Electrical properties of evaporated silicon films

Abstract

Silicon films were deposited by electron beam evaporation onto titanium-coated stainless steel substrates held at temperatures T s ranging between 300 and 800°C. Doping was achieved by the in situ co-evaporation of antimony or aluminum. The a.c. and d.c. conductivities were measured as functions of the temperature in sandwich structures with aluminium contacts. P-n junctions and SnO 2/nSi heterojunctions were also fabricated. Conduction in amorphous silicon (a-Si) samples is interpreted as due to hopping at the Fermi level E F , the gap state density at E F being between 10 19 and 10 20 cm −3 eV −1. With regard to the electrical properties two different types of behaviour are found in microcrystalline silicon depending on the substrate temperature T s . Films deposited at 400° C < T s < 500° C are similar to a-Si. The transport properties of films deposited at T s > 500° C are explained using a model involving a mixture of amorphous and crystalline components. The electrical characteristics of the p-n junctions are consistent with this model.