Showing papers on "Antimonide published in 2013"

First-Principles Determination of Ultrahigh Thermal Conductivity of Boron Arsenide: A Competitor for Diamond?

Abstract: We have calculated the thermal conductivities (κ) of cubic III-V boron compounds using a predictive first principles approach. Boron arsenide is found to have a remarkable room temperature κ over 2000 W m(-1) K(-1); this is comparable to those in diamond and graphite, which are the highest bulk values known. We trace this behavior in boron arsenide to an interplay of certain basic vibrational properties that lie outside of the conventional guidelines in searching for high κ materials, and to relatively weak phonon-isotope scattering. We also find that cubic boron nitride and boron antimonide will have high κ with isotopic purification. This work provides new insight into the nature of thermal transport at a quantitative level and predicts a new ultrahigh κ material of potential interest for passive cooling applications.

Synthesis and properties of antimonide nanowires

Abstract: Antimonide semiconductors are suitable for low-power electronics and long-wavelength optoelectronic applications. In recent years research on antimonide nanowires has become a rapidly growing field, and nano-materials have promising applications in fundamental physics research, for tunnel field-effect transistors, and long-wavelength detectors. In this review, we give an overview of the field of antimonide nanowires, beginning with a description of the synthesis of these nano-materials. Here we summarize numerous reports on antimonide nanowire growth, with the aim to give an overall picture of the distinctive properties of antimonide nanowire synthesis. Secondly, we review the data on the physical properties and emerging applications for antimonide nanowires, focusing on applications in electronics and optics.

Electronic Structures of Single-Layer Boron Pnictides

Abstract: Single-layer materials such as graphene and boron nitride promise alternative routes to electronic devices. Hybrid density functional calculations for single-layer boron pnictides boron nitride (BN), boron phosphide (BP), boron arsenide (BAs), and boron antimonide (BSb) show that these materials exhibit a direct bandgap of 6.1, 1.4, 1.2, and 0.6 eV, respectively, that originates from the energy difference of the pz orbitals of the species and is tunable by strain. The bandgap linearly decreases with strain for BN, while it increases non-linearly for BP, BAs, and BSb. The calculated natural band offsets between the various boron pnictides are all of type I.

Bi-alkali antimonide photocathodes for high brightness accelerators

Abstract: Alkali-antimonide photocathodes were grown on Si(100) and studied by means of XPS and UHV-AFM to validate the growth procedure and morphology of this material. The elements were evaporated sequentially at elevated substrate temperatures (first Sb, second K, third Cs). The generated intermediate K-Sb compound itself is a photocathode and the composition of K2.4Sb is close to the favored K3Sb stoichiometry. After cesium deposition, the surface layer is cesium enriched. The determined rms roughness of 25 nm results in a roughness domination of the emittance in the photoinjector already above 3 MV/m.

Electronic and thermoelectric properties of CoSbS and FeSbS

Abstract: We present a combined theoretical and experimental study of the potential thermoelectric performance of three transition metal antimonide sulfides, CoSbS, FeSbS, and NiSbS. From theory we find that NiSbS is metallic and hence of little interest regarding thermoelectric performance. CoSbS and FeSbS are both semiconductors with rather heavy valence and conduction bands, whose thermopower can exceed 200 $\ensuremath{\mu}$V/K at temperatures of 900 K and carrier concentrations of 10${}^{21}$cm${}^{\ensuremath{-}3}$, which is similar to the $n$-type high performance thermoelectric filled skutterudites. The experimental results on several non-optimized $n$-type CoSbS samples confirm its semiconducting nature and indicate a potential for good high temperature thermoelectric performance, finding a $ZT$ for two of the samples of 0.35 at 773 K. Substantially higher $ZT$ values may be possible if the lattice thermal conductivity can be reduced by alloying and the effects of extrinsic scattering, which appear to be substantial in the experimental results, are reduced.

Raman spectroscopy of self-catalyzed GaAs(1-x)Sb(x) nanowires grown on silicon.

