Showing papers on "Antimonide published in 2022"

Mid-infrared III–V semiconductor lasers epitaxially grown on Si substrates

Abstract: There is currently much activity toward the integration of mid-infrared semiconductor lasers on Si substrates for developing a variety of smart, compact, sensors based on Si-photonics integrated circuits. We review this rapidly-evolving research field, focusing on the epitaxial integration of antimonide lasers, the only technology covering the whole mid-to-far-infrared spectral range. We explain how a dedicated molecular-beam epitaxy strategy allows for achieving high-performance GaSb-based diode lasers, InAs/AlSb quantum cascade lasers, and InAs/GaInSb interband cascade lasers by direct growth on on-axis (001)Si substrates, whereas GaAs-on-Si or GaSb-on-Si layers grown by metal-organic vapor phase epitaxy in large capability epitaxy tools are suitable templates for antimonide laser overgrowth. We also show that etching the facets of antimonide lasers grown on Si is a viable approach in view of photonic integrated circuits. Remarkably, this review shows that while diode lasers are sensitive to residual crystal defects, the quantum cascade and interband cascade lasers grown on Si exhibit performances comparable to those of similar devices grown on their native substrates, due to their particular band structures and radiative recombination channels. Long device lifetimes have been extrapolated for interband cascade lasers. Finally, routes to be further explored are also presented.

Single-Crystal Alkali Antimonide Photocathodes: High Efficiency in the Ultrathin Limit

Abstract: The properties of photoemission electron sources determine the ultimate performance of a wide class of electron accelerators and photon detectors. To date, all high-efficiency visible-light photocathode materials are either polycrystalline or exhibit intrinsic surface disorder, both of which limit emitted electron beam brightness. In this Letter, we demonstrate the synthesis of epitaxial thin films of Cs_{3}Sb on 3C-SiC (001) using molecular-beam epitaxy. Films as thin as 4 nm have quantum efficiencies exceeding 2% at 532 nm. We also find that epitaxial films have an order of magnitude larger quantum efficiency at 650 nm than comparable polycrystalline films on Si. Additionally, these films permit angle-resolved photoemission spectroscopy measurements of the electronic structure, which are found to be in good agreement with theory. Epitaxial films open the door to dramatic brightness enhancements via increased efficiency near threshold, reduced surface disorder, and the possibility of engineering new photoemission functionality at the level of single atomic layers.

Mid-infrared III–V semiconductor lasers epitaxially grown on Si substrates

Abstract: There is currently much activity toward the integration of mid-infrared semiconductor lasers on Si substrates for developing a variety of smart, compact, sensors based on Si-photonics integrated circuits. We review this rapidly-evolving research field, focusing on the epitaxial integration of antimonide lasers, the only technology covering the whole mid-to-far-infrared spectral range. We explain how a dedicated molecular-beam epitaxy strategy allows for achieving high-performance GaSb-based diode lasers, InAs/AlSb quantum cascade lasers, and InAs/GaInSb interband cascade lasers by direct growth on on-axis (001)Si substrates, whereas GaAs-on-Si or GaSb-on-Si layers grown by metal-organic vapor phase epitaxy in large capability epitaxy tools are suitable templates for antimonide laser overgrowth. We also show that etching the facets of antimonide lasers grown on Si is a viable approach in view of photonic integrated circuits. Remarkably, this review shows that while diode lasers are sensitive to residual crystal defects, the quantum cascade and interband cascade lasers grown on Si exhibit performances comparable to those of similar devices grown on their native substrates, due to their particular band structures and radiative recombination channels. Long device lifetimes have been extrapolated for interband cascade lasers. Finally, routes to be further explored are also presented.

