GB1300235A - Preparation and purification of semiconducting gallium compounds - Google Patents

Abstract

1300235 Semi-conducting gallium compounds SUMITOMO ELECTRIC INDUSTRIES Ltd 31 Dec 1969 63481/69 Heading C1A Semi-conducting compounds of gallium such as GaAs, GaP, (Ga, In)As, (Ga, Al)As, Ga(As, P) or (Ga, In)P are obtained in the form of crystals having a low or controlled silicon content by forming a melt containing the constituents of the required compound in a reaction vessel (usually made of silica) which is enclosed in a silica tube, in the presence of a first additive selected from Si, Al, B and compounds of these, other than oxides, and a second additive which reacts with the melt to form a gallous oxide atmosphere and is selected from O 2 , CO 2 , and metal oxides which decompose under the reaction conditions, such as Ga 2 O 3 , As 2 O 3 or AS 2 O 5 , and forming the crystals from the melt. The Ga 2 O oxide atmosphere reacts with the first additive (and any other silicon initially present in the melt) to form an oxide film which protects the melt from contamination by reaction with silica in the reaction vessel and/or tube, even if the Ga 2 O pressure subsequently drops, e.g. due to reaction with Ga or As. If the first additive is silicon or a silicon compound, products having a controlled level of silicon contamination may be produced by selecting the quantities of the two additives so that not enough Ga 2 O is produced to remove all the silicon. Other dopants may also be added to the melt, Sn, Te and Cr being exemplified. In Examples 1 to 6 GaAs is prepared by the "horizontal Bridgeman" technique in the presence of As 2 O 3 and silicon. Fig. 3 shows apparatus which may be used and the temperature profile of the furnace. The silica reaction tube, 9, contains arsenic, 13, at one end while the other, hotter, end contains gallium and silicon in a silica vessel, 14, and some As 2 O 3 . The narrowness of the connecting tube, 11, prevents the Ga 2 O which is formed in the hot zone from diffusing to the cooler zone and condensing. The vessel, 14, also contains a seed crystal of GaAs, 15, on to which the product crystallizes as the furnace is moved slowly to the left. The method of the invention may also be used to purify pre-formed gallium compounds by melting them in the presence of the two additives and re-crystallization: the "zone refining" and "zone levelling" techniques may also be used.