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High-flux capable semiconductor x-ray detectors are essential in various applications, but the detrimental effects of detector polarization limit their use in many cases. Here, we studied the polarization of perovskite CsPbBr3 semiconductor detectors using ultrahigh flux synchrotron x rays (106–1012 photons s−1 mm−2 at 58.61 keV). The CsPbBr3 detectors did not show immediate polarization prominently until a flux higher than 1010 photons s−1 mm−2. Using the pump-and-probe technique, we visualized the spatial and temporal effects of polarization. The polarized region, represented by reduced photocurrent, extended beyond the area under direct irradiation, and the reduced photocurrent persisted after potential de-polarization treatments. We found that stronger applied electric fields and fewer carrier traps can mitigate polarization, represented by less photocurrent deficit. By examining the detectors’ current response under controlled ambient light, low, and high-flux x rays, we studied the trap filling and release behavior of CsPbBr3. We discovered that the polarization is caused by partial detector damage due to deep defects generated by ultrahigh flux x-ray irradiation. Our work provides insight into CsPbBr3 polarization under extremely intense x-ray radiation and shows that reducing crystal defects and increasing detector bias voltage are effective solutions.

Excitons in Bridgman grown halide perovskite CsPbBr3 single crystals were examined using photoluminescence (PL) spectroscopy to determine the nature of the electronic states. The photoluminescence intensity was strongly temperature-dependent and depended upon the specific exciton band. At low temperatures intrinsic disorder and its related shallow below bandgap tail states determine the emission properties. Photoluminescence at low temperature revealed the presence of several strong bands at the band edge that is attributed to free or trapped/bound excitons. This PL emission results from strong electron-phonon coupling with an average phonon energy Eph of 6.5 and 27.4 meV for the emissions, comparable to that observed in other perovskites. The Huang-Rhys parameter S was calculated to be 3.81 and 1.51, indicating strong electron-phonon coupling. The interactions between electrons and phonons produce small polarons that tend to bind charge carriers and result in trapped/bound excitons. The transient photoluminescence response of each specific band was studied, and the results indicated a multiphonon recombination process. Average PL lifetimes of ∼17 ns for free excitons and ∼38 ns for trapped/bound excitons were determined. The observed edge states could be associated with native defects such as vacancies and interstitials, as well as twinning due to the cubic-to-tetragonal phase transition in CsPbBr3. Elimination of the trapping sites for binding excitons could lead to improved charge transport mobilities, carrier lifetimes, and detector properties in this system.

The detection of γ-rays at room temperature with high-energy resolution using semiconductors is one of the most challenging applications. The presence of even the smallest amount of defects is sufficient to kill the signal generated from γ-rays which makes the availability of semiconductors detectors a rarity. Lead halide perovskite semiconductors exhibit unusually high defect tolerance leading to outstanding and unique optoelectronic properties and are poised to strongly impact applications in photoelectric conversion/detection. Here we demonstrate for the first time that large size single crystals of the all-inorganic perovskite CsPbCl3 semiconductor can function as a high-performance detector for γ-ray nuclear radiation at room temperature. CsPbCl3 is a wide-gap semiconductor with a bandgap of 3.03 eV and possesses a high effective atomic number of 69.8. We identified the two distinct phase transitions in CsPbCl3, from cubic (Pm-3m) to tetragonal (P4/mbm) at 325 K and finally to orthorhombic (Pbnm) at 316 K. Despite crystal twinning induced by phase transitions, CsPbCl3 crystals in detector grade can be obtained with high electrical resistivity of ∼1.7 × 109 Ω·cm. The crystals were grown from the melt with volume over several cubic centimeters and have a low thermal conductivity of 0.6 W m-1 K-1. The mobilities for electron and hole carriers were determined to ∼30 cm2/(V s). Using photoemission yield spectroscopy in air (PYSA), we determined the valence band maximum at 5.66 ± 0.05 eV. Under γ-ray exposure, our Schottky-type planar CsPbCl3 detector achieved an excellent energy resolution (∼16% at 122 keV) accompanied by a high figure-of-merit hole mobility-lifetime product (3.2 × 10-4 cm2/V) and a long hole lifetime (16 μs). The results demonstrate considerable defect tolerance of CsPbCl3 and suggest its strong potential for γ-radiation and X-ray detection at room temperature and above.

