载流子输运性能对CdZnTe晶体脉冲X射线响应特性的影响

采用生长态高电阻CdZnTe晶体制备出平面电极探测器,室温下测试了其在脉冲X射线作用下的诱导电流曲线。分析了脉冲电流的上升时间以及脉冲衰减过程,发现脉冲上升时间约为2 ns,且不受外加偏压影响,而脉冲衰减过程可分为3阶段。利用α粒子结合飞行时间技术研究了CdZnTe晶体的载流子传输特性,分析了结构缺陷的散射和俘获-佉俘获对载流子传输特性的影响。同时对比了不同厚度的CdZnTe探测器在不同电压下对脉冲X射线的响应特性。结果表明,当外加电场强度增加时,诱导脉冲电流曲线的半峰宽呈指数衰减,但当探测器厚度大于0.2 mm时,随着探测器厚度的增加变化不明显。可能是由于材料中结构缺陷的浓度增加,对载流子的俘获和散射作用加剧,严重影响了载流子的传输过程和复合时间。     

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.     

CdZnTe晶体欧姆接触电极的制备工艺研究

高阻CdZnTe晶体是X射线及γ射线探测最优秀的材料.制备CdZnTe探测器最关键的技术之一就是在CdZnTe表面制备出欧姆接触薄膜电极.关于在CdZnTe晶体表面制备接触电极用导电薄膜,大都是采用蒸发镀膜技术,膜层与CdZnTe晶体结合不很牢固.本论文主要开展了在CdZnTe晶体上欧姆接触电极的选材和制备工艺的研究.理论分析了金属与CdZnTe半导体的接触关系,根据影响因素选择Cu/Ag合金作为电极薄膜材料.利用射频磁控溅射法成功地在CdZnTe晶体上制备出Cu/Ag膜.研究发现Cu/Ag合金膜的电阻率随溅射功率的增大而增大、衬底温度的升高而降低.从理论上对这一规律进行了解释.     

近空间升华法制备CdZnTe厚膜及其性能研究

采用近空间升华法在FTO玻璃衬底上制备CdZnTe多晶厚膜,并采用扫描电镜(SEM)、能谱仪(EDS)、X射线衍射仪(XRD)、紫外-可见光谱仪、I-V测试仪等对CdZnTe厚膜的表面形貌、成分、结构以及光电性能进行分析表征。结果表明,所制备的CdZnTe膜均匀致密,随生长时间的延长,晶粒尺寸明显增大;不同厚度的CdZnTe膜均表现出沿(111)晶面的择优生长;CdZnTe厚膜的禁带宽度在1.53～1.56eV之间;电阻率在1010Ω.cm数量级,具有较好的光电响应,试制的薄膜探测器可用作计数型探测器。     

室温核辐射探测材料PbI2晶体生长及退火改性研究

以多晶碘化铅(PbI_2)为原料,采用垂直布里奇曼法进行单晶生长,研究了PbI_2单晶的生长特性,随后对单晶进行真空退火和气氛退火,并测试了生长态、真空退火态以及气氛退火态3种不同状态下晶体的光致发光谱(PL)、I-V特性以及红外透过率。研究表明,在碘蒸汽中气氛退火后的碘化铅单晶质量较高,PL谱中激子(EX)峰的半峰宽有所下降,红外透过率从生长态的10%提升至30%左右,电阻率从生长态的3.3×10~9Ω·cm提高至5.6×10~9Ω·cm,可以有效提高晶体的探测效率。气氛退火有利于提高碘化铅的单晶质量,使其各项性能更加适用于室温核辐射探测器。     

室温辐射探测器用CdZnTe晶体生长及器件制造工艺进展

半绝缘CdTe和CdZnTe室温半导体探测器已在工业监测、医疗和成像、核安全及科学研究等多方面得到应用。Cd1-xZnxTe室温X射线和Y射线探测器的性能与材料和器件中的缺陷(它控制器件中载流子输运)密切相关。欲提高该种器件及器件阵列的性能，需不断改进晶体生长与器件制造工艺，重点是降低晶体内、界面、亚表面和器件表面上的缺陷。     

