Sb Flux Research Articles

Growth of droplet-free InSbBi on GaAs substrate

Indium antimonide bismide (InSbBi) has emerged as a highly promising material for long-wavelength infrared photodetection devices due to its unique small energy bandgap (<0.17 eV) compared to existing III–V compound semiconductors. Despite its potential, experimental studies on InSbBi are still incomplete and scarce. Furthermore, the challenges associated with incorporating Bi and producing high-quality, defect-free samples are yet to be adequately addressed. To tackle these issues, we systematically investigated the growth of InSbBi on a GaAs substrate in this study. We incorporated up to 3.4% of Bi into InSbBi material. Our research contributes significantly to the field by demonstrating a technique for growing high-quality InSbBi material with Bi content of up to 2.3%, which is free of droplets and features a smooth surface. We achieved this goal by dynamically adjusting the Sb flux, carefully controlling the interplay between the Bi flux and the growth temperature, and implementing a post-growth annealing process. Our work is crucial for developing InSbBi technology as it contributes to the understanding of the growth process and surface morphology of InSbBi. Moreover, our results provide a path toward producing high-quality InSbBi samples.

Oxide desorption process from InSb surface under Sb flux

In this work, the process of oxide removal from the InSb (001) surface was studied in situ by high-energy electron diffraction in vacuum and under an antimony flux. The dependence of the oxide thickness on the annealing temperature was obtained. It has been found that the antimony flux slows down the process of oxide removal due to the oxide formation reaction. The oxide removal process was described by a system of kinetic equations, the activation energy of oxide decomposition was determined Keywords: InSb, oxide, activation energy, desorption.

Optimized molecular beam epitaxy process for lattice-matched narrow-bandgap (0.8 eV) GaInNAsSb solar junctions

High performance narrow-bandgap GaInNAsSb solar cells are instrumental for the development of lattice-matched GaAs-based solar cells with more than four junctions. To this end a comprehensive optimization process including the effects of growth temperature, As/III beam equivalent pressure ratio, and Sb flux on the performance of 0.8 eV GaInNAsSb solar cells grown by molecular beam epitaxy is reported. For this, sets of GaInNAsSb p-i-n solar cell structures with 5–6% nitrogen compositions were fabricated, while varying the key growth parameters. The quantum efficiency and current generation increased significantly when the narrow gap materials were grown at elevated growth temperatures, close to phase separation. A further improvement in the current generation was observed by employing lower As/III beam equivalent pressure ratios. The best GaInNAsSb cell exhibited about 94% peak external quantum efficiency and generated a short-circuit current of 17.7 mA/cm 2 with AM1.5D (1000 W/m 2 ) illumination at wavelengths above 900 nm without employing a back surface reflector. Our analysis indicates that the best cell is already close to being absorption limited. While the N composition should be kept as low as possible (i.e., ≲5%) to achieve high performance, increasing the Sb flux generally results in improved the material quality, i.e., leading to a slight improvement for the open-circuit voltages and fill factors. In addition, it was found that the phase separation observed at the growth temperature of 480 °C could effectively be inhibited by employing higher Sb fluxes. • Optimized MBE growth for 0.8 eV GaInNAsSb solar junctions with 5–6% N content. • High current obtained using high growth temperatures and lower As pressures. • High peak external quantum efficiency of 94% demonstrated. • Background doping level as low as 1.1 × 10 15 cm −3 for GaInNAsSb with 6% N. • Phase separation is suppressed, and power output improved by optimizing Sb flux.

(Invited) Molecular Beam Epitaxy and Dislocation Dynamics of Metamorphic Inassb for Long-Wavelength Infrared Applications

