Spin-dependent processes in amorphous and microcrystalline silicon: A survey

Basic concepts of spin-dependent recombination and transport as well as applications in disordered Si-based semiconductors are reviewed. The magnitude of spin-dependent changes in conductivity or luminescence is outlined following the ideas developed by Lepine and Kaplan, Solomon, and Mott. Undoped a-Si:H serves as a model system for the discussion of recombination mechanisms in disordered semiconductors, in particular distant electron-hole pair recombination, recombination via excitonic pairs (spin triplets), and via dangling bond defects. Electrical detection of magnetic resonance at low magnetic fields (∼0.0155 T) can be used to study the hyperfine interaction between dangling bonds and hydrogen, and the results are discussed with respect to microscopic models for metastability phenomena in amorphous silicon. Optical detection of magnetic resonance in Si-based amorphous alloys with Ge, C, N, or O confirm the importance of dangling bonds as non-radiative recombination centers. In wide band-gap alloys, excitonic triplet states appear to be the dominant radiative recombination channel. In addition, recent results concerning spin-dependent transport in microcrystalline Si as well as new experimental approaches for the detection of magnetic resonance via noise or capacitance measurements are presented.