Study of Disorder in Flash-Evaporated Amorphous InP Films

Abstract

The similarities between the structure and the electronic properties of amorphous III–V compounds and their elemental counterparts, amorphous Ge and Si, have early been emphasized ^1,2. However, due to the presence of two constituents, and to the partial ionic character of the bonding, both the type of disorder and the nature of defects are likely to be different in the amorphous compounds. The possibility of chemical disorder must in particular be comtemplated. Amorphous InP is a good candidate for studying these problems. Its high ionicity (f_i = 0.421 according to Phillips’ scale ³) should energetically favour heteropolar bonding, and oppose the formation of bonds between atoms of the same constituent, or wrong bonds. However, real samples are obtained by atom-by-atom deposition processes, under conditions far from equilibrium, which may be responsible for a certain amount of chemical disorder, accompanying structural disorder. The effects of such chemical disorder should be strongly apparent, both in the structure, because of the large difference in atom size between the two constituents, and in the electronic properties, due to important potential fluctuations related to the ionic contribution to the bonding. The purpose of this paper is to investigate the disorder in flash-evaporated a-InP films, and to compare the results to those previously reported for amorphous Ge and other amorphous III–V compounds.