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 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 Tl₆SeI₄. If the growth condition of Tl₆SeI₄ 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 Tl₆SeI₄ crystals were grown by the two-zone vertical Bridgman method using the purified precursors. The detector made of Tl₆SeI₄ crystal maintains the high resistivity on the order of 10¹¹ 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 ⁵⁷Co radiation source. The electron mobility-lifetime product μ_eτ_e for Tl₆SeI₄ detector is 8.1 × 10^–5 cm²·V^–1. On the basis of the carrier rise time measured from output pulses induced by 5.5 MeV α-particles from ²⁴¹Am, the electron and hole mobilities were estimated to be 112 ± 22 and 81 ± 16 cm²·V^–1·s^–1, respectively, comparable to those of the leading detector materials HgI₂ 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.

中文翻译：

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核辐射探测器Tl ₆ SeI ₄的有效纯化工艺

半导体Tl ₆ SeI ₄先前被确定为用于室温核辐射检测的有前途的半导体。由于检测性能和载流子传输很大程度上取决于充当散射中心和载流子捕获的杂质能级的浓度，因此材料纯化是获得光谱级检测器性能的关键先决条件。在此贡献中，我们提出使用弯曲安瓿用于蒸发硒，铊一种高效纯化方法₂ Se和的TlI前体用于TL ₆ SEI ₄。根据辉光放电质谱法进行的杂质分析，Tl _2中的主要杂质硒被确定为Pb，Bi和Al，而在TlI中主要杂质为Al和Sn。弯曲安瓿法成功地从Se前驱体中减少或去除了Cl，Pb和Te杂质，从Tl ₂ Se前驱体中去除了Pb，Bi和Al杂质，并从TlI中去除了Sn。根据分析结果，进行了密度泛函理论计算，以研究识别出的杂质和相关缺陷。计算结果表明，Bi和Al充当了深缺陷水平，这可能对Tl ₆ SeI ₄的探测器性能有害。Tl ₆ SeI ₄的生长条件由于Tl含量高/ Se含量低，Si的杂质会引入深的施主。然而，如果生长条件是贫Tl /富硒的，而Sn和Pb杂质是浅的施主，则它在电学上是良性的。使用纯化的前体，通过两区垂直Bridgman方法生长厘米大小的Tl ₆ SeI ₄晶体。由TL的检测器₆ SEI ₄晶体维持10的数量级上的高电阻率¹¹ Ω·纯化后厘米，理想用于抑制漏电流。该探测器在来自⁵⁷ Co辐射源的122 keVγ射线下展现出全能和T1逸出光峰。电子迁移率寿命产品μ _Ë τ _Ë用于TL ₆SeI ₄检测器为8.1×10 ^–5 cm ² ·V ^–1。根据由²⁴¹ Am产生的5.5 MeVα粒子引起的输出脉冲测量的载流子上升时间，估计电子和空穴迁移率分别为112±22和81±16 cm ² ·V ^–1 ·s ^–1，分别与领先的探测器材料HgI ₂和TlBr相当。这些结果验证了该化合物在硬辐射检测中的潜力，这里提出的杂质分析使将来的工作可以集中在降低已鉴定杂质的浓度上。