| 摘要 |
An electric semiconducting device for use as a rectifier or a crystal triode is prepared by depositing on a base plate a mixture of semiconducting material and a small percentage of donor or acceptor <PICT:0682105/III/1> <PICT:0682105/III/2> impurity material, by reducing a volatile compound of semiconducting and impurity material with a volatile or gaseous reducing agent in the presence of the base plate. In one example, Fig. 1, hydrogen is passed at a controlled rate through silicon tetrachloride in vessel 3 at temperature T1, and at a separately controlled rate through a mixture of silicon tetrachloride and boron trichloride in vessel 4 at temperature T2. The outputs are combined and passed through an oven 8 where the reaction product is deposited on a base plate 9 of carbon, or a high melting point conducting material which does not alloy with silicon, or aluminium oxide or a ceramic material. The proportion of boron which acts as an acceptor impurity may thus be controlled to provide layers of desired characteristics in selected positions in the resulting silicon element. A small percentage of germanium or tin tetrachloride may be added to vessel 3. Alternatively, germanium may be substituted for silicon in the process, and arsenic hydride or antimony hydride may replace boron to provide a donor impurity. Zinc may alternatively be used as a reducing agent, and since this material has a high vapour pressure, reduction may be effected without using a continuous flow of gas through the apparatus. In Fig. 3, a vapour mixture of silicon tetrachloride and boron trichloride is supplied from a tube 30 to a tube 25 which is situated in an outer tube 28. The reducing agent consists of aluminium vapour supplied from a chamber 29 at the end of tube 25. Tube 28 is connected to a pump for removing unwanted gases. Reaction takes place in a central compartment of tube 25 where base plate 9 is provided. Partitions may be used to direct the vapour flow. |
