Polarization of tunneling-assisted recombination of two-dimensional holes

We have studied the polarization anisotropy of the radiative recombination of a two-dimensional hole gas (2DHG) confined at the interface of a modulation-doped ${\mathrm{Al}}_{\mathit{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As/GaAs heterostructure. The observed ‘‘cleaved-side’’ luminescence from the heavy-hole ground subband is due to indirect optical transitions in real space and is found to be polarized perpendicular to the plane of the 2DHG. This unexpected behavior is ascribed to the admixture of light-hole states to the heavy-hole ground subband. For increasing in-plane wave vector, the degree of linear polarization decreases due to an enhanced penetration of the heavy-hole states into the bulk GaAs layer. These results can be qualitatively explained by our calculations.