Thin GaSb Research Articles

Strucrural Properties of GaSb Layers Grown on InAs, AlSb, and GaSb Buffer Layers on GaAs (001) Substrates

The strain-relief and the structural properties of GaSb films with thin InAs, AlSb, and GaSb buer layers grown on GaAs (001) substrates at low temperature (LT) by molecular beam epitaxy were investigated using atomic force microscopy, transmission election microscopy, and X-ray diraction. The strain arising from depositing the thin buer layer onto the GaAs substrate was relieved by a periodic array of 90 misfit dislocations with a Burgers vector of 1/2a for the AlSb/GaAs and the GaSb/GaAs systems, but by both 60 and 90 misfit dislocations for the InAs/GaAs system. The 90 misfit dislocation arrays at the AlSb/GaAs and GaSb/GaAs interface had average spacing of 4.80 nm and 5.59 nm, respectively. The mean roughnesses and the full widths at half maximum of the rocking curves of the GaSb films on the thin AlSb and GaSb buer layers were found, respectively, to be less than 1 nm and about three times lower than the corresponding values for the system with an InAs buer layer. These results clearly demonstrate that the presence of a thin, low-temperature AlSb or GaSb buer layer is very useful for improving the quality of GaSb crystals grown on GaAs substrates.

Metalorganic chemical vapor deposition growth of high-quality InAs∕GaSb type II superlattices on (001) GaAs substrates

InAs layers and InAs∕GaSb type II superlattices (SLs) were grown on (001) GaAs substrates by metalorganic chemical vapor deposition. A thin low-temperature GaSb nucleation layer and a thicker high-temperature metamorphic GaSb buffer layer were introduced before the growth of InAs or the SLs. By optimizing the growth temperature, the interface gas switching and the growth rate, morphology, and structural properties of the grown structures are significantly improved. In some cases, nanopipes are found in these structures. Morphology studies of the InAs heteroepitaxial layers show that (1) the diameter of these nanopipes decreases with the growth temperature; (2) nanopipes are nucleated from the interface of GaSb∕InAs; and (3) the density of nanopipes depends on the passivation of GaSb surface before the growth of the InAs. In growing InAs∕GaSb SLs, we show that the growth rate of GaSb has a strong effect on the morphology and that the unintentional interfacial InSb layer formed at the InAs∕GaSb interfaces is the origin of the nanopipes. Through the optimization of the growth parameters, high-quality 100-period SLs without nanopipes and with good optical absorption in 3–8μm infrared region have been realized.

Solid-state phase formation between Pd thin films and GaSb

Knowledge of the interaction between a thin metal film and a compound semiconductor can be used to engineer electrical contacts to the semiconductor. In this study, we examine the reaction between a 50 nm layer of Pd and a GaSb substrate annealed at 100–350°C for 10–360 min using transmission electron microscopy (TEM) and x-ray diffraction (XRD). We report on the formation of Pd-rich nanocrystalline and polycrystalline ternary phases at temperatures below 200°C, followed by Pd-Ga and Pd-Sb binary phases above 200°C.

Thin GaSb insertions and quantum dot formation in GaAs by MOCVD

Self-organized formation of GaSb quantum dots during MOCVD growth has been studied. Thin GaSb layers are deposited on GaAs (0 0 1), followed by a growth interruption before the deposition of a GaAs layer. The GaSb growth is performed using low V/III ratios and growth temperatures between 510°C and 550°C. Undercritical GaSb depositions lead to inhomogenities in the composition and thickness of such layers. Photoluminescence measurements suggest these quantum islands to provide zero-dimensional confinement for holes. The dependence of the luminescence on the growth temperatures indicates the formation of the quantum islands to be kinetically controlled.

