Temperature-dependent absorption spectra investigation of shallow levels in HgCdTe grown by liquid phase epitaxy

Temperature-dependent absorption spectra in temperature range of 11-300 K are recorded for a series of unintentionally doped HgCdTe grown by liquid phase epitaxy. The abnormal energy shift of about 7-20 meV of absorption edge in the low temperature range ( < 70 K) has been analyzed. The results suggest this the phenomenon to be caused by the Hg vacancies and the abnormal red-shift is related to the composition and the carrier density of the materials. The Hg vacancy level is estimated to be at 20 meV above the valence band, which is well consistent with the results of Hg vacancy acceptor level calculated by the empirical expression. The results may provide a preliminary explanation that the bandgap obtained by the conventional transmission spectroscopy is slightly higher than the cutoff energy of the photocurrent response in practical device applications.