Abstract: Thanks to their wide band structure tunability, GaAs(1-x)Sb(x) nanowires provide exciting perspectives in optoelectronic and energy harvesting applications. The control of composition and strain of these ternary alloys is crucial in the determination of their optical and electronic properties. Raman scattering provides information on the vibrational properties of materials, which can be related to the composition and strain. We present a systematic study of the vibrational properties of GaAs(1-x)Sb(x) nanowires for Sb contents from 0 to 44%, as determined by energy-dispersive x-ray analyses. We find that optical phonons red-shift with increasing Sb content. We explain the shift by alloying effects, including mass disorder, dielectric changes and ionic plasmon coupling. The influence of Sb on the surface optical modes is addressed. Finally, we compare the luminescence yield between GaAs and GaAs(1-x)Sb(x), which can be related to a lower surface recombination rate. This work provides a reference for the study of ternary alloys in the form of nanowires, and demonstrates the tunability and high material quality of gold-free ternary antimonide nanowires directly grown on silicon.

Antimonide-Based Heterostructure p-Channel MOSFETs With Ni-Alloy Source/Drain

Abstract: In this letter, we study the formation and electrical properties of Ni-GaSb alloys by direct reaction of Ni with GaSb. It is found that several properties of Ni-antimonide alloys, including low thermal budget processing (300°C), low Schottky barrier height for holes (~0.1 eV), low sheet resistance of Ni-InGaSb (53 Ω/\square), and low specific contact resistivity (7.6×10)-7Ω cm2), show good progress toward antimonide-based metal source/drain (S/D) p-channel metal-oxide-semiconductor field-effect transistors. Devices with a self-aligned metal S/D were demonstrated, in which heterostructure design is adopted to further improve the performance, e.g., ON/OFF ratio , subthreshold swing (140 mV/decade), and high effective-field hole mobility of ~510 cm2/Vs at sheet charge density of 2×1012 cm-2.

Growth and characterization of rugged sodium potassium antimonide photocathodes for high brilliance photoinjector

Abstract: Sodium potassium antimonide photocathodes with Quantum Efficiency (QE) in the range of few percent have been grown, and their photoemission properties are measured. We report the intrinsic emittance and response time of electron bunches extracted from this material. It is possible to recover the QE of an overheated cathode by simple potassium addition, and the cathode is rugged enough to deliver tens of mA of average current with no or minimal degradation.

Superconductivity in 122 antimonide SrPt2Sb2

Abstract: Measurements of electrical resistivity ρ, magnetization M and specific heat C have revealed that SrPt2Sb2 is a type-II superconducting material with a superconducting critical temperature (Tc) of 2.1 K. The electronic specific heat coefficient γ and the ratio ΔC(Tc)/γTc are 9.2(1) mJ mol−1 K−2 and 1.29, respectively. The temperature dependence of ρ exhibits anomalies around 270 K. Synchrotron x-ray diffraction patterns at 295 and 134 K clearly indicate that SrPt2Sb2 undergoes a structural phase transition in the temperature range from 134 to 295 K, suggesting that the anomalies observed in ρ around 270 K are related to a structural phase transition.

Effect of Interface States on the Performance of Antimonide nMOSFETs

Abstract: Antimonide (Sb) quantum-well MOSFETs are demonstrated with an integrated high- κ dielectric (1-nm Al2O3 /10-nm HfO2). The effect of interface trap density Dit on the dc drive current and transconductance gm is studied in detail using split C-V/G -V, pulsed I -V, and radio-frequency measurements. Pulsed I-V measurements show improved on current, transconductance, and subthreshold slope due to reduced charge trapping in the dielectric at high frequencies. The long-channel Sb nMOSFET exhibits effective electron mobility of 6000 cm2/V·s at high field (2 × 1012/cm2 of charge density Ns), which is 15× higher than Si NMOS inversion layer mobility, and one of the highest values reported for III-V MOSFETs. The short-channel Sb nMOSFET (LG = 150 nm) exhibits a cutoff frequency fT of 120 GHz, an fT × LG product of 18 GHz·μm , and a source-side injection velocity veff of 2.7 × 107 cm/s at a drain bias VDS of 0.75 V and a gate overdrive of 0.6 V.

Bowtie nanoantenna integrated with indium gallium arsenide antimonide for uncooled infrared detector with enhanced sensitivity.

