Effects of interdiffusion on the electronic properties of HgTe-CdTe superlattices

Abstract

The growth of HgTe-CdTe superlattices has shown the importance of the interdiffusion of constituent atoms across the interfaces of heterostructures. We study the effect of these processes on the electronic properties of these superlattices in the semiconducting regime using a multiband envelope-function approach. The influence of the strain resulting from the lattice mismatch for HgTe-CdTe superlattice growth on CdTe substrates is found to weakly modify the light-hole subbands while heavy-hole levels are lowered. The conduction and the light-hole subbands are found to have large amplitudes at the HgTe-CdTe interfaces. The evolution of the band gap as a function of the time during which interdiffusion occurs has been studied. This process widens the band gap, and its occurrence can explain the discrepancy between the measured values and those predicted by the theory, which are larger. The conduction subbands are pushed up in energy, while the hole subbands are lowered, and, for samples annealed for a long time, their energies reach limit values that correspond to the energy bands of the alloy folded into the superlattice period. The interfacial feature of conduction and light-hole states is very sensitive to the abrupt variation of the band edges near the interfaces. It is found that the interdiffusion process, which creates transition layers between the two semiconductor layers, leads to a disappearance of the localization near the interfaces. Our results indicate that there is already appreciable modification of the electronic properties for temperatures in the range of the superlattice growth temperature.