Optical and electrical properties of type III HgTe/Hg1-xCdxTe heterostructures

ABSTRACT By means of an optical investigation involving the envelope function approximation using the full 8 x 8 Kane Hamiltonian, it has been demonstrated that the valence band is primarily responsible for the separation betweenthe Hi — El and Li — El intersubband transition energies of semiconducting HgTe/HgiCdTe superlattices witha normal band structure. This results in an unequivocal determination of the valence band offset between HgTe and CdTe, A, which is 570 60 meV at 5 K for both the (001) and the (112)B orientations. In order to correctly predict the temperature dependence of both intersubband transition energies, the following is required: A is alsotemperature dependent according to dA/dT = —0.40 0.04 meV/K; the heavy hole effective mass has a significanttemperature dependence; and the energy gap E(HgTe, 300 K)= — 160 5 meV which is appreciably lower than theextrapolated values found in the literature.Both n and p type modulation doped HgTe/Hgi_CdTe quantum wells, QW, have been investigated. Magneto-transport measurements of n type QWs show very pronounced Shubnikov-de Haas, SdH, oscillations and well de-veloped quantum Hall plateaus for temperatures up to approximately 60 K. The SdH oscillations for asymmetricn type modulation doped structures display spin splitting at zero magnetic field, whereas this is not the case forsimilar symmetric structures. This effect increases with increasing quantum well width and preliminary calculationsqualitatively agree with these results which we tentatively ascribe to Rashba spin splitting.