Transfer of n-type GaSb onto GaAs substrate by hydrogen implantation and wafer bonding

Many GaSb devices would greatly benefit from the availability of a semi-insulating substrate. Since semi-insulating GaSb is not currently available, the formation of thin GaSb layers through wafer bonding and tranfer onto a semi-insulating GaAs substrate was investigated. GaSb-on-insulator structures, formed on GaAs substrates, were realized by the ion-cut process using H+ ions. Blistering, bonding and layer splitting phenomena were studied to optimize the ion dose and the process window. Bonded structures of thin layers of GaSb bonded to GaAs wafers were formed using a borosilicate glass (BSG) layer. The transferred GaSb layers were characterized by atomic force microscopy, MeV helium ion channeling and high-resolution x-ray diffractometry. The transferred film possessed a narrow x-ray linewidth of about 140 arcsec indicating improved crystalline quality over the direct growth of GaSb on GaAs.

P-GaSb/n-GaAs heterojunction diodes for TPV and solar cell applications

A series of samples has been grown to investigate the effect of doping and GaSb epilayer thickness on dark and photo I-V curves, and on spectral response. The optimum GaSb thickness is a trade-off between the diffusion length and the thickness required to maximise light absorption. The highest open circuit voltage, Voc , ∼0.33V, to date has been obtained from a thin (0.3 μm) GaSb layer doped at 6×1019 cm−1, under illumination by a focused tungsten-halogen lamp (∼1 W cm−2). The short circuit current, Isc, was ∼13 mA/cm2 with a corresponding fill factor of 0.63, and an external quantum efficiency of ∼10%. The devices were not anti-reflection coated, and some parameters important for solar cells, such as contact form and series resistance, have not been optimised. The shape of the spectral response is strongly dependent on GaSb thickness. Increasing the thickness of the epilayer increases the external quantum efficiency above 870 nm (i.e. above the GaAs band edge) while the external quantum efficiency in the short wavelength range (below 870 nm) reduces.

Effect of GaSb growth temperature on p-GaSb/n-GaAs diodes grown by MOVPE

Despite the 7% lattice mismatch, the reverse bias dark current of p-GaSb/n-GaAs junctions has been found to be unexpectedly low. MOVPE-grown diodes exhibited dark currents up to two orders of magnitude lower than comparable GaSb homojunctions. The initial nucleation of GaSb on GaAs was found to play an important role in determining the properties of the bulk layer. A larger number of small nucleation sites produced diodes with lower reverse bias leakage currents and growth temperature was in turn critical in determining the size of these nucleation islands. The authors present a study correlating growth temperature with nucleation site density, dark current and open circuit voltage under illumination. Diodes were grown at temperatures ranging from 490-550/spl deg/C using TMGa and TMSb. A reduction in reverse bias dark current of several orders of magnitude was observed across this narrow temperature range. The 'turn-on' voltage also increased with reduction in growth temperature and there was a corresponding increase in the average open voltage, V/sub oc/, under illumination. However, V/sub oc/ did exceed /spl sim/0.25 V. This is low compared to GaSb homojunctions (typically 0.45 V) and it may be limited by a low shunt resistance under illumination as well as low efficiency from the thin GaSb layers. Other alkyls [TIPGa and t-DMASb], which allow a further reduction in growth temperature, are being investigated.

InAs/AlGaSb nanoscale device fabrication using AFM oxidation process

We describe an atomic force microscope (AFM) oxidation process as a nanoscale fabrication method that is particularly useful for InAs/(Al)GaSb heterostructures. The fabrication is carried out by oxidizing the GaSb surface layer and is followed by water immersion, which selectively removes the oxidized GaSb. We show that an improvement in the shape of the fabricated structure is achieved by using a thin GaSb surface layer. We fabricated preliminary wire-geometry devices with an 0.2 μm period corrugated surface made by the AFM oxidation process. Magnetotransport measurements performed at 4.2 K imply that the modification in the two-dimensional electron gas concentration corresponding to the corrugation is achieved in addition to the increase in the average electron concentration.

