Theory of light emission polarization reversal in zinc-blende and wurtzite nanowires

Abstract

The envelope function method is applied to hole and exciton states in wurtzite and zinc-blende structure cylindrical nanowires using the axial Kohn-Luttinger Hamiltonian including a crystal-field splitting for the wurtzite case. The quantized states are found to be mixtures of heavy- and light-hole band derived states. Explicit expressions for the mixing coefficients and the conditions giving the quantized energy states are derived. These are then applied to obtain the relative intensity of light emitted polarized parallel and perpendicular to the nanowire for the lowest-energy excitons. Slightly different expressions are obtained in the weak quantization and strong quantization limits. In the latter case, an overlap integral of the hole and electron envelope function is involved, while in the former case only an integral over the hole envelope function is required. An expression for the degree of polarization of the spectrally integrated photoluminescence as a function of temperature is obtained by summing over the excitons within the integration range. The degree of polarization as a function of temperature is explored numerically as a function of nanowire radius and crystal-field splitting for GaAs and GaN nanowires. Examples of complete reversal of the polarization are illustrated.