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-${\mathrm{Si}}_{\mathit{x}}$ ${\mathrm{Ge}}_{1\mathrm{-}\mathit{x}}$:H). The a-Ge:H SDPC signal is found to be strongly affected by the larger spin-orbit coupling λ, when compared to a-Si:H (${\lambda }_{\mathrm{Ge}}$≊7${\lambda }_{\mathrm{Si}}$), 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 (-Δσ/σ≤${10}^{\mathrm{-}6}$); (ii) a linear dependence on microwave power, and strong temperature dependence. In a-${\mathrm{Si}}_{\mathit{x}}$ ${\mathrm{Ge}}_{1\mathrm{-}\mathit{x}}$: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-${\mathrm{Si}}_{\mathit{x}}$ ${\mathrm{Ge}}_{1\mathrm{-}\mathit{x}}$:H is discussed.