Defect evaluation and electrical characteristics of GaSb and In0.17Ga0.83Sb films grown by molecular beam epitaxy

MBE GaSb and In0.17Ga0.83Sb films are grown on GaSb(100) and GaAs(100) substrates and the film defects are investigated by using chemical etching and optical microscopic techniques. A new wet chemical etching method that revealed film defects in thin MBE GaSb and In0.17Ga0.83Sb films is evaluated, and it is found that a hot HCl solution under illumination is most effective in revealing the defects of the thin MBE films. Dislocations and stacking faults, which are related to the substrate material selected, substrate quality, substrate surface preparation, and the insertion of a buffer layer are clearly observed. In particular, in the growth of In0.17Ga0.83Sb, the huge lattice mismatch between the In0.17Ga0.83Sb and GaAs substrate causes severe dislocations, as well as stacking faults. Meanwhile, the AISb buffer layer is able to eliminate stacking faults and reduce dislocations in In0.17Ga0.83Sb films and thereby improve the electrical characteristics of the In0.17Ga0.83Sb film.

Molecular beam epitaxy growth and characterization of thin (

This paper reports the effect of growth parameters and buffer structure on the luminescence electrical and structural characteristics of thin (<2 mu m) GaSb layers grown by molecular beam epitaxy (MBE) on GaAs(100) substrates. A two-stage substrate temperature growth regime has been developed on the basis of a thermodynamic consideration of the growth process, taking into account the additional Gibbs free energy due to the strain at the initial growth. This regime permits the growth of GaSb epilayers with a small Sb/Ga ratio at high substrate temperatures; it provides a greater exciton photoluminescence (PL) intensity and Hall mobility (over 5000 cm2 V-1 s-1 at 77 K) and improves the layer quality. The appearance of a free exciton luminescence line (809 meV) in the PL spectra of MBE GaSb/GaAs is reported for the first time. It is also shown that a (50 AA AlSb/50 AA GaSb)10 short-period superlattice prevents non-radiative recombination centres and carrier scattering centres from propagating in the top GaSb layer but does not bend the misfit dislocation growing through the layer from the GaSb/GaAs interface.

Non-destructive determination of free carrier density of epitaxial layers of GaSb by IR reflectivity measurement

IR reflectivity measurements were made on thin epitaxial GaSb layers grown on n + GaSb and semi-insulating GaAs substrates. The results were interpreted using a two-oscillator dielectric model and free carrier concentrations were determined and compared with electrical measurements.

Interaction of optical phonons with electrons in an InAs quantum well.

The cyclotron resonance (CR) of electrons confined in a thin InAs quantum well sandwiched between thin GaSb layers has been studied experimentally. Since the transmission of radiation in thin polar layers is suppressed only near the TO frequency, we can tune the CR through the TO-LO frequency region of both materials. We find that there is a drastic influence of TO phonons on the CR line profile, resulting in split CR. This interaction is shown to be dominantly of optical origin; resonant polaron effects, both at TO or LO frequency, are, if present, very small.

X-ray photoemission core level determination of the GaSb/AlSb heterojunction valence-band discontinuity

The valence-band discontinuity ΔEv has been determined for the (100) GaSb/AlSb strained-layer heterojunction with a room-temperature lattice mismatch of 0.65%, using x-ray photoemission core level spectroscopy. For 30 Å epitaxial layers of AlSb grown on GaSb, the measured valence-band offset was ΔEv=0.40±0.15 eV. The reverse growth sequence consisting of a thin GaSb layer grown on an AlSb buffer exhibited the same valence-band offset, indicating that for the (100) oriented heterojunction ΔEv is not strongly affected by the growth sequence.

96. Structure of thin GaSb films in the amorphous state: A G Mikolaichuk and Y I Dutchak,Soviet Phys Cryst,9(1), Aug 1964, 86–87. English translation of Russian original in Kristallografiya,9(1), Jan 1964, 106–108

96. Structure of thin GaSb films in the amorphous state: A G Mikolaichuk and Y I Dutchak,Soviet Phys Cryst,9(1), Aug 1964, 86–87. English translation of Russian original in Kristallografiya,9(1), Jan 1964, 106–108