Abstract: A novel high-impedance nanoantenna with an embedded matching network is implemented to realize a highly sensitive infrared detector. A bowtie antenna is operated at its antiparallel resonance and loaded with a small low-bandgap (Eg=0.52 eV) indium gallium arsenide antimonide (InGaAsSb) p-n junction. The structure is optimized for maximum power transfer and significant field enhancement at its terminals for a desired frequency band where the maximum quantum efficiency of InGaAsSb is observed. The sensitivity improvement of the proposed detector is evaluated against the traditional bulk detector and it is shown that the detectivity is improved by the field enhancement factor, which is approximately 20 for the case considered here.

Ohmic contacts to n-type GaSb grown on GaAs by the interfacial misfit dislocation technique

Abstract: Low resistance ohmic contacts have been successfully fabr icated on n-GaSb layers grown by MBE on semi-insulating (SI) GaAs substrates using the Interfacial Misfit Dislocation (IMF) technique. Although intended for photovoltaic applications, the results are applicable to many antimonide-based devices. The IMF technique enables the growth of epitaxial GaSb layers on semi-insulating GaAs substrates resulting in vertical current confinement not possible on unintentionally doped ~ 1e17 cm -3 p-doped bulk GaSb. Results for low resistance ohmic contacts using NiGeAu, PdGeAu, GeAuNi and GeAuPd metallizations for various temp eratures are reported. Specifi c transfer resistances down to 0.12 Ÿ -mm and specific contact resistances of < 2e-6 Ÿ -cm 2 have been observed. Keywords: Ohmic contacts, GaSb, GaAs, Interfacial Misfit Di slocation, TLM pattern, Sp ecific contact resistance 1. INTRODUCTION Antimonide semiconductors such as GaSb and InSb have a great potential to provide heterojunction structures that absorb or emit light in the longer wavelength IR regime. The GaSb lattice parameter is matched with various ternary and quaternary III-V compounds covering bandgaps from 0.3 eV to 1.58 eV

Effect of Roughness on Emittance of Potassium Cesium Antimonide Photocathodes

Abstract: Here we present first measurements of the effect of roughness on the emittance of K2CsSb photocathodes under high fields. We show that for very thin cathodes the effect is negligible at up to 3 MV/m but for thicker and more efficient cathodes the effect becomes significant. We discuss ways to modify the deposition to circumvent this problem.

Mid-Wave and Long-Wave Single Uni-polar Barrier Infrared Detectors Based on Antimonide Material Systems

Abstract: Infrared detectors are very important technological tools for many different applications. Infrared detectors have existed as far back as the late 1700s but received a tremendous push 200 years later during World War II. Both thermal and photon based infrared detectors have had significant advancements with many different varieties becoming available with varying degrees of sensitivity, speed, and wavelength sensitivity. One of the best performing technologies is based on Mercury Cadmium Telluride. However, it still has limitations with regard to low operating temperature, material yield and processing difficulties. A newer material technology known as type-II indium arsenide/gallium antimonide strain-layered superlattice has received much attention for its potential superior performance from lower dark current, mature III-V material fabrication techniques, and design versatility. However, superior

Thermal conductivity tensors of the cladding and active layers of antimonide infrared lasers and detectors

Abstract: The in-plane and cross-plane thermal conductivities of the cladding layers and active quantum wells of interband cascade lasers and type-II superlattice infrared detector are measured by the 2-wire 3ω method. The layers investigated include InAs/AlSb superlattice cladding layers, InAs/GaInSb/InAs/AlSb W-active quantum wells, an InAs/GaSb superlattice absorber, an InAs/GaSb/AlSb M-structure, and an AlAsSb digital alloy. The in-plane thermal conductivity of the InAs/AlSb superlattice is 4–5 times higher than the cross-plane value. The isotropic thermal conductivity of the AlAsSb digital alloy matches a theoretical expectation, but it is one order of magnitude lower than the only previously-reported experimental value.

