Photoluminescence of HgTe/CdTe superlattices under high hydrostatic pressures.

Abstract

We have measured the photoluminescence (PL) of HgTe/CdTe superlattices under high hydrostatic pressures up to 30 kbar at liquid-nitrogen temperature. We observed several photoluminescence peaks with energies ranging from \ensuremath{\sim}130 to \ensuremath{\sim}700 meV. The most prominent peak at \ensuremath{\sim}130 meV, which has been attributed to the recombination across the superlattice band gap, moves higher in energy with a pressure coefficient of \ensuremath{\lesssim}1 meV/kbar. Other peaks, whose origins are not well established, have higher energies and their pressure coefficients are in the range of 0--2 meV/kbar. A calculation based on the envelope-function approximation gives a pressure coefficient of at least \ensuremath{\sim}6.5 meV/kbar for the superlattice band gap. This is far outside the error bars of the measured pressure dependence of the main peak, \ensuremath{\lesssim}1 meV/kbar. Varying the input parameters for the calculation, including the valence-band offset, changes the result of the calculation by less than 10%. Possible explanations for this disagreement, including a modification of the current model of HgTe/CdTe superlattice bands and a reinterpretation of the PL peaks, are examined.