We present infrared charge-modulation absorption spectra on phosphorus-doped amorphous silicon (a-Si:H:P) with doping levels between 0.17% - 5%. At higher doping levels (1% - 5%) we find a sharp spectral line near 0.75 eV with a width of 0.1 eV. We attribute this line to the internal optical transitions of a complex incorporating four fold coordinated phosphorus and a dangling bond. This line is barely detectable in samples with lower doping levels (below 1%). In these samples a much broader line dominates the spectrum that we attribute to uncomplexed dopants. The relative strength of the two spectral features is in rough agreement with a model proposed by Street that has not been previously tested experimentally.
"Infrared Charge-Modulation Spectroscopy of Defects in Phosphorus Doped Amorphous Silicon," Kai Zhu, E. A. Schiff, and G. Ganguly, in Amorphous and Heterogeneous Silicon-Based Films‑ 2002, edited by J.R. Abelson, J.B. Boyce, J.D. Cohen, H. Matsumura, J. Robertson (Materials Research Society Symposium Proceedings Vol. 715, Pittsburgh, 2002), 301--306.
harvested from author's c.v.