SPIN-DEPENDENT PHOTOCONDUCTIVITY IN HYDROGENATED AMORPHOUS-GERMANIUM AND SILICON-GERMANIUM ALLOYS

In this work we use spin-dependent photoconductivity (SDPC) to study the recombination process of photoexcited carriers in hydrogenated amorphous germanium (a-Ge:H) and silicon germanium alloys (a-SixGe1-x:H). The a-Ge:H SDPC signal is found to be strongly affected by the larger spin-orbit coupling, lambda, when compared to a-Si:H (lambda(Ge) almost-equal-to 7 lambda(Si)), which results in a reduced spin-lattice relaxation time. The decrease in the spin-lattice relaxation time gives the following characteristics to the a-Ge:H SDPC signal: (i) small amplitudes (-DELTAsigma/sigma < 10(-6)); (ii) a linear dependence on microwave power, and strong temperature dependence. In a-SixGe1-x:H alloys, the incorporation of Ge is marked by a sudden change in the SDPC signal from Si-like to Ge-like, for x < 0.9. The origin of the spin-dependent recombination in a-Ge:H and a-SixGe1-x:H is discussed.