Generation of Dense Lying Ga(As)Sb Quantum Dots for Efficient Quantum Dot Lasers

Abstract: Two different approaches are pursued to realize densely packed gallium (arsenic) antimonide (Ga(As)Sb) quantum dots (QDs) for efficient QD lasers. In the first method nano¬structures are realized by self-organization using mask-less dry-etching. GaSb cone structures are achieved with a maximum density of 1.2 ∙ 1011 cm-2. During etching a 5 nm thick amor¬phous Ga layer is formed, also the surface oxidizes immediately under atmosphere, and as a consequence the dots are optoelectronically inactive, thus no photoluminescence (PL) can be achieved. Several attempts are made to revoke these effects, but the nanostructures stay inactive. In the second approach self-assembled optoelectronically active GaAsSb QDs are grown on GaAs in Stranski-Krastanov mode. With these QDs efficient lasers are grown, exemplarily with an emission wavelength around 900 nm. In pulsed mode a minimum thres¬hold current density of jth = 121.7 A/cm2 and a maximum in differential quantum effi¬ciency of ηd = 0.66 are measured at T = 130 K. The internal quantum efficiency is ηi = 0.76 with internal losses of αi = 4.86 cm-1.

Alkali Antimonide Photocathodes for Everyone

Abstract: The next generation of x-ray light sources will need reliable, high quantum efficiency photocathodes. These cathodes will likely be from the alkali antimonide family, which currently holds the record for highest average current achieved from a photoinjector. In this work, we explore a new option for delivering these cathodes to a machine which requires them: use of sealed commercial vacuum tubes. Two sealed tubes have been introduced into a vacuum system and separated from their housing, exposing the active photocathode on a transport arm suitable for insertion into an injector. The separation was achieved without loss of QE in one case. These cathodes are compared to those grown via traditional methods, both in terms of QE and in terms of crystalline structure, and found to be similar.

Effects of oxidant dosing on GaSb (100) prior to atomic layer deposition and high-performance antimonide-based P-channel MOSFETs with Ni-alloy S/D

Abstract: Antimonide-based compound semiconductors have recently emerged as potential candidates for replacement of silicon in future high-performance, low-power CMOS technologies, as both n- and p-channel MOSFETs with high electron and hole mobilities have been demonstrated. The high trap density at the interface of GaSb and high-k dielectric is a challenge in fabricating antimonide-based MOSFETs. Recently, wet-clean and in-situ hydrogen plasma exposure prior to atomic layer deposition (ALD) of gate dielectrics have been used to reduce interface trap density. In this paper, we study the effects of in-situ oxidant dosing on the Al2O3/GaSb (100) interface. This surface passivation scheme is integrated with a self-aligned Ni-alloy S/D MOSFET process.

In situ characterization of alkali antimonide photocathodes

Abstract: Alkali antimonide photocathodes are a prime candidate for use in high-brightness photoinjectors of free electron lasers and 4th generation light sources. These materials have complex growth kinetics - many methods exist for forming the compounds, each photocathode having different grain size, roughness, and crystalline texture. These parameters impact the performance of the cathodes, including quantum efficiency (QE), intrinsic emittance and lifetime. In situ analysis of the growth of these materials has allowed investigation of correlations between the growth parameters and the resulting cathode performance. This work explores the relationship between the crystallinity of the initial antimony film and the roughness of the final cathode. Two growth methods are compared ‐ a “traditional” recipe which uses a crystalline initial antimony film and a “yo-yo” process which builds the cathode through an iterative process using sub-crystalline antimony layers. The traditional method provides exemplary QE (7.5% @ 532 nm), but an exceptionally rough surface. The “yo-yo” produces a somewhat lower final QE (4.9% @ 532 nm) but a much smoother surface, as observed by grazing incidence small angle x-ray scattering (GISAXS).

TEM based analysis of III-Sb VECSELs on GaAs substrates for improved laser performance.