New Spin-Polarized Electron Source Based on Alkali Antimonide Photocathode

Abstract: New spin-dependent photoemission properties of alkali antimonide semiconductor cathodes are predicted based on the detected optical spin orientation effect and DFT band structure calculations. Using these results, the Na2KSb/Cs3Sb heterostructure is designed as a spin-polarized electron source in combination with the Al0.11Ga0.89As target as a spin detector with spatial resolution. In the Na2KSb/Cs3Sb photocathode, spin-dependent photoemission properties were established through detection of a high degree of photoluminescence polarization and high polarization of the photoemitted electrons. It was found that the multi-alkali photocathode can provide electron beams with emittance very close to the limits imposed by the electron thermal energy. The vacuum tablet-type sources of spin-polarized electrons have been proposed for accelerators, which can exclude the construction of the photocathode growth chambers for photoinjectors.Received 10 May 2022Accepted 20 September 2022DOI:https://doi.org/10.1103/PhysRevLett.129.166802© 2022 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasElectron emissionSpin injectionSpin optoelectronicsSpin polarizationPhysical SystemsDevice fabricationElectron sourcesLayered semiconductorsSolid-state detectorsTechniquesDensity functional theoryPhotoemission spectroscopyPhotoluminescenceAccelerators & BeamsCondensed Matter, Materials & Applied Physics

Simulation of the Band Structure of InAs/GaSb Type II Superlattices Utilizing Multiple Energy Band Theories

Abstract: Antimonide type II superlattices is expected to overtake HgCdTe as the preferred materials for infrared detection due to their excellent photoelectric properties and flexible and adjustable band structures. Among these compounds, InAs/GaSb type II superlattices represent the most commonly studied materials. However, the sophisticated physics associated with the antimonide-based bandgap engineering concept started at the beginning of the 1990s gave a new impact and interest in the development of infrared detector structures within academic and national laboratories. InAs/GaSb superlattices are a type II disconnected band structure with electrons and holes confined in the InAs and GaSb layers, respectively. The electron miniband and hole miniband can be regulated separately by adjusting the thickness of InAs and GaSb layers, which facilitates the design of superlattice structures and optimizes the value of band offset. In recent years, both domestic and foreign researchers have made many attempts to quickly and accurately predict the bandgaps of superlattice materials before superlattice materials grow. These works constituted a theoretical basis for the effective utilization of the InAs/GaSb system in material optimization and designing new SL structures; they also provided an opportunity for the preparation and rapid development of InAs/GaSb T2SLs. In this paper, we systematically review several widely used methods for simulating superlattice band structures, including the k·p perturbation method, envelope function approximation, empirical pseudopotential method, empirical tight-binding method, and first-principles calculations. With the limitations of different theoretical methods proposed, the simulation methods have been modified and developed to obtain reliable InAs/GaSb SL energy band calculation results. The objective of this work is to provide a reference for designing InAs/GaSb type II superlattice band structures.

Synthesis and Application of Alkali Metal Antimonide—A New Approach to Antimony Chemistry

Abstract: Abstract Alkali metal dihydrogen‐antimonides [M(L) x SbH2], short: alkali metal antimonides (M=Li, Na, K, Rb, Cs; 1: L=pmdta; 2: L=crown‐ether), were prepared from stibine and n‐Butyllithium, M(hmds) (hmds=hexamethyldisilazane) or MOtBu, respectively. We developed a generally applicable synthesis route for these compounds and the obtained compounds were examined on their stability depending on the alkali metal and stabilizing additives used, whereby the use of appropriate crown‐ethers allowed their isolation and characterization at room temperature. Moreover, the 1,4‐dioxane adduct [Na(dioxane) x SbH2] was the appropriate starting compound for the synthesis of the first primary silylstibane (Me3Si)3SiSbH2 (3) which was characterized by NMR and IR spectroscopy. Reaction of 3 with (Dipp2NacNac)Ga (Dipp2NacNac=HC{C(Me)N(Dipp)}2; Dipp=2,6‐iPr2C6H3) resulted in the formation of (Dipp2NacNac)GaH(SbHSi(SiMe3)3) (4) which was furthermore characterized by single crystal x‐ray diffraction.

