Semiconductor Wafer technology at Xiamen PowerwayPAM XIAMEN

Effect of temperature on GaSb nanocell lattice fabrication by void formation and development utilizing a focused ion beam

The effect of sample temperature on GaSb nanocell fabrication using a focused ion beam was investigated. Two-dimensional nanocell lattices with a cell interval of 100 nm were fabricated on GaSb at 135 K and 293 K. It was shown that the lattice develops slowly at 135 K with increasing ion dose, and that it does so quickly at 293 K, being disturbed by newly created secondary voids. These results were discussed using the migration parameters of point defects deduced from the recovery data of electron-irradiated GaSb by [Thommen, Phys. Rev. 161, 769 (1967)].

Source:IOPscience

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MBE growth of very short period InAs/GaSb type-II superlattices on (0 0 1)GaAs substrates

First, GaSb epilayers were grown on (0 0 1)GaAs substrates by molecular beam epitaxy. We determined that the GaSb layers had very smooth surfaces using atomic force microscopy. Then, very short period InAs/GaSb superlattices (SLs) were grown on the GaSb buffer layer. The optical and crystalline properties of the superlattices were studied by low-temperature photoluminescence spectra and high resolution transition electron microscopy. In order to determine the interface of SLs, the samples were tested by Raman-scattering spectra at room temperature. Results indicated that the peak wavelength of SLs with clear interfaces and integrated periods is between 2.0 and 2.6 µm. The SL interface between InAs and GaSb is InSb-like.

Source:IOPscience

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Nanocontact heteroepitaxy of thin GaSb and AlGaSb films on Si substrates using ultrahigh-density nanodot seeds

A film of GaSb grown epitaxially on a Si substrate is a direct transition semiconductor useful for application as a light source in Si photonics and channel material in next-generation field effect transistors because its energy bandgap is close to the optical fibre communication wavelength and it possesses high carrier mobility. Here, we report a novel method for heteroepitaxial growth of high-quality GaSb/Si films, despite having a lattice mismatch as large as ~ 12%, using elastically strain-relaxed GaSb nanodots with ultrahigh density as seed crystals for film growth. The nanodot seed crystals were grown epitaxially by restricted contact with the Si substrate through nanowindows in an ultrathin SiO2 film on the Si substrate. A light-emitting diode containing GaSb/Si films with a thickness of ~ 90 nm fabricated by this method operated at room temperature. The growth method was also used to fabricate AlGaSb films of high quality. Our method provides a new avenue for heteroepitaxial growth of high-quality film in systems with large lattice mismatch.

Source:IOPscience

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Edge transport in the trivial phase of InAs/GaSb

We present transport and scanning SQUID measurements on InAs/GaSb double quantum wells, a system predicted to be a two-dimensional topological insulator. Top and back gates allow independent control of density and band offset, allowing tuning from the trivial to the topological regime. In the trivial regime, bulk conductivity is quenched but transport persists along the edges, superficially resembling the predicted helical edge-channels in the topological regime. We characterize edge conduction in the trivial regime in a wide variety of sample geometries and measurement configurations, as a function of temperature, magnetic field, and edge length. Despite similarities to studies claiming measurements of helical edge channels, our characterization points to a non-topological origin for these observations.

Source:IOPscience

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Selective and non-selective wet-chemical etchants for GaSb-based materials

A series of wet-chemical etchants for materials lattice-matched to GaSb was investigated. The etch rates for GaSb, AlAsSb, InAsSb and InAs with etch solutions based on KNa–tartaric acid (C4H4KNaO6), citric acid (C6H8O7) and hydrochloric acid were determined and the selectivities for the four different etching solutions are shown. The applicability of the selectivity between GaSb and InAs (respectively InAsSb) with C4H4KNaO6:HCl: H2O2:H2O (selectivity higher than 15:1) and C6H8O7:H2O2 (selectivity around 1:100) is proved by a substrate removal experiment. Also a new etchant for AlAsSb is proposed: HCl:H2O2:H2O etches AlAsSb versus GaSb with a selectivity of 5:1 and the GaSb surface underneath is smooth and without any remaining particles of oxidized aluminium.

Source:IOPscience

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Selective lateral etching of InAs/GaSb tunnel junctions for mid-infrared photonics

We have studied selective etching of the InAs/GaSb tunnel junction (TJ). We show that efficient lateral etching can be achieved with a citric acid:hydrogen peroxide solution. A slight etching anisotropy of around 10% is observed between [1 1 0] and [1 0 0] crystal orientations. The electrical properties of etched TJs do not depend on the diameter of the device which reveals efficient passivation and the absence of current leakage. Specific resistivities in the 2–5 × 10−5 Ω cm−2 range are measured even for diameters compatible with vertical-cavity surface emitting lasers. This work demonstrates that selective lateral etching of an InAs/GaSb tunnel junction is an efficient means to confine the current in GaSb-based heterostructures.

Source:IOPscience

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Very long wavelength infrared focal plane arrays with 50% cutoff wavelength based on type-II InAs/GaSb superlattice

A very long wavelength infrared(VLWIR) focal plane array based on InAs/GaSb type-II super-lattices is demonstrated on a GaSb substrate. A hetero-structure photodiode was grown with a 50% cut-off wavelength of 15.2  m, at 77 K. A 320×256 VLWIR focal plane array with this design was fabricated and characterized. The peak quantum efficiency without an antireflective coating was 25.74% at the reverse bias voltage of −20 mV, yielding a peak specific detectivity of  cmHz W−1. The operability and the uniformity of response were 89% and 83.17%. The noise-equivalent temperatur

Source:IOPscience

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The intrinsic relationship between the kink-and-tail and box-shaped zinc diffusion profiles in n-GaSb

Different diffusion sources were used to study Zn diffusion in n-GaSb. We found that the Ga atoms from the diffusion sources suppressed the formation of the high-concentration surface diffusion fronts in Zn profiles, thus converting the kink-and-tail-shaped profile to the box-shaped profile. Our analysis demonstrated that both the surface and the tail regions in the kink-and-tail profiles showed high-quality regularities. The analysis also revealed that the formation mechanism of the box profiles is the same as that of the tail region of the kink-and-tail profiles. The similarities of the photoluminescence signals between the main region of the box profiles and the tail region of the kink-and-tail profiles substantiated our findings.

