The sub-gap optical absorption of layers which had been grown by means of low-temperature molecular beam epitaxy was measured by using photo-thermal deflection spectroscopy. It was found that, at a given wavelength, the absorption increased as the growth temperature was decreased. The defect densities which were deduced from the absorption spectra, and known absorption cross-sections, were between 1018 and 1019/cm3. It was shown that complementary photo-thermal deflection phase spectra could be used to distinguish the absorption of epitaxial layers from that of the bulk.

M.H.Chan, S.K.So, K.T.Chan, F.G.Kellert: Applied Physics Letters, 1995, 67[6], 834-6