CdZnTe晶体生长中掺 In量对晶体电学性能的影响

通过在富Te环境下生长In掺杂CdZnTe晶体,实验研究了不同掺In量对晶体电学性能的影响,重点讨论了不同掺In量与晶体电阻率、载流子浓度及迁移率之间的关系.并对CdZnTe晶体中In掺杂的补偿机理进行了分析探讨.结果表明,当In掺杂量为5×1017cm-3时,得到了电阻率达1.89×1010Ω·cm的高阻CdZnTe晶体.     

高阻In掺杂CdZnTe晶体缺陷能级的研究

利用低压垂直布里奇曼法制备了不同In掺杂量的CdZnTe晶体样品, 采用低温光致发光谱(PL)、深能级瞬态谱(DLTS)以及霍尔测试等手段研究了In掺杂CdZnTe晶体中的主要缺陷能级及其可能存在的补偿机制. PL测试结果表明, 在In掺杂样品中, In原子占据了晶体中原有的Cd空位, 形成了能级位于E_c-18meV的替代浅施主缺陷[In_Cd^+], 同时 [In_Cd⁺]还与[V_Cd^2-]形成了能级位于E_v+163meV的复合缺陷[(In_Cd⁺-V_Cd^2-)^-]. DLTS分析表明, 掺In样品中存在导带以下约0.74eV的深能级电子陷阱能级, 这个能级很可能是Te反位[Te_Cd]施主缺陷造成的. 由此, In掺杂CdZnTe晶体的电学性质是In掺杂施主缺陷、Te反位深能级施主缺陷与本征受主缺陷Cd空位和残余受主杂质缺陷补偿的综合结果.     

近空间升华法制备CdZnTe外延厚膜及其性能研究

采用近空间升华法在GaAs(100)衬底上外延生长CdZnTe单晶厚膜,用化学腐蚀的方法去除掉GaAs(100)衬底后,对CdZnTe外延膜上、下表面的形貌、成分、结构以及电学性能进行了表征分析。SEM和EDS的结果表明,CdZnTe外延膜表面平滑致密且膜中成分分布较均匀;红外透过成像分析的结果表明,CdZnTe厚膜中无明显的Te夹杂相;X射线摇摆曲线、PL谱的结果表明,随着薄膜厚度的增加,CdZnTe外延膜中的晶体缺陷减少,应变弛豫,结晶质量提高,通过增加膜厚可以获得高质量的CdZnTe外延膜;电学测试表明,CZT外延膜的电阻率在1010Ω·cm数量级,且具有较好的光电响应特性,可用于高能射线探测。     

温度梯度溶液生长法制备x=0.2的Cd1-xZnxTe晶体及性能研究

利用温度梯度溶液生长法(TGSG)在较低生长温度下制备了掺Al和掺In的x=0.2的Cd1-xZnxTe晶体,晶体起始生长温度约为1223K,温度梯度为20～30K/cm,坩埚的下降速度为1mm/h。采用红外显微镜、傅里叶红外光谱仪、扫描电镜能谱仪(SEM/EDS)和I-V测试分别研究了晶体中的Te夹杂相、红外透过率、Zn组分分布和电阻率。结果显示CdZnTe晶锭初始生长区、稳定生长区的Te夹杂相密度分别为8.3×103、9.2×103/cm-2,比垂直布里奇曼法生长的晶体低约1个数量级,红外透过率分别为61%、60%。Al掺杂CdZnTe晶体的电阻率为1.05×106Ω.cm,而In掺杂CdZnTe晶体的电阻率为7.85×109Ω.cm。晶锭初始生长区和稳定生长区的Zn组分径向分布均匀。     

