Subband related structure in the absorption coefficient of HgTe/CdTe superlattices

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Abstract
The current interest in HgTe/CdTe superlattices (SL’s) stems in part from their potential usefulness in advanced IR applications. Of particular interest is the photon energy dependence of the optical absorption coefficient α(E) of these superlattices. Structure in α(E) of superlattices is expected because of the relatively narrow energy subbands (compared with bulk semiconductors) resulting from the large SL period (∼100 Å). Determination of this structure will help to reveal the electronic subband structure of the superlattice. We report here the experimental and theoretical extraction of α(E) at 300 K for six HgTe/CdTe superlattices. The experimentally determined αexp(E) were obtained from transmission/reflection data in conjunction with a computer model. The theoretically calculated αcalc(E) was computed using a two-band tight-binding model for the superlattice energy bands in the growth direction and a nonparabolic approximation in the superlattice plane. Subband related structure is observed for all six superlattices with excellent agreement between theory and experiment for three of the superlattices. The level of correlation between αexp(E) and αcalc(E) appears to be an indicator of superlattice quality as defined by results from x-ray and far-infrared spectroscopy studies.