Effect of lateral confinement on valence-band mixing and polarization anisotropy in quantum wires

The optical properties of high-quality $\mathsf{V}$-groove GaAs/${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}$As quantum wires have been investigated using low-temperature photoluminescence (PL) and photoluminescence excitation (PLE) techniques. We systematically study the evolution of PL and PLE spectra as a function of the wire size. This comparison allows us to analyze the modification of one-dimensional subbands with decreasing wire thickness. We clarify the influence of surface corrugation and localization effects on PL and PLE spectra and we observe large polarization anisotropy unambiguously related to the one-dimensional character of our quantum wires. The results of a polarization analysis of the excitonic transitions are combined with a calculation of the electronic band structure to identify the nature of the transitions and the impact of two-dimensional quantum confinement on valence-band mixing. The observed large polarization anisotropy is directly compared to the effects predicted by a four-band $\mathbf{k}\cdot \mathbf{p}$ model calculation of the valence-band structure. The set of experimental results combined with our model calculations is consistent with a strong suppression of band-edge absorption in these one-dimensional structures.