N.J. Mason

Growth of GaSb by MOVPE

High-quality homo- and hetero-epitaxial GaSb has been grown from TMGa and TMSb using atmospheric pressure metal-organic vapour-phase epitaxy (MOVPE). Unintentionally doped material was p-type. At 295 K it had a carrier concentration of around 3.0*1016 cm-3 and a corresponding Hall mobility in the range of 670 to 1000 cm2 V-1 s-1. Growth parameters were carefully correlated with surface morphology, electrical quality and photoluminescence data to establish the growth window for this material.

Self-assembled InSb quantum dots grown on GaSb: A photoluminescence, magnetoluminescence, and atomic force microscopy study

We report a study of self-assembled quantum dots (QDs) of InSb embedded in a GaSb matrix grown by metalorganic vapor phase deposition. Growth temperatures and deposition times have been optimized for maximal photoluminescence peak intensities. Photoluminescence (PL), magneto-PL, and atomic force microscopy (AFM) have been performed to estimate the size of the QDs. The quantum dots luminesce in the midinfrared at around 0.73 eV. The application of magnetic fields up to 15 T both parallel and perpendicular to the growth direction enhanced the wetting layer and bulk PL intensity and enabled an estimate to be made of the QD height and widths as 2–4 and 20–30 nm, respectively. These sizes were confirmed by AFM.

Growth of GaSb by MOVPE; Optimization of electrical quality with respect to growth rate, pressure, temperature and IIIV ratio

Abstract Factors which affect the very narrow range of optimum III V ratios for hetero-epitaxial GaSb on GaAs have been investigated. The GaSb was grown from trimethylgallium (TMGa) and trimethylantimony (TMSb) in a horizontal MOVPE reactor. The growth rate, pressure, temperature, inlet geometry of the cell and/or liner, III V ratio and total gas flow rate were investigated with regard to their effect on electrical properties. It was found firstly, that the optimum III V ratio varies with reactor pressure. Secondly, the growth rate of GaSb depends on the TMGa concentration, reactor pressure and total flow rate, but not on the TMSb concentration. Finally it was found that the best electrical quality GaSb was obtained with growth rates below 2.5 μm/h irrespective of pressure.

Photoluminescence of GaSb grown by metal-organic vapour phase epitaxy

Low-temperature photoluminescence of epitaxial GaSb grown by MOVPE from TMGa and TMSb on various substrates is studied and compared with existing results for GaSb grown by other techniques. The effects of growth conditions are considered. It is found that a growth temperature of 650 degrees C is too high, and the layers are of very poor quality, while below the optimum temperature of 600 degrees C the growth rate slows, although the optical quality appears unaffected. Investigations into the range of III/V ratios over which good quality material could be grown indicated that this factor was more critical for GaSb than for GaAs; Sb-rich conditions produced samples with poor radiative efficiency, while samples grown under Ga-rich conditions were covered in excess Ga droplets. In addition, the authors found that, in common with other growth techniques, the concentration of the native defect in GaSb could be controlled using the III/V ratio, and an excellent correlation was found between electrical results and features in the photoluminescence spectra. For layers not lattice-matched to the substrate, the spectrum is red-shifted. They surmise that this is due to differential thermal contraction of the epilayer and substrate. A homoepitaxial sample was chosen for detailed study and from the dependence of the spectra on temperature and excitation intensity, a previously observed bound exciton was confirmed and an acceptor of 15 meV binding energy was found.

GaSb heterostructures grown by MOVPE

GaSb based heterostructures have been grown with a varying degree of strain in the GaSb layer as a result of the lattice mismatch. The GaSb/Ga1−xAlxSb system has ⩽0.65% mismatch making it potentially attractive for epitaxial growth. However, both the crystallinity and electrical quality of MOVPE grown Ga1−xAlxSb were found to be limited by carbon contamination from the TMAl starting material. Quantum wells (QWs) of GaSb/Ga1−xInxSb, with ≈ 1.2% mismatch for x=0.2, were successfully grown with abrupt interfaces and few dislocations. Shubnikov-De Hass oscillations in the transverse magnetoresistance (ϱxx) and the associated quantum Hall effect indicated that a two-dimensional (2D) hole gas was present in these structures. Unusually, the strongest oscillations were seen for occupancy of an odd number of (spin split) Landau levels (ν=1,3,5,…, etc.) Finally, QWs have been grown in the highly strained GaSb/GaAs system (7% lattice mismatch). TEM micrographs showed the critical thickness for 2D epitaxial growth to be about 15 A. Photoluminescence spectra and photoconductivity both show a transition at ≈ 1.27 eV, arising from the effect of the strain on the GaSb energy gap.