High performance and gate-controlled GeSe/HfS2 negative differential resistance device

Abstract: Transition metal dichalcogenides (TMDs) have received significant attention owing to their thickness-dependent folded current–voltage (Ids–Vds) characteristics, which offer various threshold voltage values. Owing to these astonishing characteristics, TMDs based negative differential resistance (NDR) devices are preferred for the realization of multi-valued logic applications. In this study, an innovative and ground-breaking germanium selenide/hafnium disulfide (p-GeSe/n-HfS2) TMDs van der Waals heterostructure (vdWH) NDR device is designed. An extraordinary peak-to-valley current ratio (≈5.8) was estimated at room temperature and was used to explain the tunneling and diffusion currents by using the tunneling mechanism. In addition, the p-GeSe/n-HfS2 vdWH diode was used as a ternary inverter. The TMD vdWH diode, which can exhibit different band alignments, is a step forward on the road to developing high-performance multifunctional devices in electronics.

Stoichiometry control and automated growth of alkali antimonide photocathode films by molecular beam deposition

Abstract: We report on a method of photoemissive film growth that controls stoichiometry in real time. We show that stoichiometry control using a feedback loop is possible because (a) photoemissive properties exhibit a distinct dependence on the stoichiometric composition and (b) stoichiometric composition strongly depends on the ratio of the incident fluxes. The reported results were obtained on Cs3Sb but are expected to be relevant to other alkali antimonides and tellurides.

Low-pressure PVD growth SnS/InSe vertical heterojunctions with type-II band alignment for typical nanoelectronics.

Abstract: Two-dimensional (2D) polarization-sensitive detection as a new photoelectric application technology is extensively investigated. However, most devices are mainly based on individual anisotropic materials, which suffer from large dark current and relatively low anisotropic ratio, limiting the practical application in polarized imaging system. Herein, we design a van der Waals (vdWs) p-type SnS/n-type InSe vertical heterojunction with proposed type-II band alignment via low-pressure physical vapor deposition (LPPVD) and dry transfer method. The performance compared with the distinctive thickness of anisotropic SnS component was first studied. The fabricated device with a thick (80 nm) SnS nanosheet exhibits a larger rectification ratio exceeding 103. Moreover, the SnS/InSe heterostructure shows a broadband spectral photoresponse from 405 to 1100 nm with a significant photovoltaic effect. Due to efficient photogenerated carrier separation across the wide depletion region at zero bias, the device with thinner (12.4 nm) SnS exhibits trade-off photoresponse performance with a maximum responsivity of 215 mA W-1, an external quantum efficiency of 42.2%, specific detectivity of 1.05 × 1010 Jones, and response time of 8.6/4.2 ms under 635 nm illumination, respectively. In contrast, benefiting from the stronger in-plane anisotropic structure of thinner SnS component, the device delivers a large photocurrent anisotropic ratio of 4.6 under 635 nm illumination in a zigzag manner. Above all, our work provides a new design scheme for multifunctional optoelectronic applications based on thickness-dependent 2D vdWs heterostructures.

Photoluminescence Spectroscopy of the InAsSb-Based p-i-n Heterostructure

Abstract: Photoluminescence in a double heterostructure based on a ternary InAsSb solid solution was observed in the mid-infrared range of 2.5–4 μm. A range of compositions of the InAs1−ySby ternary solid solution has been established, where the energy resonance between the band gap and the splitting-off band in the valence band of the semiconductor can be achieved. Due to the impact of nonradiative Auger recombination processes, different temperature dependence of photoluminescence intensity was found for the barrier layer and the narrow-gap active region, respectively. It was shown that efficient high-temperature photoluminescence can be achieved by suppressing the nonradiative Auger recombination (CHHS) process. Increased temperature, for which the energy gap is lower than the split-off band energy, leads to violation of the resonance condition in narrow gap antimonide compounds, which explains the observed phenomenon. This finding might influence future application of the investigated material systems in mid-infrared emitters used for, e.g., optical gas sensing.

