Min Jiahua

A novel two-step chemical passivation process for CdZnTe detectors

The spectrum resolution of cadmium zinc telluride (CZT) room temperature nuclear radiation detectors is often limited by the presence of conducting surface species that increase the surface leakage current. Surface passivation plays a dominant role in reducing the surface leakage current and therefore decreasing the noise and improving the spectral energy resolution of the detectors. In this paper, a novel two-step chemical passivation process for CZT detectors, in which the mixed solution of bromine?methanol and lactic acid in ethylene glycol (BMLB) treated CZT wafer was first etched by using a KOH aqueous solution, and then by using a NH4F/H2O2 mixed solution, is presented. The Auger electron spectroscopy (AES) and atomic force microscopy (AFM) results show that the first-step KOH process consumed the Te-rich layer caused by BMLB and left a more stoichiometric surface and the second-step NH4F/H2O2 process oxidized the elemental constituents of the CZT surface obtained by the KOH etching and formed an oxide layer on the surface. The I?V characteristics show that the novel process leads to a lower surface leakage current compared to the processing by using either a KOH or NH4F/H2O2 agent. The results indicate that this two-step passivation process has a promising potential in the fabrication of CZT detectors.

A novel surface passivation process for CdZnTe detector packaging

The CdZnTe (CZT) micro-strip detector packaging plays a dominant role in detector performance, which can decrease the noise of the detectors and improve the spectral energy resolution. The surface passivation of CdZnTe detectors is an important step in the device packaging. In this paper, comparison between chemical and physical passivation processes has been made. In particular, a new surface passivation process for CZT has been studied by depositing diamond like carbon (DLC) film with radio frequency plasma chemical vapor deposition (RFPCVD) method. The micro-structural, chemical and electric characteristics of the passivation layers were identified by AFM, AES and micro Raman spectroscopy and ZC36 micro-current testing instrument. The results show that the DLC on the detector has the characteristic diamond peak of the sp/sup 3/ structure and can prevent the outward diffusions of Cd or Te components from the CZT surface. The inter-strip resistance in a coplanar grid detector by the DLC passivation is about 12GQ with inter-strip distance 25 /spl mu/rn. Therefore, it could be inferred that DLC seems a more likely candidate for maintaining high long-term performance, especially for technology facilitation of the fabrication of micro-strip detectors.

Optimized Process of Thermal Treatment of Au/CdZnTe Contacts

Abstract Effects of thermal treatment temperatures from 323 K to 473 K in air atmosphere on the Au/CdZnTe contacts fabricated by thermal vacuum evaporation was investigated systematically. The results show that the optimized performances of the Au/CdZnTe contacts after thermal treatment in air at a range of 353-373 K can be obtained, that is, the contacts possess lower barrier height, smaller contact resistance and better ohmic coefficient, without damaging bulk CdZnTe properties. Nevertheless, performing thermal treatment over 400 K, the deposited surface of Au electrodes will grow worse apparently, and the leakage current of CdZnTe samples enhances significantly. This might be attributed to the increase of the Cd vacancies produced by Cd sublimation from the CdZnTe into air atmosphere with the increase of temperature.

A primary study on the synthesis and characterization of ZnS clusters in chitosan film

A novel process using chitosan containing ligand groups as a medium for forming ZnS clusters by an ion-coordination method is investigated for the first time. The ZnS clusters in the chitosan film have been identified by x-ray diffraction, ultraviolet - visible absorption and photoluminescence spectra. The ZnS cluster size was estimated to be about 2 - 6 nm, depending on the processing conditions. Blue luminescence for the undoped ZnS clusters was observed and its mechanism is briefly discussed.

Te vapor annealing of indium-doped CdMnTe crystals

Thermal annealing in Te vapor atmosphere was adopted to improve the properties of indium-doped Cd1−xMnxTe (x = 0.2, CdMnTe) wafers grown by the vertical Bridgman method. The wafers before and after annealing were characterized by measuring the Te inclusions, etch pit density (EPD), Mn composition, resistivity, and impurity. IR transmission microscopy and EPD measurements revealed that the densities of Te inclusions reduced from (5–9) × 104 cm−3 to (2–4) × 104 cm−3 and EPD from 105 cm−2 to 104 cm−2 after annealing. NIR transmission spectroscopy showed that the Mn composition increased by 0.002–0.005 mole fractions during the annealing. The resistivity of the wafers improved from (2.0–4.5) × 108 Ωcm to (1.7–3.8) × 109 Ωcm, which suggested that the deep-level donor of Te antisites was successfully introduced after annealing. Inductively coupled plasma-mass spectrometry (ICP-MS) revealed that the concentrations of impurities in the wafer decreased, which indicated the purifying effects of Te vapor annealing on the wafers. All the results demonstrate that the Te vapor annealing of the indium-doped CdMnTe crystal has positive effects on the crystallinity, resistivity and purity of CdMnTe wafers.