Growth of InAs/GaSb strained layer superlattices. I

Abstract InAs/GaSb strained layer superlattices (SLSs) have been grown by metalorganic vapour phase epitaxy (MOVPE) at atmospheric pressure. Whilst long period SLSs have been successfully grown by this technique, the growth of short period structures is adversely affected by step-bunching. By growing the SLSs faster and cooler, good periodicity was achieved as measured by Raman spectroscopy, transmission electron microscopy (TEM) and X-ray diffraction (XRD) in SLSs with bilayer (GaSb + InAs) thicknesses as thin as 50 A. We have also detected the InSb-like and GaAs-like interface modes from room temperature Raman measurements for the first time in MOVPE grown samples. The most promising samples have been assessed by FIR photoconductivity at 4.2 K and show bandgaps (dependent on the bilayer thickness) between 5 and 20 μm.

GaAs/GaSb strained‐layer heterostructures deposited by metalorganic vapor phase epitaxy

The growth of strained GaSb/GaAs quantum wells has been attempted for the first time (7% lattice mismatch), with the antimonide layers being constrained to take on the GaAs lattice parameter in the interface plane. The critical thickness for pseudomorphic growth of the strained layer was about 15 A, with further growth resulting in islands of GaSb crystallites over the wafer surface. Photoluminescence spectra and photoconductivity from both single and double wells showed a strong signal at approximately 1.3 eV, identified as a Γ point transition. This was not consistent with band structure calculations for a GaSb/GaAs well, suggesting an error in the estimation of the band offsets and/or As incorporation in the strained layer.

GaSb/GaInSb quantum wells grown by metalorganic vapor phase epitaxy

Single and multiple quantum wells of GaSb/GaInSb were grown by metalorganic vapor phase epitaxy. X‐ray diffraction on an 80 A single well confirmed the Ga1−xInxSb composition to be x=0.15, for which the lattice mismatch is ≊1.0%. Photoluminescence and photoconductivity from this sample both showed a signal due to carriers in the well, the position of which was in good agreement with the calculated band diagram. Shubnikov–de Haas oscillations in the transverse magnetoresistance (ρxx) of a four‐period multiquantum well, and the associated quantum Hall effect, indicated that a two‐dimensional hole gas was present in one of the wells. Unusually, the strongest oscillations were seen for occupancy of an odd number of (spin split) Landau levels (ν=1,3,5,...,etc.) This sample also showed luminescence peaks at 738 and 755 meV which were attributed to recombination in the wells.

Geometry and interface structure of island nuclei for GaSb buffer layers grown on (001) GaAs by metalorganic vapour phase epitaxy

Atomic force microscopy and transmission electron microscopy have been used to investigate the geometry and interface structure of island nuclei formed in the initial stages of buffer layer growth for MOVPE GaSb on (001) GaAs. There is a bimodal distribution of island sizes with a high density of small, homogeneous nuclei and a lower density of larger, secondary nuclei. The smaller islands have pronounced crystallographic facets which are consistent with those which would be expected for minimization of surface energy and lateral growth anisotropy. The secondary islands are present at junctions between primary nuclei and may have formed due to enhancement of growth rates at emergent threading segments of misfit dislocations. The lattice misfit is accommodated by a regular square arrangement of edge-type misfit dislocations but unusual strain contrast arises in HREM images due to either a “stand-off” of dislocations from the interface or a corrugated interface.

Growth of InAs by MOVPE: A comparative study using arsine, tertiarybutylarsine and phenylarsine

Abstract The growth of bulk heteroepitaxial layers of InAs on GaAs substrates (and in some cases on InP substrates) by atmospheric pressure MOVPE is described. The indium source used was trimethylindium and we present a comparative study of the use of arsine, tertiarybutylarsine (TBAs) or phenylarsine (PhAs). The quality of the epitaxial layers was established from electrical and morphology measurements and showed a marked improvement with TBAs as a result of improved pyrolysis at lower temperatures. The 77 K mobility was found to increase from about 11,000 cm2/V·s for samples grown from arsine, to nearly 30,000 cm2/V·s for those grown from tertiarybutylarsine. The use of tertiarybutylarsine allows low growth temperatures close to those used in MBE to be used in MOVPE. PhAs was found to pyrolyse at a temperature very similar to arsine and grown layers were very similar to those obtained from arsine.