Excitonic transitions in nanometer scale quantum wires produced by in-plane lattice-constant modulation

Quantum wires of <10 nm in lateral dimension, smaller than the bulk exciton diameter, have been produced. The quantum wires were fabricated by growing AlGaAs/GaAs quantum wells on a cleaved edge of an InGaAs/GaAs strained-layer superlattice. Two wells were grown with widths of 70 and 30 angstrom, respectively. The lateral confinement in these structures is a consequence of the strain modulation of the in-plane lattice constant of the (110)-oriented GaAs quantum wells. The wires produced by this technique exhibit excellent optical properties, allowing them to be studied by means of low-temperature cathodoluminescence, photoluminescence, and photoluminescence excitation spectroscopies. The cathodoluminescence spectrum of the strain-induced quantum wires is shown and compared with the spectrum of the side-grown quantum well. The decrease in bandgap of the strained regions red shifts the luminescence of the quantum wires with respect to that of the unstrained quantum wells. The quantum wires also exhibit increased luminescence intensity compared with the unstrained quantum wells. Photoluminescence excitation spectra of the quantum wires exhibit strong polarization dependence and shifts of the peak positions compared with those of the unstrained wells.