The epitaxial growth of germanium films onto NaCl/mica substrates

We investigated the epitaxial growth of germanium films by evaporation in ultrahigh vacuum onto substrates consisting of an NaCl (111) film previously evaporated onto air-cleaved mica and the influence of the prior heat treatment of the mica. It was found that germanium grows partially in a parallel orientation to the substrate. The degree of orientation depends on the substrate temperature during film growth and the mica pretreatment. Water liberated from the mica seems to favour the epitaxial growth of the germanium on the NaCl (111) surface, up to an optimum substrate temperature. Beyond this temperature is causes the agglomeration of the NaCl and a decrease in the degree of orientation. Heat pretreatment of the mica, which reduces the amount of water, increases the optimum substrate temperature and hence the degree of orientation. Thick self-supporting single- crystal germanium films can be obtained with an extended mica pretreatment at 500°C and a substrate temperature of 500°C.