GB2181747A

GB2181747A - A molecular beam epitaxial growth apparatus

Info

Publication number: GB2181747A
Application number: GB08621746A
Authority: GB
Inventors: Takahiro Suyama; Kohsei Takahashi; Saburo Yamamoto; Toshiro Hayakawa; Masafumi Kondo
Original assignee: Sharp Corp
Current assignee: Sharp Corp
Priority date: 1985-09-11
Filing date: 1986-09-10
Publication date: 1987-04-29
Also published as: GB2181747B; JPS6261315A; FR2587040A1; GB8621746D0

Abstract

A molecular beam epitaxial growth apparatus has a vacuum chamber (1), a sample holder-supporting means (3) disposed in a manner to turn around its axis (4) within said vacuum chamber (1), at least one sample holder (6) supported on said sample holder-supporting means (3), and a plurality of molecular beam source groups (9, 10) for the molecular beam epitaxial growth of semiconductor crystals on a substrate (5) to be supported on said sample holder (6), wherein molecular beams from each of said molecular beam source groups (9, 10) converge on at least two points (16, 17) which are positioned in the orbiting path of said sample holder (6). This apparatus is used to produce a superlattice composed of a plurality of thin layers made of a variety of semiconductor materials without repeating the opening and the closing of the shutters of molecular beam sources, thereby preventing the leakage of vacuum in the apparatus and also has the advantage of producing a superlattice structure on each of a plurality of substrates at the same time. A particular superlattice is GaAs-AlGaAs formed on a GaAs substrate. <IMAGE>

Description

SPECIFICATION A molecular beam epitaxial growth apparatus The present invention relates to a molecular beam epitaxial growth apparatus, and in particularto an apparatus forthe formation of asuperlatticedstruc- ture, using a molecular beam epitaxial growth technique.

Molecular beam epitaxial growth apparatuses are suitable for the fomration of a heterojunction at the interface between two different semiconductors, the production of extremely thin semiconductor layers and/or the production of a superlatticed structure since these products can be obtained under an excellent composition control and excellent layerthickness control. These apparatuses have provided novel devices such as high electron-mobilitytransistors and quantum well lasers.

A superlatticed structure obtained from two or more kinds of semiconductor materials by these conventional molecular beam epitaxial growth apparatuses is composed of a plurality ofthin growth layers, each of which has a thickness in the range of several angstroms (10 angstroms inm)to several hundred angstroms. Because of the novel structure, the superlatticed structure is expected to provide a device having a new function.

In orderto form a heterojunction atthe interface between the semiconductor layers using liquid phase epitaxy, the lattice constants of these semiconductor layers must be matched therebetween. On the contrary, with a superlatticed structure produced by molecular beam epitaxy, even though a lattice mismatch of several percent exists between the semiconductor layers, these semiconductor layers can be epitaxially grown. Such kinds of superlatticed structures have been studied as a strained layersuperlattice. The fact that the allowable limit of lattice mismatch in a superlatticed structure produced by molecular beam epitaxy is great may indicate that the allowable limit of the difference in composition between the semi-conductor layers constituting the superlattice is also great.

In order to produce a superiatticed structure by the use of a conventional molecularbeamepitaxial growth apparatus, shutters disposed in front of the molecular beam sources of semiconductor materials must be repeatedly opened and closed. Thus, when a superlattice having a thickness of several thousand angstroms is formed, the opening and closing ofthe shutters must be repeated several hundreds oftimes, causing leakage ofthe vacuum in the molecular beam epitaxial growth apparatus, the inside of which mustbeunderextremelyhighvacuum.

In accordance with the present invention, a molecular beam epitaxial growth apparatus comprises a vacuum chamber, a sample holder-supporting means adapted to turn within said vacuum chamber about an axis of rotation, at least one sample holder supported on said sample holder-supporting means, and a plurality of molecular beam source groups for the molecular beam epitaxial growth of semiconductor crystals on a substrate to be supported on said sample holder, wherein molecular beams from each of said molecular beam source groups converge on at least two points which are positioned in the orbiting path of said sample holder.

In a preferred embodiment, the angle at which each of the molecular beams radiates the substrate supported on said sample is set to be at a selected value and/or a shielding plate is disposed between the convergency points, thereby preventing leakage of molecular beams from one molecular beam source group to the convergency point correspond ingto molecularbeamsfrom anothermolecular beam source group.

Thus, the invention described herein makes possible the objects of (1) providing an apparatus which produces a superlattice composed of a plurality of thin layers made of a variety of semiconductor materials without repeating the opening and the closing of the shutters of molecular beam sources, thereby preventing the leakage of vacuum in the apparatus during the production ofthe superlattice; and (2) providing an apparatus which can produce a superlatticed structure on each of a plurality of substrates at the same time.

Byway of example only, a specific embodiment of the present invention will now be described, with reference to the accompanying drawing, which is a front sectional view showing an embodiment of molecular beam epitaxial growth apparatus in accordance with the present invention.

The accompanying drawing shows a molecular beam epitaxial growth apparatus ofthe present invention,which comprises a vacuum chamber 1, a sample holder-supporting means 3 disposed in a mannertoturn around its axis 4 within the vacuu m chamber 1, at leastone sample holder6supported on the sample holder-supporting means 3, a molec ular beam source group 9forthe growth of,forexample, GaAs crystals on a substrate 5 supported on the sample holder 6, and a molecular beam source group 10 for the growth of,for example, AIGaAs crys- tals on the substrate 5.