Abstract: The antimonide based vertical external cavity surface emitting lasers (VECSELs) operating in the 1.8 to 2.8 Tm wavelength range are typically based on InGaAsSb/AlGaAsSb quantum wells on AlAsSb/GaSb distributed Bragg reflectors (DBRs) grown lattice-matched on GaSb substrates. The ability to grow such antimonide VECSEL structures on GaAs substrates can take advantage of the superior AlAs based etch-stop layers and mature DBR technology based on GaAs substrates. The growth of such III-Sb VECSELs on GaAs substrates is non-trivial due to the 7.78% lattice mismatch between the antimonide based active region and the GaAs/AlGaAs DBR. The challenge is therefore to reduce the threading dislocation density in the active region without a very thick metamorphic buffer and this is achieved by inducing 90 ° interfacial mist dislocation arrays between the GaSb and GaAs layers. In this presentation we make use of cross section transmission electron microscopy to analyze a variety of approaches to designing and growing III-Sb VECSELs on GaAs substrates to achieve a low threading dislocation density. We shall demonstrate the failure mechanisms in such growths and we analyze the extent to which the threading dislocations are able to permeate a thick active region. Finally, we present growth strategies and supporting results showing low-defect density III-Sb VECSEL active regions on GaAs.

The Antimonide Oxides LnZnSbO and LnMnSbO (Ln: Ce, Pr) — An XPS Study.

Abstract: X-ray photoelectron spectroscopy reveals that the praseodymium species in the title compounds are in a pure +3 oxidation state, whereas cerium exists in both +3 and +4 states.

Correlating structure and function - in situ x-ray analysis of high qe alkali-antimonide photocathodes

Abstract: Alkali antimonide photocathodes have high quantum efficiency and low emittance when illuminated by visible light, and are thought to be well suited for use in highbrightness photoinjectors for 4th generation light sources. Here we report on the growth of multi-alkali K2CsSb cathodes on [100] silicon substrates measured using in situ x-ray scattering. Correlations between cathode structure, growth parameters and the resulting quantum efficiency (QE) are also explored. The best cathodes in this study have a QE at 532 nm in excess of 6% and are structurally textured K2CsSb with grain sizes in excess of 20 nm. In an attempt to reduce the complexity of the current growth methodology, we are also making alkali antimonides in parallel via the reaction of bulk materials in an inert environment. This approach has the advantage that the desired stoichiometry can be obtained exactly. Initial diffraction results from prepared bulk materials are promising and show the formation of well reacted K3Sb. In the future, we intend to transfer this material to smooth thin photocathode films by either sputtering or pulsed laser deposition.

Hyperfine magnetic interactions in iron antimonide on 57Fe, 121Sb, and 119Sn

Abstract: The Mossbauer spectroscopy on iron, antimony, and tin isotopes was applied to study the hyperfine magnetic interactions in the iron antimonide Fe1.22Sb of a B8-type crystal structure. The values of effective magnetic fields in the temperature range 10–150 K were calculated for the iron atoms at structurally nonequivalent positions. It was shown that antimony in Fe1.22Sb is not involved into magnetic interactions at T = 77 K in contrast to tin introduced into the compound as a Mossbauer probe.

Stability of arsenide and antimonide surfaces during molecular beam epitaxy growth

Abstract: The impact of different group-V overpressure schemes on the surface stability of aluminum-, gallium-, and indium-containing binary III–V compounds is examined. The deleterious effect of including arsenic in the overpressure scheme is shown for GaSb, AlSb, InSb, and arsenide–antimonide alloy surfaces using reflection high-energy electron diffraction and cross-sectional transmission electron microscopy. Thermodynamic analysis indicates that the arsenic-for-antimony exchange proceeds only in the direction of increasing the arsenic composition. It is shown that an overpressure scheme containing only antimony results in stable surfaces that are suitable for growth of arsenic–antimony alloys in practical heterostructures.

Fabrication, Transport and Characterization of Cesium Potassium Antimonide Cathode in Electron Guns

Abstract: We have fabricated two cesium potassium antimonide cathodes at BNL, transported them in a UHV load-lock chamber to JLab and tested their performance in DC gun at 100 kV and 200 kV. These cathodes have delivered current of 16 mA and current density up to 8 A/cm 2 without significant degradation. Two more load-lock chambers have been built to transport and insert similar cathodes in SRF guns operating at 704 MHz and 112 MHz. In this paper, we will describe the design of the load-lock chambers, transfer mechanisms, transport of the cathodes over ~ 750 km in UHV environment and the cathode performance in the gun environment.