High Electron Research Articles

Adaptation of Interspecific Mesoamerican Common Bean Lines to Acid Soils and High Temperature in the Amazon Region of Colombia.

Knowledge of the physiological basis for improved genetic adaptation of common bean (Phaseolus vulgaris L.) lines to acid soils and high temperature conditions in the Amazon region of Colombia is limited. In this study, we evaluated the differences among 41 common bean lines in energy use, leaf cooling, photosynthate partitioning to pod formation and grain filling, and grain yield over two seasons under acid soil and high temperature stress in the Amazon region of Colombia. Common bean lines evaluated included medium and large seeded interspecific lines of Mesoamerican and Andean gene pools with different levels of adaptation to abiotic stress conditions and some lines are improved for iron and zinc (biofortified) concentration in seeds. We found three bean lines (GGR 147, SMG 21 and SMG 12) that were superior in their photosynthetic response, leaf cooling, photosynthate partitioning ability to pod formation and grain filling, resulting in grain yields exceeding 1900 kg ha−1 under acid soil and high temperature stress conditions. The superior photosynthetic performance was attributed to the efficient use of absorbed energy on the electron level in thylakoids, which is mainly oriented to a higher quantum yield of PSII (ΦII), lower energy dissipation in the form of heat (ΦNPQ), high linear electron flow (LEF) and high fraction of PSI centers in open state (PSIopen). We speculate that these photosynthetic and photosynthate partitioning responses of superior bean lines are part of the genetic adaptation to acidic soils and high temperature stress conditions. Among the evaluated bean lines, three lines (GGR 147, SMG 21 and SMG 12) combined the desirable attributes for genetic improvement of stress tolerance and biofortification. These lines can serve as parents to further improve traits (energy use efficiency and multiple stress resistance) that are important for bean production in the Amazon region.

Nano-photoluminescence of natural anyon molecules and topological quantum computation

The proposal of fault-tolerant quantum computations, which promise to dramatically improve the operation of quantum computers and to accelerate the development of the compact hardware for them, is based on topological quantum field theories, which rely on the existence in Nature of physical systems described by a Lagrangian containing a non-Abelian (NA) topological term. These are solid-state systems having two-dimensional electrons, which are coupled to magnetic-flux-quanta vortexes, forming complex particles, known as anyons. Topological quantum computing (TQC) operations thus represent a physical realization of the mathematical operations involving NA representations of a braid group Bn, generated by a set of n localized anyons, which can be braided and fused using a “tweezer” and controlled by a detector. For most of the potential TQC material systems known so far, which are 2D-electron–gas semiconductor structure at high magnetic field and a variety of hybrid superconductor/topological-material heterostructures, the realization of anyon localization versus tweezing and detecting meets serious obstacles, chief among which are the necessity of using current control, i.e., mobile particles, of the TQC operations and high density electron puddles (containing thousands of electrons) to generate a single vortex. Here we demonstrate a novel system, in which these obstacles can be overcome, and in which vortexes are generated by a single electron. This is a ~ 150 nm size many electron InP/GaInP2 self-organized quantum dot, in which molecules, consisting of a few localized anyons, are naturally formed and exist at zero external magnetic field. We used high-spatial-resolution scanning magneto-photoluminescence spectroscopy measurements of a set of the dots having five and six electrons, together with many-body quantum mechanical calculations to demonstrate spontaneous formation of the anyon magneto-electron particles (eν) having fractional charge ν = n/k, where n = 1–4 and k = 3–15 are the number of electrons and vortexes, respectively, arranged in molecular structures having a built-in (internal) magnetic field of 6–12 T. Using direct imaging of the molecular configurations we observed fusion and braiding of eν-anyons under photo-excitation and revealed the possibility of using charge sensing for their control. Our investigations show that InP/GaInP2 anyon-molecule QDs, which have intrinsic transformations of localized eν-anyons compatible with TQC operations and capable of being probed by charge sensing, are very promising for the realization of TQC.