Halide perovskite semiconductors are poised to revitalize the field of ionizing radiation detection as they have done to solar photovoltaics. We show that all-inorganic perovskite CsPbBr3 devices resolve 137Cs 662-keV γ-rays with 1.4% energy resolution, as well as other X- and γ-rays with energies ranging from tens of keV to over 1 MeV in ambipolar sensing and unipolar hole-only sensing modes with crystal volumes of 6.65 mm3 and 297 mm3, respectively. We report the scale-up of CsPbBr3 ingots to up to 1.5 inches in diameter with an excellent hole mobility–lifetime product of 8 × 10−3 cm2 V−1 and a long hole lifetime of up to 296 μs. CsPbBr3 detectors demonstrate a wide temperature region from ~2 °C to ~70 °C for stable operation. Detectors protected with suitable encapsulants show a uniform response for over 18 months. Consequently, we identify perovskite CsPbBr3 semiconductor as an exceptional candidate for new-generation high-energy γ-ray detection. Energy resolution of high-energy photon detectors is desired for applications ranging from biomedical imaging to homeland security. In this work, perovskite-based γ-ray detection with 1.4% energy resolution is demonstrated.

Highly efficient neutron detectors are critical in many sectors, including national security1,2, medicine3, crystallography4 and astronomy5. The main neutron detection technologies currently used involve 3He-gas-filled proportional counters6 and light scintillators7 for thermalized neutrons. Semiconductors could provide the next generation of neutron detectors because their advantages could make them competitive with or superior to existing detectors. In particular, solids with a high concentration of high-neutron-capture nuclides (such as 6Li, 10B) could be used to develop smaller detectors with high intrinsic efficiencies. However, no promising materials have been reported so far for the construction of direct-conversion semiconductor detectors. Here we report on the semiconductor LiInP2Se6 and demonstrate its potential as a candidate material for the direct detection of thermal neutrons at room temperature. This compound has a good thermal-neutron-capture cross-section, a suitable bandgap (2.06 electronvolts) and a favourable electronic band structure for efficient electron charge transport. We used α particles from an 241Am source as a proxy for the neutron-capture reaction and determined that the compact two-dimensional (2D) LiInP2Se6 detectors resolved the full-energy peak with an energy resolution of 13.9 per cent. Direct neutron detection from a moderated Pu–Be source was achieved using 6Li-enriched (95 per cent) LiInP2Se6 detectors with full-peak resolution. We anticipate that these results will spark interest in this field and enable the replacement of 3He counters by semiconductor-based neutron detectors. The semiconductor 6LiInP2Se6 is used for the direct detection of thermal neutrons at room temperature, demonstrating good energy resolution.

The search for new halide perovskites has recently expanded to the double perovskites A2M+M3+X6, which form in the 3D elpasolite structure with alternating M+ and M3+ octahedra. Here, we report the...

The wide-band-gap semiconductor Tl6SI4 (2.14 eV) has high photon stopping power and is a promising material for detecting X-rays. In order to improve its photoresponse to low-flux γ-rays, material ...

Here we report the first spectroscopic alpha particle detection based on CsPbBr 3 detectors with asymmetric contacts. The CsPbBr3 single crystal was grown from the melt using Bridgman method and then fabricated into detectors with different contacts. The In/CsPbBr 3/Au detector presented a low dark current density ( ∼ 100 nA/cm2 ) and temporal stable performance under high electric field (1000 V/cm). Such detector demonstrated excellent gamma ray resolving capability with a full-width at half maximum (FWHM) of ∼ 5.9 keV for the 57Co 122 keV γ ray. The CsPbBr3 detector was capable of simultaneously resolving both the alpha particle (5.5 MeV) and γ ray (59.5 keV) peaks from 241Am radioactive isotope. The transport properties of CsPbBr3 were then determined based on the alpha particle spectra and corresponding rise time distributions. The equivalent values of electron and hole mobilities were indicated as 63 and 49 cm2/(V ⋅ s) respectively. The calculated electron and hole mobility-lifetime products were 4.5 × 10−4 and 9.5 × 10−4 cm2/V, respectively, demonstrating superior transport properties of holes over electrons in CsPbBr3 . This work widens the scope of perovskite detectors to encompass charged radiation as well as high energy X/ γ rays, and will significantly promote and guide further studies on perovskite materials for radiation detection applications.

