JPH0334848B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a liquid phase growth method used for forming a quantum well type epitaxial layer.

Conventional technology Conventionally, the formation of a quantum well type epitaxial layer is
Molecular beam epitaxial methods and metal-organic vapor phase epitaxy methods are mainly used, and liquid phase epitaxial methods are rarely used to form quantum well epitaxial layers because it is extremely difficult to control ultrathin films (300 Å). was not implemented.

However, it is widely known that the liquid phase epitaxial method is currently the most superior in terms of the simplicity and cost of the epitaxial layer growth equipment, and the crystallinity of the growth layer itself. Therefore, it is extremely important in practice to form a quantum well type epitaxial layer with good controllability.

The formation of quantum well type, especially multi-quantum well type epitaxial layers using the conventional liquid phase epitaxial method is usually performed by sequentially stacking epitaxial layers using a rotating method using a vertical electric furnace. Ta.

However, in general, horizontal electric furnaces are widely used because it is troublesome to put the growth boats in and out of the growth tube, and the size of the substrate is also limited. This is the current situation.
Therefore, here, a conventional example of forming a liquid phase epitaxial quantum well layer using a widely used horizontal electric furnace will be described.

In fact, a method for producing a quantum well structure using a liquid phase epitaxial method is disclosed in Japanese Patent Application No. 59-216654.
It has been filed under No. The outline of this patent will be briefly explained below.

When forming an extremely thin epitaxial layer (500 Å) by liquid phase growth, it is necessary to grow it in a very short growth time, usually one second or less. Therefore, the sum (t ₁ + t ₃ ) of the time t ₁ required to slide the substrate to completely contact the solution and the time t ₃ required to completely wipe off the solution by sliding the substrate is the difference between the substrate and the solution. If the time t ₂ is the same as or longer than the time t 2 in which the substrate is stopped and held, the growth time cannot be defined and the thickness of the grown layer cannot be controlled, so the substrate was slid without stopping during contact with the solution. We use the method of ``sliding growth,'' which allows growth to occur under certain conditions. A schematic diagram of the conventional device system used in the above patent application is shown in FIG. 1 is a substrate; 2, 3, and 4 are growth solutions; 5 is a slider that accommodates the slidable substrate; 6 is a solution holder that accommodates the growth solution; and 7 is a boat stand. However, when producing a multi-quantum well structure, if the growth solutions 2 and 4 are barrier layer solutions and 3 is a well layer solution for an extremely thin film, the substrate 1 is the barrier layer solution 2.
and 4, the substrate 1 is stopped and the barrier layer is grown;
A well layer is grown by sliding the substrate 1 between solutions 2 and 4 (Y. Sasai et al., Japanese Journal of Abrid Physics).
etal JJAP) vol.24.1985P.L137-L139) In this case, the forbidden band width of the well layer shifts slightly, and the half-value width of the spontaneously emitted light of the multiple quantum layer becomes wider than that of the bulk layer. A phenomenon of compositional fluctuations occurs that leads to a rise in temperature. The reason for this is that when the substrate 1 is slid back and forth, the well layer solution 3 is mixed into the slider 5.
It is thought that this is because the bottom surface of the well layer solution 3 is shaken and the convection of the solute in the solution is accelerated, causing fluctuations in the solute concentration. Furthermore, in the conventional growth using a barrier layer solution, sliding growth is not performed, so the film thickness controllability of the barrier layer is poor.

Problems to be Solved by the Invention As described above, the conventional method has a drawback in that the composition of each well layer differs slightly when a multi-quantum well structure is fabricated by liquid phase growth. Therefore, the present invention provides a method for making the composition of each well layer uniform and making each well layer sufficiently thin. Furthermore, the present invention provides a method for forming an extremely thin epitaxial multilayer film with good uniformity by simultaneously providing a method for improving the film thickness controllability of the barrier layer.

Means for Solving the Problem In order to solve the above problem, the side wall of the solution hole for the barrier layer and well layer in the solution holder is such that the hole at the bottom of the solution hole is smaller than the hole at the top. By making the solution hole sloped so that the width of the solution hole is smaller than the substrate, the convection of the solute concentration at the bottom of the solution is effectively prevented, and the width of the outer wall of the solution hole is made larger than the substrate. When producing a multi-quantum well layer, the barrier layer and well layer each having a thickness of 500 Å or less are made uniform in composition to obtain a good ultra-thin epitaxial multilayer film.

