JPH02293391A - Method for hot-wall epitaxial growth - Google Patents

Abstract

PURPOSE:To obtain an epitaxially grown crystal having improved crystallinity by forming a space between the opening of a source crucible and a substrate for epitaxial growth in such a manner as to keep high concentration of low- vapor pressure molecule having a specific action and exposing the substrate to the atmosphere of the space. CONSTITUTION:A GaAs substrate 3 for epitaxial growth is placed on a substrate-holding table 5 provided with a heater 4 and the substrate 3 is positioned above the opening 11 of a source crucible 2 containing the source material 6 for CdTe. The GaAs substrate 3 is heated at about 350 deg.C and the source material 6 is heated at about 500 deg.C. The crucible is evacuated at a specific rate to remove Cd molecule 13 having high vapor pressure through the gap between the bottom face 5A of the substrate-holding table 5 and the opening 11 and to form a concentrated phase of Te2 molecule in the space encircled with the substrate 3 and the substrate-holding table 5. The Te2 molecule is a low vapor-pressure component of the volatile components of CdTe. A CdTe single crystal of (100) plane is formed on the substrate 3 by this process.

Description

[Detailed Description of the Invention] [Summary] Regarding a hot wall epitaxial growth method, the present invention aims to provide a real wall epitaxial growth method in which a compound semiconductor crystal having a composition different from that of the substrate can be epitaxially grown on a substrate in a desired crystal growth direction. An epitaxial growth substrate is placed on a source crucible that is installed in a room, has an open top, and contains a source material for epitaxial growth that is composed of atoms with different vapor pressures, and heats the source material in the source crucible. In the method for depositing an evaporated component of the source material on a substrate for evitaxial growth, the evaporation component of the source material for evixaxial growth is placed between the upper opening of the source crucible and the substrate surface of the substrate for epitaxial growth. Among the components, a space is formed to maintain a high concentration of low vapor pressure molecules that regulate the epitaxial crystal growth surface to a predetermined crystal growth surface, and an atmosphere with a high concentration of low vapor pressure molecules is formed in the space. It is constructed by exposing the substrate to epitaxial growth.

[Industrial application field]

The present invention relates to a hot wall epitaxial growth method, and more particularly to a real wall epitaxial growth method in which an epitaxial crystal of a compound semiconductor can be formed on a substrate in a predetermined crystal growth direction.

The hot wall epitaxial growth method uses lead tellurium (
■ PbTe), lead, tin, tellurium (PbsnTe), etc.
Group III compound semiconductor crystals, gallium arsenide (GaAs)
It is becoming established as a crystal manufacturing technology for forming optical devices and integrated circuits using III-V group compound semiconductor crystals such as those represented by III-V compound semiconductor crystals, and II-Vl group compound semiconductor crystals such as cadmium tellurium (CdTe).

In this hot wall epitaxial growth method, a source crucible containing a source material for a compound semiconductor crystal to be formed and a heated side wall is placed in a room evacuated to high vacuum, and an epitaxial layer is formed in the opening of the crucible. A substrate to be formed is placed, and the evaporated components in the crucible are attached to the substrate as an epitaxial layer. Therefore, it is similar to the closed-tube vapor phase growth method, and the evaporated components of the source material reach the substrate while colliding with the sidewalls of the hot wall, allowing epitaxial growth in a state close to thermal equilibrium. A thin layer crystal with a uniform composition and uniform carrier concentration without segregation can be obtained.

In addition, as materials for forming infrared rays, mercury, cadmium, tellurium (Hg+-x c
A compound semiconductor crystal such as dXTe) is used, and in order to form such a compound semiconductor crystal in a large area and thin film state convenient for device formation, the Hg
+-x Cd)I Hg+-x Cd.
Te crystal is grown epitaxially.

By the way, it is difficult to obtain a large-area single crystal of CdTe, so CdTe is grown using the above-mentioned photowall epitaxial growth method on a gallium arsenide (GaAs) substrate, where it is relatively easy to obtain a large-area single crystal. An epitaxial layer is formed, and this is used as a substrate crystal, on which an epitaxial crystal of HgI-XCdXTe is formed.

[Conventional technology]

FIG. 3 is an explanatory diagram of a conventional hot wall epitaxial growth apparatus, which is an apparatus for forming a CdTe epitaxial layer on a GaAs substrate.

