GROWTH OF DEVICE-QUALITY AMORPHOUS SIGE-H ALLOYS WITH HIGH DEPOSITIONRATE UNDER HELIUM DILUTION

Highly photoconductive amorphous silicon-germanium alloy (a-SiGe:H) fi lms have been developed by plasma-enhanced chemical-vapor deposition u sing helium dilution (HeD) of the process gases (silane and germane). On comparison with high-quality a-SiGe:H alloys prepared under hydroge n dilution it has been observed that HeD films have higher deposition rates as well as higher mobility lifetime products eta mu tau througho ut the alloy range; however, midgap defect densities and Urbach energy values of the two types of materials are nearly the same. Improvement in eta mu tau values of HeD films are found to be consistent with the reduction of microstructural defects in the films. Device potential o f the helium-diluted a-SiGe:H films has also been investigated. (C) 19 94 American Institute of Physics.