The vacuum chamber 1 is under an extremely high vacuum by means of a vacuum system (notshown).

During the growth of a superlattice, liquid nitrogen flows through a liquid nitrogen shroud 2 disposed on the inner surface of the vacuum chamber 1, so that contamination gases such as CO, etc., liberated while the superlattice is grown, can be effectively absorbed by the liquid nitrogen shroud 2, thereby maintaining the cleanliness ofthe growth atmosphere within the vacuum chamber 1. The sample holder-supporting means 3 is held by the axis 4within thevacuum chamber 1 in a mannerto revolve around the axis4 by a turning means (not shown) connected to the axis 4. Thus, the sample holder 6, on which the substrate 5 of,forexample, GaAs issupported by a soldering material such as indium,turns around the axis 4with the turning ofthe sample holder-supporting means 3.

A heater 7 for heating the substrate 5 and a thermocouple 8 for monitoring temperature of the substrate 5 are disposed at the back of the sample holdersupporting means 3. The molecular beam source groups 9 and 10 which are used for the growth of GaAs crystals and the growth ofAlGaAs crystals, re spectively, to form a GaAs-AIGaAs superlattice on the substrate 5, are disposed in front of the sample holder-supporting means 3. The molecular beam source group 9 is composed of a gallium molecular beam source 11 and an arsenic molecular beam source 12. The molecular beam source group 10 is composed of a gallium molecular beam source 13, an aluminum molecular beam source 14and an arsenic molecular beam source 15.The molecular beamsfrom both the gallium molecular beam source 11 and the arsenic molecular beam source 12 ofthe group 9 converge on a convergency point 16which is positioned in the orbiting path of the sample holder 6. The molecular beams from the gallium molecular beam source 13, the aluminum molecular beam source 14 and the arsenic molecular beam source 15 ofthe group 10 converge on a convergency point 17 which is positioned in the orbiting path of the sample holder 6.

A GaAs-AIGaAs superlattice can be formed on the GaAs substrate by using the above-mentioned apparatus as follows: When the sample holdersupporting means 3 turns around the axis 4 by a turning means connected to the axis 4, the sample holder 6turns around the axis 4,so that the GaAs substrate5 supported on the sample holder 6 is irradiated with both the gallium molecular beam and the arsenic molecular beam from the molecular beam source group 9 whenever the GaAs substrate is positioned atthe point 16 in the orbiting path of the sample holder6, and moreover the GaAs substrate 5 is irradiated with an aluminum molecular beam, a gallium molecular beam and an arsenic molecular beam from the group 10 whenever the GaAs substrate 5 is positioned atthe point 17 on the orbiting path ofthe sample holder 6, resulting in a GaAs-AIGaAssuper- lattice on the GaAs substrate 5.

When leakage of gallium molecular beams from the gallium molecular beam source11 totheconvergency point 17 and/or leakage of gallium molecular beams and aluminum molecular beamsfrom the gal- lium molecular beam source 13 and the aluminum molecular beam source 14, respectively, to the convergency point 16 arise to a large extent, a purposed superlattice cannot be prepared. In orderto minimize the leakage of molecular beams, the angle at which each molecular beam radiates the substrate is set to be a selected value. Moreover, when a shielding plate 18 is placed between the convergency points 16 and 17, leakage of molecular beams can beef- fectively prevented.

When a plurality of sample holders 6 are disposed on the sample holder-supporting means 3, a plurality of GaAs substrate 5 can be supported on the corresponding sample holders 6 so that a plurality of superlatticed wafers can be formed by one cycle. In orderto usethis apparatus inthe same manneras in a conventional molecular beam epitaxial growth apparatus, shutters by which the irradiation of each ofthe molecular beams is shielded or allowed can be positioned in front of each of the molecular beam sources.

It is understood that various other modifications will be apparent to and can be readily made by those skilled in the art without departing from the scope and spirit of this invention. Accordingly, it is not in tended that the scope of the claims appended hereto be limited to the description as set forth herein, but ratherthatthe claims be construed as encompassing all thefeatures of patentable noveltythat reside in the present invention, including all featuresthat would be treated as equivalents thereof by those skilled in the art to which this invention pertains.

Claims

1. A molecular beam epitaxial g rowth apparatus comprising a vacuum chamber, a sample holdersupporting means adapted to turn within said vacuum chamber about an axis of rotation, at least one sample holder supported on said sample holder- supporting means, and a plurality of molecular beam source groupsforthe molecular beam epitaxial growth ofsemiconductorcrystals on a substrate to be supported on said sample holder, wherein molecular beams from each of said molecular beam source groups converge on at least two points which are positioned in the orbiting path of said sample holder.

2. A molecular beam epitaxial growth apparatus as claimed in claim 1,whereintheangleatwhich each of the molecular beams irradiates the substrate supported on said sample is set to be at a selected value, thereby minimizing leakage of molecular beams from one molecular beam source grouptothe convergency point corresponding to molecular beams from another molecular beam source group.

3. A molecular beam epitaxial growth apparatus as claimed in claim 1 or claim 2, wherein a shielding plate is disposed between the convergency points, thereby preventing leakage of molecular beams from one molecular beam source group orthe convergency point corresponding to molecular beams from another molecular beam source group.

4. A molecular beam epitaxial group apparatus substantially as herein described, with reference to, and as illustrated in, the accompanying drawings.