Influence of minority charge carrier lifetime and concentration on crystalline silicon solar cells based on double antireflection coating: A simulation study

In this work, the optoelectrical properties of silver doped zinc oxide (Ag–ZnO)/ZnO double antireflection coating (ARC) layer were investigated by a simulation approach in terms of their minority charge carriers and surface charge carrier concentrations. From the experimental results, the Ag–ZnO/ZnO double ARC layer on Si solar cells presented the reduced average reflectance by 7.58% which was lowered to ZnO and Ag–ZnO single ARC layer. The simulation study demonstrated the reasonable electron and hole densities of 1.75 × 10 16 cm −3 and 1.51 × 10 16 cm −3 on c-Si solar cells with Ag–ZnO/ZnO double ARC layer. The simulated I–V characteristics evidenced that the performances of Ag–ZnO/ZnO double ARC layer-based Si solar cells gradually increased with the increase of the minority carrier lifetimes. As compared to a single ARC layer, the Ag–ZnO/ZnO double ARC layer-based Si solar cell achieved the highest conversion efficiency 14.32% with a fill factor of 81.35% at a minority carrier lifetime of 10 μs and carrier concentration of 1 × 10 17 cm −3 . The enhanced photovoltaic performance in Ag–ZnO/ZnO double ARC layer-based Si solar cells might be attributed to the high generation of electron-hole pairs, improved minority lifetime, and excellent carrier concentrations. • A simulation study was performed for optoelectrical properties of Ag–ZnO/ZnO double antireflection coating layer > Photovoltaic properties with respect to minority charge carriers/charge carrier concentrations studied > High electron and hole densities of 1.75 × 10 16 cm −3 and 1.51 × 10 16 cm −3 were observed > Ag–ZnO/ZnO double ARC layer based Si solar cell achieved the highest PCE 14.32%.

Graphene-induced lasing mode tailoring in GaN floating microring cavity

Due to its unique properties, such as high electron and thermal conductivities, graphene has attracted much attention, especially in its applications to optoelectronic devices. Herein, graphene is used in the tailoring of the lasing mode from a floated GaN microring cavity. The lasing performances of the GaN cavities are investigated, including its lasing intensity, full width at half maximum (FWHM) and mode properties for samples with or without the presence of graphene. We show that clear side-mode suppression, and an improvement in the photoluminescence (PL), is obtained for samples containing graphene. For samples covered with graphene, the threshold values are reduced by half and the PL intensity is enhanced by over 20 times. Based on observations of the PL evolution in terms of spontaneous emission, the side-mode suppression phenomenon can be attributed to electrons transfer induced PL modulation. Our work reveals a promising strategy for fabricating high-performance optoelectronic device.

Preparation and Characterization of Mg Doped ZnAI₂O₄Spinel Nanoparticles.

In the present study, combustion technique is adopted to study the impact of Mg2+ ion doping on ZnAI₂O₄ nanoparticles (NPs). L-arginine is used as a fuel component. The Mg2+ ions play a pivotal role in persuading various characteristics of ZnAI₂O₄ NPs. Various characterization technqiues such as Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), energy dispersive X-ray analysis (EDX), high resolution scanning electron microscopy (HR-SEM), diffuse reflectance spectroscopy (DRS), Thermo-gravimetric/differential thermal analysis (TG-DTA) and vibrating sample magnetometer (VSM) were carried out in order to synthesize the nanoparticles. Single phase cubic spinel structure of ZnAl₂O₄ (gahnite) formation was confirmed from the XRD characterization process of the nanoparticles. Estimated average crystallite size range of 11.85 nm to 19.02 nm was observed from Debye-Scherrer. Spherical morphology with uniform distributions was observed from HR-SEM characterization images. From the band gap studies, the attained band gap values were found to lie within 5.41 eV-4.66 eV range. The ZnAl₂O₄ and Mg:ZnAl₂O₄ NPs exhibited super-paramagnetic nature confirmed by magnetic measurements. The obtained results make ZnAl₂O ₄and Mg:ZnAl₂O₄ NPs appropriate for various optical, catalytic, energy and data storage applications.

