Anomalous temperature dependence of absorption edge in narrow-gap HgCdTe semiconductors

Abstract

Abnormal temperature dependence of absorption edge is reported for narrow-gap Hg1−xCdxTe semiconductors at low temperature. Infrared absorption spectra are taken for bulk and molecular-beam epitaxial Hg1−xCdxTe, respectively, in the temperature range of 11–300K. The results indicate an abnormal shift of the absorption edge around the temperature range of 30–70K. Analysis suggests that (i) the phenomenon is introduced by Hg vacancies in the samples, of which the energy level locates about 9–12meV above the Hg1−xCdxTe valence band, and (ii) the conventional criterion for the determination of band gap energy, Eg, from absorption spectra is not accurate enough as soon as Hg vacancies exist, especially at a temperature above 77K. It hence provides an explanation why there should exist difference between the cutoff wavelength of the detector and the absorption-edge (Eg) wavelength of the material the detector was made of.