Potential fluctuations due to inhomogeneity in hydrogenated amorphous silicon and the resulting charged dangling-bond defects

We consider the thermodynamic equilibrium statistics of the ‘‘dangling-bond’’ undercoordination defect in undoped hydrogenated amorphous silicon (a-Si:H), assuming that material inhomogeneity causes electrostatic potential fluctuations whose peak-to-peak magnitude is greater than the (positive) effective correlation energy. We show that the fluctuations cause the formation of significant concentrations of charged dangling-bond defects. The negative defects form in regions of high potential and have transition energies below the Fermi energy (${\mathit{E}}_{\mathit{F}}$). The positive defects form in regions of low potential and have transitions above ${\mathit{E}}_{\mathit{F}}$. We discuss evidence for the model and consequences of the charged dangling-bond defects for electron-spin resonance, transport, and photostability in a-Si:H.