新型红外探测器材料Hg1-x-y CdxZnyTe研究

采用移动加热器法(THM)进行了新型红外探测器材料 Hg1-x-yCdxZnyTe(MCZT)的晶体生长,获得的MCZT晶片经汞源退火后进行了光学特性、结构特性、电学性能和组分均匀性的检测与分析,并且初步制作成近室温工作的长波光电导器件,对器件性能进行了测试与分析。结果表明用移动加热器法生长Hg1-x-yCdxZnyTe晶体是成功的,获得晶片的材料特性与器件性能初步达到了应用水平。     

CdZnTe晶体中微米级富Te相与PL谱的对应关系

采用红外透过显微镜(IRTM)观察了不同条件下生长的CdZnTe晶体中微米级富Te颗粒.结合实际生长条件分析了不同富Te颗粒的产生以及形态演化.通过低温光致发光(PL)谱研究了CdZnTe晶体中杂质、缺陷的状态,以及晶体的结晶质量,并测试了相应晶体的电阻率.归纳出不同富Te颗粒的产生与对应晶体10 K温度下PL谱中特征...     

探测器级CdZnTe晶体变温特性研究

采用未经准直能量为5.48MeV的241 Amα粒子,研究了温度在230～300K范围内,不同电场作用下CdZnTe晶体的脉冲响应信号,分析了载流子传输特性随温度变化的规律。对比了室温(298K)以及280K下探测器对241 Am@59.5keVγ射线的响应光谱。同时分析了1500V/cm电场作用下探测器漏电流随温度的变化规律。研究表明,对于性能优异的CdZnTe晶体,载流子迁移率寿命积随温度变化较小。而对于存在de-trapping(去俘获)缺陷的CdZnTe样品,光生载流子在晶体中的传输会显著减缓,且随温度的降低,其对脉冲波形的影响加剧。而温度降低可以减少提高探测器的能量分辨率。     

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。     

Detector-grade CdZnTe:In crystals obtained by annealing

A method for successfully obtaining detector-grade CdZnTe:In (CZT:In) crystals by annealing is described in this article. Pure Te is used as annealing source, which can provide sufficient deep-level Te antisites. Characterizations reveal that the resistivity is greatly enhanced by more than five orders after this annealing, thus the crystals can be use for radiation detectors. This is due to introduce efficient Te antisites to pin the Fermi level to the middle of the band gap. The EPD of dislocation reduces because the star-like Cd inclusions are eliminated by annealing. Investigation of annealing time shows that 240 h annealed CZT:In crystal with 7.8% energy resolution and 2.01×10⁻³ cm²/V μτ value has the best detector performance.     

CdZnTe晶体表面Au电极薄膜的制备及其欧姆接触性质

为了研究不同制备工艺对电极欧姆接触特性的影响, 分别采用真空蒸发法、溅射法及化学沉积法在CdZnTe晶片表面制备了Au薄膜电极, 通过测试样品的SEM、I-V曲线及交流阻抗谱, 研究了不同电极制备工艺及退火处理对Au薄膜电极的微观结构及欧姆接触特性的影响。结果表明化学沉积法制备的Au薄膜表面更加平整、致密, 接触势垒的高度较低, 电极欧姆接触特性最好。退火处理可以改善电极的欧姆接触特性, 100℃退火后, 化学沉积法制备的Au电极的欧姆系数由0.883提高至0.915, 势垒高度由0.492降低至0.487 eV。交流阻抗谱分析表明, 化学沉积法制备电极具有最低的接触势垒, 这与界面处晶片表面的掺杂及缺陷的变化有关。     

Structural defects as a result of Zn diffusion into CdTe single crystals

The presence of defects in CdZnTe crystals is detrimental for optoelectronic devices fabrication and therefore should be minimized. In this paper we present the characterization of structural defects on the surface and the cross-section of CdTe single crystals that were subjected to high temperature (up to 950 °C) diffusion of Zn. The defects were characterized by various X-ray techniques, optical microscopy, scanning electron microscopy (SEM) and atomic force microscopy (AFM). Quantitative data are obtained, a practical solution for reducing the defects is suggested and some implementations are discussed. Further effort is currently being made to investigate the lattice sites which are involved with the diffused Zn atoms near the surface and in the bulk.     