Thermally stimulated current (TSC) spectroscopy was used to characterize electronic trap states in the perovskite CsPbCl3 bulk single crystals which are promising for gamma ray detection. The TSC spectra indicate the presence of multiple traps over the temperature range from 80 K to above room temperature. The possible analytical defects identified were VCs and VCl vacancies and Pbi interstitials that have concentrations of the order of 1011−1016 cm−3 and capture cross sections of ∼10−18 cm2. A comparison of crystals grown from different ingots reveals that the concentration of defects in the crystal with an improved growth procedure is about one to four orders of magnitude less than those of a crystal from an earlier growth process. A further reduction and elimination of trap states within the perovskite ingot should lead to crystals with improved mobilities, carrier lifetimes, and detector response characteristics.

The detection of γ-rays at room temperature with high-energy resolution using semiconductors is one of the most challenging applications. The presence of even the smallest amount of defects is sufficient to kill the signal generated from γ-rays which makes the availability of semiconductors detectors a rarity. Lead halide perovskite semiconductors exhibit unusually high defect tolerance leading to outstanding and unique optoelectronic properties and are poised to strongly impact applications in photoelectric conversion/detection. Here we demonstrate for the first time that large size single crystals of the all-inorganic perovskite CsPbCl

As an advanced ferroelectric material, barium titanate (BaTiO 3 ) crystal has an electro-optic effect higher than lithium niobate (LiNbO 3 ) crystal by 20-40 times, so it has been taken to be one of the best materials to realize the ultra-high bandwidth electro-optic modulators. In this paper, we model and simulate the transmission coefficient S 21 of the microwave signal to the frequency of drive microwave through an embedded waveguide-electrode structure, and further simulate the S 21 with a software tool - Sonnet. As a result, when the electrode length, electrode width, electrode thickness, electrode gap, BaTiO 3 thin film thickness, magnesium oxide (MgO) substrate thickness and embedded depth were 1mm, 80μm, 1μm, 8μm, 450nm, 500μm and 0.1μm, respectively, the electro-optic modulation bandwidths have reached 50-70GHz, and it can be optimized to 100GHz at 250μm MgO substrate thickness.

Alternative all-inorganic halide perovskites are sought to replace the hybrid lead halide perovskites because of their increased stability. Here, the (111)-oriented defect perovskite family A3M2X9 based on trivalent M3+ is expanded through the use of mixed halides, resulting in Cs3Bi2I6Cl3. This compound shares the (111)-oriented 2D bilayer structure of α-Cs3Sb2I9 (space group P3m1), with Cl occupying the bridging positions of the bilayers and I in the terminal sites, in contrast to the parent compound Cs3Bi2I9, which consists of 0D molecular [Bi2I9]3– dimers. The increased dimensionality induces a direct band gap as calculated by density functional theory but has an absorption edge of 2.07 eV, nearly identical to the indirect band gap compound Cs3Bi2I9. Intriguingly, there is a remarkable lack of Cl orbital contribution to the band edge states of Cs3Bi2I6Cl3, despite Bi–Cl bonds binding all octahedra together. This highlights the importance of interlayer interactions in the defect perovskite family, whi...

The chalcohalide compound Hg3Se2I2 with a defect anti-perovskite structure has been demonstrated to be a promising semiconductor for room temperature X- and γ-ray detection. In this work, we use tr...

We report on the measurement of frequency dependent noise spectra of photoconductive ternary compounds Cs3Sb2I9, Rb3Sb2I9, Hg3Se2I2, and TlSn2I5 for hard radiation detectors. The major sources of noise in these detectors are attributed to pickup noise, white noise, and frequency related 1/ f noise. At low frequencies, the noise spectral density function exhibited 1/ f α behavior where α is less than or equal to one. For those samples with α equal to one, radiation detection performances of the detectors, in terms of spectral measurements, have been reported in previous publications. The origin of 1/f noise of those samples is attributed to carrier fluctuations associated with deep centers/trapped holes. For those samples with α less than one, the origin of the deviation from a linear 1/f dependence is unknown and currently under investigation. However, this deviation is correlated with higher background white noise and lowered detector performance, and thus indicates that the material needs to be further optimized. Noise measurements are a useful indicator for screening prospective materials and samples for detectors.