CdZnTe晶体沉淀物特性的研究

通过观察和分析CdZnTe晶体中富Te和富Cd沉淀物在红外透射显微镜下的形貌特征,从实验上证实在正四面体或八面体结构的富Te沉淀物内部存在空洞。分析表明,和正四面体沉淀物相邻的CdZnTe材料表面为(111)B面,构成八面体的另外4个面为(111)A面,(111)B面为表面能密度最低的慢生长面。结合化学腐蚀的观察结果发现,红外透射显微镜下呈星状结构的富Cd沉淀物由中心区沉淀物和外围高密度位错集聚区构成,中心区沉淀物大多为不规则形状。通过分析〈111〉和〈110〉晶向上富Cd沉淀物的形貌特征,确定了星状结构的延伸方向为〈211〉晶向,高密度位错集聚区的大小比沉淀物尺寸大出数倍。对沉淀物与周边材料的作用机理也进行了分析。     

三温区坩埚下降法生长Cd_(1-x)Zn_xTe单晶体

CdZnTe晶体是一种性能优畀的室温核辐射探测器材料.在熔体法生长CdZnTe晶体的过程中,生长炉的内部温场分布对获得的晶体结构和性能有很大影响.根据CdZnTe晶体的生长习性,设计了三温区单晶炉,用坩埚下降法生长出CdZnTe单晶体.通过X射线衍射、红外透过率、I-V测试等分析研究,得到了红外透过率约为61%,腐蚀蚀坑密度(EPD)为104 cm-2,电阻率为109～1010 Ω·cm的Cd0.9 Zn0.1 Te单晶体.表明三温区坩埚下降法生长的单晶体结晶质量好、成分分布均匀、EPD低、红外透过性能好且电阻率高.     

铝诱导对磁控溅射制备CdZnTe薄膜结晶的影响

选用Cd0.9Zn0.1Te晶体和纯度为99.999%的铝为靶材,结合Al诱导晶化技术,采用磁控溅射法在普通玻璃衬底上制备了CdZnTe薄膜。研究了铝诱导CdZnTe薄膜的结构和形核机理。研究表明,铝诱导的CZT薄膜为闪锌矿结构,且为(111)晶面的取向生长;在薄膜生长过程中,覆盖在CdZnTe表面的铝首先与ZnTe结合,形成了ZnAl2Te4相,并以此为核心,诱导CdZnTe异质形核结晶,重新形成了小晶粒团簇的较致密颗粒状薄膜,提高了薄膜(111)面的优势取向结晶,提高了CdZnTe薄膜的结晶质量。讨论了薄膜的光学性能。     

CdZnTe像素探测器表面的氧离子刻蚀工艺

本文报道了CdZnTe像素探测器电极的氧离子刻蚀工艺。通过I-V特性、PL谱以及XPS等实验结果分析了氧离子刻蚀对CdZnTe表面成分、缺陷以及漏电流的影响。研究结果表明,表面氧离子刻蚀在CdZnTe晶体表面形成了致密氧化层。刻蚀功率过大时,刻蚀过程中氧离子轰击会对CdZnTe晶体表面造成损伤,使表面漏电流急剧增大。减小刻蚀功率,延长刻蚀时间,可以增强刻蚀过程中的化学作用,减少CdZnTe晶片的表面氧化与损伤,使表面漏电流降低。     

溅射功率对CdZnTe薄膜成分和结构的影响

采用Cd0.9Zn0.1Te晶体作为溅射靶在玻璃衬底上利用磁控溅射法制备出CdZnTe薄膜,研究了溅射功率对CdZnTe薄膜的成分、结构特性的影响。制备的CdZnTe薄膜是具有闪锌矿结构的多晶薄膜,沿（111）择优取向。随着溅射功率的增大,薄膜沉积速率增大,薄膜结晶质量提高。采用晶体靶Cd0.9Zn0.1Te溅射CdZnTe薄膜时,无论是在何种功率下CdZnTe薄膜中的Cd原子成分均高于Te原子成分,Cd原子表现为择优溅射原子。     

坩埚中自由空间量对Bridgman法生长的CdZnTe晶体缺陷的影响

采用Bridgman法生长CdZnTe晶体.分别采用红外透过显微镜和正电子湮灭寿命谱仪研究了CdZnTe晶体中的Te夹杂相、Cd空位等缺陷与坩埚中的自由空间量大小的关系. 结果表明: 随着坩埚自由空间量的减小, 晶体中Te夹杂相密度从6.67×10⁴/cm²降低到2.36×10³/cm², 且Te夹杂相尺寸减小; 晶体的正电子平均寿命值随着坩埚自由空间量的减小从325.4 ps降低到323.4 ps, 表明晶体的Cd空位浓度及微结构缺陷减少; 晶体的红外透过率和电阻率则随着坩埚自由空间量的减小大幅提高, 进一步表明坩埚中自由空间量的减小能够有效地降低晶体中的缺陷浓度.     

