Patent GB-757672-A (GB)
Title: Improvements in or relating to melted-on electrodes for semi-conductor apparatus
IPC: H01L21/24
Filed: 1954-09-15
Abstract: 757,672. Semi-conductor devices. SIEMENSSCHUCKERTWERKE AKT.-GES. Sept. 15, 1954 [Sept. 15, 1953], No. 26817/54. Class 37. In producing semiconductor devices made from predominantly homopolar semi-conductor compounds a selected electrode material in the molten state dissolves the semi-conductor compound but does not decompose the semi-conductor compound into its components so that upon cooling and subsequently setting the electrode material separates out from the semi-conductor compound. The process is thus similar to that obtaining when the semi-conductor is an element and the system of selected semi-conductor and selected electrode behaves as a quasi-binary system. The electrode material may comprise a component of the semi-conductor compound. Semi-conductor compounds:- (a) A 111  By type with A 111 , e.g. aluminium (A1), gallium (Ga) or indium (In) and By nitrogen (N), phosphorous (P), arsenic (As) or antimony (Sb); specifically mentioned: AlSb, GaSb and InSb. (b) A 1v  B v1  type such as PbS, PbSe and PbTe. (c) A 11  B 1v  type such as Mg2 Si, Mg 2  Ge, Mg 2  Sn and Mg 2  Pb. (d) ZnSb and CdSb. The Specification also comprises a complete list, Fig. 1 (not shown), of the elements which can be considered for semi-conductor compounds of a predominantly homopolar character. Electrode materials :- (a) Aluminium. (b) Gallium. (c) Indium.. (d) Antimony. (e) Cadmium For use with semi-conduc- (f) Zinc tor compounds of A 111  (g) Tellurium By type. (h) Antimony with zinc or cadmium (for use e.g. with AlSb as semi-conductor). (i) Aluminium or antimony with selenium or tellurium (for use e.g. with AlSb as semiconductor). (j) Tin (for use e.g. with semi-conductor AlSb). (k) Mercury, e.g. as cadmium amalgam (for use with A 111  By type semi-conductor compounds). The mercury may be used to facilitate the melting on of cadmium and subsequently removed by evaporation. (1) An alloy consisting of (in atomic per cent proportions) 60/Sb and 40/GaSb for use with semi-conductor GaSb. (m) The eutectic alloy (in atomic per cent proportions) 75/Sb and 25/GaSb for use with semi-conductor. GaSb. (n) An alloy having a coefficient of heat expansion substantially equal to that of the semi-conductor. In Fig. 2 when Al as electrode material 3 is melted on semi-conductor body 1 (AlSb) the zone 2 of body 1 is dissolved in the material 3 and finally when the temperature has dropped to the melting point of pure Al all the zone 2 AlSb has separated out and comprises traces of A1 and Al is formed as the outer electrode 3. The zone 2 may be of different conductivity type to body 1 (for PN junction electrodes) or similar conductivity type, but increased conductivity in relation to body 1 (for barrier-free electrodes). The Specification includes AlSb, GaSb and InSb phase diagrams, Figs. 3 to 5 (not shown), and from these may be seen (i) the temperature required to dissolve a required quantity of semi-conductor compound and (ii) the penetration depth of the boundary surface between the melt and the unmelted parent semi-conductor (i.e. the penetration depth of zone 2 in Fig. 2). The penetration depth may also be changed by altering the time during which a semi-conductor is maintained at the necessary temperature. If desired, the cooling rate can be regulated to control the semiconductor properties of zone 2 and during the melting-on of the electrode material (e.g. by ultrasonic methods) the semi-conductor surface may be uniformly wetted. The following publications are referred to: Specification 719,873 (which gives details adverting to A 111  Bv semiconductor compounds) and the book, " The Nature of the Chemical Bond " (1950).