Physically and chemically smooth cesium-antimonide photocathodes on single crystal strontium titanate substrates

Abstract: The performance of x-ray free electron lasers and ultrafast electron diffraction experiments is largely dependent on the brightness of electron sources from photoinjectors. The maximum brightness from photoinjectors at a particular accelerating gradient is limited by the mean transverse energy (MTE) of electrons emitted from photocathodes. For high quantum efficiency (QE) cathodes like alkali-antimonide thin films, which are essential to mitigate the effects of non-linear photoemission on MTE, the smallest possible MTE and, hence, the highest possible brightness are limited by the nanoscale surface roughness and chemical inhomogeneity. In this work, we show that high QE Cs3Sb films grown on lattice-matched strontium titanate (STO) substrates have a factor of 4 smoother, chemically uniform surfaces compared to those traditionally grown on disordered Si surfaces. We perform simulations to calculate roughness induced MTE based on measured topographical and surface-potential variations on the Cs3Sb films grown on STO and show that these variations are small enough to have no consequential impact on the MTE and, hence, the brightness.

Electronic and Magnetic Properties of Eutectoid Growth Mn-rich Ge1-xMnx Dilute Magnetic Semiconductors

Abstract: Dilute magnetic semiconductors (DMSs) have attracted great attention in recent years due to its potential applications in spintronic devices. This study aimed to investigate the magnetic and electronic properties of Mn-rich Ge semiconductors. The magnetic and electronic properties of eutectoid growth Mn-rich Ge1-xMnx dilute magnetic semiconductors (DMSs) with a high Mn dopant close to the composition of Ge2Mn are investigated by the first-principles calculations. Using the diamond structure models of Ge24Mn8, Ge22Mn10 and Ge20Mn12, we show that the magnetic interactions of Mn atoms are dominated by ferrimagnetic coupling, and that the Mn 3d states are substantially hybridized with the valence bands of Ge matrix. This indicates that Mn-rich Ge1-xMnx DMSs demonstrates a ferromagnetic and metallic character and its carriers can mobilize in the lattice more freely. The present investigation could provide some insights into understanding the nature of transition-metal-rich dilute magnetic semiconductors.

Vapor–liquid assisted chemical vapor deposition of Cu2X materials

Abstract: Transition metal dichalcogenides (TMDs) are known for their layered structure and tunable functional properties. However, a unified understanding on other transition metal chalcogenides (i.e. M2X) is still lacking. Here, the relatively new class of copper-based chalcogenides Cu2X (X = Te, Se, S) is thoroughly reported. Cu2X are synthesized by an unusual vapor–liquid assisted growth on a Al2O3/Cu/W stack. Liquid copper plays a significant role in synthesizing these layered systems, and sapphire assists with lateral growth and exfoliation. Similar to traditional TMDs, thickness dependent phonon signatures are observed, and high-resolution atomic images reveal the single phase Cu2Te that prefers to grow in lattice-matched layers. Charge transport measurements indicate a metallic nature at room temperature with a transition to a semiconducting nature at low temperatures accompanied by a phase transition, in agreement with band structure calculations. These findings establish a fundamental understanding and thrust Cu2Te as a flexible candidate for wide applications from photovoltaics and sensors to nanoelectronics.

HOT MWIR technology at SCD

Abstract: SCD is a leading manufacturer of MWIR InSb Focal Plane Arrays (FPA) with formats up to 3 megapixels. Using photodiode layers grown by Molecular Beam Epitaxy (MBE), the operating temperature is raised to ∼ 100 K, compared with 80 K for our legacy implanted junction technology. Due to the excellent manufacturability of III-V MBE materials, we have extended this approach in the development of our newer High Operating Temperature (HOT) MWIR technologies, all of which are based on XBn and XBp barrier devices which suppress the dark current generated by traps in the depletion layer. As a result we now produce a family of InAsSb XBn FPAs operating at 150 K with a cut-off wavelength of λC = 4.2 μm. Formats range between 0.33 megapixels and 5.24 megapixels and our latest "Crane" FPA has a pitch of just 5 μm. These detectors are ideal for 24/7 surveillance and long-range applications, due to large formats, increased HOT cooler reliability and very high atmospheric transmission. For applications requiring HOT full MWIR (HFMW) performance (λC = ∼ 4.9 μm), we have explored three approaches, all of which have produced operating temperatures in the range 115 - 125 K with high FPA operability and uniformity. Using a suitable design of buffer layer, we have extended the InAsSb XBn cut-off wavelength while maintaining a high quantum efficiency above 70%. Comparable performance has also been obtained in two lattice matched type II superlattice (T2SL) architectures: XBn InAs/InAsSb and XBp InAs/GaSb. The three technologies give great flexibility in design optimization, and initial production of HFMW detectors is scheduled for mid 2022.

