Strain-induced shift in photoluminescence energy in In0.2Ga0.8As/GaAs quantum wires

Abstract

Quantum, wires, ranging in width from 900 to 42 nm, were patterned onto a 10-nm-thick In0.2Ga0.8As quantum well in GaAs cladding then regrown by migration-enhanced epitaxy. Atomic-resolution transmission electron microscopy images of two of the quantum wires, one 400 nm wide and the other 42 nm wide, show lattice deformation of the quantum wires due to compression by the cladding. The lattice constant in the growth direction varies with horizontal position inside each wire, from largest in the wire center to smallest at the sidewalls. In the 400 nm wire, the lattice constant in the growth direction fully reaches the pseudomorphically strained value of 5.83 Å at a distance of 165 Å from the sidewall, while the lattice constant in the 42 nm wire reaches only 5.79 Å, at 75 Å from the sidewall. From the value of the compressed lattice constant in the center of the 42 nm wire, the amount of strain in the center of the wire is inferred and, from this strain, the expected strain-induced band-gap energy shift is calculated. Photoluminescence measurements are made on the wires, showing a strain-induced increase in peak emission energy with decreasing wire size. That this energy shift is strain induced is verified by comparing it to the far smaller energy shift of an unregrown but, otherwise, identical sample, which has no regrowth-induced compressive strain. For the 42 nm quantum wire, after the calculated contribution due to increased quantum confinement is accounted for, the energy shift measured by photoluminescence is consistent with the calculated value to within the experimental error.