Long-wavelength infrared (IR) III-V based devices have long been of interest for potential applications such as chemical sensing and large format IR imaging. Within the III-V family, only the InAs1-xSbx bulk alloy in composition range 0.45 ≤ x ≤ 0.8, offers the required bandgap energy (Eg ) from 100 to 125 meV at an operating temperature of 80K and below [1]. Over this composition range however, the InAs1-xSbx lattice constant varies from 6.24 to 6.39 Å, where a lack of conventional substrates has restricted progress on the growth and study of this material system. To bridge this lattice-constant gap while maintaining relatively low defect densities, we employed a metamorphic step-graded InAs1-xSbx buffer on GaSb, enabling the study of low-Eg InAs1-xSbx as a function of growth conditions. Using this method, we investigated the effect of substrate temperature (Tsub ) and group V to group III flux ratio (beam equivalent pressure, V/III) on Sb incorporation of the lowest-Eg cap layer [2]. We also used x-ray reciprocal space mapping (RSM) to examine the effect of growth conditions on strain and dislocation dynamics. Following these growth studies, we employed the metamorphic InAs1-xSbx in an InAs/InAsSb superlattice designed with a cutoff wavelength of 9 µm which leads to improved absorption compared with the lattice-matched counterpart.We first grew, via molecular beam epitaxy, several InAs1-xSbx step-graded structures in which the Sb/(As+Sb) flux ratio was varied from 0.05 to 0.50 in 0.05 increments (see figure), under various Tsub and V/III. Nomarski imaging revealed smoother surfaces under a V/III=10, the highest ratio we attempted. At this higher V/III, we observed the cross-hatch morphology expected for metamorphic materials and found that the cross-hatch spacing changes, implying a change in dislocation dynamics, with Tsub . We then used photoluminescence (PL) to measure the Sb-content in the cap layer as well as compare intensities between samples. We found the highest Sb-incorporation to occur when Tsub =415 C and V/III=10, while the most intense samples used Tsub =415-430 C and V/III=10 [2].Using RSM along [110] with (004) and (115) reflections, we identified the Sb composition in each layer. This allowed comparison of Sb-content as a function of Sb/(As+Sb) for various Tsub and V/III. The results suggest that V/III has little effect on Sb incorporation, in direct conflict with our previous PL results [2]. To understand the discrepancy between PL and RSM, we measured (004) RSM of the same three samples with the x-ray beam incident along [1-10], revealing extremely different strain relaxation compared to the [110] case (see figure). Asymmetric strain relaxation has been observed in other III-V graded buffer systems and has been explained by different dislocation formation energies and glide velocities along each direction resulting from the core structure of the dislocation being terminated with either a group-III or a group-V element [3]. Transmission electron microscopy is ongoing to further understand the dislocation dynamics in these samples.Taking this all together allowed us to investigate the effect of substrate lattice-constant on strain-balanced InAs/InAsSb superlattices designed for 9 µm cutoff wavelength [4]. Theoretically, by using a larger substrate lattice-constant the superlattice design results in larger electron-hole wavefunction overlap, ultimately increasing photon absorption. Our experimental results confirm this theory, even in the presence of increased threading dislocations inherent to the required lattice-mismatch.[1] I. Vurgaftman et al. JAP 89, 5815-5875 (2001).[2] Tomasulo et al. J. Vac. Sci. and Technol. B 36, 02D108 (2018).[3] France et al. J. Appl. Phys. 107, 103530 (2010); Gelczuk et al., J. Cryst. Growth 310, 3014 (2008).[4] Affouda, Tomasulo et al., Appl. Phys. Lett. 110, 181107 (2017). Figure 1

Bulk-like magnetic properties in MBE-grown unstrained, antiferromagnetic CuMnSb

A detailed study of the influence of molecular beam epitaxial growth conditions on the structural and magnetic characteristics of CuMnSb films on lattice matched GaSb is presented. For a set of nine 40 nm thick layers, the Mn and Sb fluxes are varied to produce material with different elemental compositions. It is found that the layers grown under a relative Mn to Sb flux ratio of ΦMn/ΦSb=1.24±0.02 are closest to the stoichiometric composition for which the Néel temperature (TN) attains its maximum values. Mn-related structural defects are believed to be the driving contribution to changes in the vertical lattice parameter. Having established the optimum growth conditions, a second set of samples with CuMnSb layer thickness varied from 5 to 510 nm is fabricated. We show that for sufficiently large thicknesses, the magnetic characteristics (TN≃62K, Curie–Weiss temperature ΘCW=−100 K) of the stoichiometric layers do correspond to the parameters reported for bulk samples. On the other hand, we observe a reduction of TN as a function of the CuMnSb thickness for our thinnest layers. All findings reported here are of particular relevance for studies aiming at the demonstration of Néel vector switching and detection in this noncentrosymmetric antiferromagnet, which have been recently proposed.

