Bulk GaSb Research Articles

Resonant cavity-enhanced (RCE) photodetector based on Ga(In)Sb for gas-sensing applications

Resonant cavity-enhanced (RCE) detectors based on the GaSb material system have been demonstrated for the first time. Calculations show that there is a four-fold increase in the external quantum efficiency for an RCE detector over a conventional non-resonant structure. The back mirror is formed by an 18-period GaAs/AlAs quarter-wave stack with the front reflector being the air-semiconductor interface and the absorber region being bulk GaSb. Optical spectra show the resonant wavelength to be at 1748 nm and the observed enhancement in the photocurrent shows a four-fold increase over a non-resonant structure.

Electrical characterization of surface defects in GaSb created by hydrogen plasma

Using steady state and transient capacitance measurements, the electrical characteristics of a defect layer on the surface of bulk GaSb created during the hydrogen plasma treatment is presented. The trap density, activation energies, and the thickness of the defect layer have been calculated. The trap densities are comparable in magnitude to the carrier concentration. The defects introduce multiple energy levels in the band gap. Typical defect layer thicknesses range from a few angstroms to a fraction of a micron.

Transmission electron microscopy investigation of extended defects in heavily Se-doped bulk GaSb

Similar to heavily Te-doped (111) Czochralski-grown GaSb, extended defects can be found in Se-doped material using high-voltage transmission electron microscopy. The defects occur on a large scale even at a low Se level of 2 × 10 18 cm −3 . Significant differences exist between the defect patterns situated in the core and non-core regions of the crystal. Ordinary as well as multiple planar defects (Frank loops) and extended perfect loops are observed in the non-core area. Frequently, the multiple stacking faults are partially unfaulted and the unfaulting reaction was analysed. All defects are extrinsic (interstitial) in nature. In the core region, by contrast, tangled clusters of perfect dislocations are predominant. The defect morphology is a result of large-scale climb processes due to high point defect supersaturation. It is assumed that these differences are caused by varying Se content and variation in crystal stoichiometry (core effect). These result in a higher surplus of Sb i interstitials which, in turn, cause an increased climb rate in the core region.

Donor-related deep level in bulk GaSb

Deep level transient spectroscopy (DLTS) and thermally stimulated capacitance (TSCAP) studies on bulk grown tellurium- selenium-, and sulphur-doped gallium antimonide reveal the presence of deep level intrinsic of the dopant species. The trap densities in Te- and Se-doped samples were found to be at least two orders of magnitude lower than the shallow donor concentration. Interestingly, the DLTS spectrum of S:GaSb exhibits DX-like nature with the trap concentration comparable to that of shallow donor concentration. However, the Te and Se related levels do not exhibit DX-like nature. The DLTS and TSCAP results are in good agreement with each other.

Electroluminescence out to 2.1 mu m observed in GaSb/InxGa1-xSb quantum wells grown by MOVPE

We describe the observation of electroluminescence from single quantum wells of GaSb/InxGa1-xSb, which covers the region from 1.8 to 2.12 mu m at room temperature. The structures are grown by MOVPE, and cover the range of well widths 25-200 A with a typical in content of 20%. The emission wavelength is found to increase with increasing well width until the critical thickness is exceeded, after which the emission is found to move back closer to the bulk GaSb band edge emission. Emission is observed up to 130 degrees C, indicating the considerable potential of this materials system for applications such as gas sensing.

Structure of Sb monolayers on Ge(111)2×1: A combined study using core-level photoemission, x-ray standing waves, and surface extended x-ray absorption fine structure

The atomic stucture of an annealed monolayer of Sb on the Ge(111)-(2×1) surface has been studied with core-level photoemission, x-ray standing waves (XSW), and surface extended x-ray absorption fine structure (SEXAFS). Phase analysis of the SEXAFS data taken over the Sb L3 edge using bulk Sb and GaSb as standards determines the bond lengths within the first Sb shell to be 2.87±0.03 Å and 2.67±0.03 Å for the Sb–Sb and Sb–Ge bonds, respectively. The XSW data for (111) planes, taken in the backreflection diffraction geometry, place the Sb layer 2.60±0.05 Å above the Ge(111) surface. A relatively high coherent fraction (0.85) indicates small disorder or buckling in the Sb overlayer. The Sb overlayer is found to quench the clean surface shifted components of the Ge 3d core-level spectrum, which indicates an ideal termination of the Ge(111) surface with all dangling bonds saturated by the Sb adatoms. Lack of chemically shifted components in both the Ge 3d and the Sb 4d core level spectra indicates a single bonding site for the Sb atoms. Although it is not possible to differentiate between Sb trimers [as found for the Sb/Si(111) interface] or zigzag chains (common for Sb/III–V interfaces) on the Ge surface, substitutional geometries, in which Sb replaces the topmost layer of the Ge surface bilayer [as found for As/Ge(111)], can be ruled out.