We report temperature-dependent photoluminescence (PL) in polycrystalline ASnI3 perovskites (A = Cs+, CH3NH3+, and HC(NH2)2+), demonstrating extremely robust emission up to very high temperatures (...

Halide perovskites exhibit remarkably high-performance as semiconductors compared to conventional materials because of an unusually favorable combination of optoelectronic properties. We demonstrate here that solution-grown single-crystals of organic–inorganic hybrid perovskite CH3NH3PbI3 (MAPbI3), implemented in a Schottky-type device design, can produce outstanding hard radiation detectors with high spectral response and low dark current for the first time. Schottky-type MAPbI3 detector achieves an excellent energy resolution of 6.8% for 57Co 122 keV gamma ray. The high detector performance is achieved due to the balanced charge collection efficiency for both electrons and holes, reflected in the high mobility-lifetime (μτ) products of both carriers (∼0.8 × 10–3 cm2/V). MAPbI3 also demonstrates remarkably long electron and hole lifetimes (τe = 10 μs and τh = 17 μs) and impressive operational stability over time. Furthermore, dual-source detection of α particle (5.5 MeV) and γ-ray (59.5 keV) from the 241...

We have investigated the defect perovskites A3M2I9 (A = Cs, Rb; M = Bi, Sb) as materials for radiation detection. The phase purity of Bridgman-grown A3M2I9 single crystals was confirmed via high-re...

The semiconductor Tl6SeI4 was previously identified as a promising semiconductor for room temperature nuclear radiation detection. As the detection performance and carrier transport strongly depend on the concentration of impurity energy levels acting as scattering centers and carrier trapping, material purification is a crucial prerequisite step to obtain spectroscopic-grade detector performance. In this contribution, we present a highly efficient purification method using a bent ampule for evaporating Se, Tl2Se, and TlI precursors for Tl6SeI4. On the basis of impurity analysis performed by glow discharge mass spectroscopy, the main impurities in Tl2Se were identified to be Pb, Bi, and Al, while in TlI the main impurities are Al and Sn. The bent-ampule method successfully reduces or removes the Cl, Pb, and Te impurities from the Se precursor, the Pb, Bi, and Al impurities from the Tl2Se precursor, and removes Sn from TlI. Informed by the analysis results, density functional theory calculations were perfo...

Gamma-ray detection and spectroscopy is the quantitative determination of their energy spectra, and is of critical value and critically important in diverse technological and scientific fields. Here we report an improved melt growth method for cesium lead bromide and a special detector design with asymmetrical metal electrode configuration that leads to a high performance at room temperature. As-grown centimeter-sized crystals possess extremely low impurity levels (below 10 p.p.m. for total 69 elements) and detectors achieve 3.9% energy resolution for 122 keV 57Co gamma-ray and 3.8% for 662 keV 137Cs gamma-ray. Cesium lead bromide is unique among all gamma-ray detection materials in that its hole transport properties are responsible for the high performance. The superior mobility-lifetime product for holes (1.34 × 10−3 cm2 V−1) derives mainly from the record long hole carrier lifetime (over 25 μs). The easily scalable crystal growth and high-energy resolution, highlight cesium lead bromide as an exceptional next generation material for room temperature radiation detection., Detection and spectroscopic measurements of gamma-ray used to rely on expensive materials such as CdZnTe crystals. Here He et al. develop a melt method to grow large size CsPbBr3 perovskite crystals and the devices achieve low cost, high energy resolving capabilities and stability.

