Effects of Uniaxial Strain on Band-Edge Optical Transitions in a Direct Zinc-Blende-Structure Semiconductor

The electric-dipole selection rules have been obtained for the lines arising from weakly bound two- or three-carrier complexes in a uniaxially strained direct zinc-blende semiconductor. The optical transitions have been studied in the group of the k vector for a crystal strained along a high-symmetry axis, and certain effects of strain are found to change with the axis considered. The effects of exchange splittings and, in the three-carrier cases, of the Pauli exclusion principle, have been included. The relative strengths of each line in the polarizations parallel and perpendicular to the strain have been determined. Each line which becomes allowed only in the presence of strain has been called "weak," since its strength must decrease continuously to zero with decreasing strain. For each complex, the ordering of the lines has been determined. The predicted number of lines, their ordering, and their strengths differ with the type of complex. The predictions agree with experiment in the case of two-carrier complexes, and appear to agree with the limited data available for three-carrier complexes. There is thus a new means to identify the types of complexes involved in band-edge optical transitions in a direct zinc-blende-structure semiconductor. Further, because each line for a given complex can be identified from its relative strengths in the two polarizations, the exchange splittings in the strained material can also be determined from experiment. The approach may be extended to structures different from zinc blende, to a change in symmetry arising from an external field rather than a strain, and possibly to an indirect semiconductor.