AZO薄膜制备工艺及其性能研究

综述了掺铝氧化锌(AZO)薄膜制备方法与光电特性,重点阐述了磁控溅射法制备工艺参数如衬底温度、溅射功率、气体压强、溅射时间、衬底和靶间距、负偏压等对AZO薄膜结构、光电性能的影响,并指出目前AZO薄膜的研究关键以及所面临的挑战,展望了未来的研究方向。     

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.     

Homogenization of zinc distribution in vertical Bridgman grown Cd0.96Zn0.04Te crystals

One of the most pressing issues in the growth of high quality single crystal Cd _0.96 Zn _0.04 Te material, is to achieve homogenization of the high axial variation of Zn concentration, caused by the larger than unity segregation coefficient of Zn in CdTe. This is achieved in our crystals (i) by thermal annealing of the CdZnTe crystal, which redistributes the as grown Zn distribution by solid state diffusion of Zn (this solid state diffusion of Zn occurs at three stages (a) during the growth when the solidified crystal is near to the melting point temperature, (b) during the post growth annealing of the crystal at a high temperature and (c) during the cooldown to room temperature) and (ii) by the reduction of Zn segregation during the growth stage by enhanced convective mixing of the melt, through a proper choice of ampoule and furnace dimensions. By adopting suitable growth parameters and sufficient post growth annealing it has been possible to grow Cd _0.96 Zn _0.04 Te crystals, which have nearly 75% of their fraction within 1% Zn concentration variation.     

Rejecting incomplete charge-collection events in CdZnTe and other semiconductor detectors

In an ideal single-carrier-type gamma ray detector, the amplitudes of the signals and the carrier drift times are correlated variables. However, if the charges produced by an incident photon are not fully collected, as is the case in CdZnTe detectors containing crystal defects, the above correlation does not hold. This permits the application of an event recognition algorithm to identify these incomplete charge collection (ICC) events, caused by the “bad” regions inside a detector, so that they can be removed from pulse height spectra. The ICC events primarily contribute to the Compton continuum and the low-energy tail of the photopeak. Thus, rejecting such events should not affect significantly the photopeak efficiency, but should improve the spectral response, e.g., the peak-to-Compton ratio, for a detector fabricated from material with relaxed crystal quality requirements. Such crystals are those currently available from vendors. The use of stronger ICC correlation-function rejection criteria can improve the energy resolution of these lower-quality crystals, but at the price of a loss in photoefficiency.     

Effect of annealing on cathodoluminescence of synthetic zincite single crystals

We have studied the effect of annealing on the luminescent properties of zincite single crystals grown from hydrothermal solutions. Annealing in the temperature range of 400–700°C increases the edge cathodoluminescence (CL) intensity in zincite. At the same time, raising the annealing temperature from 800 to 1100°C leads to quenching of the edge emission and increases the intensity of the green band. In addition, annealing leads to broadening of the edge luminescence band and shifts it to lower energies. In contrast, annealing shifts the impurity band to higher energies. The observed changes in the CL behavior of zincite are tentatively interpreted in terms of the temperature effect on the concentration of structural defects, in particular, oxygen vacancies and their complexes.     

CdZnTe薄膜的CdCl2退火及性能表征

采用近空间升华法制备了CdZnTe薄膜,并对其进行CdCl2退火,采用扫描电镜(SEM)、能谱仪(EDS)、X射线衍射仪(XRD)、紫外光谱仪、I-V测试仪等研究了退火对薄膜表面形貌、成分、结构以及光电性能的影响。结果表明,经过CdCl2退火后薄膜的晶粒尺寸明显增大,晶粒分布更加均匀;XRD分析结果显示,退火后薄膜的最强峰(111)峰的半峰宽变窄,薄膜沿(111)方向的择优取向明显增强;退火后薄膜的光学透过率降低,截止边红移,光学禁带宽度减小;薄膜的电阻率在退火后下降了两个数量级。