Patent GB-1076465-A (GB)
Title: Process for the preparation of crystalline semiconductor material
IPC: C01B33/02
Filed: 1964-08-04
Abstract: Crystalline semi-conductor material in pure or doped form is formed by a reversible chemical transport reaction in which solid semi-conductor material is converted at an elevated temperature into a gaseous substance or substances by reaction with a reaction gas, and the semi-conductor material is reformed and deposited from the gaseous substance or substances at a different place by the use of a suitable temperature gradient between the starting material and the deposition point.  The reaction gas comprises hydrogen and hydrogen sulphide or a substance which will form hydrogen sulphide at the elevated temperature e.g. carbon disulphide the composition of the reaction gas being adjusted in accordance with the elevated temperature so that during the deposition the formation of a non volatile sulphide layer on the semi-conductor material source is prevented, and the gaseous substance or at least one of the gaseous substances formed by the reaction of the reaction gas with the semi-conductor material is a volatile sub-sulphide.  The source may be a shaped body consisting at least in part of the semi-conductor material, or in powder form. In Fig. 1 (not shown) sealed reaction vessel 1 made of quartz contains semi-conductor material 2 e.g. polycrystalline gallium arsenide, and is filled with a H2S/H2 mixture. The vessel is placed within carbon tube 5 disposed in tubular furnace 3 such that where 2 is located the temperature is say 950 DEG C. whilst the other end of the vessel is at 250 DEG C. Semi-conductor material is transported and deposited at 4. Heating of the carbon tube may be by high frequency induction heating.  In a further embodiment, Fig.2 (not shown) material is transported from the upper surface of a support 11 consisting at least in part of the semi-conductor material to be transported to the underside of a monocrystalline disc 12 serving as a carrier formed of a semi-conductor material and separated from the support by spacers 14. The arrangement is accommodated in a quartz reaction vessel provided with one valve each for introducing and withdrawing the transport gas mixture.  The support 11 is heated by a heater 13, and the temperature difference between the upper surface of the support and the underside of the carrier should be 15 to 50 DEG C. A heater made of say graphite or silicon carbide may be coated with semi-conductor material and used as the support. Gallium arsenide may be deposited on gallium arsenide, germanium on germanium, silicon on silicon, and carbides or nitrides may be deposited e.g. silicon carbide on silicon carbide. Hetero-junctions may be produced e.g. by depositing gallium arsenide on germanium and vice-versa.  Doping of grown layers can be achieved by using a support consisting of or containing doped semi-conductor material e.g. gallium arsenide - containing germanium and built into the grown layer, or by admixing doping substances with the transport gas stream.ALSO:Crystalline semi-conductor material in pure or doped form is formed by a reversible chemical transport reaction in which solid semi-conductor material is converted at an elevated temperature into a gaseous substance or substances by reaction with a reaction gas, and the semi-conductor material is reformed and deposited from the gaseous substance or substances at a different place by the use of a suitable temperature gradient between the starting material and the deposition paint.  The reaction gas comprises hydrogen and hydrogen sulphide or a substance which will form hydrogen sulphide at the elevated temperature e.g. carbon disulphide, the composition of the reaction gas being adjusted in accordance with the elevated temperature so that during the deposition the formation of a non-volatile sulphide layer on the semi-conductor material source is prevented, and the gaseous substance or at least one of the gaseous substances formed by the reaction of the reaction gas with the semi-conductor material is a volatile sub-sulphide. The source may be a shaped body consisting at least in part of the semi-conductor material, or in powder form.  In Fig. 1 (not shown), sealed reaction vessel 1 made of quartz contains semi-conductor material 2 e.g. polycrystalline gallium arsenide, and is filled with a hydrogen sulphide-hydrogen mixture.  The vessel is placed within carbon tube 5 disposed in tubular furnace 3 such that where 2 is located the temperature is say 950 DEG  C. whilst the other end of the vessel is at 250 DEG  C. Semi-conductor material is transported and deposited at 4. Heating of the carbon tube may be by high-frequency induction heating.  In a further embodiment (Fig. 2, not shown), material is transported from the upper surface of a support 11 consisting at least in part of the semi-conductor material to be transported to the underside of a monocrystalline disc 12 serving as a carrier formed of a semi-conductor material and separated from the support by spacers 14. The arrangement is accommodated in a quartz reaction vessel provided with one valve each for introducing and withdrawing the transport gas mixture.  The support 11 is heated by a heater 13, and the temperature difference between the upper surface of the support and the underside of the carrier should be 15 DEG  to 50 DEG  C. A heater made of say graphite or silicon carbide may be coated with semi-conductor material and used as the support.  Gallium arsenide may be deposited on gallium arsenide, germanium on germanium, silicon on silicon, and carbides or nitrides may be deposited e.g. silicon carbide on silicon carbide. Heterojunctions may be produced e.g. by depositing gallium arsenide on germanium and vice versa. Doping of grown layers can be achieved by using a support consisting of or containing doped semi-conductor material e.g. gallium arsenide-containing germanium and built into the grown layer, or by admixing doping substances with the transport gas stream.