(Invited) Two-Dimensional Characterization of Wide-Bandgap Materials and Contact Interfaces by Using Scanning Internal Photoemission Microscopy

Scanning internal photoemission spectroscopy (SIPM) has been developed to map the electrical characteristics of metal/semiconductor interfaces nondestructively. Our experimental demonstrations of the mapping characterization are reviewed from the several aspects. (1) Thermal degradation: For the development of high-power devices, the thermal degradation is more important. In the case of Ni/n-SiC Schottky contacts, the local interfacial reaction between Ni and SiC was observed in the photoyield (Y)image after annealing at 500° C or higher. The lower Schottky barrier height was determined in such regions. In the case of Au/Ni/n-GaN Schottky contacts, we found that surface scratches on the metal dot enhanced interfacial degradation.(2) Device degradation by applying high-voltage: Applying reverse bias voltage (Vbias) down to −45 V during theYmeasurement is possible in our SIPM. For most of the Ni/n-GaN Schottky contacts formed on a thick n-GaN layer grown on a freestanding GaN substrate, uniform distribution of Y was observed over the electrode. On the other hand, for the contacts with a slightly larger reverse current, the Y distribution was also uniform at Vbias = 0 V, but over Vbias = −36 V, Y was intensively increased at small spots. After the SIPM measurements, the I–V characteristics became leaky, and the same spots were observed in the microscope image. These results indicate that SIPM is useful for in situ monitoring of the initial stage of the degradation under applying reverse bias voltage.(3) Process-induced surface damages: The electrical characteristics of the Schottky contacts have a sensitive nature to the damages located on the semiconductor surface. We applied SIPM to the damage characterization. Firstly, the surface damages were intentionally induced by focused ion beam, or selective ion-implantation: Ga ions to n-GaAs, N ions to n-GaN, and N ions to n-SiC. The implanted images were clearly observed as the same Y images, and no extension of the induced damages was found. For the GaAs and SiC contacts, Y increased in the implanted regions, while for the GaN, Y decreased. Different roles of the damages as generation or recombination centers were clarified.(4) Grain boundaries of semiconductors and printed metal particles: SIPM is also available for the contacts formed on a semiconductor surface with poor crystal quality. Among the SiC poly-types, 3C-SiC has the advantages of an isotropic crystal structure and high electron and hole mobilities for electron device applications. However, owing to a lack of 3C-SiC bulk crystals, heteroepitaxial growth on Si, 4H-, or 6H-SiC substrates is unavoidable. Thus, the crystal quality of 3C-SiC is not as good as those of 4H- and 6H-SiC. We measured Ni Schottky contacts on p-3C-SiC layers grown on 4H or 6H-SiC substrates. The sample surface consists of 3C-SiC domains with a flat top. The domain pattern was clearly visualized in a Y map. By combining Ymaps measured with red and green lasers, we found that Schottky barrier height is smaller and larger recombination occurs in the boundary regions than in the flat regions. (5) Expansion to semiconductor/ semiconductor and metal-insulator-semiconductor interfaces: Finally, the structural expansion of the samples is described. As long as a hetero junction and an electrical field at the interface exist, a photocurrent can be generated upon monochromatic light irradiation. We characterized p+-Si/n−-SiC heterojunctions formed by surface-activated bonding. In the internal photoemission spectra, a linear relationship was found between Y 1/2 and hν, and threshold energy was reasonably obtained to be 1.34 eV. In the SIPM results, Y maps were successfully obtained, and nanometer-deep scratches, which were formed on the SiC surface in wafer polishing, were sensitively visualized as a pattern.This technique was confirmed to be useful for the development of the wide-bandgap-semiconductor high-power devices.

Study on Electric Field Modulation and Avalanche Enhancement of SiC/GaN IMPATT Diode

This paper proposes a 6H-materials silicon carbide (SiC)/gallium nitride (GaN) heterogeneous p-n structure to replace the GaN homogenous p-n junction to manufacture an impact-ionization-avalanche-transit-time (IMPATT) diode, and the performance of this 6H-SiC/GaN heterojunction single-drift-region (SDR) IMPATT diode is simulated at frequencies above 100 GHz. The performance parameters of the studied device were simulated and compared with the conventional GaN p-n IMPATT diode. The results show that the p-SiC/n-GaN IMPATT performance is significantly improved, and this is reflected in the enhanced characteristics in terms of operating frequency, rf power, and dc-rf conversion efficiency by the two mechanisms. One such characteristic that the new structure has an excessive avalanche injection of electrons in the p-type SiC region owing to the ionization characteristics of the SiC material, while another is a lower electric field distribution in the drift region, which can induce a higher electron velocity and larger current in the structure. The work provides a reference to obtain a deeper understanding of the mechanism and design of IMPATT devices based on wide-bandgap semiconductor materials.