Understanding the Morphological Evolution of InSb Nanoflags Synthesized in Regular Arrays by Chemical Beam Epitaxy.

InSb nanoflags are grown by chemical beam epitaxy in regular arrays on top of Au-catalyzed InP nanowires synthesized on patterned SiO2/InP(111)B substrates. Two-dimensional geometry of the nanoflags is achieved by stopping the substrate rotation in the step of the InSb growth. Evolution of the nanoflag length, thickness and width with the growth time is studied for different pitches (distances in one of the two directions of the substrate plane). A model is presented which explains the observed non-linear time dependence of the nanoflag length, saturation of their thickness and gradual increase in the width by the shadowing effect for re-emitted Sb flux. These results might be useful for morphological control of InSb and other III-V nanoflags grown in regular arrays.

Intrinsic V vacancy and large magnetoresistance in V1 — δ Sb2 single crystal

The binary pnictide semimetals have attracted considerable attention due to their fantastic physical properties that include topological effects, negative magnetoresistance, Weyl fermions, and large non-saturation magnetoresistance. In this paper, we have successfully grown the high-quality V1 – δ Sb2 single crystals by Sb flux method and investigated their electronic transport properties. A large positive magnetoresistance that reaches 477% under a magnetic field of 12 T at T = 1.8 K was observed. Notably, the magnetoresistance showed a cusp-like feature at the low magnetic fields and such feature weakened gradually as the temperature increased, which indicated the presence of a weak antilocalization effect (WAL). In addition, based upon the experimental and theoretical band structure calculations, V1 – δ Sb2 is a research candidate for a flat band.

Interface quality in GaSb/AlSb short period superlattices

Heterostructures including the members of the 6.1 Å semiconductor family (AlSb, GaSb, and InAs) are used in infrared optoelectronic devices as well as a variety of other applications. Short-period superlattices of these materials are also of interest for creating composite materials with designer infrared dielectric functions. The conditions needed to create sharp InAs/GaSb and InAs/AlSb interfaces are well known but the AlSb/GaSb interface is much less well-understood. In this article, we test a variety of interventions designed to improve interface sharpness in AlSb/GaSb short-period superlattices. These interventions include the substrate temperature, the III:Sb flux ratio, and the use of a bismuth surfactant. Superlattices are characterized by high-resolution x-ray diffraction and infrared spectroscopy. We find that AlSb/GaSb short-period superlattices have a wide growth window over which sharp interfaces can be obtained.

Fermi surface of the skutterudite CoSb3 : Quantum oscillations and band-structure calculations

The unfilled skutterudite ${\mathrm{CoSb}}_{3}$ is a small-gap semiconductor which was predicted to be close to a strain-induced transition to a topological-insulator phase passing through a topological quantum critical point. As a starting point to strain measurements, the aim of this work is to characterize the electronic structure of as-grown samples. Two types of samples, one grown in Sb flux and the other by an inclined rotary Bridgman technique, are compared based on structural properties, resistivity, Hall effect, and magnetization. All samples appear metallic with small growth-dependent hole doping. Measurements of quantum oscillations in magnetization and angle-dependent electronic transport confirm the calculated band structure at ambient pressure. The Fermi surface consists of a single spherical sheet at the $\mathrm{\ensuremath{\Gamma}}$ point, and the purest samples grown by the Bridgman technique have a Fermi energy lying 25 meV below the valence-band edge. Band-structure calculations provide an accurate description of the experimental results. Hence, this compound is suitable for an investigation of topological states under strain.

Magnetic and electronic properties of a topological nodal line semimetal candidate: HoSbTe

We report the experimental and theoretical studies of a magnetic topological nodal line semimetal candidate HoSbTe. Single crystals of HoSbTe are grown from Sb flux, crystallizing in a tetragonal layered structure (space group: P4/nmm, no.129), in which the Ho-Te bilayer is separated by the square-net Sb layer. The magnetization and specific heat present distinct anomalies at 4 K related to an antiferromagnetic (AFM) phase transition. Meanwhile, with applying magnetic field perpendicular and parallel to the crystallographic c axis, an obvious magnetic anisotropy is observed. Electrical resistivity undergoes a bad-metal-like state below 200 K and reveals a plateau at about 8 K followed by a drop due to the AFM transition. In addition, with the first-principle calculations of band structure, we find that HoSbTe is a topological nodal line semimetal or a weak topological insulator with or without taking the spin-orbit coupling into account, providing a platform to investigate the interplay between magnetic and topological fermionic properties.

