Effects of Gas Dilution on the Growth and Properties of Glow Discharge a-Ge:H

Abstract

ABSTRACTWe compare films of a-Ge:H deposited by plasma enhanced chemical vapor deposition (PECVD) using GeFLi diluted with H2, He and Ar. The nominal deposition conditions used were those which have produced high quality a-Ge:H with H2 dilution. Using H2 and He as diluents, three studies were done in which the parameters of substrate temperature, diluent gas flow and electrode gap spacing were independently varied. The photoelectronic properties of the films made with He dilution were quite good, although never better than those made with H2 dilution. The overall results indicated that for our nominal conditions hydrogen plays an important and crucial role in producing high quality films, and we believe that this role is mainly to reduce the probability of germane radical incorporation. In contrast to He and H2 dilution, dilution with Ar produced films with much poorer microstructure and a photoresponse two orders of magnitude lower. We attribute this to polymerization of the germane radicals which led to observed dust particles and a reduction in ion bombardment of the growing film.