The optical absorption of p-type single crystals was measured for photon energies ranging from 0.03 to 1.1eV, and the photo-reflectance was studied in the region of the fundamental edge. As well as a predominant contribution to the absorption coefficient, which arose from inter-valence band transitions below about 0.75eV, the spectra revealed 5 additional structures that could be attributed to defect-induced optical transitions with characteristic energies of between 0.48 and 0.72eV. On the basis of a comparison of the near-edge optical absorption and photo-reflectance spectra, a shallow defect (donor or acceptor) with an ionization energy of about 0.046eV was identified.

H.Neumann, P.A.Jones, H.Sobotta, W.Hörig, R.D.Tomlinson, M.V.Yakushev: Crystal Research and Technology, 1996, 31[1], 63-74