Cu2I2Se6 is a new wide-bandgap semiconductor with high stability and great potential toward hard radiation and photon detection. Cu2I2Se6 crystallizes in the rhombohedral R3m space group with a density of d = 5.287 g·cm–3 and a wide bandgap Eg of 1.95 eV. First-principles electronic band structure calculations at the density functional theory level indicate an indirect bandgap and a low electron effective mass me* of 0.32. The congruently melting compound was grown in centimeter-size Cu2I2Se6 single crystals using a vertical Bridgman method. A high electric resistivity of ∼1012 Ω·cm is readily achieved, and detectors made of Cu2I2Se6 single crystals demonstrate high photosensitivity to Ag Kα X-rays (22.4 keV) and show spectroscopic performance with energy resolutions under 241Am α-particles (5.5 MeV) radiation. The electron mobility is measured by a time-of-flight technique to be ∼46 cm2·V–1·s–1. This value is comparable to that of one of the leading γ-ray detector materials, TlBr, and is a factor of 30 ...

Pb2P2Se6 as a heavy element, chemically robust semiconductor, has been identified as a promising material for cost-effective room temperature X/γ-ray detection. Here, we report the properties of Pb2P2Se6 crystals grown by a vertical Bridgman method under off-stoichiometric Se-rich and Pb-rich conditions. Regardless of the conditions the resulting single crystals exhibited high bulk resistivity on the order of 1011 Ω·cm. However, the photoconductivity and charge transport properties varied based on growth condition indicating the different dominant defects associated with the type of stoichiometric deviation. The formation and nature of intrinsic defects in Pb2P2Se6 crystals were also studied by first-principles density functional theory (DFT) calculations as well as thermally stimulated current (TSC) spectroscopy. The TSC results indicated that four traps were common to both Se-rich and Pb-rich Pb2P2Se6, while a higher density of shallow defects were observed in Se-rich Pb2P2Se6. DFT calculations predict ...

Tl6SeI4 is a promising wide-bandgap semiconductor for room-temperature high-energy photon detection. Because of the air-sensitive Tl precursor or Tl-based binary precursors used in the synthesis, this material can contain deleterious Tl oxide impurities. These impurities lead to problems during syntheses and crystal growth including glass attack, tube rupture, and parasitic nucleation, which subsequently deteriorate detector performance. In this work, we present a facile way to chemically reduce Tl oxides and eliminate oxygen impurities in Tl6SeI4 by adding high-purity graphite powder during synthesis. The addition of carbon leads to reduction of the residual Tl oxides and formation of CO2 and CO. The resistivity and hard radiation detection performance for 122 keV γ-rays of Tl6SeI4 single crystals were significantly improved. The improvement in the crystallinity was also confirmed by a narrower near-band-edge emission band in the photoluminescence spectra. We confirmed that the reaction between Tl oxide ...

We report the quasi-2D semiconductor compound TlSbS2 as a new hard radiation detection material. This compound crystallizes in the triclinic P-1 space group, with a direct bandgap of 1.67 eV and high chemical stability. Thanks to its congruent melting at 484 °C, 1 cm-sized single crystals were grown from stoichiometric melts by the Bridgman method. The device exhibits a high resistivity of >1010 Ω·cm, and responds to 22.4 keV Ag X-rays and 5.5 MeV a-particles from 241Am at room temperature. Power-dependent photoluminescence spectra at 17 K reveal that the near-band emission bands peaked at 1.61 and 1.53 eV can be ascribed to donor–acceptor pair recombination. The mobility-lifetime product for electrons along the perpendicular direction with respect to the (0k0) cleavage planes was estimated as 2.4 × 10–6 cm2·V–1, based on spectral response against a-particles. Drift mobility measurements based on a time-of-flight technique using a-particle response reveals an electron mobility of 13.2 ± 2.6 cm2·V–1·s–1. E...

The semiconductor TlSn2I5 with a two-dimensional crystal structure and an antiperovskite topology is a promising novel detection material. The compound crystallizes in the I4/mcm space group, has an indirect band gap of 2.14 eV, and melts congruently at 314 °C. Electronic band structure calculations reveal that the most facile electron transport is along the ab layered plane. Compared to CH3NH3PbX3 (X = Br, I), TlSn2I5 features higher long-term stability, higher photon stopping power (average atomic number of 55), higher resistivity (∼1010 Ω·cm), and robust mechanical properties. Centimeter-size TlSn2I5 single crystals grown from the melt by the Bridgman method can be used to fabricate detector devices, which detect Ag Kα X-rays (22 keV), 57Co γ-rays (122 keV), and 241Am α-particles (5.5 MeV). The mobility-lifetime product and mobility for electrons were estimated to be 1.1 × 10–3 cm2·V–1 and 94 ± 16 cm2·V–1·s–1, respectively. Unlike other halide perovskites, TlSn2I5 shows no signs of ionic polarization u...

