The hydrogen effusion induced structural changes and defects in hydrogenated amorphous SiGe films: Dependence upon the microstructure

To better understand the relations between deposition conditions, microstructure, H incorporation and the optoelectronics properties of undoped a-Si_1-x Ge_x:H alloys, we performed a comparative study of samples (with x ≈ 0.5) prepared by plasma enhanced chemical vapour deposition at total pressures varying from 900 to 2200 mTorr. The hydrogen bonding, detected by infra-red absorption measurements and H thermal desorption experiments, as well as the optoelectronic properties, determined by a combination of standard optical and photothermal deflection spectroscopy measurements, were found to depend on the total pressure. The results obtained in the as-deposited state and after annealing at increasing temperatures are analysed as a whole in terms of specific local H bonding environment, degree of order, and defects.