Influence of plasma chemistry on the properties of a-(Si,Ge):H alloys

Abstract

We report on the effect of plasma chemistry on the growth and properties of a-(Si,Ge):H films and devices. The films and devices were grown using low pressure electron-cyclotron-resonance (ECR) discharge, with hydrogen or helium as the diluent gas. The plasma chemistry at the surface of the growing film was changed by changing the diluent gas from hydrogen to helium, and by changing the deposition pressure. Optical and electronic properties, including band gap ,defect density, Urbach energy and mobility–lifetime products for both electrons and holes were found to depend upon plasma chemistry. Lower pressure growth produced films with properties approaching device properties. The device properties also depended upon pressure and plasma chemistry. Defect density was measured in nin type devices, and was smaller under conditions of lower pressure and greater ion bombardment.