S. Tixier

Molecular beam epitaxy growth of GaAs1−xBix

GaAs1−xBix epilayers with bismuth concentrations up to x=3.1% were grown on GaAs by molecular beam epitaxy. The Bi content in the films was measured by Rutherford backscattering spectroscopy. X-ray diffraction shows that GaAsBi is pseudomorphically strained to GaAs but that some structural disorder is present in the thick films. The extrapolation of the lattice constant of GaAsBi to the hypothetical zincblende GaBi alloy gives 6.33±0.06 A. Room-temperature photoluminescence of the GaAsBi epilayers is obtained and a significant redshift in the emission of GaAsBi of ∼84 meV per percent Bi is observed.

Band gap of GaAs1−xBix, 0<x<3.6%

The band gap of GaAsBi epitaxial layers as a function of bismuth concentration up to 3.6% is determined. The optical transitions were measured by modulated electroreflectance. The energy of the band gap decreases at a linearized rate of 88 meV/% Bi, or 83 meV/% Bi for the heavy hole to conduction band transition for GaAsBi strained to GaAs. The valence-band splitting increases faster than that of GaAs under similar compressive strain whereas the temperature dependence of the observed GaAsBi transitions is similar to that of GaAs.

Surfactant enhanced growth of GaNAs and InGaNAs using bismuth

Dilute nitride GaNAs thin films and InGaNAs single quantum wells (QWs) have been grown by molecular beam epitaxy with a concurrent bismuth flux. Bi does not incorporate into the films and acts as a surfactant. Atomic force microscopy images reveal that, at sufficiently high bismuth flux, step flow growth occurs in GaN0.004As0.996 even at substrate temperatures as low as 4601C. This results in an order of magnitude decrease in the surface roughness. A similar smoothing effect is obtained when growing GaAs and AlGaAs thin films with bismuth. Furthermore, Bi is found to enhance the incorporation of nitrogen into GaNAs. The peak photoluminescence intensity from an In0.26Ga0.74N0.011As0.989 QW is increased by more than a factor of two with the surfactant. We conclude that Bi reduces the incorporation of defects and/or impurities in the dilute GaNAs based alloys. r 2002 Elsevier Science B.V. All rights reserved. PACS: 81.15.Hi; 68.35.Ct

Band gaps of the dilute quaternary alloys GaNxAs1−x−yBiy and Ga1−yInyNxAs1−x

We report strong band gap photoluminescence at room temperature in dilute quaternary GaNxAs1−x−yBiy alloys (x<1.6%,y<2.6%) grown by molecular beam epitaxy. The band gap of the alloy can be approximated by the band gap of GaAs minus the reduction in gap associated with the effects of N and Bi alloying individually. A one-parameter method for fitting the composition dependence of the band gaps of dilute quaternary semiconductor alloys is proposed which is in excellent agreement with data for Ga1−yInyNxAs1−x.

Photogenerated plasmons in GaAs1- xBix

Light scattering measurements in the dilute isoelectronically doped alloy GaAs1−xBix reveal a large free electron population photogenerated by continuous-wave laser excitation at low temperature. Low-temperature time-resolved photoluminescence of the bismuth related near-band-gap states show carrier lifetimes of several nanoseconds. The authors attribute this to trapping of photoexcited holes at bismuth pair or cluster states located near the valence band maximum.

ELECTRON MOMENTUM SPECTROSCOPY OF SURFACES

Electron momentum spectroscopy [binary (e,2e) spectroscopy] using transmission geometry is a unique experimental tool for imaging the electron momentum distribution in gas phase samples as well as in thin films. In a solid, the electron momentum distribution is related to the band structure. Development of the (e,2e) technique using a more versatile reflection geometry is attractive since a much wider range of surfaces could be studied. The design of a new reflection (e,2e) spectrometer is presented. It is based on a two-step scattering model in which an incident electron successively reflects and ejects a valence electron from the surface. The scattered and ejected electrons are detected in coincidence and their energies and momentum vectors are simultaneously determined using a high throughput 90° truncated spherical electrostatic analyzer and position-sensitive detectors.

Surfactant enhanced growth of GaNAs and InGaNAs using a Bi flux

InGaNAs containing a dilute amount of nitrogen is a promising new material for fabricating optoelectronic devices in the 1.3 - 1.55 /spl mu/m wavelength range on GaAs substrates, in particular as the active material for vertical cavity surface emitting lasers. Recent edge-emitting InGaNAs lasers have demonstrated an improvement in both threshold currents and characteristic temperatures over those of an InP based reference laser. A flux of bismuth was applied during the growth of InGaNAs quantum wells and bulk GaNAs layers by elemental source MBE.