Antimony uptake by mangroves and its environmental fate in the Sundarbans, India

Antimony (Sb), a naturally occurring trace element, tends to be enriched in the top-soil and contributes to soil contamination due to continued human activities. However, little is known about plant uptake of Sb, its storage in plant biomass and recycling in large littoral zones of tropical regions, subjected to strong anthropogenic impact. Biogeochemistry of Sb has been studied in the world's largest Sundarbans mangroves by measuring Sb concentration in sediment, plant organs, river water, sea water and pore water, and by determining Sb fluxes within the ecosystem reservoirs. Mangrove estuarine water and sediment appeared to be non-polluted in Sb as confirmed by their ecotoxicological indices. Sediment represented major pool of Sb (2170 g ha−1) compared to plant biomass (2.2 g ha−1). Antimony concentration (μg kg−1) in mangrove roots was highest (17 ± 6) followed by leaf and wood (10.5 ± 6, 9 ± 4, respectively, n = 24). Species-specific variability in Sb concentration was observed with Aegiceras corniculatum, showing highest concentration (48.8 μg kg−1) and Avicenna marina lowest (16.6 μg kg−1). Riverine input of Sb (9.3–12 Mg yr−1) was 3-order of magnitude higher than the mangrove sediment-derived input (0.02–0.05 Mg yr−1), suggesting the latter as negligible contributor of Sb to the Sundarbans coastal water. The mass balance calculations demonstrate that 63–88% of the annual riverine discharge of Sb export to the Bay of Bengal. Further biogeochemical studies should address Sb transport and speciation in surface waters and pore waters of this region.

Semi-adsorption-controlled growth window for half-Heusler FeVSb epitaxial films

The electronic, magnetic, thermoelectric, and topological properties of Heusler compounds (composition $XYZ$ or $X_2 YZ$) are highly sensitive to stoichiometry and defects. Here we establish the existence and experimentally map the bounds of a \textit{semi} adsorption-controlled growth window for semiconducting half Heusler FeVSb films, grown by molecular beam epitaxy (MBE). We show that due to the high volatility of Sb, the Sb stoichiometry is self-limiting for a finite range of growth temperatures and Sb fluxes, similar to the growth of III-V semiconductors such as GaSb and GaAs. Films grown within this window are nearly structurally indistinguishable by X-ray diffraction (XRD) and reflection high energy electron diffraction (RHEED). The highest electron mobility and lowest background carrier density are obtained towards the Sb-rich bound of the window, suggesting that Sb-vacancies may be a common defect. Similar \textit{semi} adsorption-controlled bounds are expected for other ternary intermetallics that contain a volatile species $Z=$\{Sb, As, Bi\}, e.g., CoTiSb, LuPtSb, GdPtBi, and NiMnSb. However, outstanding challenges remain in controlling the remaining Fe/V ($X/Y$) transition metal stoichiometry.

In situ monitoring of GaSb1 − xBix growth using desorption mass spectrometry

Incorporation of bismuth into GaSb is of interest because the alloy bandgap can be substantially reduced while avoiding strain relaxation. Thus, the GaSb1 − xBix alloy is potentially useful in extending the wavelength in optoelectronic devices. However, the epitaxial growth of this alloy via molecular beam epitaxy is challenging because the parameter space is relatively small. Additionally, a precise relationship between Bi incorporation and growth parameters is not well understood. In this study, the authors have utilized the in situ desorption mass spectrometry (DMS) technique to make relative measurements of Sb and Bi desorption during GaSb1 − xBix growth. Employed in this material system for the first time, the authors were able to identify critical growth parameters and correlate these parameters with Bi incorporation as well as accumulation at the growth surface. Specifically, the authors used the ability of DMS to precisely adjust the Sb/Ga flux ratio in order to determine the sensitivity of Bi incorporation to this flux ratio, in particular, as it approaches unity. Additionally, the authors used DMS to provide information on the surface accumulation of Bi and how this population can be purged from the surface using an incident Sb flux. The authors found that DMS can be very useful in rapidly locating the appropriate growth parameter window for this alloy as well as identifying relationships between Bi incorporation and other parameters such as substrate temperature and incident fluxes within that window.

