【作者】 李强；

【导师】 介万奇；

【作者基本信息】 西北工业大学 ， 材料加工工程， 2006， 博士

【摘要】 Cd_1-xZn_xTe（CZT）晶体具有优异的光电性能，是迄今制造室温X射线及γ射线探测器最为理想的半导体材料。尽管对CZT的研究由来已久，但在CZT晶体的表面处理、金属与CdZnTe晶体接触及In掺杂特性研究上尚存在诸多难题，本文对之进行了探索。CZT晶体钝化工艺主要是为了减小晶体表面富Te层的电导，减小表面漏电流，提高CZT探测器的性能。钝化可以是物理或者化学过程，可以给晶体表面提供与外界成化学和电学惰性的绝缘层。处理的方法主要有：（1）在晶体表面沉积绝缘物质（ZnS和SiO₂）；（2）在晶体表面制备本征薄膜层（氧化物、硫化物以及氟化物）；（3）原位生长宽禁带的Ⅱ-Ⅵ化合物异质结。用NH₄／H₂O₂对CZT晶体钝化，表面主要生成了TeO₂。钝化后（[Cd]+[Zn]）／[Te]原子比接近于1，表明钝化后表面更接近CZT的标准化学计量配比，而且改善了晶体近表面区的晶体结构，同时钝化后明显新增了O的含量。光致发光（PL）特性研究结果表明，钝化不仅减小了晶体表面的陷阱态密度，而且减小了与Cd空位复合的深能级杂质浓度。用Agilent 4339B高阻仪进行了CZT晶片I-V特性测试以及Agilent 4294A高精度阻抗分析仪进行了CZT晶片的C-V特性研究，结果表明钝化均能不同程度提高Au／CZT接触的势垒高度，减小漏电流。主要原因是在Au／CZT表面钝化生成的TeO₂氧化层增加了接触势垒高度，并减小了电荷因隧道效应而穿过氧化层TeO₂的几率。采用同步辐射X射线光电子能谱分析结果计算了Au／CZT接触的势垒高度，腐蚀和钝化处理后Au／CZT接触的Schottky势垒高度分别是0.88±0.02 eV和1.17±0.02 eV。根据I-V测试结果计算出钝化前后的Schottky势垒高度分别是0.85±0.02 eV和0.96±0.02eV。用C-V方法测试出钝化前后Schottky势垒高度分别是1.39±0.02 eV和1.51±0.02 eV。研究了溅射沉积不同金属与CZT晶体接触的电学性能。I-V测试和扫描电子显微镜（SEM）分析结果表明，Au是与CZT晶体最适合的电学接触材料，可以与高阻CZT晶体形成近乎理想的欧姆接触，而与低阻CZT晶体形成了0.95±0.02 eV的Schottky接触势垒。X射线光电子能谱分析，形成欧姆接触的原因主要是由于Au原子在退火的时候扩散进入高阻CZT晶体中，同时Cd与Te原子扩散进入Au接触层。扩散的Au未与CZT晶体中的任何元素形成化合物，而是形成了重掺杂层以及欧姆接触。光致发光谱分析结果表明，互扩散的施主[Au]³⁺与受主[V_Cd]^2-在溅射过程中进行了复合。同时，Au接触的施主复合体峰(D_complex)强度明显强于无Au接触的CZT晶体复合体峰的强度，施主[Au]³⁺和[Au³⁺·V_Cd^2-]⁺可以与[V_Cd]^2-空位进行复合并产生不同的缺陷复合体。对In掺杂CZT晶体特性通过10 K下的光致发光能谱（PL）和室温下的红外透过率能谱来进行了分析研究。分析结果表明，In原子代替Cd空位[V_Cd]^2-，形成了电离施主[In_Cd]⁺，以及单负性缺陷复合体A-中心[In_Cd⁺·V_Cd^2-]^-和中性缺陷复合体[2In_Cd⁺·V_Cd^2-]⁰和[In_Cd⁺·(In_Cd⁺·V_Cd^2-)^-]⁰。根据高阻In掺杂CZT晶体位于1.6014eV的浅能级施主—受主对峰（DAP）位置，得出位于E_DS=13.3 meV的浅施主能级[In_Cd]⁺和位于E_AS=29.5 meV的浅受主能级[V_Cd-In_Cd]^-。同时根据CdZnTe：In晶体的10 K～60 K的PL温度依存关系，得出电离能分别为65.5 meV的深施主能级[Te_Cd]⁴⁺和87.4 meV的深受主能级[V_Cd]^2-。用傅立叶变换红外能谱仪（FT-IR）测试了掺杂CZT与未掺杂CZT晶体的红外透过率。未掺杂的CZT晶体红外透过率为58％。掺杂In分别为10ppm、15ppm和30ppm时，CZT晶体红外透过率平均值分别为37％、21％和4％。CZT晶体的红外吸收机理可以归结于晶体的晶格吸收与自由载流子吸收。更多还原