Effects The effects based on the above means are as follows. That is, by making the side wall of the solution hole have the above-mentioned slope shape, the weight of the solution is applied toward the bottom of the solution, and especially by making the width of the bottom part smaller than that of the substrate, the side wall of the bottom part of the solution is The pressure in the vicinity becomes even greater, the flow at the bottom of the solution is considerably relaxed against the sliding of the slider, and the solute concentration at the bottom of the solution hardly changes, making it possible to homogenize the composition with good reproducibility. can. Furthermore, by making the width of the outer solution wall where the substrate is stopped larger than that of the substrate, a uniform ultra-thin epitaxial multilayer film can be formed without causing growth during the stoppage.

Example First, the effect of the inclined solution hole will be explained using FIG. 1. In FIG. 1, the same components as those in FIG. 5 are designated by the same numbers and their explanations will be omitted. In addition, in order to simplify and make the explanation more concrete,
An example of forming a multi-quantum well type epitaxial layer of InGaAsP and InP is shown below.

The difference between this boat structure and the conventional one is that, as can be seen by comparing Figures 1 and 5, the side wall 8 of the solution hole for the well layer solution is wider at the top surface of the solution hole and narrower at the bottom surface. It has a gentle slope, and the width of the bottom surface is smaller than that of the substrate 1.

Growth conditions are solution soak at 620℃ for 1 hour, cooling rate
Growth was performed in a hydrogen gas atmosphere from 590°C by decreasing the temperature at a rate of 0.7°C/min. To start the growth, first slide the InP substrate 1, stop it in the InP barrier layer solution 2, grow the InP barrier layer on the substrate 1, and then slide the substrate 1 at a constant speed (20 mm/sec). The InP barrier layer solution 4 is slid all at once, and during the sliding, the InP substrate 1 comes into contact with the InGaAsP well layer 3, so an extremely thin (~100 Å) InGaAsP well layer is formed, and then the InP barrier layer grows. After the InP barrier layer is grown using the barrier layer solution 4, the substrate 1 is again slid all at once to the InP barrier layer solution 2, and an InGaAsP well layer and an InP barrier layer are sequentially grown as described above. The width of the bottom of the solution hole of the well layer solution 3 is 5 mm, and as is clear from FIG.
smaller than As described above, by sliding the substrate 1 back and forth between the barrier layer solutions 2 and 4, a multiple quantum well layer is formed. InGaAsP (λg=1.25μm, Lz~200Å)/InP prepared in this way
Figure 2 shows the photoluminescence spectrum at 77K of a five-layer pair of multiple quantum well layers. For comparison, a multi-quantum well layer fabricated by a conventional method and a thick film layer (thickness ~1 μm) of InGaAsP with the same composition are also attached for comparison.
An Ar laser with a wavelength of 5145 Å was used as the excitation light source.
The emission intensity on the vertical axis in FIG. 2 is in arbitrary units. What should be noted about Fig. 2 is that the spectral half-width is approximately 50 meV for the conventional method, while that for the spectral half-width produced using the method shown in Fig. 1 is approximately 50 meV.
A half-value width of 16 meV, which is comparable to that of a thick film layer, is obtained, and it can be seen that the compositional variation between each well layer is considerably suppressed. In fact, in the conventional manufacturing method, there are three peaks in the emission spectrum as shown by the arrows, and the composition of the five well layers is split even though the same growth well layer solution is used. It clearly shows what is happening.

As described above, it is clear that according to the method shown in FIG. 1, the composition of each well layer can be made uniform in the production of a multiple quantum well layer. on the other hand,
When the barrier layer is made of a multi-component mixed crystal such as InGaAsP, uniform composition is similarly required. In such a case, as shown in FIG. 3, if the shape of the barrier layer solution hole is made to have an inclined side wall, the composition can be made uniform, and a multi-quantum well layer with excellent characteristics can be formed.