Evaluating the mobility and labile of As and Sb using diffusive gradients in thin-films (DGT) in the sediments of Nansi Lake, China

Arsenic (As) and antimony (Sb) contamination in the aquatic environment have received significant attention recently due to the potential risks they pose. However, there have been few studies about the simultaneous behaviors of As and Sb, resulting in a poor understanding of their occurrence at the sediment-water interface (SWI), especially at the millimeter scale. In this study, soluble and labile concentrations of As and Sb were investigated using high-resolution dialysis (HR-Peeper) and diffusive gradients in thin films technique (DGT) in Nansi Lake, China, respectively. Results showed mean soluble concentrations of As and Sb were 5.00 μg/L and 2.05 μg/L, respectively. DGT-labile concentrations of As and Sb ranged from 0 to 0.80 μg/L and from 0.50 to 0.67 μg/L, respectively. In the vertical profile, different tends for DGT-labile concentration As and Sb were observed. The reductive dissolution of Fe/Mn (hydr)oxides was considered as a crucial driver for As release and mobility, which was supported by its significant correlation (r = 0.348, p < .05) with Fe. While DGT-labile Sb concentration was negatively correlated with DGT-labile Fe (r = −0.24, p < .05) and Mn (r = −0.324, p < .05), this may be attributed to the absorption of the Sb(III) by the green rusts in sub-oxic and mildly alkaline environments. The significant differences between DGT-labile concentration and community Bureau of Reference (BCR) sequential extraction were shown using a linear regression relationship, indicating that BCR chemical fractions cannot reflect the mobility of As and Sb in the sediment. Furthermore, the net diffusive fluxes of As and Sb based on DGT-labile concentration were 0.24 and − 0.56 μg∙m−2∙day−1, respectively. There was a potential risk of toxicity to the overlying water from As.

Bismuth as a Reactive Solvent in the Synthesis of Multicomponent Transition-Metal-Bearing Bismuthides.

Employment of liquid bismuth (Bi) allows the facile single-crystal growth of compounds containing elements with high melting points, provided that these elements have reasonably high solubility in Bi. Utilization of the Bi flux approach yielded two new ternary bismuthides, SrNi0.17(1)Bi2 [a defect variant of the BaCuSn2 type, space group Cmcm, a = 4.879(2) Å, b = 17.580(6) Å, and c = 4.696(2) Å] and CaTi3Bi4 [NdTi3(Sn0.1Sb0.9)4 structure type, space group Fmmm, a = 5.6295(7) Å, b = 9.8389(1) Å, and c = 23.905(3) Å]. In addition, the ternary antimonide CaV3Sb4, isostructural with CaTi3Bi4, was synthesized from antimony (Sb) flux, and analyzed with the goal of validating structural assessment of the bismuthide analogue, where the X-ray crystallographic work proved to be very challenging. All synthesized compounds exhibit complex crystal structures featuring quasi-two-dimensional building blocks of different topologies. First-principle calculations reveal hypervalent bonding in the homoatomic Bi subunits. Physical property measurements indicate metallic conductivity and the absence of localized magnetism in the studied compounds.

Ballistic InSb Nanowires and Networks via Metal-Sown Selective Area Growth.

Selective area growth is a promising technique to realize semiconductor-superconductor hybrid nanowire networks, potentially hosting topologically protected Majorana-based qubits. In some cases, however, such as the molecular beam epitaxy of InSb on InP or GaAs substrates, nucleation and selective growth conditions do not necessarily overlap. To overcome this challenge, we propose a metal-sown selective area growth (MS SAG) technique, which allows decoupling selective deposition and nucleation growth conditions by temporarily isolating these stages. It consists of three steps: (i) selective deposition of In droplets only inside the mask openings at relatively high temperatures favoring selectivity, (ii) nucleation of InSb under Sb flux from In droplets, which act as a reservoir of group III adatoms, done at relatively low temperatures, favoring nucleation of InSb, and (iii) homoepitaxy of InSb on top of the formed nucleation layer under a simultaneous supply of In and Sb fluxes at conditions favoring selectivity and high crystal quality. We demonstrate that complex InSb nanowire networks of high crystal and electrical quality can be achieved this way. We extract mobility values of 10 000-25 000 cm2 V-1 s-1 consistently from field-effect and Hall mobility measurements across single nanowire segments as well as wires with junctions. Moreover, we demonstrate ballistic transport in a 440 nm long channel in a single nanowire under a magnetic field below 1 T. We also extract a phase-coherent length of ∼8 μm at 50 mK in mesoscopic rings.

