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。     

温度梯度溶液法生长的Cr掺杂的ZnTe晶体的表征

以CrTe作为掺杂源、以Te作为溶剂, 用温度梯度溶液法生长了Cr掺杂的ZnTe晶锭。晶锭头部的晶粒尺寸较大(>10 mm×10 mm), 且Te夹杂相较少。Te夹杂相的大小、形状和分布可以反映晶锭中的温场分布。晶锭的径向非对称温场导致富Te相沿径向非对称分布。Te夹杂相在温度梯度作用下的热迁移会导致其相互融合长大、变长。Te夹杂相也会在晶体中引入裂纹和空洞等缺陷。部分未被掺入ZnTe中的CrTe富集于固液界面处, 表明温度梯度溶液法生长晶体时具有一定的排杂作用。Cr掺杂的ZnTe晶体的电阻率(约1000 Ω·cm)高于未掺杂的ZnTe(约300 Ω·cm)。Cr掺杂晶体在约1750 nm处的吸收峰表明Cr²⁺离子被成功地掺入了ZnTe中。但是Cr掺杂后晶体的红外透过率降低, 表明Cr掺杂引入了较多的缺陷。     

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.     

溶剂熔区移动法生长Cd0.9Zn0.1Te晶体的工艺优化研

为了解决Cd_0.9Zn_0.1Te(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 cm²/V。     

Cd/Zn气氛退火过程中CdZnTe晶体内Te夹杂的迁移研究

通过红外透过成像研究了Cd/Zn气氛退火过程中Cd0.9Zn0.1Te∶In晶体内Te夹杂的密度及尺寸分布的演变。结果发现,Cd/Zn气氛退火前,晶体中的Te夹杂密度分布比较均匀;退火后,晶体高温端近表面区域的Te夹杂密度较退火前提高了1个数量级,而晶体内部的Te夹杂密度则较退火前降低了1个数量级,且其密度沿温度梯度方向逐渐增加。退火前,晶体表面和内部的Te夹杂的直径主要分布在1~25μm;退火后,在晶体表面,直径45μm的Te夹杂密度显著增大;而在晶体内部,直径5μm和25μm的Te夹杂密度显著增大。导致这些现象的原因是退火过程中,Te夹杂沿着温度梯度方向不断向晶体表面迁移,在迁移过程中尺寸相近的Te夹杂通过合并长大,尺寸相差较大的Te夹杂则以Ostwald熟化方式长大,并使小尺寸的Te夹杂更小。但由于熟化不充分,在Ostwald熟化长大过程中留下了很多尺寸5μm的Te夹杂颗粒。     

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.     

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...     

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。     

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。     

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0~10μm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。     

Effects of gradient heat treatment on Te-rich CdZnTe crystal

The gradient heat treatment was performed on Te-rich CZT crystal grown by the vertical Bridgman (VB) method, which was under the temperature of 1073 K and the temperature gradient of 2 K/mm and the velocity of 1.8 mm/h. IR transmission, IR microscope, I-V curves and glow discharge mass spectrometry (GDMS) revealed that Te inclusions moved towards the last-to-freeze region in CZT ingot, which proved that the gradient heat treatment has the possibility to purify the CZT ingot. Finally, after the gradient heat treatment, the resistivity of the CZT ingot was enhanced, and the IR transmittance was also improved.     

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.     

Effect of extended defects in planar and pixelated CdZnTe detectors

We evaluated a spectroscopy-grade 15×15×7 mm³ CdZnTe (CZT) crystal with a high μτ-product, >10⁻² cm²/V, but impaired by microscopic extended defects, such as walls of dislocations, low-angle and sub-grain boundaries, and Te inclusions. First, we evaluated a planar detector fabricated from this crystal using a Micro-scale X-ray Detector Mapping (MXDM) technique. Then, we fabricated from the same crystal a pixel detector to study local non-uniformities of the electric field. The measured X-ray response maps confirmed the presence of non-uniformities in the charge transport, and they showed that the global- and local-distortions of the internal E-field correlated to the extended defects and space-charge buildup on the side surfaces.     

Charge transport properties of as-grown CZT by traveling heater method

In this present work we have grown Cd_0.9Zn_0.1Te doped with indium by the traveling heater method (THM) technique. Large 2 in diameter CZT ingots of more than 1 kg each were successfully grown by the THM technique in vertical configuration. In order to evaluate our as-grown CZT samples, charge transport characteristics were studied at and below room temperature. The key parameter investigated for as-grown CZT samples was the mobility-trapping time product and its temperature variation. Mobility-trapping time values as high as 9×10⁻³ cm²/V at 30 °C were measured for samples exhibiting resistivities in the 1-2×10¹⁰ Ω cm range. The as-grown samples showed moderately good resolution of 1.5-3.5% at 662 keV when fabricated. The variation of the internal electric field along the depth of the detector was studied for as-grown material to evaluate deformations inside the crystal due to the presence of residual stress or other defects.     

The formation of thermochemically stable Schottky barriers on p-Cd0.95Zn0.05Te using Titanium

The electrical properties of Ti-based contacts on p-Cd_0.95Zn_0.05Te (CZT) were investigated. Ti contacts with a Cd or a Te interlayer were produced and compared with the pure Ti contact using current-voltage characteristics (I–V). The barrier heights can be perceived using data on the interface reactions and the phase formation in direct contact with CZT. The percept of the dominating influence of phase formation could be validated for stoichiometric CZT substrate surfaces and also for etched (Te-rich) substrates. It was found that Ti, i.e. the Ti₃Te₄ phase that forms at the interface, produces high barriers in the range of 1 eV. In addition, various Au capped Ti-contacts were investigated. Thermally stable, near-ideal Au/Ti-contacts with a barrier height of 0.76 eV were produced.     

碲镉汞晶体辐射损伤的分析电镜研究

用分析电子显微镜观察了碲镉汞晶体的显微结构。发现在大剂量电子辐射下,显微结构有较强的损伤。进一步用 X线能谱分析和高分辨电子显微术研究表明,大剂量电子辐射引起了碲镉汞晶体的超结构、叠栅、无序化和 Hg 含量减少。