The high Z chalcohalides Hg3Q2I2 (Q = S, Se, and Te) can be regarded as of antiperovskite structure with ordered vacancies and are demonstrated to be very promising candidates for X- and γ-ray semiconductor detectors. Depending on Q, the ordering of the Hg vacancies in these defect antiperovskites varies and yields a rich family of distinct crystal structures ranging from zero-dimensional to three-dimensional, with a dramatic effect on the properties of each compound. All three Hg3Q2I2 compounds show very suitable optical, electrical, and good mechanical properties required for radiation detection at room temperature. These compounds possess a high density (>7 g/cm3) and wide bandgaps (>1.9 eV), showing great stopping power for hard radiation and high intrinsic electrical resistivity, over 1011 Ω cm. Large single crystals are grown using the vapor transport method, and each material shows excellent photo sensitivity under energetic photons. Detectors made from thin Hg3Q2I2 crystals show reasonable respons...

The optical and electronic properties of Bridgman grown single crystals of the wide-bandgap semiconducting defect halide perovskites A3M2I9 (A = Cs, Rb; M = Bi, Sb) have been investigated. Intense Raman scattering was observed at room temperature for each compound, indicating high polarizability and strong electron–phonon coupling. Both low-temperature and room-temperature photoluminescence (PL) were measured for each compound. Cs3Sb2I9 and Rb3Sb2I9 have broad PL emission bands between 1.75 and 2.05 eV with peaks at 1.96 and 1.92 eV, respectively. The Cs3Bi2I9 PL spectra showed broad emission consisting of several overlapping bands in the 1.65–2.2 eV range. Evidence of strong electron–phonon coupling comparable to that of the alkali halides was observed in phonon broadening of the PL emission. Effective phonon energies obtained from temperature-dependent PL measurements were in agreement with the Raman peak energies. A model is proposed whereby electron–phonon interactions in Cs3Sb2I9, Rb3Sb2I9, and Cs3Bi...

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

We systematically investigate the recombination mechanism of photogenerated charge carriers in bulk $\mathrm{CsPbB}{\mathrm{r}}_{3}$ by means of time-resolved photoluminescence (TR-PL) spectroscopy at low temperature and various laser excitation powers. A dynamic recombination model is proposed to describe the TR-PL that predicts the time-dependent exciton and free-charge populations. It provides a clear representation of competing mono- and bimolecular recombination processes. A decrease in carrier lifetime with increasing laser intensity was observed that was attributed to exciton-exciton scattering. A bimolecular recombination coefficient of $\ensuremath{\sim}{10}^{\ensuremath{-}7}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{3}/\mathrm{s}$ was obtained for exciton recombination. As the concentration of photoexcited carriers increases, stronger exciton-exciton annihilation occurs. The exciton-exciton annihilation rate for $\mathrm{CsPbB}{\mathrm{r}}_{3}$ is $3.63\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{3}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$ at 10-mW laser power. Notably, the exciton-exciton annihilation rate in bulk material is comparable to that obtained for photoexcited $\mathrm{CsPbB}{\mathrm{r}}_{3}$ nanoscale quantum dots.

Highly efficient neutron detectors are critical in many sectors, including national security

The chalcohalide compound Tl6SeI4 is a promising wide-bandgap semiconductor for efficient hard radiation detection at room temperature due to its high density, average atomic number and mobility-lifetime product. However, the nature of its charge transport kinetics, especially the role of defects in recombination, has not been examined in detail. To determine the charge transport kinetics in Tl6SeI4 single crystals, electrical conductivity and photoinduced current transient spectroscopy were measured over the temperature range 105–330 K. These measurements reveal the existence of multiple defect states with energy levels in the range 0.10–0.90 eV, within the bandgap of Tl6SeI4. Large persistent photoconductivity (PPC) is observed at low temperature that shows strong thermal quenching at 160 K. The quenching of PPC is described using a configuration coordinate model involving a deep level donor state, which is tentatively attributed to the presence of iodine vacancies or Si interstitial impurities.