Source:IOPscience

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Electron g-factor study in Ga1 − xInxAsySb1 − y–GaSb and GaSb–Ga1 − xInxAsySb1 − y–GaSb quaternary alloy semiconductor spherical quantum dots

Within an interpolation scheme, we have determined the electron g-factor and the Kane interband energetic parameter of Ga1 − xInxAsySb1 − y–GaSb semiconductors quaternary alloy and used them to determine the electron g-factor in GaSb–Ga1 − xInxAsySb1 − y–GaSb spherical quantum dots (SQDs) as well as to calculate the Landau levels. In the low-dimensional systems a framework of an eight-band effective-mass model in which the contribution of the conduction remote bands and the mixing between the conduction band Γc6 and the valence bands Γv8 and Γv7 states are considered. Our results show that the dependence of the bulk electron g-factor as a function of x can be fit with a cubic polynomial. We have established a relation between the electron g-factor and both the radius and the indium concentration in GaSb–Ga1 − xInxAsySb1 − y–GaSb SQDs. For these quaternary SQDs with a parabolic confining potential we have found that the difference between the electron energy levels corresponding to spin-up and spin-down states is larger (~ 10 meV) than the corresponding states in GaAs–(Ga, Al)As quantum wells (QWs) (~ 0.2 meV) of comparable dimensions and increases with the applied magnetic field.

Source:IOPscience

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Passivation properties of CdS thin films grown by chemical bath deposition on GaSb: the influence of the S/Cd ratio in the solution and of the CdS layer thickness on the surface recombination velocity

Evidences of the passivation effect are given when thin films of CdS are deposited on GaSb crystalline substrates, using a bath chemical deposition method. The passivation process is studied through photoacoustic and photoluminescence experiments. The surface recombination velocity calculated from photoacoustic measurements decreases and the radiative recombination rate as measured from photoluminescence spectra increases when the nominal S/Cd ratio in the layer deposition solution increases. The influence of the CdS layer thickness on the surface passivation of GaSb is also studied.

Source:IOPscience

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Anisotropic interface induced formation of Sb nanowires on GaSb(111)A substrates

The growth of Sb nanowires on GaSb(111)A substrates is studied by in situ azimuthal scan reflection high-energy electron diffraction (ARHEED). Bulk and layer contributions can be distinguished in the ARHEED transmission pattern through the Sb nanowires. The three-dimensional structure of the growing Sb nanowires is identified by post-growth atomic force microscopy (AFM) and x-ray diffraction (XRD). The lattice match of the Sb crystal along the  and the GaSb crystal along directions lead to a preferential orientation of the Sb nanowires. The Sb adsorption and desorption kinetics is studied by thermal desorption spectroscopy.

Source:IOPscience

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Below bandgap optical absorption in tellurium-doped GaSb

Enhancement in below bandgap room temperature infrared transmission has been observed in tellurium (Te)-doped GaSb bulk crystals. The effect of Te concentration on the transmission characteristics of GaSb has been experimentally and theoretically analysed. Undoped GaSb is known to exhibit p-type conductivity with residual hole concentration of the order of (1–2) × 1017 cm−3 at room temperature due to the formation of native defects. For such samples, inter-valence band absorption has been found to be the dominant absorption mechanism. The residual holes could be compensated by n-type dopants such as Te. With increasing Te concentration, free carrier absorption due to electrons and inter-valley transitions in the conduction subband become significant. The dependences of various absorption mechanisms as a function of wavelength have been discussed in this paper.

Source:IOPscience

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Room Temperature CW Operation of GaSb/AlGaSb MQW Laser Diodes Grown by MBE

CW operation was achieved by a mesa-stripe (10 µm wide and 200 µm long) GaSb(12 nm)/Al0.35Ga0.65Sb(3 nm) modified multi-quantum-well (MQW, 6 wells) laser diode grown by molecular beam epitaxy (MBE) with threshold current Ith=145 mA at 14°C. Lasing wavelength was 1.662 µm at 9°C. Keys to this achievement were optimizations in (i) MBE growth condition, (ii) layer structure of the MQW wafer (introduction of a superlattice buffer layer and high barrier layers in MQW), and (iii) device fabrication processes. This is the first realization of room temperature cw operation among any type of laser diodes made from an Al-Ga-Sb material system.

Source:IOPscience

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H 2 O 2 : HF : C 4 O 6 H 6 ( Tartaric Acid ) : H 2 O Etching System for Chemical Polishing of GaSb

We present the results of a study of  solution for chemical polishing of  wafers. The influence of etching solution composition on surface morphology was studied. The solutions investigated varied in  (2.0–3.0 mol) and (0.0–5.0 mol) concentrations, but contained a constant concentration of tartaric acid (0.7 mol). It was found that the etchant has excellent polishing properties for  wafers when the  concentration was less than 1.5 mol. For  concentration larger than 1.5, the etchant solution produced rough surfaces. The dependencies of the etching rate on solution composition, temperature, and etching time were studied.

Source:IOPscience

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