Charge modulation spectra in phosphorus-doped a-Si:H

We discuss models for the infrared spectrum peaked at 0.8 eV reported in voltage-modulated optical absorption measurements on a-Si:H based diodes. We associate this spectrum with interface charge modulation of the optical properties of the phosphorus-doped a-Si:H used as one electrode. We propose that the spectrum originates with the internal optical transitions of a complex incorporating four-fold coordinated phosphorus and a dangling bond. We discuss prior evidence against complexing, and suggest further experiments.