Hg3Se2Br2 is a wide band gap semiconductor (2.22 eV) with high density (7.598 g/cm3) and crystallizes in the monoclinic space group C2/m with cell parameters of a = 17.496 (4) A, b = 9.3991 (19) A, c = 9.776(2) A, β = 90.46(3)°, V = 1607.6(6) A3. It melts congruently at a low temperature, 566 °C, which allows for an easy single crystal growth directly from the stoichiometric melt. Single crystals of Hg3Se2Br2 up to 1 cm long have been grown using the Bridgman method. Hg3Se2Br2 single crystals exhibit a strong photocurrent response when exposed to Ag X-ray and blue diode laser. The resistivity of Hg3Se2Br2 measured by the two probe method is on the order of 1011 Ω·cm, and the mobility-lifetime product (μτ) of the electron and hole carriers estimated from the energy spectroscopy under Ag X-ray radiation are (μτ)e ≈ 1.4 × 10–4 cm2/V and (μτ)h ≈ 9.2 × 10–5 cm2/V. Electronic structure calculations at the density functional theory level indicate a direct band gap and a relatively small effective mass for carrie...

Charge transport in semi-insulating Pb2P2Se6 single crystals was investigated. The dark current was dominated by the ionization of deep-level defects within the gap of the material, with activation energies between 0.6 and 0.8 eV. A model for charge transport was developed where a continuum of these midgap defect levels determined the conductivity of Pb2P2Se6. Current–voltage characteristics in Pb2P2Se6 single crystals showed nonlinear behavior at high voltages. The nonlinear characteristics are attributed to competing Poole–Frenkel emission and phonon-assisted tunneling processes, such that at lower fields the former effect dominates, while at higher electric fields the latter mechanism emerges. Calculated tunneling times in the 250–500 fs range indicate that the deep traps promote weak electron–phonon coupling and that the tunneling involves deep defect levels. Transient multi-terahertz spectroscopy and temperature-dependent photoconductivity measurements reveal signatures of dispersive transport and lo...

The refined synthesis and optimized crystal growth of high quality Pb2P2Se6 single crystals are reported. Improved experimental procedures were implemented to reduce the oxygen contamination and improve the stoichiometry of the single crystal samples. The impact of oxygen contamination and the nature of the stoichiometry deviation in the Pb2P2Se6 system were studied by first-principles density functional theory (DFT) electronic structure calculations as well as experimental methods. The DFT calculations indicated that the presence of interstitial oxygen atoms (Oint) leads to the formation of a deep level located near the middle of the gap, as well as a shallow acceptor level near the valence band maximum. In addition, total energy calculations of the heat of formation of Pb2P2Se6 suggest that the region of thermodynamic stability is sufficiently wide. By refining the preparative procedures, high quality Pb2P2Se6 single crystal samples were reproducibly obtained. These Pb2P2Se6 single crystals exhibited ex...

We assess the mercury chalcohalide compound, β-Hg3S2Cl2, as a potential semiconductor material for X-ray and γ-ray detection. It has a high density (6.80 g/cm3) and wide band gap (2.56 eV) and crystallizes in the cubic Pm3n space group with a three-dimensional structure comprised of [Hg12S8] cubes with Cl atoms located within and between the cubes, featuring a trigonal pyramidal SHg3 as the main building block. First-principle electronic structure calculations at the density functional theory level predict that the compound has closely lying indirect and direct band gaps. We have successfully grown transparent, single crystals of β-Hg3S2Cl2 up to 7 mm diameter and 1 cm long using a new approach by the partial decomposition of the quaternary Hg3Bi2S2Cl8 compound followed by the formation of β-Hg3S2Cl2 and an impermeable top layer, all happening in situ during vertical Bridgman growth. The decomposition process was optimized by varying peak temperatures and temperature gradients using a 2 mm/h translation ...

