Reflection electron energy loss spectroscopy during initial stages of Ge growth on Si by molecular beam epitaxy

Using a conventional reflection high-energy electron diffraction gun together with an electron energy loss spectrometer, we have combined in situ measurements of inelastic scattering intensities from Si L2,3 and Ge L2,3 core losses with reflection electron diffraction data in order to analyze the initial stages of Ge heteroepitaxy on Si(001). Diffraction data indicate an initial layer-by-layer growth mode followed by island formation for Ge thicknesses greater than 0.8–1.1 nm. The electron energy core loss data are consistent with a simple model of grazing incidence electron scattering from the growing Ge film. Reflection electron energy loss spectroscopy is found to be highly surface sensitive, and the energy resolution and data rate are also sufficiently high to suggest that reflection electron energy loss spectroscopy may be a useful real-time, in situ surface chemical probe during growth by molecular beam epitaxy

Nonlithographic epitaxial Sn_xGe_(1–x) dense nanowire arrays grown on Ge(001)

We have grown 1-µm-thick Sn_xGe_(1–x)/Ge(001) epitaxial films with 0 < x < 0.085 by molecular-beam epitaxy. These films evolve during growth into a dense array of Sn_xGe_(1–x) nanowires oriented along [001], as confirmed by composition contrast observed in scanning transmission electron microscopy in planar view. The Sn-rich regions in these films dominate optical absorption at low energy; phase-separated Sn_xGe_(1–x) alloys have a lower-energy band gap than homogeneous alloys with the same average Sn composition

Strain modification in coherent Ge and SixGe1–x epitaxial films by ion-assisted molecular beam epitaxy

We have observed large changes in Ge and SixGe1–x layer strain during concurrent molecular beam epitaxial growth and low-energy bombardment. Layers are uniformly strained, coherent with the substrate, and contain no dislocations, suggesting that misfit strain is accommodated by free volume changes associated with injection of ion bombardment induced point defects. The dependence of layer strain on ion energy, ion-atom flux ratio, and temperature is consistent with the presence of a uniform dispersion of point defects at high concentration. Implications for distinguishing ion-surface interactions from ion-bulk interactions are discussed

Nanometer-scale GaAs clusters from organometallic precursors

We report the synthesis of crystalline nanometer-scale GaAs clusters by homogeneous vapor-phase nucleation from organometallic precursors. Cluster synthesis is performed in a hot wall organometallic vapor-phase epitaxy reactor at atmospheric pressure. High resolution transmission electron microscopy studies reveal that the aerosol produced is composed of highly faceted single crystal GaAs particles in the 10–20 nm range. The influence of growth temperature and reactant concentration on cluster morphology is discussed

Vapor phase synthesis of crystalline nanometer-scale GaAs clusters

We report the synthesis of crystalline nanometer-scale GaAs clusters in the 5-10 nm size regime. The clusters are formed by the homogeneous nucleation of a nonequilibrium vapor created by the explosive vaporization of a bulk GaAs sample in an inert atmosphere. High resolution electron microscopy and diffraction show that the clusters have zincblende crystal structure and are faceted. Optical measurements on the particles are suggestive of quantum confinement effects

Orientation filtering by growth-velocity competition in zone-melting recrystallization of silicon on SiO_2

We describe a method of controlling the in-plane directions of grains in (100)-textured silicon films produced by zone-melting recrystallization over amorphous SiO2. Grains having in-plane orientation within a narrow range are able to grow through an orientation filter consisting of a pattern of crystallization barriers, while grains having other orientations are occluded. The results of experiments using an orientation filter, and the parameters which optimize filter performance, are reported

Electroluminescence and photoluminescence of Ge-implanted Si/SiO_2/Si structures

Electroluminescent devices were fabricated in SiO_2 films containing Ge nanocrystals formed by ion implantation and precipitation during annealing at 900 °C, and the visible room‐temperature electroluminescence and photoluminescence spectra were found to be broadly similar. The electroluminescent devices have an onset for emission in reverse bias of approximately −10 V, suggesting that the mechanism for carrier excitation may be an avalanche breakdown caused by injection of hot carriers into the oxide. The electroluminescent emission was stable for periods exceeding 6 h

Microphotonic parabolic light directors fabricated by two-photon lithography

We have fabricated microphotonic parabolic light directors using two-photon lithography, thin-film processing, and aperture formation by focused ion beam lithography. Optical transmission measurements through upright parabolic directors 22 μm high and 10 μm in diameter exhibit strong beam directivity with a beam divergence of 5.6°, in reasonable agreement with ray-tracing and full-field electromagnetic simulations. The results indicate the suitability of microphotonic parabolic light directors for producing collimated beams for applications in advanced solar cell and light-emitting diode designs

Local order measurement in SnGe alloys and monolayer Sn films on Si with reflection electron energy loss spectrometry

Measurements of local order are demonstrated in Sn-containing alloys and epitaxial monolayer thickness films by analysis of extended-edge energy loss fine structure (EXELFS) data obtained by reflection electron energy loss spectrometry (REELS). These measurements of short-range order provide a complement to the chemical information obtained with REELS and long-range order obtained using reflection high energy electron diffraction. The results suggest that EXELFS measurements are practical for samples mounted on the growth manipulator in a molecular beam epitaxy chamber. Advantages and limitations of reflection EXELFS are discussed