Dangling bonds in doped amorphous silicon: Equilibrium, relaxation, and transition energies

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Abstract
The phenomenology of the dangling-bond defect in doped hydrogenated amorphous silicon (a-Si:H) is analyzed in a thermodynamic equilibrium framework with use of positive correlation energy and defect relaxation energies taken from previous theoretical calculations. Good agreement is obtained between theoretical predictions and the optical absorption, luminescence, and deep-level transient spectroscopy energies from the experimental literature. Because the charge and hybridization of the dangling bond in doped a-Si:H are known, considerable information about dangling-bond energy levels and relaxations in a-Si:H is obtained. The controversy over an anomaly of about 0.9 eV in the sum of n-type and p-type films’ optical-absorption-peak energies is largely resolved by recognizing that the optical transitions are vertical. A small residual anomaly is taken as evidence for a small (∼0.2 eV) electronic-level deepening caused by dopant-defect pairing or potential fluctuations. Comparison of defect optical and luminescence energies suggests Stokes shifts of 0.3 and 0.4 eV for the dangling-bond levels of n-type and p-type a-Si:H, respectively.

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