Annealing Induced Saturation in Electron Concentration for V-Doped CdO

As-grown Ar-deposited Cd1−xVxO and Ar/O2-deposited Cd1−yVyO feature lower and higher electron concentrations than 4 × 1020 cm−3, respectively. After isothermal and isochronal annealing under N2 ambient, we find that the two series exhibit a decrease or increase in electron concentrations until ~4 × 1020 cm−3 which is close to Fermi stabilization energy (EFS) level of CdO, with the assistance of native defects. An amphoteric defects model is used to explain the changing trends in electron concentrations. The tendencies in mobility further confirm our results. This work may provide some strategies to predict the electrical properties in CdO.

Trigger slow control system of the Belle II experiment

The Belle II experiment at the SuperKEKB e+e− collider in KEK, Japan, started physics data-taking with a complete detector from early 2019. An online trigger system is indispensable for the Belle II experiment to reduce the beam background events associated with high electron and positron beam currents without sacrificing the target physics-oriented events. During the Belle II operation upon beam collision, the trigger system must be consistently controlled and its status must be carefully monitored in the process of data acquisition against unexpected situations. For this purpose, we have developed a slow control system for the newly developed Belle II trigger system based on the custom-made Belle II DAQ/slow control package. Around seventy thousand configuration parameters are saved in the Belle II central database server for every run when a run starts and stops. These parameters play an essential role in offline validation of the quality of runs. Around three thousand real-time variables are stored in the Belle II main archiving server, and the trend of some of these variables are regularly used for online and offline monitoring purposes. Various operator interface tools have been prepared and used. When the configuration parameters are not correctly applied, or some of the processes are unexpectedly terminated, the slow control system detects it, stops the data-taking process, and generates an alarm. In this article, we report how we constructed the Belle II trigger slow control system, and how we successfully managed to operate during its initial stage.

Unveiling the Intramolecular Ionic Diels–Alder Reactions within Molecular Electron Density Theory

The intramolecular ionic Diels–Alder (IIDA) reactions of two dieniminiums were studied within the Molecular Electron Density Theory (MEDT) at the ωB97XD/6-311G(d,p) computational level. Topological analysis of the electron localization function (ELF) of dieniminiums showed that their electronic structures can been seen as the sum of those of butadiene and ethaniminium. The superelectrophilic character of dieniminiums accounts for the high intramolecular global electron density transfer taking place from the diene framework to the iminium one at the transition state structures (TSs) of these IIDA reactions, which are classified as the forward electro density flux. The activation enthalpy associated with the IIDA reaction of the experimental dieniminium, 8.7 kcal·mol−1, was closer to that of the ionic Diels–Alder (I-DA) reaction between butadiene and ethaniminium, 9.3 kcal·mol−1. However, the activation Gibbs free energy of the IIDA reaction was 12.7 kcal·mol−1 lower than that of the intermolecular I-DA reaction. The strong exergonic character of the IIDA reaction, higher than 20.5 kcal·mol−1, makes the reaction irreversible. These IIDA reactions present a total re/exo and si/endo diastereoselectivity, which is controlled by the most favorable chair conformation of the tetramethylene chain. ELF topological analysis of the single bond formation indicated that these IIDA reactions take place through a non-concerted two-stage one-step mechanism. Finally, ELF and atoms-in-molecules (AIM) topological analyses of the TS associated with the inter and intramolecular processes showed the great similarity between them.

