X-ray studies on the structure of p-(Pb_1−xSn_x)_1−y Te_y thin films

Abstract

Thin films were deposited by vacuum evaporation of p-(Pb_1−x Sn _x )_1−y Te_y powders (wherex ≃ 0.71 andy ≃ 0.508) on to glass, mica and natural NaCl substrates heated to various temperatures. X-ray diffractograms show that films deposited on colder substrates exhibit inferior crystalline quality. Films deposited atT _sub ≃ 457±5 K are polycrystalline, showing strong (2 0 0) or (2 2 2) peaks along with weaker (2 2 0), (4 0 0) or (4 2 0) peaks. Variance analyses performed on intense line profiles show that the crystallite size, r.m.s. strain and dislocation density are fairly high even in polycrystalline films. PbSnTe crystallites show a preference for (1 0 0)-oriented growth on heated glass and (1 0 0)-cleaved NaCl substrates; but on equally heated mica, their growth shows an initial preference for the (1 1 1) orientation, which gradually switches over to the (1 0 0) orientation for higher thicknesses. Probably due to a higher SnTe content, PbSnTe crystallites show evidence of misorientation on heated glass and natural NaCl substrates.