Next, as an example using the above manufacturing method
An example of a method for manufacturing an epitaxial wafer for a 1.3 μm band multi-quantum well semiconductor laser will be described below with reference to FIG. In FIG. 4, the same components as those in FIG. 5 are designated by the same numbers and their explanations will be omitted. 10 is the board 1
Melt bag solution for etching the surface of 11
1 is an n-type InP buffer layer solution, 12 is a p-type InP cladding layer solution, and 13 is a p-type InGaAsP contact layer solution. The growth conditions were as follows: First, the solution was dissolved at 620°C for 1 hour, then the temperature was lowered at a cooling rate of 0.7°C/min, and the substrate 1 was slid from 595°C and brought into contact with the melt bag solution for several seconds. Perform a meltback. Next, slide the substrate 1 and
The n-type InP buffer layer is grown by contacting with the InP buffer layer solution 11 for several hundred seconds.

Next, for the production of a multi-quantum well layer, immediately after the growth of the n-type InP buffer layer described above, the substrate 1 is placed between the solutions 4 and 12 to a sufficient extent that the substrate 1 does not come into contact with the solutions 4 and 12. Solution wall 14 with a
λg = 1.05μm InGaAsP barrier layer (thickness 200mm).
Å), λg = 1.3 μm InGaAsP well layer (Lz ~ 200
Å) and λg=1.05 μm InGaAsP barrier layer (thickness 200 Å), three layers were sequentially grown by sliding growth. Since the outer solution wall of the solution hole, wall 4, is wider than the substrate 1, no growth occurs when the substrate 1 stops below it. Therefore, in the method shown in FIG. 5, the barrier layer and well layer are formed only when the substrate is slid, making it possible to form a more uniform multiple quantum well layer. Then, the substrate 1 is slid at a constant speed (20 mm/sec) all at once to the solution wall 15, which was prepared in the same manner as the solution wall 14, and
Sequentially, λg = 1.05 μm InGaAsP barrier layer (thickness 200
Å), λg = 1.3 μm InGaAsP well layer (Lz ~ 200
Å), λg = 1.05 μm InGaAsP barrier layer (thickness 200
A) Grow. In this way, the multiple quantum well layer is
Growth is performed by sliding the growth 1 back and forth between the solution walls 14 and 15, and after the growth of the multiple quantum well layer, the substrate 1 is sequentially slid to form the p-type InP cladding layer and the p-type InGaAsP contact layer. grow
Fabrication of epitaxial wafer for 1.3 μm band multi-quantum well semiconductor laser has been completed.

In addition, in the examples, a multi-quantum well type layer was used for the structure of the epitaxial layer. Needless to say, it is also effective. Regarding the solution hole having an inclined side wall, relatively good results were obtained when the angle of inclination was in the range of 60° to 80°. Furthermore, even greater effects can be expected if an appropriate weight is placed on top of the solution stored in the solution hole having an inclined side wall.

Effects of the Invention As described above, according to the present invention, a solution hole having an inclined sidewall is used in sliding growth, the bottom surface of the solution hole is made smaller than the substrate, and the outer wall of the solution hole is made wider than the substrate. If grown in this way, barrier layers and well layers with extremely high compositional uniformity (500
This makes it possible to obtain an extremely thin epitaxial multilayer film with good reproducibility (less than Å), which greatly contributes to the production of semiconductor devices having a quantum well structure.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a growth boat for explaining the liquid phase growth method of the present invention, and Figure 2 is a photoluminescence at 77K of a sample prepared by the liquid phase growth method of Figure 1 and a conventional method. 3 is a cross-sectional view of a growth boat for explaining the liquid phase growth method in one embodiment of the present invention, and FIG. 4 is a multi-quantum well semiconductor laser using the method of the same embodiment. FIG. 5 is a cross-sectional view of a growth boat for explaining a conventional liquid phase growth method. 2, 4... Barrier layer solution, 3... Well layer solution,
8...Slanted side wall, 14, 15... Space for board standby.

Claims (1)

[Claims] 1. Using a growth boat that has a substrate holder for storing a substrate and a solution holder provided with solution holes for storing barrier layer and well layer solutions, respectively, and in which the substrate holder and the solution holder are movable relative to each other, The sides of the solution hole in the solution holder are sloped so that the top part is larger than the bottom part, and the width of the bottom part is smaller than the substrate to suppress the convection of the solution at the bottom part that occurs during sliding. The outer wall of the hole is wide enough so that the substrate does not come into contact with the solution when it is under the solution wall, so that the substrate is stopped under the outer wall and the substrate is not stopped between outside the solution wall. A liquid phase growth method characterized in that an ultrathin epitaxial multilayer film having the barrier layer and well layer of 500 Å or less is formed by sliding the substrate holder and the solution holder at a constant speed.