Amorphous semiconductors: deposition chemistry and bonding

Abstract

The deposition chemistry and bonding of the hydrogenated amorphous materials a-C:H, a-Si:H and a-Ge:H are discussed. The general principles governing the gas phase reactions and surface chemistry during deposition are outlined. Data obtained on single-crystal surfaces can be used to extract information on the important molecular processes such as hydrogen desorption and the non-equilibrium nature of chemical vapour deposition. The dependence of the electronic and mechanical film properties on the molecular structure is considered. On the basis of the constraint-counting model, the average coordination number is estimated from elastic film properties by assuming a random network. The central role played by hydrogen during film growth and in modifying the properties of the amorphous film is discussed in detail. Hydrogen is considered as one of the key species in optimizing the deposition chemistry and material properties.