As shown in the figure, a source crucible 2 with an open top is installed in a vacuum chamber 1 evacuated to a high vacuum of about 10-7 torr, and an epitaxial growth substrate 3 made of GaAs is held in the upper part of the source crucible 2. A substrate installation stand 5 is provided which includes a built-in heater 4 for heating the substrate.

Inside the source crucible 2, C was formed by the Bridgman method.
A source material 6 made of a single crystal of dTe is accommodated, and the crystal growth surface is (100”) as a substrate for epitaxial growth.
A planar GaAs single crystal is used.

Furthermore, surface theory of substrates for epitaxial growth and substrate installation stand 5
The source crucible 2 is placed on a substrate mounting table with a distance from the bottom path of about 1 to 1.5, and the heater 7 on the side wall 2^ of the source crucible 2 is heated to a temperature of 500''C to heat the substrate. By heating at a temperature of about 350° C., components evaporated from the CdTe source material are deposited on the substrate, thereby growing an evixaxial crystal of CdTe on the GaAs substrate.

In addition, cadmium, zinc, tellurium (
CdZnTe) and GaAs
A method of growing an epitaxial layer of CdZnTe on a substrate has also been adopted.

[Problem to be solved by the invention]

However, when a GaAs single crystal with a (100) crystal growth plane is used in the above conventional method and a CdTe epitaxial crystal is grown thereon, the CdTe epitaxial crystal that is formed will have a (100) plane or a (100) plane. 1 1 1)
A problem arises in that an epitaxial crystal is formed in which both the ('100) and (111) crystal growth planes coexist.

When a substrate having an epitaxial crystal with different crystal growth planes or mixed crystal growth planes is used as an epitaxial growth substrate, an epitaxial layer of og, -XCdxTe having a desired crystal growth plane is formed on the substrate. There is an inconvenience that it is not formed.

The present invention solves the above-mentioned problems, and provides a GaAs substrate with a predetermined crystal growth surface.
The object of the present invention is to provide a true wall epitaxial growth method that can reliably obtain dTe epitaxial crystals.

[Means to solve the problem]

The hot-wall epitaxial growth method of the present invention for achieving the above object uses a source crucible 2 containing a source material for epitaxial growth as shown in the principle diagram of FIG.
Between the upper opening 1l and the substrate surface 3A of the epitaxial growth substrate 3, among the evaporated components of the epitaxial growth source material, low vapor pressure molecules that regulate the epitaxial crystal growth surface to a predetermined crystal growth surface are present. The purpose is to form a space 12 that maintains a large concentration, and to expose the epitaxial growth substrate 3 to an atmosphere with a high concentration of low vapor pressure molecules formed in the space 12 to perform epitaxial growth.

[For production]

When CdTe source material is heated in a high vacuum, Cd atoms and Te. It turns into molecules and evaporates.

Then, Te. When the concentration occupied by molecules is larger than the concentration occupied by Cd atoms (10
The present inventors have experimentally confirmed that an epitaxial layer of CdTe having a growth surface of 0) plane is easily formed.

By the way, the boiling point of Te is 1390'C at 1 atm, and the boiling point of Cd is 767'C, and Cd molecules evaporate more easily and have a higher vapor pressure than Tez molecules.Therefore, the substrate surface and the opening of the crucible The distance between the crucible and the bottom of the substrate mounting table was increased from the conventional 1 to 1.5 m to 15 mm, and the substrate was installed at a position deeper than the opening of the crucible. By exhausting Cd atoms with a high vapor pressure from the gap between them, a Te-rich CdTe vapor atmosphere with a high concentration of Te molecules is formed on the substrate surface, and this Te'J-rich CdTe vapor atmosphere is created. When an epitaxial layer of CdTe is grown on a GaAs substrate using
CdT with (100) crystal growth plane on As substrate
It is possible to form an epitaxial crystal of e.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 2 is an explanatory diagram of a main part of an embodiment of the hot wall epitaxial growth method of the present invention.

As shown in the figure, in the hot wall epitaxial growth apparatus that implements the method of the present invention, a substrate mounting table 5 (100
) crystal growth plane and a diameter of 35IIII
An epitaxial growth substrate 3 made of As is installed.