Investigation of Te inclusions in CdZnTe crystalline material using Raman spectroscopy and IR techniques

IR images reveal that Te inclusions exist in CdZnTe crystal in the form of square, hexagonal and triangular shapes. The density of Te inclusions for sizes above 5 μm sharply varied from 2.27 × 10³ cm⁻² to 4.52 × 10⁵ cm⁻² with a consequent reduction in IR transmittance from ∼60.5% to ∼55% when the Te-rich volume increased to 83 ppma. Raman spectra suggested that the origin of a new peak at 262.5 cm⁻¹ could be a secondary phonon with A1 symmetry and E symmetry of Te inclusions. The peaks of triangular Te inclusions in Te-rich CdZnTe wafers were shifted to high energy, suggesting that compressive stress existed around the Te inclusions.     

Type and formation mechanism of thermal etch pit on annealed (111) CdZnTe surface

Type and formation mechanism of thermal etch pits on annealed (111) CdZnTe surface were studied with scanning electron microscopy and atomic force microscopy. Four kinds of thermal etch pits on CdZnTe (111) Te face and two kinds of thermal etch pits on (111) Cd face were identified. The density of thermal etch pits on (111) Te face was estimated; it was two orders of magnitude higher than that of (111) Cd face. A formation mechanism of the thermal etch pits on (111) CdZnTe during the annealing process is proposed. The different behaviors of the thermal etch pits on the two faces of (111) CdZnTe are discussed.     

室温辐射探测器用碲锌镉晶体的退火改性研究进展

碲锌镉(CdZnTe)作为一种重要的Ⅱ-Ⅵ族化合物半导体,因其具备优异的光电性能,成为制备室温辐射探测器的理想材料。但生长态的CdZnTe晶体中不可避免地会引入Cd空位、沉淀/夹杂相、杂质和位错等缺陷,严重影响了所制备器件的质量和光电性能。因此,需对生长态晶体进行退火改性处理以提高晶体的质量。本文分析了CdZnTe材料中存在的主要缺陷,重点综述了退火改性工艺如退火温度、退火时间、退火气氛以及退火方式对CdZnTe晶体质量及探测器性能的影响。     

The growth and the interfacial layer of CdZnTe nano-crystalline films by vacuum evaporation

Nano-crystalline CdZnTe films were fabricated by thermal vacuum evaporation. The structure and surface morphology of the CdZnTe films were determined by XRD and SEM. The CdZnTe films were poly-crystalline with preferential (111) orientation. The CdZnTe films exhibited a typical particle size of 15 nm and a blue shift in the absorption with an effective band gap of 2.26 eV. An amorphous Te interfacial layer with thickness of 3 nm was observed with high resolution transmission electron microscopy, which should be formed at the initial stage of the growth. This is because the equilibrium vapor pressure of Cd is largely higher than that of Te₂ at the growth temperature, and the desorption rate of Cd atoms is much higher than that of and Te₂ molecules. The amorphous interfacial layer should be favorable for the formation of nano-crystalline CdZnTe film.     

The growth and the interfacial layer of CdZnTe nano-crystalline films by vacuum evaporation

Nano-crystalline CdZnTe films were fabricated by thermal vacuum evaporation. The structure and surface morphology of the CdZnTe films were determined by XRD and SEM. The CdZnTe films were poly-crystalline with preferential (111) orientation. The CdZnTe films exhibited a typical particle size of 15 nm and a blue shift in the absorption with an effective band gap of 2.26 eV. An amorphous Te interfacial layer with thickness of 3 nm was observed with high resolution transmission electron microscopy, which should be formed at the initial stage of the growth. This is because the equilibrium vapor pressure of Cd is largely higher than that of Te₂ at the growth temperature, and the desorption rate of Cd atoms is much higher than that of and Te₂ molecules. The amorphous interfacial layer should be favorable for the formation of nano-crystalline CdZnTe film.     