Influence of source electrode metal work function on polar gate prompted source hole plasma in arsenide/antimonide tunneling interfaced junctionless TFET

Abstract: Numerous studies have explored the impact of control gate and polar gate (PG) on the retention of hole and electron charge plasma to induce the source and channel region polarity in junctionless tunnel field effect transistor (JLTFET). However, PG is not the only one responsible for the retention of hole plasma in the p+ prompted source but the hole plasma near the interface of source electrode metal (SEM) and p+ prompted source (SEM/S) is influenced by the choice of SEM work function too. This paper features a comprehensive investigation of the mutual significance of PG and SEM work function on p+ prompted source to study key analog characteristics of arsenide/antimonide tunneling interfaced hetero-material JLTFET (HJLTFET), which is unexplored in the literature otherwise. We have considered three metals—W (4.55 eV), Mo (4.65 eV), and Pd (5.3 eV) as the source electrodes in HJLTFET. For SEM work function lesser than p+ prompted source (W and Mo), the Schottky contact is formed by the depletion of hole plasma near SEM and p+ prompted source interface. This results in the immediate current inhibition at source to channel interface caused by an undesired movement of electrons en route to the Schottky interface. The Schottky tunneling phenomenon is considered by implementing the universal Schottky tunneling (UST) model to study the underestimated drain current of HJLTFET. However, the UST model becomes inconsequential for SEM work function higher than p+ prompted source (Pd) as hole plasma is preserved by the ohmic contact formation.

Cesium intercalation of graphene: A 2D protective layer on alkali antimonide photocathode

Abstract: Alkali antimonide photocathodes have wide applications in free-electron lasers and electron cooling. The short lifetime of alkali antimonide photocathodes necessitates frequent replacement of the photocathodes during a beam operation. Furthermore, exposure to mediocre vacuum causes loss of photocathode quantum efficiency due to the chemical reaction with residual gas molecules. Theoretical analyses have shown that covering an alkali antimonide photocathode with a monolayer graphene or hexagonal boron nitride protects it in a coarse vacuum environment due to the inhibition of chemical reactions with residual gas molecules. Alkali antimonide photocathodes require an ultra-high vacuum environment, and depositing a monolayer 2D material on it poses a serious challenge. In the present work, we have incorporated a novel method known as intercalation, in which alkali atoms pass through the defects of a graphene thin film to create a photocathode material underneath. Initially, Sb was deposited on a Si substrate, and a monolayer graphene was transferred on top of the Sb film. Heat cleaning around 550–600 °C effectively removed the Sb oxides, leaving metallic Sb underneath the graphene layer. Depositing Cs on top of a monolayer graphene enabled the intercalation process. Atomic force microscopy, Raman spectroscopy, x-ray photoelectron spectroscopy, low energy electron microscopy, and x-ray diffraction measurements were performed to evaluate photocathode formation underneath the monolayer graphene. Our analysis shows that Cs penetrated the graphene and reacted with Sb and formed Cs 3 Sb.

Synthesis and characterization of Zn doped AlSb thin films for photovoltaic and energy applications

Abstract: Abstract Thin films of zinc doped aluminum antimonide (Zn:AlSb) have been dumped on glass substrate using chemical bath deposition method. The morphological, structural, as well as optical properties of deposited thin films are investigated using XRD, optical microscopy, and UV-V is spectroscopy along with four-point probe technique. The XRD results exhibit that Zn is doped in AlSb and maximum grain size has been obtained at 4% Zn-concentration. Optical micrographs of pure and zinc doped aluminum antimonide (AlSb) at different concentrations of Zn have been shown to confirm the doping by observing changes in morphology and it has been observed that optimized films of AlSb are obtained at 4% of Zn-content. The optical bandgap of Zn doped AlSb films at varying concentrations of 0%, 1%, 2%, 3% and 4% has been found to decrease with enhancement in Zn-concentration and values are measured as 1.8, 1.7, 1.6, 1.4, and 1.3 eV respectively. The sheet resistivity also depends on Zn-content and has been observed to decrease as AlSb is doped with Zn, indicating an increase in electrical conductivity. The explored results indicate a significant potential of these deposited thin films to be used in photonics, photocatalysis, and energy industry.

