Inorganic ternary halide semiconductors for hard radiation detection

#Compound semiconductors are highly interesting for room-temperature radiation detection applications, including homeland security, medical scanning, and dirty bomb scanning. However, only a handful of compounds have been identified as potential hard radiation detector materials, as a set of strict physical property requirements must be simultaneously satisfied to yield X-ray and γ-ray responses. Even the commercialized room temperature detector, Cd0.9Zn0.1Te (CZT), still suffers from growth and fabrication problems related to its intrinsic defects. (See, Szeles, C., IEEE T Nucl Sci 2004, 51 (3), 1242-1249; and Milbrath, B. D., et al., J Mater Res 2008, 23 (10), 2561-2581.) TlBr is another kind of high mobility-lifetime (μτ) (electron: ˜10−3 cm2/V) detection material with a high energy resolution of 2.4% at 662 KeV Gamma-rays. (See, Churilov, A. V., et al., IEEE T Nucl Sci 2009, 56 (4), 1875-1881; Churilov, A. V., et al., J Cryst Growth 2010, 312 (8), 1221-1227; Churilov, A. V., et al., Hard X-Ray, Gamma-Ray, and Neutron Detector Physics X 2008, 7079; and Kim, H., et al., IEEE T Nucl Sci 2009, 56 (3), 819-823.) However, TlBr is subject to polarization-induced instability at room temperature operation. (See, Hitomi, K.; Shoji, T.; Ishii, K., J Cryst Growth 2013, 379, 93-98.)

#Methods and devices for detecting incident particle radiation or electromagnetic radiation, such as incident X-rays, gamma-rays, and/or alpha particle radiation are provided. The devices include photodetectors, including photodiodes.

#One embodiment of a method for the detection of gamma, X-ray radiation, and/or alpha particle radiation, comprises the steps of: exposing a material comprising an inorganic semiconductor having the formula AB2X5, where A represents Tl or In, B represents Sn or Pb, and X represents Br or I, to incident gamma radiation, X-ray radiation, alpha particle radiation, or a combination thereof, wherein the material absorbs the incident radiation and electron-hole pairs are generated in the material; and measuring at least one of the energy or intensity of the absorbed incident radiation by detecting the generated electrons and/or holes.

#Illustrative embodiments of the invention will hereafter be described with reference to the accompanying drawings, wherein like numerals denote like elements.

#FIG. 1A depicts estimated attenuation length as a function of incident photon energy in TlSn2I5, Cd0.9Zn0.1Te and CH3NH3PbI3. FIG. 1B shows estimated attenuation efficiency as a function of thickness in TlSn2I5, Cd0.9Zn0.1Te and CH3NH3PbI3 to 122 keV γ-ray from 57Co FIG. 1C shows the UV-vis-Near IR optical absorption spectrum of TlSn2I5.

#FIG. 2A shows a view of the unit cell along the ab crystallographic plane. FIG. 2B depicts the building block of the {Sn2I5}− layers indicating the Sn—I bond lengths. FIG. 2C shows an extended view of the {Sn2I5}− layers emphasizing on the connectivity of the planar {ISn4}7+ units. The arrows indicate the most likely location of the lone pair. FIG. 2D shows the coordination of the polyhedral of Tl(1). FIG. 2E shows the coordination of the polyhedral of Sn(1). FIG. 2F shows the coordination of the polyhedral of I(1). FIG. 2G shows a comparison between the anti-perovskite topology of TlSn2I5 and FIG. 2H. FIG. 2H shows the perovskite topology of the hybrid inorganic-organic perovskite CH3NH3PbI3. The lattice of the TlSn2I5 is significantly more distorted than that of CH3NH3PbI3.

#Methods and devices for detecting incident radiation, such as incident X-rays or gamma-rays, and/or alpha particles, are provided. The methods and devices use high-purity, high-quality single crystals of inorganic semiconductor compounds having the formula AB2X5, where A represents Tl or In, B represents Sn or Pb, and X represents Br or I, as photoelectric materials to convert the incident radiation into an electric signal. The devices include optoelectronic and photonic devices, such as photodetectors and photodiodes. The formula AB2X5 covers solid solutions that include both A elements, both B elements, and/or both X elements, as well as the end members of the formula. For the solid solutions, the formula can be written as (Tl, In)(Sn, Pb)2(I, Br)5. Thus, the formula covers the compounds TlSn2I5, InSn2I5, TlSn2Br5, TlPb2I5, TlPb2Br5, InSn2Br5, InPb2I5, and InPb2Br5, as well as the solid solutions Tl1-xInxSn2-yPbyI5-zBrz, In1-xTlxSn2-yPbyI5-zBrz, Tl1-xInxSn2-yPbyBr5-zIz, Tl1-xInxPb2-ySnyI5-zBrz, Tl1-xInxPb2-ySnyBr5-zIz, In1-xTlxSn2-yPbyBr5-zIz, In1-xTlxPb2-ySnyI5-zBrz, and In1-xTlxPb2-ySnyBr5-zIz, where 0≤x≤0.5; 0≤y≤1; and 0≤x≤0.2.5 and at least one of x, y, and z is >0.

#The compounds desirably have a band gap of at least 1.5 eV. This includes compounds having a band gap of at least 1.8 eV, and further includes compounds having a bandgap of at least 2.0 eV. For example, in some embodiments the compounds have a band gap in the range from about 1.6 eV to about 3 eV. Methods of determining the bandgap of a material are described in the Example.

#Detector-grade materials comprising the semiconductor compounds can be grown with high chemical purity and high crystal quality. The compounds are stable in air. Methods of making detector-grade materials using a Bridgman method are demonstrated in the Examples below, using TlSn2I5 as an illustration. The methods described in the Examples can be adapted to make detector-grade materials comprising the other inorganic semiconductor compounds having the formula AB2X5, including InSn2I5, TlSn2Br5, InSn2Br5, TlPb2I5, TlPb2Br5. Moreover, crystals can be grown using other methods, including various flux methods, solution methods, and vapor transport methods. These include the Czochralski method, top seeded flux methods, optical floating zone methods, temperature cooling solution methods, solvent evaporation solution methods, physical or chemical vapor transport methods, and the like.