高能射线探测用新型三元化合物半导体CsPbBr3单晶的垂直温度梯度凝固法生长及其特性研究

Due to its high effective atomic number, high density, wide band gap, and especially its highly optimized mobility lifetime product (μτ) values for electrons and holes in the crystals, CsPbBr3 has been discovered as a promising alternative ternary compound suitable for high energy radiation detection. Compared with CdZnTe (CZT), a leading nuclear radiation detector material, CsPbBr3 displays lower melt point and simpler crystal growth conditions, and therefore it has the merit to overcome the disadvantages of the crystal growth of CZT such as composition fluctuation, as well as the formation of Te precipitates during crystal growth resulting from high melt point of CZT. In the present proposal, CsPbBr3 crystals will be grown by vertical gradient freezing method under our own intellectual property. And therefore, some problems will be circumvented that usually appear in Bridgman growth method and travelling molten zone method, for example, due to movements of ampoules or heaters, the local composition fluctuation in the solid along with the wide difference in the lattice constants and the thermal expansion coefficients of constituent binary compounds introducing considerable strain. The influence of several key parameters, such as stoichiometric ratio, temperature gradient, and growth rate on the shape of solid-liquid boundary, homogeneity in composition, and crystal perfection of the as-grown crystals will be systematically investigated. To understand the mechanism of the crystal growth and to obtain CsPbBr3 crystals with less defects, good perfection, and good electrical and optical characteristics, the dynamics of crystal growth and thermodynamics of defects will be investigated through various characterization. The aim of this research is to obtain high quality single crystals and room-temperature detectors with good time stability, good energy resolution and high detection efficiency.

溴铅铯（CsPbBr3）具有原子序数高、密度大、禁带宽的特点，尤其是CsPbBr3单晶中电子和空穴具有大的且数量级相同的载流子迁移率寿命积，这些优良物理特性使其成为一种极具潜力的新型三元化合物半导体室温核辐射探测候选材料。与目前广泛采用的三元化合物CdZnTe相比，溴铅铯熔点低易于熔融生长，能克服由于熔点高易出现成分起伏及沉淀相等的缺点。本项目拟采用具有自主知识产权的垂直温度梯度凝固法生长CsPbBr3单晶，解决布里奇曼法或区熔法因需移动安瓿或加热器易产生温度波动导致组分起伏及结晶热应力等缺陷的问题。系统研究化学计量比、温度梯度、生长速率等关键参数对晶体生长的固液界面、晶体组分均匀性及完整性的影响。结合各种表征手段来研究CsPbBr3晶体生长动力学及缺陷热力学，控制晶体热缺陷的产生，从而制备出结晶缺陷少、完整性好、光电特性优良的CsPbBr3单晶及探测器单元。

该项目以制备结晶缺陷少、完整性好、光电特性优良的CsPbBr3单晶及探测器单元为目标。项目提出并采用具有自主知识产权的垂直温度梯度凝固法生长CsPbBr3单晶，其原理是通过控制缓慢降温来精密移动晶体生长界面，从而实现单晶的生长。由于生长过程中生长安瓿和加热器均固定，从而有效减少温度波动所导致组分起伏及结晶热应力等缺陷的问题。.研究内容包括：CsPbBr3多晶粉体的合成及提纯研究；CsPbBr3晶体生长的动力学及热力学研究；晶体中缺陷生成机理研究及晶体生长过程中热条件的优化；元素掺杂及性能调控；晶片的精细加工及探测器元件的制备、性能测试。项目组根据以上研究内容，进行了大量开拓性的实验及创新研究：.在CsPbBr3多晶粉体合成方面，研究了反应因素对所得合成物的物相、微观形貌、元素组成的影响，获得了粉体合成的优化工艺参数；.系统研究了晶体生长的动力学及热力学，探索了CsPbBr3单晶的制备方法及生长工艺参数对晶体质量的影响，成功生长了直径为815mm的高质量CsPbBr3单晶。通过在垂直温度梯度凝固法晶体生长过程中引入对流过程，优化了CsPbBr3 多晶粉体合成及单晶生长的工艺，晶体的性能得到较大提高。采用热激发电流谱（TSC）为表征手段，采用多峰同步分析法对TSC做解谱分析，计算了晶体内本征缺陷的激活能、浓度以及俘获截面等信息，结合第一性原理理论计算确定了缺陷种类，分析了本征缺陷的形成机理、分布规律及离子迁移特性。在此基础上，进行了Pb位和Br位的元素掺杂改性研究，通过Pb位掺杂使单晶电阻率提高一个数量级。单晶电阻率达到1010Ω·cm，载流子迁移率寿命积达到10-4 cm2/V数量级，I-V呈现了良好的线性，晶体红外透过率超过了80%。.研究了晶体的精细加工、电极材料种类以及电极结构对晶片表面质量及晶片性能的影响，获得了符合CsPbBr3探测器元件要求的电极材料，制备了平面型CsPbBr3探测器元件，测试结果表明，其对脉冲激光及各类放射源表现出明显的响应，其中对241Am(5.48MeV)α射线的能量分辨率为为27.8%。.项目执行期间，在CrystEngComm, J. Phys. Chem. C, ACS Appl. Mater. Interfaces, Chem. Eng.J.等权威期刊上发表学术论文9篇，获授权发明专利4项，培养博士生2名，培养硕士生7名。