention. In the figure, 11 is a slider, 12 is a base, 13, 14
is a solution, 15 is a dummy Ga bamboo plate, 16 is a substrate, 17,
Reference numeral 18 indicates a solution reservoir. Figure 1 Figure 2 Figure 2 Figure 3

Claims (1)

[Claims] 1. In layers other than the final layer closest to the surface, the primary crystal X is 0.
When growing a multilayer structure epitaxially including a thick layer of Ga_1__XAl_XAs with a thickness not exceeding 56 μm and a layer thickness of 40 μm or more using a slow cooling liquid phase epitaxial method that lowers the temperature. After the thick film layer is epitaxially grown, a dummy crystal is separately added to each solution used to form an epitaxial growth layer that is subsequently grown on the thick film layer to maintain a thermal equilibrium state of the composition. and the composition of each solution is set in advance so as to deviate from the composition that should be set at the start of growth by the composition variation that occurs in response to the temperature drop during the growth of the thick film layer. Multilayer epitaxial growth method including thick films.