DX-like centre in bulk GaSb:S

Hall, conductance, capacitance transients and DLTS measurements were carried out on Czochralski grown GaSb doped with sulphur. A deep centre with a small and temperature dependent capture cross section and with a high concentration was observed. Such features together with the detected persistent photoconductivity indicate that the observed centre is sulphur related DX-like centre. Some properties of the centre are presented and discussed.

Growth of Al xGa 1− xSb and GaSb bulk crystals with liquid phase electro-epitaxy (LPEE)

A vertical LPEE system was developed for growing thick layers from a source material. Al xGa 1− x Sb and GaSb layers with a thickness of more than 3 mm and a diameter of 15 mm were successfully grown on GaSb substrates from Ga-rich solutions. The growth temperature was in the range of 550–575°C and the current density varied from 5to 10 A/cm 2. It was proven that the growth velocity is a linear function of the current density.

GaSb solution growth by the solute feeding Czochralski method

A new technique of pulling a GaSb bulk crystal from Ga solution fed with a GaSb source was developed. The stable growth condition was realized using the two-chamber (growth and source) crucible, in which a hole connecting the two chambers controlled the amount of solute supplied from the source chamber and a piston mechanism kept the volume of growth solution constant during the growth. The pulling was successfully continued at a constant temperature below the melting point of GaSb. The samples grown at low temperature emitted a strong edge-emission in PL measurements.

MOMBE growth of AlSb and AlGaSb using trimethylamine alane

MOMBE (metalorganic molecular beam epitaxy) growth of AlSb and AlGaSb using trimethylamine alane (TMAAl), triethylgallium (TEGa) and solid antimony (Sb 4) is reported for the first time. The growth rate of AlSb shows a monotonic increase with substrate temperature ( T sub) and a decrease with increasing Sb flux. The activation energy for the AlSb growth is 14 kcal/mol at T sub > 460°C and 30 kcal/mol at T sub<460°C. In the AlGaSb growth, the enhancement of the partial growth rate of GaSb is observed and is caused by the TEGa decomposition enhancement effect of the hydrogen atoms from AlH 3. 4.2 K photoluminescence (PL) spectra for the undoped AlGaSb layers exhibit a sharp band-to-band transition with an intensity comparable to that for the GaSb bulk crystal.

Band Edge Optical Absorption of Molecular Beam Epitaxial GaSb Grown on Semi-Insulating GaAs Substrate

AbstractThe optical absorption of the band edge of GaSb layers grown on semi-insulating GaAs substrates by the molecular beam epitaxy (MBE) technique is studied as a function of temperature. A free exciton absorption peak at 0.807 eV was observed at 10 K. The free exciton line is observed in either thick samples (5μm thick) or samples with ∼0.1 μm thick AlSb buffer layers. The latter samples suggest that the AlSb buffer layer is very effective in preventing some of the dislocations from propagating into the MBE GaSb layers. The fitting of the band gap of the GaSb layers as a function of temperature gives a Debye temperature different than that of the bulk GaSb calculated from the elastic constants.

Deep levels in type-II InAs/GaSb superlattices.

The theory of ${\mathit{sp}}^{3}$-bonded substitutional deep impurity levels is extended to type-II gap-misaligned InAs/GaSb superlattices. The theory predicts that some shallow impurities (donors or acceptors) in either bulk InAs or bulk GaSb can become deep traps in a thin-layer superlattice. This happens because the deep levels associated with point defects in either InAs or GaSb layers (when measured relative to the valence-band maximum of InAs) are much less sensitive to changes of the layer thicknesses of the superlattice than the superlattice band edges. Some common column-IV dopants may lose their amphoteric character [i.e., being a donor when substituting for the column-III host atom (${\mathit{C}}_{\mathrm{In}}$ in InAs) and an acceptor when substituting for the column-V host atom (${\mathit{C}}_{\mathrm{As}}$ in InAs)] and become deep traps for some superlattice layer thicknesses and can even become ``false valence'' dopants (e.g., ${\mathit{C}}_{\mathrm{In}}$ is predicted to be an acceptor in a 10\ifmmode\times\else\texttimes\fi{}10 InAs/GaSb [001] superlattice) for other layer thicknesses. The deep-level splitting and shifting in the type-II superlattice is found to follow the same physics as in the type-I superlattice. A semiconductor-semimetal-semiconductor transition is predicted to occur as the InAs layer thickness increases.

High-resistivity GaSb grown by molecular-beam epitaxy

GaSb undoped layers grown by molecular-beam epitaxy on GaSb or on semi-insulating GaAs substrates at temperatures between 600 and 630 °C are shown to have carrier concentrations in the low 1013 cm−3 range, corresponding to almost intrinsic conditions. The materials have been characterized using current-voltage, capacitance-voltage, Hall effect, photoluminescence, thermally stimulated current, and secondary-ion mass spectrometry. Bulk GaSb (n type) is also found to have converted to high-resistance p type after a heat treatment at 630 °C. Speculations are offered for the responsible mechanism, but a definitive explanation does not exist at this time.

