Separation of strain and quantum-confinement effects in the optical spectra of quantum wires

The photoluminescence (PL) and PL-excitation (PLE) spectra of InyCa1-yAs/Al xGa1-xAs compressively strained V-groove quantum wires (QWR's) are compared to that of lattice-matched GaAs/AlyGa1-xAs QWR's with the same wire geomet ry. The PL is preferentially polarized along the QWR axis and the PL anisot ropy increases with increasing indium content y. The observed PLE anisotrop y also increases with y at the ground subband transition but is nearly inde pendent of excited subband indices, unlike the case of lattice-matched QWR' s. We calculated the absorption spectra of the QWR's using an 8 x 8 k.p mod el to separate the effects of quantum confinement (QC) and strain on the va lence-band (VB) mixing. The modification of the optical anisotropy is expla ined by the strain-induced decoupling of the heavy-hole and light-hole subb and edges, lifting the strong VB mixing observed in the GaAs/AlxGa1-xAs cas e. The subband separation energies are, however, nearly unaffected by the s train as they are mainly governed by QC effects in the conduction band.