Optical properties of HgTe/CdTe superlattices in the normal, semimetallic, and inverted-band regimes

Abstract

The optical properties of HgTe/CdTe superlattices (SL’s) in the three principal regimes are summarized. Experimental results from the photoluminescence and the cyclotron resonance of electrons and holes both parallel and perpendicular to the SL layer plane in the SL’s in the normal semiconducting regime are presented. These results, together with the previously reported optical and magneto-optical spectra of a series of SL’s in the inverted-band regime, are analyzed systematically under the framework of a six-band k⋅p model. Using a single value of 550 meV for the valence-band offset (VBO) the model correctly predicts all the major experimental results. These include (i) the energy gap between the electron subband and the heavy-hole subband and the energy gap between the electron subband and the light-hole subband of the SL’s in the normal regime over the temperature range from 4.5 to 150 K, (ii) the in-plane masses of the electrons and holes and the Voigt geometry mass of electrons of the SL’s in the normal semiconducting regime, (iii) the in-plane electron and hole masses in a SL in the semimetallic regime, (iv) the energy gap between the second electron subband and the second heavy-hole subband in the SL’s in the inverted-band regime, and (v) the electron in-plane masses of the SL’s in the inverted-band regime. The value of VBO that fits the experimental results is 550±50 meV at 5 K and it reduces, probably linearly, to 500±50 meV at 120 K. The origin of the discrepancy between the value of VBO found in this work and the ones reported in earlier works is discussed.