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P-N Junctions in II-VI Compounds

IP.com Disclosure Number: IPCOM000096240D
Original Publication Date: 1963-Feb-01
Included in the Prior Art Database: 2005-Mar-07
Document File: 3 page(s) / 68K

Publishing Venue

IBM

Related People

Dunne, TG: AUTHOR [+3]

Abstract

Vacuum evaporation apparatus shown schematically in A is used to obtain different conductivity types of II-VI compounds. The three substrate positions are shown in A, B and C. Materials evaporated are the II-VI compounds CdS, CdTe, CdSe and ZnS.

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P-N Junctions in II-VI Compounds

Vacuum evaporation apparatus shown schematically in A is used to obtain different conductivity types of II-VI compounds. The three substrate positions are shown in A, B and C. Materials evaporated are the II-VI compounds CdS, CdTe, CdSe and ZnS.

Runs in apparatus shown in B indicate an angular dependence of conductivity type. When CdS, CdTe and CdSe are evaporated, they change conductivity type as summarized by the adjacent table. The type change is in some way angularly dependent. There is apparently no detectable interference or diffraction effect involved in the observed type change. The lower width of one type is approximately 1 cm. The mechanism apparently involves the energy spectrum of the components emerging from the source, but there is no obvious mechanism by which this segregation is accomplished.

To test the angular dependence of the segregation of the evaporating components further, the apparatus shown in C is used. Here, a semicircular substrate is used so that the source-substrate distance is everywhere the same. This distance varies with the angle in B. The angular dependence of conductivity type is verified by the fact that the same conductivity type change is symmetrical about the source as shown in C. Annealing is not required in films produced by the apparatus shown in B or C.

The process produces junctions of the same material or heterojunctions. In B, junctions of the same material can be made by linearly shifting the substrate after one deposition either up or down or both. A similar effect can be obtained by rotating the substrate in C to the left or right or both. In these cases, the vacuum is not broken and the evaporating material is not changed. For heterojunctions, the substrate in B and C remains in the same position, but the evaporating material is changed to one having a different conductivity type angular dependence. For example, CdS and CdTe can be alternately evaporated to produce a p-n junction. With various combinations of substrate motion and material change, complex junctions and matrices of junctions can be obtained.

Drawings D and E show added configurations produced by two molecular beams due to dissociation of constituent materials upon evaporation. During evaporation, partial separation of the molecular beams takes place. This effect results in a continuous composition change of the deposited film. In the case of CdS and CdSe, film formation with a well-defined molecular beam gives n-type conductivity in the center and p-type conductivity at the edges. In the case of CdTe, the opposite effect is produced.

The charge carrier sign is controlled either by impurity doping for most semiconductors or by the control of vacancy concentration in some cases. However, in the case of CdSe neither impurity nor vacancy concentration control produces p-type conductivity which is produced by the molecular beam method described. The reason for this is probably the low sol...