Sb dissociative surface coverage model for incorporation of antimony in GaAsSb layers grown on GaAs (0 0 1) substrates

A Sb dissociative surface coverage model for the incorporation of antimony in GaAsSb layers, has been used to analyze and predict the composition of GaAsSb layers grown on GaAs substrates. The surface coverage model is based on adatoms behaving according to a modified Langmuir isotherm when on the growth surface. After obtaining key parameters for describing the desorption of Sb atoms from a GaAs surface the model was used to fit the composition variation with changing Sb flux of pseudomorphic GaAsSb layers grown by molecular beam epitaxy on GaAs(0 0 1) substrates at growth temperatures of 470 °C, 500 °C and 530 °C. The set of parameters that provided the best fit to the data for all of these temperatures was then used to predict the incorporation rate as a function of As flux and growth rate with good agreement showing the validity of the Sb dissociative surface coverage model.

Growth and properties of AlSbBi thin films by molecular beam epitaxy

AlSbBi thin films with a Bi content up to 15% have been successfully grown by molecular beam epitaxy for the first time. The effect of growth temperature, Sb flux and Bi flux on Bi incorporation are systematically studied. The incorporation of small size Al atoms is proven to be beneficial to improve the stability of AlSbBi with no change of Bi content in the growth temperature range of 360–420 °C. The AlBi lattice constant is determined to be about 6.37 Å by the combination of Rutherford backscattering spectroscopy and high resolution X-ray diffraction. The new AlBi vibration modes located at 286 cm−1 and 295 cm−1 are observed and attributed to AlBi TO and LO mode, respectively, in agreement with theoretical simulations.

CMOS-Compatible Antimony-Doped Germanium Epilayers for Mid-Infrared Low-Loss High-Plasma-Frequency Plasmonics.

Antimony (Sb) heavily-doped germanium (Ge)-on-silicon (Si) epitaxial films are investigated as mid-infrared (MIR) plasmonic materials. Structural, electrical, and optical properties have been improved by proper choice of dopant species (i.e., Sb) and optimization of the growth parameters (i.e., Sb flux and substrate temperature). The increased electron conductivity can be attributed to the elevated carrier concentration (1.5 × 1020 cm-3) and carrier mobility (224 cm2 V-1 s-1) in the Sb-doped Ge epilayers. The measured MIR reflectivities of the Sb-doped Ge films show free-carrier-dependent properties, which leads to tunable real and imaginary parts of permittivities. Localized surface plasmon polaritons of the bowtie antennas fabricated from the Sb-doped Ge films are demonstrated. The fabricated antennas can provide signal enhancement for the molecular vibrational spectroscopy when these vibrational lines are spectrally in proximity to the localized plasmon resonance. These CMOS-compatible Sb-doped Ge epilayers offer a platform to study the interaction of MIR plasmon with nanostructures on chips.

Distribution characteristics, sources and ecological risk of antimony in the surface sediments of Changjiang Estuary and the adjacent sea, East China

The distribution characteristics, sources and ecological risk of antimony (Sb) in the surface sediments of Changjiang Estuary and the adjacent sea were studied. Sb concentrations ranged from 0.320 to 0.968 μg g−1 with mean value of 0.577 μg g−1. Sb concentrations were relatively high in sediments of the south Yellow Sea, the Hangzhou Bay mouth and the inner Changjiang Estuary. The variation trend of Sb concentrations was controlled by hydrodynamics, Al/Fe/Mn oxides. Sb also showed strong chalcophile property. Correlation analysis and enrichment factor showed Sb came mainly from natural sources. Total Sb sediment flux in the study area was 446.3 t/yr. The Changjiang River, the Yellow River and atmospheric inputs accounted for 85.7%, 13.9%, and 0.4% of the total sediment Sb flux, respectively. The result of potential ecological index indicated the very low Sb concentrations could hardly threat the ecological environment of the study area.