Preparation of polycrystalline CdZnTe thick film Schottky diode for ultraviolet detectors

High resistivity (3 × 10⁹ Ω cm) polycrystalline CdZnTe thick films with thickness of 25 μm–150 μm were grown on SnO₂: F-coated glass substrates by close-spaced sublimation method. The properties of polycrystalline CdZnTe films were studied by XRD, SEM and EDS, respectively. A CdZnTe film Schottky diode detector was also fabricated and investigated using current–voltage and capacitance–voltage methods. The photo-current density of the device was about 1508.69 nA/mm² under light illumination (λ = 260 nm), at an applied negative voltage of 15 V. The results showed that polycrystalline CdZnTe thick film was suitable for application in ultraviolet detectors.     

Chalcogenide phase-change memory nanotubes for lower writing current operation

We report the synthesis and characterization of Sb-doped Te-rich nanotubes, and study their memory switching properties under the application of electrical pulses. Te-rich nanotubes display significantly low writing currents due to their small cross-sectional areas, which is desirable for power-efficient memory operation. The nanotube devices show limited resistance ratio and cyclic switching capability owing to the intrinsic properties of Te. The observed memory switching properties of this new class of nanostructured memory elements are discussed in terms of fundamental materials properties and extrinsic geometrical effects.     

Investigation of CdTex and Cd1-xZnxTe Schottky Barrier Diode Structure Based γ-Ray Detectors

Cadmium Telluride (CdTe) and Cadmium Zinc Telluride (CdZnTe) based detectors have been developed for hard X-ray and γ -ray detection. These semiconducting materials have high resistivity because of the wide bandgap and also have high photon absorption efficiency because of the large atomic number (Z_Cd = 48, Z_Te = 52). CdTe and CdZnTe substrates (7 mm × 9 mm × 0.5 mm) with different stoichiometry were taken for the fabrication of γ-ray detectors. The substrate was prepared by polishing the bulk crystals grown by the rotational Bridgman method. Crystals with maximum electrical resistivity were grown in this way. For fabrication of Schottky barrier diode structures, the Schottky contacts were made by electroless deposition for gold (Au) and thermal evaporation for Indium (In). The Au/CdTe/In and Au/CdZnTe/In Schottky barrier diodes were linked to the charge sensitive preamplifier by gold wires. Then, I-V measurement and detector efficiency like charge collection performance with energy resolutions were analyzed at room temperature by using ⁵⁷Co and ¹³⁷Cs gamma sources. The good energy resolutions of ⁵⁷Co (122 KeV) and ¹³⁷Cs (662 KeV) sources are obtained for both CdTe and CdZnTe diode detectors.     

真空蒸发沉积CdZnTe纳米薄膜的结构与形貌

采用真空蒸发沉积技术在ITO玻璃上制备得到CdZnTe纳米晶薄膜,并利用台阶仪、X射线能谱仪(EDS)、X射线衍射仪(XRD)和原子力显微镜(AFM)研究了CdZnTe薄膜厚度、成分、结构和形貌特征。实验结果表明,薄膜在(111)面表现出明显的择优生长特性。在薄膜生长初期,纳米薄膜中存在一定程度的非晶态富集Te,但随着沉积时间延长,薄膜成分向化学计量比逼近,结构也向闪锌矿CdZnTe转变。薄膜表面形貌平整,粗糙度Ra约为2～5nm。随着沉积时间的延长,薄膜形貌由晶粒堆砌状向多晶层片连接状转变。在沉积时间分别为15、30和45min时,薄膜的厚度依次分别约为100、300和500nm,而薄膜的晶粒平均尺寸依次分别为43.15、30.81和71.94nm。