Optical properties of self-assembled Ge wires grown on Si(113)

We report photoluminescence and Raman scattering measurements of Ge wires formed by self-assembly on Si(113) substrates. The samples were grown at a growth temperature of 500 degreesC on Si(113) substrates by solid-source molecular-beam epitaxy. Atomic force microscopy results clearly show the formation of coherent wire-shaped islands elongated in the [33-2] direction, some with lengths exceeding 500 nm. Micro-Raman measurements indicate that at this low growth temperature intermixing of the silicon and germanium is restricted with an average Ge fraction exceeding 0.7. Capping of the wires with a 20 nm Si epilayer enables the observation of low-temperature photoluminescence. A series of samples with increasing Ge coverage were studied and the onset of Ge islanding is observed to occur at a coverage of 5 monolayers. Wire formation occurs at coverages of 6 monolayers or greater. The observed emission band from the wires has a line shape quite different from that observed from Ge islands on Si[100], being substantially narrower in energy. A stochastic calculation based on idealized quantum wires is presented which reproduces the observed photoluminescence line shape well. (C) 2002 American Institute of Physics.