Preparation of ZnO Thin Films on Free-Standing Diamond Substrates

Highly c-axis-oriented ZnO films were deposited successfully on the nucleation sides of free-standing diamond (FD) films by the direct current (DC) magnetron sputtering method. The effect of the sputtering parameters, such as power, gas pressure and sputtering plasma composition of Ar-to-O2, on the properties of ZnO thin films was investigated in detail. X-ray diffraction (XRD) measurements showed that, at a sputtering power of 200 W, gas pressure of 0.5 Pa and an Ar-to-O2 composition of 1:1, a higher intensity of the (002) diffraction peak and a narrower full width at half maximum (FWHM) were detected which meant high c-axis orientation and high quality of the ZnO films. To improve the quality of the ZnO film, a thin ZnO layer was pre-grown as a homo-buffer layer. XRD measurements showed that this buffer layer had a beneficial effect on the structural and morphological properties of the post-grown ZnO film.

Failure analysis of the CdZnTe detector electrode contacts

The characteristics of the Au contacts deposited by three different processes before and after accelerating aging tests have been investigated in this paper. The experimental results indicate that the aging tests can cause the degradation of the contact interfacial properties, such as continuities, adhesion strength and ohmic characteristics, especially for the contact interface deposited by the thermal vacuum processing, which would influence the performance of CdZnTe detectors

溶剂熔区移动法生长Cd 0.9 Zn 0.1 Te晶体的工艺优化研究

为了解决Cd 0.9 Zn 0.1 Te(CZT)晶体生长温度高、单晶率低、成分不均匀等问题, 采用溶剂熔区移动法(THM)在优化工艺参数下生长了掺In的CZT晶体, 在优化晶体的生长温度、固液界面处的温度梯度、原位退火过程等生长条件后, 生长出直径为45 mm的低Te夹杂浓度、高电阻率、高透过率、均匀的高质量CZT晶体。 X射线衍射结果显示, 晶体的结晶性较好、Zn成分轴向偏析小。红外透过光谱测试结果显示, 晶体内部的杂质、缺陷水平相对较少, 晶体整体的红外透过率在60%左右。紫外-可见光吸收光谱测试结果也进一步表明, 晶体的均匀性良好。采用红外显微镜对晶体内部的Te夹杂形貌及其尺寸进行观察, 结果表明Te夹杂的尺寸主要分布在0~10 μm之间。采用直流稳态光电导技术测得电子的迁移率寿命积约为8×10 -4 cm 2 /V。

Study of assembling ZnO nanowires on AFM tips

The study of nanomaterial characteristics and its construction is important to the design of nanodevices. In this paper, we present assembling ZnO nanowires on atomic force microscope (AFM) probes for the first time for AFM imaging. It was found that different catalyzing conditions might influence the quality of the nanowires grown on the tips. Controlled imaging experiments with the ZnO nanowires probe and with the normal AFM probe have been carried out. In-situ imaging experiment confirmed that AFM imaging can be got by using the ZnO nanowires on the tips and the image quality would be affected by the quality of the ZnO nanowires on the AFM probes, grown under different conditions. The problems existing in in-situ imaging, such as tip expansion, the reflection of laser signal and the multi-tips phenomenon, are also discussed

A novel structure for CdZnTe capacitive frisch grid radiation detector

CdZnTe gamma spectrometers with capacitive Frisch grid structure can potentially achieve a higher detecting resolution and their geometrical structures have an important role in optimizing the detector performance. In the paper, three geometrical structures of capacitive Frisch grid detectors were investigated by using Finite element method based on the 3-dimensional weighting potential and field distribution. Simulation results indicated the trapezoid prism model could get better detector performance, whose novel structure has not only a better weighting potential distribution but also a bigger detector volume than the cuboid models