Previously, the p-n-p bipolar magnetic junction transistor was demonstrated using a magnetic semiconductor InMnAs as the collector. A current gain $\beta _{\text {dc}}$ as high as 20 of the transistor is observed at 300 K. A negative magnetoamplification of −150% is obtained when the applied magnetic field is 8 T. In order to assess the gain mechanism for such transistors, we measured the minority carrier lifetime in a p-n InMnAs/InAs heterojunction diode. A minority carrier lifetime of 320 ns was obtained at room temperature. For the p-n-p MJT, a decrease in the emitter injection efficiency with the magnetic field is observed for the various base currents, which is attributed to the positive magnetoresistance of the p-type InMnAs. The emitter injection efficiency decreases with the magnetic field leading to the observed negative magnetic amplification.

The heavy metal selenophosphate, Pb2P2Se6, is a promising new material for cost-effective X-ray/γ-ray detection. Crystal boules of Pb2P2Se6 up to 25 mm in length and 15 mm in diameter are grown by a vertical Bridgman method. They are cut and processed into size-appropriate wafers for physical, photo-transport property studies, as well as γ-ray detector testing. The material is a semiconductor with an indirect bandgap of 1.88 eV and has electrical resistivity in the range of 1 × 1010 Ω cm. Pb2P2Se6 single crystal samples display a significant photoconductivity response to optical, X-ray, and γ-ray radiation. When tested with a 57Co γ-ray source, Pb2P2Se6 crystals show spectroscopic response and several generated pulse height spectra resolving the 122.1 and 136.5 keV 57Co radiation. The mobility–lifetime product of Pb2P2Se6 is estimated to be ≈3.5 × 10−5 cm2 V−1 for electron carriers. The Pb2P2Se6 compound melts congruently at 812 °C and has robust chemical/physical properties that promise low cost bulk production and detector development.

Cu

The cascading of logic gates is a critical challenge for the development of spintronic logic circuits. Here we propose the first logic family exploiting magnetoresistive bipolar spin-transistors to achieve a complete spintronic logic family in which logic gates can be cascaded. This logic family, emitter-coupled spin-transistor logic (ECSTL), is an extension of emitter-coupled logic (ECL) that leverages the advanced features of spintronic devices. The current through the ECL differential amplifier is routed to create a magnetic field that modulates the magnetoamplification of the spin-transistors. This cascading mechanism supplements the voltage cascading available in conventional ECL, providing additional inputs to each logic stage. Each gate therefore has increased logical functionality, leading to logic minimization and compact circuits. No additional current is required to employ this added spintronic switching, resulting in improved speed, area, and power characteristics. This logic family achieves a power-delay product 10–25 times smaller than conventional ECL, inspiring a pathway for high-performance spintronic computing beyond 10 GHz.

Halide perovskites have emerged as a potential photoconducting material for photovoltaics and hard radiation detection. We investigate the nature of charge transport in the semi-insulating chalcohalide ${\mathrm{Hg}}_{3}{\mathrm{Se}}_{2}{\mathrm{I}}_{2}$ compound using the temperature dependence of dark current, thermally stimulated current (TSC) spectroscopy, and photoconductivity measurements as well as first-principles density functional theory (DFT) calculations. Dark conductivity measurements and TSC spectroscopy indicate the presence of multiple shallow and deep level traps that have relatively low concentrations of the order of ${10}^{13}\ensuremath{-}{10}^{15}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}3}$ and capture cross sections of $\ensuremath{\sim}{10}^{\ensuremath{-}16}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{2}$. A distinct persistent photoconductivity is observed at both low temperatures ($l170\phantom{\rule{0.16em}{0ex}}\mathrm{K}$) and high temperatures ($g230$ K), with major implications for room-temperature compound semiconductor radiation detection. From preliminary DFT calculations, the origin of the traps is attributed to intrinsic vacancy defects (${V}_{\mathrm{Hg}}, {V}_{\mathrm{Se}}$, and ${V}_{\mathrm{I}}$) and interstitials (${\mathrm{Se}}_{\mathrm{int}}$) or other extrinsic impurities. The results point the way for future improvements in crystal quality and detector performance.

The high Z chalcohalides Hg

The chalcohalide compound Tl