G. J. Gualtieri

Raman scattering from anodic oxide‐GaAs interfaces

The nature of the interface between anodically grown oxide films and gallium arsenide substrates was studied using Raman backscattering. Room‐temperature spectra of GaAs covered with as‐grown anodic films as well as anodized samples dried under nitrogen at 250°C showed only the first‐order longitudinal (LO) and transverse (TO) optical modes and the less‐intense two‐phonon features of the GaAs substrate. Heating the films at 450°C and above results in the appearance of intense LO (257 cm−1) and TO (198 cm−1) bands due to crystalline arsenic and the structureless Raman scattering near 200–250 cm−1 due to amorphous arsenic. Polarized Raman spectra indicate that elemental arsenic is not an intrinsic oxidation product of the room‐temperature anodization. We suggest that the thermally induced solid‐state interfacial reaction, As2O3+2GaAs→Ga2O3+4As, is responsible for the presence of arsenic at the oxide‐semiconductor interface following annealing.

Thermal oxidation and native oxide-substrate reactions on InAs and InxGa1−xAs

The condensed phase portion of the In-As-O phase diagram has been used in conjuction with Raman scattering and photoemission studies to examine certain compositional aspects of native oxide-substrate reactions and thermal oxidation patterns on InAs and InxGa1−xAs. Elemental arsenic is found to be an intrinsic interfacial phase in native oxides grown under conditions close to thermodynamic equilibrium. Thermally driven oxide-substrate reactions yielding elemental arsenic can also be induced in anodic films which initially contained no elemental arsenic.

Optical properties and water absorption of anodically grown native oxides on InP

The optical properties from 1.5–6.0 eV and the absorption of H2O for an electrochemically grown anodic oxide on InP 〈100〉 have been measured. The oxide thickness was observed to increase by roughly 40% and the refractive index to decrease by 7% in the range of 2 eV when exposed to an ambient containing H2O. The oxide film was also heated to a temperature of 200 °C. The results indicate a change in the chemical composition of the oxide when exposed to either an ambient containing water or an elevated temperature.

Thermal and pulsed laser evaporation of single phase AsxP1−x alloys

The atomic and molecular species evolved during thermal and pulsed laser evaporation of single phase AsxP1−x alloys have been examined using mass spectroscopy. Thermal evaporation yields tetratomic molecules of the form As4−nPn (n=0, 1, 2, 3, 4) as well as diatomic As2, P2, and AsP. Pulsed laser vaporization using a Q‐switched train of 1.06‐μ neodymium: yttrium aluminum garnet (Nd:YAG) pulses primarily evolves atomic As and P species, some fraction of which are ionized. The generation of atomic beams containing one or more of the group V elements from a homogeneous source of controllable stoichiometry has some potential applications for the growth of optoelectronic thin films.

Arsenic incorporation in native oxides of GaAs grown thermally under arsenic trioxide vapor

The presence of crystalline and amorphous elemental arsenic in films grown by the thermal oxidation of GaAs under arsenic trioxide vapor was observed using Raman backscattering. Arsenic was detected for all oxidation temperatures (350–500 °C) and resulting film thicknesses (∼80–1000 A). Chemical etching demonstrated that the arsenic is retained in the interfacial region during growth and does not result from physical adsorption of gas‐phase species during cooling.

Elemental arsenic in native oxide films on AlxGa1−xAs

Surface reflection Raman scattering has been used to detect the presence of elemental arsenic in native oxide films grown on epitaxial (100) AlxGa1−xAs layers. Oxide films formed either by direct thermal oxidation in air at 450 °C or by electrochemical anodization followed by thermal aging (450 °C, in vacuo) were both found to contain elemental arsenic. Anodic films which were not subjected to a heat treatment showed no evidence for elemental arsenic inclusions within the detection limits of the technique. These observations are consistent with the occurrence of a thermally induced interfacial reaction involving As2O3 in the anodic film and the substrate.

Condensed phase diagram for the In-As-O system

An estimate of the condensed phase portion of the equilibrium In-As-O ternary diagram has been constructed from thermodynamic calculations and checked against binary mixture reaction experiments. Utilization of the diagram to explain the phase composition of thin films associated with thermal oxidation and native oxide-substrate reaction processes on InAs and InxGa1-xAs are presented in a companion paper.

Raman characterization of single defect layers embedded in finite superlattices

Single defect layers embedded in finite, nominally periodic superlattices have been examined using Raman scattering. The spectrum of zone‐folded acoustic phonons exhibits defect‐associated peaks due to the broken symmetry of the lattice. The frequencies and intensities of these additional modes can be qualitatively estimated using a simple photoelastic coupling model. Shifts in the defect mode frequencies are observed when the spatial location of the defect layer is moved from the substrate to the air interface.

Molecular beam epitaxy growth and characterization of GaSb / AlSb strained-layer superlattices on nonvicinal (001) and 111 (B) GaSb substrates

Abstract A comparison of the MBE growth of GaSb/AlSb strained-layer structures has been carried out for (001) and (111)B GaSb substrates. Optimal in vacuo cleaning procedures were found to differ and are delineated. The growth rate for (111)B is 10% larger than (001) for the same beam fluxes and substrate temperature. Growth on the (001) orientation is specular, whereas growth on nonvicinal (111)B is faceted. Varying the substrate temperature and V/III flux ratio did not result in specular growth on the (111)B orientation. Strong excitonic luminescence is observed for single and multiple quantum well structure grown on both substrate orientations. Systematic excitonic peak shifts are observed from strained and unstrained GaSb wells by changing the buffer layer which separates the substrate and superlattice. The degree of strain retained in the GaSb wells has been examined from analysis of the optical mode frequency shifts measured by Raman scattering.

Raman scattering from periodic and nonperiodic GaSbA1Sb strained-layer lattices

Abstract Raman scattering measurements have been performed on a series of periodic and nonperiodic strained-layer GaSb A 1 Sb lattices. In the optical frequency region quantum confined longitudinal optic phonons are observed in GaSb layers when the layer width is less than 25A. Spatially extended interface modes lying within the LO-TO regions for both GaSb and A1Sb are also seen. The interface mode frequencies are not well fit by current macroscopic theories. The confinement-induced Γ to L crossover in GaSb manifests itself via the observation of a scattering structure which resembles the optical phonon density of states. In structures grown with supercell or nonperiodic symmetry, the acoustic spectra display zone folding as well as nominally forbidden modes whose frequencies lie close to but are not exactly coincident with zone boundary phonons. Acoustic phonons in a quasiperiodic Fibonacci lattice have been measured and compared to periodic rational approximant lattices with (ABAAB) or (ABAABAAB) repeat units.