(Invited) Interface Treatment Related Defects During Ge Gate Stack Formation

Germanium as a high mobility channel material is currently of considerable interest since Ge has both higher electron and hole mobility as compared to silicon (1). The deposition of high-k dielectrics on Ge has been a significant challenge because of high interface defects density, Dit (2). By considering the interface reaction kinetics, thermal budget various atomic layer deposition (ALD) schemes and interface treatments can be identified to get a stable dielectric with a robust interface. However, understanding of the interface kinetics and defect distribution into gate stack and/or Ge is still limited.In this work, we report the impact of different interface treatments on the p type Ge prior to any high-k layer deposition on defect generation. Ge surface was oxidized by a controlled chemical oxidation, slot-plane-antenna plasma oxidation and oxidation through vapor O3 treatment before ALD deposition of 1nm Al2O3/3.5nm ZrO2 for gate stack formation. These devices were characterized to evaluate the interface and possible bulk defects by deep level transient spectroscopy (DLTS), capacitance spectroscopy, conductance method in addition to standard I-V and C-V measurements. DLTS has the advantage to have the spectrum comparison among the interface treatments. Signature of these spectra can reveal the difference, which is more accurate than the defects estimated by Conductance method. DLTS also provides the signature of slow traps (~1ms) (Fig. 1) originating from the bulk or interface depending on the type of GeOx formation.Furthermore, we evaluate the defect distribution when the gate stack was subjected to a slot-plane antenna plasma oxidation prior to metal deposition. A TiN/Hf1-xZrxO2/Al2O3/Ge gate stack with six different Zr content was investigated (Fig. 2). Al2O3 was used to impede the Ge diffusion into the gate stack. Interface state density (Dit) and C-V hysteresis show that the mid-gap Dit tend to increase with decrease in EOT, possibly due to the undesirable native oxide formation on Ge.The author would like to thank Drs. Y.M. Ding (Western Digital Corporation, Shanghai, China), M.N. Bhuyian (Globalfoundries, Malta, NY, USA), K.L. Ganapathi (Indian Institute of Technology Madras, India), N. Bhat, (Indian Institute of Science, Bangalore, India) and K. Tapily, R. D. Clark, S. Consiglio, C. S. Wajda, G. Nakamura, and G. J. Leusink of TEL Technology Center, America, Albany, NY, for their help in this work. References Arimura et al, IEDM Technical Digest, (2020)N. Bhuyian et al, ECS Journal of Solid-St. Sci. and Tech., vol. 7(2), N1-N6, (2018)G. Kolla et al, J. Vac. Sci. Technol. B, 36(2), 021201 (2018)Ding et al, IEEE Trans. on Dev. and Materials Reliability, 17(2), 349-354, (2017)Ding, et al, J. of Vac. Sci. and Technol. B, 34(2), 021203, 2016. Figure 1

Design of High Energy Photon Source Booster beam size monitor

High Energy Photon Source (HEPS) Booster is designed to ramp up the energy of the beam from linac and inject high quality electron beam to the storage ring. To measure the transverse beam size, emittance and energy spread of HEPS Booster, we designed two beam diagnostic beamlines at visible-UV spectrum region. The source points are at two bending magnets with different chromatic dispersion, one has no dispersion while the other has large dispersion. By measuring the transverse beam sizes with synchrotron imaging system, beam emittance and energy spread can also be calculated. This paper introduces the extraction of visible-UV light, and the optical imaging system, the spatial resolution. It also introduces the design of beam spot changes measurement during beam ramping process.

OC-0016 High dose rate brachytherapy versus electron boost for tumor bed after breast conserving therapy

OC-0016 High dose rate brachytherapy versus electron boost for tumor bed after breast conserving therapy

Terahertz emission increase in GaAs films exhibiting structural defects grown on Si (100) substrates using a two-layered LTG-GaAs buffer system

Terahertz (THz) emission increase is observed for GaAs thin films that exhibit structural defects. The GaAs epilayers are grown by molecular beam epitaxy on exactly oriented Si (100) substrates at three different temperatures (Ts = 320 °C, 520 °C and 630 °C). The growth method involves the deposition of two low-temperature-grown (LTG)-GaAs buffers with subsequent in-situ thermal annealing at Ts = 600 °C. Reflection high energy electron diffraction confirms the layer-by-layer growth mode of the GaAs on Si. X-ray diffraction shows the improvement in crystallinity as growth temperature is increased. The THz time-domain spectroscopy is performed in reflection and transmission excitation geometries. At Ts = 320 °C, the low crystallinity of GaAs on Si makes it an inferior THz emitter in reflection geometry, over a GaAs grown at the same temperature on a semi-insulating GaAs substrate. However, in transmission geometry, the GaAs on Si exhibits less absorption losses. At higher Ts, the GaAs on Si thin films emerge as promising THz emitters despite the presence of antiphase boundaries and threading dislocations as identified from scanning electron microscopy and Raman spectroscopy. An intense THz emission in reflection and transmission excitation geometries is observed for the GaAs on Si grown at Ts = 520 °C, suggesting the existence of an optimal growth temperature for GaAs on Si at which the THz emission is most efficient in both excitation geometries. The results are significant in the growth design and fabrication of GaAs on Si material system intended for future THz photoconductive antenna emitter devices.

