The Effect of Mesh Bias and Substrate Bias on the Properties of a-Si:H Deposited by Triode Plasma Chemical Vapour Deposition

Abstract

A new deposition parameter in the plasma enhanced chemical vapour deposition (PECVD) technique for the control of the optoelectronic properties of hydrogenated amorphous silicon (a-Si:H) is presented. The technique utilises a triode electrode configuration with a wire mesh placed between the cathode and anode of a conventional diode type PECVD system. A dc bias, applied to the mesh, affects the plasma-substrate distance or the extent of plasma confinement between the mesh and the cathode, and subtly alters the gas phase chemistry in the plasma. Using this technique, films of undoped a-Si:H have been deposited with pure silane as the source gas. Our results show that the defect density, hydrogen content, and hydrogen bonding configuration are determined by the mesh bias. Measurement of the defect density of the as-grown films by the constant photocurrent method (CPM) reveals that this technique can be used to produce high quaility films with low defect density (14 cm^-3) by application of an appropriate bias on the mesh during deposition.