Electron spin resonance (ESR) is an important tool for providing detailed microscopic information about electronic states located within the energy gap in hydrogeated amorphous silicon (a-Si:H). There always exists an ESR signal in a-Si:H on the order of 1015 spins cm-3 which is attributed to silicon dangling bonds. After optical excitation with band-gap light, a metastable increase in the dangling bond ESR signal is observed. After rapid quenching of a sample from -200°C to room temperature, there is also an increase in the ESR signal with time (without optical excitation) as the sample approaches thermal equilibrium.
P. C. Taylor,
W. D. Ohlsen,
"Esr And The Density Of Deep Gap States In A-Si:H", Proc. SPIE 0763, Physics of Amorphous Semiconductor Devices, (21 August 1987); doi: 10.1117/12.940155; https://doi.org/10.1117/12.940155