【Abstract】 Cd_1-xZn_xTe（CZT） possesses excellent optoelectronic properties and is thereforethe most promising material for room temperature X-ray and gamma-ray detectors.Although the study on CZT has lasted for a long period, there still exist someproblems in the surface treatment of CdZnTe crystal, metal-CdZnTe contact propertiesand indium doping behaviors of CZT, which are investigated in this work.The process of passivation had been typically required to reduce the conductivityof Te-riched surface layer of CZT crystal and decrease the surface leakage current.Passivation is a chemical and /or physical process that renders the surface of amaterial chemically and/or electrically inert to its environment. Typical surfacepassivation technologies include the deposition of dielectric materials （ZnS, SiO₂）,coating the surface with the native inert films, such as oxides, sulphides and fluorides,and in-situ growth of heterostuctures of wide band gapⅡ-Ⅵcompound. The oxideformed on CZT surface through the passivation treatment with NH₄/H₂O₂ agent isTeO₂, which offers an inert surface. After passivation,（[Cd]+[Zn]）/[Te] ratioapproches to 1, which means the stoichiometry composition is restored and thecrystallinity, is improved near the surface. Photoluminescence（PL） spectra confirmedthat the passivation treatment minimized the surface trap state density and decreasedthe deep level defects related to recombination of Cd vacancies. I-V and C-Vcharacteristics of Au/CZT contacts with different surface treatments on CZT wafer’ssurface were measured with Agilent 4339B High Resistance Meter and Agilent 4294APrecision Impedance Analyzer, respectively. It was shown that the passivationtreatment increased the barrier height of the Au/CZT contact and decreased theleakage current. The main reason is that higher barrier of Au/CZT contacts decreasesthe possibility for electrons to pass through the sandwich TeO₂ layer between CZTand Au contact.The interface barrier between Au/CZT contact was studied by synchrotron-basedX-ray photoemission spectroscopy（SXPS）. The interface barrier was determined to be 0.88±0.02eV for Au/CZT without passivation and 1.17±0.02eV for Au/CZT afterpassivation, respectively. Schottky barrier height was determined to be 0.85±0.02eVwithout passivation and 0.96±0.02eV after passivation by current-voltagemeasurement. However, 1.39±0.02eV without passivation and 1.51±0.02eV withpassivation were obtained according to the capacitance-voltage measurement.The electrical properties of different metal-CZT contacts produced by sputteringdeposition method are investigated. The results of current-voltage and SEM analysesshow that Au is the most suitable electrical contact materials, which forms a nearlyideal Ohmicity contact with high resistivity CZT crystals and 0.95±0.02 eV barrierwith low resistivity ones. XPS analyses show that Au atoms diffuse into highresistivity CZT crystal during annealing, meanwhile Cd and Te atoms diffuse into Aucontact. Diffused Au did not form any compound with any element in CZT crystal.Thus, the heavy doped layer is formed and Ohmic contact is obtained. PL spectraanalysis results of CZT crystals with deposited Au layer show that the inter-diffuseddonors[Au]³⁺ recombine with acceptors [V_Cd]^2-during sputtering process.Meanwhile, the intensity of (D_complex) peak of CZT surface with Au contact increasessharply in comparison with un-deposited CZT crystal. Meanwhile, donor [Au]³⁺ and[Au³⁺·V_Cd^2-]⁺ compensates Cd vacancy [V_Cd]^2- and produce different defectcomplexes.The indium doped CZT crystal was characterized by PL spectra at 10 K and IRtransmission spectra at room temperature. The results showed that indium atomssubstituted Cd vacancy and produced ionized donor [In_Cd]⁺, i. e. indium dopingelement recombined with [V_Cd]^2- and formed the single negative defect complexA-center[In_Cd⁺·V_Cd^2-]^- and the neutral ones [2In_Cd⁺·V_Cd^2-]⁰ and [In_Cd⁺·(In_Cd⁺·V_Cd^2-)^-]⁰.According to shallow level DAP peak at 1.6014 eV in high resistivity In-doped CZT,shallow donors level [In_Cd]⁺ and shallow acceptors level [V_Cd-In_Cd]^- are EDS=13.3meV, E_AS=29.5 meV, respectively. According to the measurements of temperaturedependence of CZT:In crystal from 10 K to 60 K, the ionization energies of deepdonors level [Te_Cd]⁴⁺ and deep acceptor level [V_Cd]^2- are determined to be 65.5 meV and 87.4 meV, respectively.IR transmission spectrum of the CZT crystal without indium dopant is about58％. The IR transmission spectra of CZT:In crystal with the concentrations of indiumdopant 10ppm, 15ppm and 30ppm are about 37％, 21％and 4％in the range from4000cm^-1 to 500cm^-1, respectively. The reason for IR absorption of CZT crystal maybe attributed to the lattice absorption and the free-carrier absorption.更多还原