Laser-induced chemical vapor deposition of hydrogenated amorphous silicon. II. Film properties

Abstract

Properties of hydrogenated amorphous silicon thin films prepared by the laser‐induced chemical vapor deposition (LICVD) of silane gas are described. We report the results of measurements of hydrogen concentration, infrared absorption, unpaired‐spin density, optical and mechanical properties, electrical conductivity, and photoconductivity experiments. We conclude that the film properties are controlled primarily by the substrate temperature T_s. LICVD films are superior to those produced by conventional CVD because of the permissibly low values of T_s. This results in an increased hydrogen content (up to 30 at. %) and a reduced defect density (∼10¹⁶ spins/cm³). The hydrogen concentration is determined by the surface chemistry for T_s20 at. %) and by H₂ evolution for T_s>300 °C([H]2 configuration and for T_s2)_n regions. All the physical properties of the films are discussed in conjunction with the LICVD process characteristics and are also compared with the properties of films prepared by the plasma‐decomposition and homogeneous chemical vapor deposition (HOMOCVD) techniques. In all cases, the differences can be attributed to variations in the processing conditions.