In Vivo Observation of Lidocaine-Encapsulated Polymyxin/Glycol Nanoparticles Wound Dressing for the Treatment and Care of Abdominal Pain Incision in Intensive Care Unit

The developments of lidocaine chloride loaded nanoparticles are encouraging biomaterials, which could be used for wound healing applications for abdominal pain management. The current work presents the composition of wound dressings based on lidocaine chloride (LCH) (anesthetic drug)-loaded Polymyxin (PMN)/Glycol (GLY). The LCH nanocomposite (LCH@PMN/GLY) were fabricated by the LCH oxide solutions within the PMN/GLY matrix. The influences of different experimental limitations on PMN/GLY nanoparticles formations were examined. The PMN/GLY and LCH@PMN/GLY nanoparticle sizes were evaluated by high resolution-scanning electron microscopy (HR-SEM). Additionally, the antibacterial efficacy of PMN/GLY and LCH@PMN/GLY was developed for gram-positive and negative microorganisms. Moreover, we examined in vivo healing of skin wounds formed in mouse models over 20 days. In contrast to the untreated wounds, rapid healing was perceived in the LCH@PMN/GLY-treated wound with less damage. These findings indicate that LCH@PMN/GLY-based bandaging materials could be a potential innovative biomaterial for tissue repair and implantation and nursing care for wound healing applications for abdominal pain incision in intensive care unit (ICU) management in an animal model.

Matrix model for collective phenomena in electron beam\u2019s longitudinal phase space

The possibility to predict, characterize and minimize the presence of spurious harmonic content in the longitudinal profile of high brightness electron beams, namely the microbunching instability, has become vital to ensure accurate modeling and reliable operation of radiofrequency and plasma-based linear accelerators such as those driving free-electron lasers. Recently, the impact of intrabeam scattering (IBS) on the instability has been experimentally demonstrated by the authors. This work complements that experimental study by extending existing theories in a self-consistent, piece-wise calculation of IBS in single pass linacs and multi-bend transfer lines. New expressions for the IBS are introduced in two different semi-analytical models of microbunching. The accuracy of the proposed models and the range of beam parameters to which they apply is discussed. The overall modeling turns out to be a fast comprehensive tool for the optimization of linac-driven free-electron lasers.

Valley relaxation of resident electrons and holes in a monolayer semiconductor: Dependence on carrier density and the role of substrate-induced disorder

Using time-resolved optical Kerr rotation, we measure the low temperature valley dynamics of resident electrons and holes in exfoliated WSe$_2$ monolayers as a systematic function of carrier density. In an effort to reconcile the many disparate timescales of carrier valley dynamics in monolayer semiconductors reported to date, we directly compare the doping-dependent valley relaxation in two electrostatically-gated WSe$_2$ monolayers having different dielectric environments. In a fully-encapsulated structure (hBN/WSe$_2$/hBN, where hBN is hexagonal boron nitride), valley relaxation is found to be monoexponential. The valley relaxation time $\tau_v$ is quite long ($\sim$10~$\mu$s) at low carrier densities, but decreases rapidly to less than 100~ns at high electron or hole densities $\gtrsim$2 $\times 10^{12}$~cm$^{-2}$. In contrast, in a partially-encapsulated WSe$_2$ monolayer placed directly on silicon dioxide (hBN/WSe$_2$/SiO$_2$), carrier valley relaxation is multi-exponential at low carrier densities. The difference is attributed to environmental disorder from the SiO$_2$ substrate. Unexpectedly, very small out-of-plane magnetic fields can increase $\tau_v$, especially in the hBN/WSe$_2$/SiO$_2$ structure, suggesting that localized states induced by disorder can play an important role in depolarizing spins and mediating the valley relaxation of resident carriers in monolayer transition metal-dichalcogenide semiconductors.

