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 purification prior to crystal growth is crucial. In this contribution, we report effective purification protocols, impurity analysis, followed by synthesis and crystal growth, charge transport, and detector performance of large-sized Tl6SI4 crystals. Purification methods of evaporation and zone refining were developed, and their high effectiveness was confirmed by impurity analysis via glow discharge mass spectrometry. Centimeter-sized single crystals were grown using the Bridgman method. The improved properties after material purification were confirmed by photoluminescence measurements. The energy of the valence band maximum of a Tl6SI4, measured with photoemission spectroscopy in air (PESA), is ∼5.34 ± 0.05 eV. Detector devices fabricated from the single crystal exhibit a high resistivity of 5 × 1012 ω·cm. The detector shows promising photoresponse under 22.4 keV Ag Kα X-rays and 122 keV γ-rays from 57Co. Spectroscopic energy resolution was achieved for 5.5 MeV α-particles from a 241Am radiation source with a full width at half-maximum of 27% at an electric field intensity of 2500 V·cm-1. On the basis of its spectral response to 57Co γ-rays, the electron mobility-lifetime product μeτe was estimated as 1.4 × 10-5 cm2·V-1.
Bibliographical noteFunding Information:
This work was supported by the Department of Homeland Security ARI program with grant 2014-DN-077-ARI086-01. This work made use of the EPIC facility of the NUANCE Center and IMSERC at Northwestern University, which has received support from the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF NNCI-1542205). Purification by the zone refining method and crystal growth were performed at Argonne National Laboratory supported by the Department of Energy, National Nuclear Security Administration, Office of Defense Nuclear Nonproliferation Research and Development under contract No DE-AC02-06CH11357. C.C.S. and K.M.M. were partially supported by National Science Foundation Grant DMR-1708254. We thank Paul Bennett, Alexei Churilov, Alireza Kargar, Leonard Cirignano, and Handong Sun from Radiation Monitoring Devices for fruitful suggestions.
© 2019 American Chemical Society.