Investigation of Antimonide Structure Types and the Structural Studies of Molybdates

Abstract: This dissertation highlights the investigation of ternary lanthanide antimonide structure types and their physical properties. In particular, these ternary phases allow for the systematic investigation of the structure in an effort to correlate structure and properties. The ternary antimonides are layered structures with two-dimensional square sheets or nets, which influence the properties of these materials. In an effort to determine how structural changes influence the physical properties, various single crystals of compounds relating to the orthorhombic CeNiSb3 structure have been grown and characterized. The layered CeNiSb3 structure consists of Sb sheets, NiSb6 distorted octahedra, and CeSb9 monocapped square anti-prisms. LnNi(Sn,Sb)3 and LnPdSb3 differ slightly from the CeNiSb3 structure in the packing of the transition metal layer. The structures and physical properties of LnNi(Sn,Sb)3 (Ln = La-Nd, Sm, Gd, Tb) are studied as a function of lanthanide. The stability of the CeNiSb3 structure was investigated by the substitution of Co or Cu for Ni in CeNiSb3 resulting in CeNixCo1-xSb3 and Ln(Cu1-xNix)ySb2 compounds. Also, the effect of Ni substitution for Cu in Ce(Cu1-xNix)Sb2 (0 ≤ x ≤ 0.8) compounds on the magnetoresistance is investigated. This dissertation also explores the different structure types of molybdates Rb4M(MoO4)3 (M = Mn, Zn, and Cu). Each analogue adopts a different structure type and contain similar subunits. The full structure determinations of each of these compounds are important to be able to understand the promising magnetic and electrical properties.

Development of MWIR and LWIR nBn photodetectors at i3system

Abstract: In modern infrared systems, barrier infrared detectors (BIRDs) have been widely used because a barrier is effective in reducing dark current by Shockley-Reed-Hall (SRH) process. Many researches have been studied on design of the barrier that prevents majority carrier flow and permits minority carrier flow. In this paper, we have studied on type-II superlattice (T2SL) nBn detectors having an unipolar barrier, where design and epi. growth are relatively simple for MWIR high operating temperature (HOT) and cooled LWIR detectors. InAs/InAsSb nBn for MWIR detection and InAs/GaSb nBn for LWIR detection were designed and fabricated. The fabricated MWIR and LWIR devices showed a dark current density of ≤ 2×10-6 A/cm2 at 150 K and ≤ 5×10-6 A/cm2 at 80 K, respectively. Also, 15 μm VGA MWIR and LWIR FPAs showed excellent performance with an average noise equivalent temperature difference (NETD) of ≤ 20 mK and operability of 99.5 % at 150 K and 80 K, respectively. MWIR HOT detector exhibited measured NETD similar to theoretical NETD considering dark current. And 10 μm SXGA HOT MWIR detector for high resolution imaging showed perfornance with an average NETD of ≤ 25 mK and operability of ≥99.5 % up to 130 K.

Research on beam quality control technology of 2 μm antimonide semiconductor laser

Abstract: Antimonide semiconductor laser is a new type of laser with unique advantages in the 2 μm band. However, employing FP cavities causes multiple transverse modes to degrade beam quality despite achieving higher power output. In this paper, an antimonide semiconductor laser operating in 2 μm band is realized by utilizing fiber coupling and combining. Fiber combining results in higher output power, while the uniform patterns in both near-field and far-field are obtained, and the beam quality is improved. The experimental results illustrate that the output power reaches 1.2 W after 7-channel beam combination, and the near-field distribution is approximately Gaussian, while the far-field distribution is a flat-top.