Heterovalent semiconductor structures and devices grown by molecular beam epitaxy

Heterovalent structures consisting of group II-VI/group III-V compound semiconductors offer attractive properties, such as a very broad range of bandgaps, large conduction band offsets, high electron and hole mobilities, and quantum-material properties such as electric-field-induced topological insulator states. These properties and characteristics are highly desirable for many electronic and optoelectronic devices as well as potential condensed-matter quantum-physics applications. Here, we provide an overview of our recent studies of the MBE growth and characterization of zincblende II-VI/III-V heterostructures as well as several novel device applications based on different sets of these materials. By combining materials with small lattice mismatch, such as ZnTe/GaSb (Δa/a ∼ 0.13%), CdTe/InSb (Δa/a ∼ 0.05%), and ZnSe/GaAs (Δa/a ∼ 0.26%), epitaxial films of excellent crystallinity were grown once the growth conditions had been optimized. Cross-sectional observations using conventional and atomic-resolution electron microscopy revealed coherent interfaces and close to defect-free heterostructures. Measurements across CdTe/InSb interfaces indicated a limited amount (∼1.5 nm) of chemical intermixing. Results for ZnTe/GaSb distributed Bragg reflectors, CdTe/MgxCd1−xTe double heterostructures, and CdTe/InSb two-color photodetectors are briefly presented, and the growth of a rock salt/zincblende PbTe/CdTe/InSb heterostructure is also described.

DFT and HAADF-STEM Investigations of the Zn Effects on β″ Phase Structure in a Zn Added Al-Mg-Si-Cu Alloy

First-principles calculations were conducted to investigate the effects of Zn on the structure of β″ phase. The effects of Cu, which was often added in the alloy, were also taken into consideration. Firstly, single Zn or Cu atom was doped on different sites of the β″ phase. Then the formation enthalpies and lattice constants of doped β″ phases were calculated. The results showed that it was more energetically favorable for single Zn or Cu atom to occupy Si3/Al sites than other sites. Furthermore, different quantities of Zn or Cu atoms were doped on Si3/Al sites. With the amounts of doping atoms increasing, the formation enthalpies of β″ phases doped by Zn were lower than which doped by Cu, indicating that it was more preferential for Zn to enter the β″ phase when Zn content was higher than Cu. Additionally, the doping of Zn could reduce the formation enthalpies of the β″ phase, which promoted the formation of the β″ phases. As a result, the aging hardening response of the alloy was improved. High angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) characterization was also conducted on a peak-aging Zn added Al-Mg-Si-Cu alloy. The HAADF-STEM image of β″ phase showed that the occupancies of Zn atoms were just on the Si3/Al sites and substituted all the Al atoms, which was consistent with the results of first-principles calculations.

Solution-Grown Formamidinium Hybrid Perovskite (FAPbBr3) Single Crystals for α-Particle and γ-Ray Detection at Room Temperature.

Compared with the widely reported MAPbBr3 single crystals, formamidinium-based (FA-based) hybrid perovskites FAPbBr3 (FPB) with superior chemical and structure stability are expected to be more efficient and perform as more reliable radiation detectors at room temperature. Here, we employ an improved inverse temperature crystallization method to grow FPB bulk single crystals, where issues associated with the retrograde solubility behavior are resolved. A crystal growth phase diagram has been proposed, and accordingly, growth parameters are optimized to avoid the formation of NH4Pb2Br5 secondary phase. The resulting FPB crystals exhibit a high resistivity of 2.8 × 109 Ω·cm and high electron and hole mobility-lifetime products (μτ) of 8.0 × 10-4 and 1.1 × 10-3 cm2·V-1, respectively. Simultaneously, the electron and hole mobilities (μ) are evaluated to be 22.2 and 66.1 cm2·V-1·s-1, respectively, based on the time-of-flight technique. Furthermore, a Au/FPB SC/Au detector is constructed that demonstrates a resolvable gamma peak from 59.5 keV 241Am γ-rays at room temperature for the first time. An energy resolution of 40.1% is obtained at 30 V by collecting the hole signals. These results demonstrate the great potential of FAPbBr3 as a hybrid material for γ-ray spectroscopy and imaging.