Then, this epitaxial growth substrate 3 is replaced with a source material 6 made of a CdTe single crystal formed by the Bridgman method.
The source crucible 2 is placed over the opening ll of the source crucible 2 containing the . The distance between the surface 3A of this epitaxial growth substrate 3 and the bottom surface 5A of the substrate installation stand 5! is 1.5 parrots compared to the conventional 1.5 parrots.
5+w, and the substrate surface 3^ is arranged so that the position of the substrate surface 3^ is located further back when viewed from the bottom surface 5A of the substrate installation stand 5 than in the conventional case.

Then, the opening 11 of the crucible and the bottom surface 5^ of the substrate mounting table are opened so that the Cd molecules l3 having a high vapor pressure among the evaporated components evaporated from the CdTe of the source material 6 are selectively and sufficiently exhausted.
Keep the dimension d between . The chamber (not shown) containing the source crucible 2 containing the source material 6 and the substrate mounting table 5 containing the epitaxial growth substrate 3 is evacuated to a degree of vacuum of 10-'to'r. .

Next, the epitaxial growth substrate 3 made of GaAs is heated to a temperature of 350°C, and the source material 6 is heated to a temperature of 500°C.
When the substrate is heated to a certain temperature and epitaxial growth is performed while the chamber is evacuated at a predetermined exhaust rate, CdTe crystals are epitaxially grown on the substrate at a rate of 1 μl/hour.

In this way, the Cd atoms 13 with high vapor pressure are selectively exhausted and removed through the gap between the bottom surface 58 of the substrate mounting table 5 and the opening 1l of the crucible, and are recessed into the side wall 5B of the substrate mounting table 5. epitaxial growth substrate 3 placed at a position
A component with a high concentration of low vapor pressure Te2 molecules 14 among the evaporated components of CdTe is formed in the space 12 formed by CdTe crystals are formed.

When the CdTe epitaxial crystal thus formed with a thickness of 4 μm was examined by X-ray diffraction, the half-width at half maximum (FWHM) of the X-ray diffraction peak indicating crystallinity was (
400) plane and was found to be a single crystal with good crystallinity.

As described above, according to the method of the present invention, an epitaxial crystal of a compound semiconductor having a growth plane with a predetermined crystal orientation is formed on a substrate with good reproducibility. 'g+-x on top
When an infrared sensing element is formed using a material in which an epitaxial layer of Cd++Te is formed, a high-quality sensing element can be obtained.

Note that instead of the CdTe epitaxial layer, CdZ
The present invention can also be applied to the case where a CdZnTe epitaxial crystal is formed using an nTe source material.

〔Effect of the invention〕

As described above, according to the method of the present invention, an epitaxial layer having a predetermined crystal direction is formed on a substrate with good reproducibility, so if an infrared sensing element is formed using such an epitaxial crystal, high This has the effect of providing a high-quality infrared sensing element.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the principle of the method of the present invention, FIG. 2 is an explanatory diagram of an embodiment of the method of the present invention, and FIG. 3 is an explanatory diagram of a conventional hot wall epitaxial growth method. In the figure, 2 is a source crucible, 3 is an epitaxial growth substrate, 4 is a heater, 5 is a substrate installation table, 5A is the bottom of the substrate installation table, 5
B is the side wall of the substrate installation stand, 6 is the source material, l1 is the opening, 12 is the space, l3 is a high vapor pressure molecule (Cd molecule), l
4 indicates a low vapor pressure molecule (Te2 molecule). Figure 1, --4''-7- Figure 2

Claims (1)

[Scope of Claims] An epitaxial growth substrate (3) is placed on a source crucible (2) that is installed in a vacuum chamber, has an open top, and contains therein an epitaxial growth source material (6) composed of atoms with different vapor pressures. ), the source crucible is heated, and the evaporated components of the source material are deposited on the substrate for epitaxial growth, the source crucible (2) having an opening (11) in the upper part thereof. ) and the substrate surface of the epitaxial growth substrate (3), there is a concentration of low vapor pressure molecules (14) among the evaporated components of the epitaxial growth source material that regulates the epitaxial crystal growth surface to a predetermined crystal growth surface. A space (1
2), and epitaxial growth is performed by exposing the substrate to an atmosphere with a high concentration of low vapor pressure molecules formed in the space.