Optical Determination of Carrier Concentration and Mobility in p and n Bulk GaSb by Infrared Reflectivity Spectral Analysis

AbstractInfrared reflectivity measurements are made on both, n and p bulk GaSb at 300 K to determine carrier concentration and mobility of the material by using a least‐square fit on a non‐linear model to experimental data after their transfer from spectrometer to a compatible computer in ASCII code. For n‐type GaSb a method is proposed for calculating density and mobility of carriers from plasma frequency and carrier scattering time given by the fit, taking into account contributions of both, Γ and L band electrons to conductivity. Good agreement is obtained between density and mobility given by reflectivity and those given by Hall measurements for density range 1.2 × 1017 to 3 × 1018 cm−3.

The Auger recombination rate is larger in a GaSb quantum well than in bulk GaSb

The band-to-band Auger recombination rate in bulk GaSb and in a GaSb quantum well is calculated. It turns out to be larger in the quantum well because the threshold of the Auger process is located at the band edge where the density of states is larger in the quantum well than in bulk. A simple picture is developed to illustrate the physics of the Auger processes in bulk and quantum-well direct-band-gap semiconductors. With this picture, we propose that the composition-disorder-induced band mixing should be considered in order to explain the unusual behavior of the Auger process in an InGaAsP quantum-well structure.

Hot carrier cooling in GaSb: Bulk and quantum wells

We have investigated hot carrier dynamics in GaSb structures, bulk and quantum wells, using picosecond time-resolved photoluminescence. Bulk samples show remarkably little carrier heating which we attribute to rapid electron relaxation within the L valleys. Quantum wells show slower cooling than the bulk, which is consistent with similar measurements of other III–V systems. Strong Auger recombination heating of the plasma is found to be responsible for maintaining relatively high temperatures at times ⩾ 25 ps.

High Pressure Optical Studies of GaSb-AlSb Multiple Quantum Wells

AbstractThe pressure coefficients (α) of the excitonic transitions arising from the conduction (CB) to the heavy (HH) and light (LH) hole sub-bands of a GaSb-AlSb multiple quantum well structure (MQW) grown on a GaAs substrate are determined. Photoreflectance (PR) and Photoluminescence (PL) studies are employed at cryogenic temperatures. The α for the ground sub-band transition is ~10% smaller than that for bulk GaSb. This effect is explained by in-plane deformation of the MQW arising from the substrate under external pressure. On the other hand, the α get progressively smaller for the higher sub-band transitions due to quantum confinement The PL intensity drops dramatically as the direct Γ CB crosses the L CB at ~10kBars but the PR intensity persists until the X CB crosses each sub-band energy.

Mbe-Growth of InAs and GaSb Epitaxial Layers on GaAs Substrates

AbstractWe have grown a number of InAs and GaSb bulk layers on GaAs substrates and studied the properties of the semiconductor films as a function of the various growth parameters. Preliminary results from GaSb growth are presented in addition to an extensive study of InAs growth. The films were characterized during growth by RHEED. RHEED-oscillations were observed during both InAs and GaSb growths. Hall effect measurements yielded peak electron mobilities for InAs of 18,900 cm2/Vs at 300 K and 35,000 cm2/Vs at 77 K. For GaSb the as grown layers were found to be p-type with a carrier concentration of 9x1015cm-3 and a hole mobility of 910 cm2 /Vs at 300 K.

Optical, Hall and cyclotron resonance measurements of GaSb grown by molecular beam epitaxy

The authors report a characterisation study of single epitaxial layers of GaSb grown by the technique of molecular beam epitaxy (MBE). Both optical and electrical properties of this material are determined by low-temperature photo-luminescence and Hall effect techniques respectively, and compared with previous work on bulk GaSb grown by other methods. Optically detected cyclotron resonance (ODCR) measurements are reported for the first time in this material in order to determine conduction band electron effective masses and carrier momentum relaxation times. Deduced electron mobilities obtained by this novel technique are of the order of 105 cm2V-1s-1 and are in close agreement with theory.

Enhanced T&amp;lt;inf&amp;gt;0&amp;lt;/inf&amp;gt;values in GaSb/AlSb multiquantum well heterostructures

The material system GaSb/AlSb is discussed with respect to laser applications. Optical gain measurements reveal that in GaSb/AlSb multiquantum well heterostructures, energy-dependent resonant loss mechanisms such as intervalence band absorption and Auger recombination are significantly reduced as compared to bulk GaSb where these losses are resonant. The switch-off of the resonant loss processes is mirrored by the large ratio of the T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</inf> values between the two-dimensional and the three-dimensional carrier system. Non-parabolicity effects present in the multiquantum well band structure are proposed to explain the switch-off of the loss resonance in GaSb/AlSb multiquantum well heterostructures.