Lin, Wenwen Kontsevoi, Oleg Y. Liu, Zhifu Das, Sanjib He, Yihui Xu, Yadong Stoumpos, Constantinos C. McCall, Kyle M. J. E. Rettie, Alexander Chung, Duck Young Wessels, Bruce W. Kanatzidis, Mercouri G. An Effective Purification Process for the Nuclear Radiation Detector Tl<sub>6</sub>SeI<sub>4</sub> The semiconductor Tl<sub>6</sub>SeI<sub>4</sub> 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, Tl<sub>2</sub>Se, and TlI precursors for Tl<sub>6</sub>SeI<sub>4</sub>. On the basis of impurity analysis performed by glow discharge mass spectroscopy, the main impurities in Tl<sub>2</sub>Se 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 Tl<sub>2</sub>Se precursor, and removes Sn from TlI. Informed by the analysis results, density functional theory calculations were performed to study the identified impurities and related defects. The calculation results show that Bi and Al act as deep defect levels, which can be detrimental to the detector performance of Tl<sub>6</sub>SeI<sub>4</sub>. If the growth condition of Tl<sub>6</sub>SeI<sub>4</sub> is Tl-rich/Se-poor, impurity of Si can introduce deep donors. However, it becomes electrically benign if growth conditions are Tl-poor/Se-rich, while Sn and Pb impurities are shallow donors. Centimeter-size Tl<sub>6</sub>SeI<sub>4</sub> crystals were grown by the two-zone vertical Bridgman method using the purified precursors. The detector made of Tl<sub>6</sub>SeI<sub>4</sub> crystal maintains the high resistivity on the order of 10<sup>11</sup> Ω·cm after purification, ideal for suppressing leakage current. The detector exhibits both full-energy and Tl escape photopeaks upon 122 keV γ-ray from <sup>57</sup>Co radiation source. The electron mobility-lifetime product μ<sub>e</sub>τ<sub>e</sub> for Tl<sub>6</sub>SeI<sub>4</sub> detector is 8.1 × 10<sup>–5</sup> cm<sup>2</sup>·V<sup>–1</sup>. On the basis of the carrier rise time measured from output pulses induced by 5.5 MeV α-particles from <sup>241</sup>Am, the electron and hole mobilities were estimated to be 112 ± 22 and 81 ± 16 cm<sup>2</sup>·V<sup>–1</sup>·s<sup>–1</sup>, respectively, comparable to those of the leading detector materials HgI<sub>2</sub> and TlBr. These results validate the potential of this compound for hard radiation detection, and the impurity analysis presented here allows future efforts to focus on reducing the concentration of the identified impurities. impurity analysis;122 keV γ- ray;detector materials HgI 2;Tl 2 Se precursor;semiconductor Tl 6 SeI 4;carrier rise time;Tl 2 Se;radiation detection;spectroscopic-grade detector performance;impurity energy levels;Tl 6 SeI 4 crystal;calculation results show;Centimeter-size Tl 6 SeI 4 crystals;5.5 MeV α- particles;Tl 6 SeI 4;Effective Purification Process;Tl 6 SeI 4 detector;57 Co radiation source;glow discharge mass spectroscopy;Nuclear Radiation Detector Tl 6 SeI 4;electron mobility-lifetime product μ e τ e 2018-04-18
    https://acs.figshare.com/articles/journal_contribution/An_Effective_Purification_Process_for_the_Nuclear_Radiation_Detector_Tl_sub_6_sub_SeI_sub_4_sub_/6185357
10.1021/acs.cgd.8b00242.s001