The synthesis, crystal growth, and structural and optoelectronic characterization has been carried out for the perovskite compound CsPbBr 3 . This compound is a direct band gap semiconductor which meets most of the requirements for successful detection of X-and γ-ray radiation, such as high attenuation, high resistivity, and significant photoconductivity response, with detector resolution comparable to that of commercial, state-of-the-art materials. A structural phase transition which occurs during crystal growth at higher temperature does not seem to affect its crystal quality. Its μτ product for both hole and electron carriers is approximately equal. The μτ product for electrons is comparable to cadmium zinc telluride (CZT) and that for holes is 10 times higher than CZT.

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.

Semiconductor materials for efficient hard radiation detection are identified by combining a powerful chemical concept called dimensional reduction and precise theoretical electronic structure calculations. After more than 50 years of research and development in the field, this constitutes a significant step forward in the search for new detector materials.

8The ternary compounds CsPbX3 (X= Br or Cl) have perovskite structures that are being 9 considered for optical and electronic applications such as lasing and gamma ray detection. 10Above bandgap excitonic photoluminescence (PL) band is seen in both CsPbX3 compounds. An

We report that the chalcohalide compound Tl(6)SeI(4) is a promising material for efficient X-ray and γ-ray detection. This material has a higher figure of merit than the current state-of-the-art material for room-temperature operation, Cd(0.9)Zn(0.1)Te (CZT). We have synthesized high-quality single-crystalline wafers of Tl(6)SeI(4) with detector-grade resistivities and good carrier transport of both electrons and holes. We demonstrate that pulse height spectra recorded using Co-57 radiation show an energy resolution matching that of a commercial CZT detector material.

Flame-melting rapid-cooling reactions were used to synthesize a number of pure phases of the Cs2MIIMIV 3Q8 family (MII = Mg, Zn, Cd, Hg; MIV = Ge, Sn; Q = S, Se, Te) whereas the more toxic members were synthesized using a traditional tube furnace synthesis. All Cs2MIIMIV 3Q8 compounds presented here crystallize in the noncentrosymmetric space group P212121, except for Cs2ZnGe3S8, which crystallizes in the centrosymmetric space group P21/n. The structures contain chains of corner-sharing MIIQ4 and MIVQ4 tetrahedra linked by edge-sharing MIV 2Q6 dimers to give a two-dimensional structure. All phases are structurally similar to the AMIIIMIVQ4 (A = alkali metal, Tl; MIII = Al, Ga, In; MIV = Si, Ge, Sn; Q = S, Se) phases; however, the members of this family have completely ordered MII and MIV sites as opposed to the occupational disorder of MIII and MIV over all tetrahedral sites present in AMIIIMIVQ4. The structural trends of the Cs2MIIMIV 3Q8 family are discussed, along with a systematic study of their optical properties. Density functional theory (DFT) electronic structure calculations were performed using the projector augmented wave method to further investigate the trends in the band gaps of the Cs2MIIMIV 3Se8 (MII = Mg, Zn; MIV = Ge, Sn) compounds. The experimental diffuse reflectance UV–vis spectroscopy results show that the Mg compounds have smaller band gaps than those containing Zn for both the Ge and the Sn families whereas the DFT calculations show the opposite trend. Cs2HgSn3Se8 was studied as a representative example of this family using differential thermal analysis and melts congruently at 595 °C. Crystal growth of this compound using the Bridgman method resulted in a polycrystalline ingot from which plate crystals ∼2 mm × 3 mm could be cleaved. The band gap of the compounds varies from a narrow 1.07 eV for Cs2ZnGe3Te8 to a wide 3.3 eV for Cs2ZnGe3S8 and Cs2CdGe3S8 making this family a potentially useful source of materials for a variety of electronic applications. Cs2HgSn3Se8 crystals exhibit photoconductivity response where the photoexcited electron and hole show mobility-lifetime products on the order of 3.69 × 10–5 cm2/V and (μτ)h∥ = 7.78 × 10–5 cm2/V, respectively.

The wide-band-gap semiconductor thallium gallium selenide (TlGaSe2) is promising for X-ray and γ-ray detection. In this study, the synthesis and crystal growth of semiconducting TlGaSe2 was accomplished using a stoichiometric combination of TlSe, Ga, and Se and a modified Bridgman method. These large detector-grade crystals can be synthesized and cut to dimensions appropriate for a detector. The crystals have mirror-like cleaved surfaces and are transparent red, in agreement with a band gap of 1.95 eV observed in absorption measurements. Single-crystal X-ray diffraction refinements confirm that TlGaSe2 crystallizes in the monoclinic C2/c space group with a layered crystal structure consisting of planes of GaSe4 corner-sharing tetrahedra connected by weak Tl–Se bonds. Electronic band structure calculations made using the full-potential linearized augmented plane wave method with the screened-exchange local density approximation, including spin orbit coupling, indicate the unusual characteristic of the hole effective mass being lower than that of the electrons. Photoconductivity measurements on the grown TlGaSe2 crystals show mobility–lifetime (μτ) products of electrons and holes approaching the values of the state-of-the-art commercial material Cd0.9Zn0.1Te. The promising properties of this material system are confirmed by the ability of a TlGaSe2-based detector to show good signal response to X-rays and resolve Ag K radiation energetically.

We report on the magnetotransport properties of epitaxial thin films of In 1−x Mn x Sb dilute magnetic semiconductor grown by metal-organic vapor-phase epitaxy. At temperatures below 10 K, a negative magnetoresistance dominates the magnetotransport that is attributed to spin-dependent scattering by localized magnetic moments. Above 10 K, the magnetoresistance is positive and is well described by a two-band model consisting of spin-split hybridized p-d subbands with different conductivities. Hall effect measurements show an anomalous behavior that persists up to room temperature, providing an indication of ferromagnetic order. In addition, magnetization measurements reveal distinct hysteresis loops at room temperature which confirms the ferromagnetism of the films.