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

Basic concepts of spin-dependent recombination and transport as well as app lications in disordered Si-based semiconductors are reviewed. The magnitude of spin-dependent changes in conductivity or luminescence is outlined foll owing the ideas developed by Lepine and Kaplan, Solomon, and Mott. Undoped a-Si:H serves as a model system for the discussion of recombination mechani sms in disordered semiconductors, in particular distant electron-hole pair recombination, recombination via excitonic pairs (spin triplets), and via d angling bond defects. Electrical detection of magnetic resonance at low mag netic fields (similar to 0.0155 T) can be used to study the hyperfine inter action between dangling bonds and hydrogen, and the results are discussed w ith respect to microscopic models for metastability phenomena in amorphous silicon. Optical detection of magnetic resonance in Si-based amorphous allo ys with Ge, C, N, or O confirm the importance of dangling bonds as non-radi ative recombination centers. In wide band-gap alloys, excitonic triplet sta tes 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 resona nce via noise or capacitance measurements are presented. (C) 2000 Elsevier Science B.V. All rights reserved.