高阻CdZnTe晶体的退火处理

获得高电阻率的、完整性好的 Cd Zn Te晶体是研制高性能的 Cd Zn Teγ射线探测器的关键 .运用热力学关系估算了 Cd1 - x Znx 熔体平衡分压 ,尝试以 Cd1 - x Znx 合金源替代 Cd源进行 Cd0 .8Zn0 .2 Te晶片的热处理 ,研究了退火对 Cd0 .8Zn0 .2 Te晶片质量的影响 .结果表明 :在 10 6 9K下用 Cd0 .8Zn0 .2 合金源 (PZn=0 .12 2e5 Pa和 PCd=1.2 0e5 Pa)对 Cd0 .8Zn0 .2 Te晶片退火 5天以上 ,可提高晶体电阻率一个数量级和晶体红外透过率 10 %以上 ,并可消除或减小晶片中的 Te沉淀 ,同时避免了 Zn的损失 ,改善 Zn的径向分布 .可见 ,采用 Cd1 - x Zn     

未掺杂CdZnTe与掺铟CdZnTe晶体的热处理

对于未掺杂Cd0.9Zn0.1Te晶片,采用在Cd/Zn气氛下,以In作为气相掺杂源进行热处理;而对于低阻In-Cd0.9Zn0.1Te晶片,则采用在Te气氛下进行热处理.分别研究了不同的热处理条件,包括温度、时间、pIn或pTe等对晶片电学性能、红外透过率以及Te夹杂/沉淀相的影响.结果表明,在Cd/Zn气氛下适当的掺In热处理和在Te气氛下适当的热处理均有效地提高了晶片的电阻率,分别达到2.3×1010和5.7×109Ω·cm,同时晶片的其他性能也得到明显改善.     

未掺杂CdZnTe与掺铟CdZnTe晶体的热处理

对于未掺杂Cd0.9Zn0.1Te晶片,采用在Cd/Zn气氛下,以In作为气相掺杂源进行热处理;而对于低阻In-Cd0.9Zn0.1Te晶片,则采用在Te气氛下进行热处理.分别研究了不同的热处理条件,包括温度、时间、pIn或pTe等对晶片电学性能、红外透过率以及Te夹杂/沉淀相的影响.结果表明,在Cd/Zn气氛下适当的掺In热处理和在Te气氛下适当的热处理均有效地提高了晶片的电阻率,分别达到2.3×1010和5.7×109Ω·cm,同时晶片的其他性能也得到明显改善.     

退火对CdZnTe晶体质量的影响

我们用红外透射光谱和X射线双晶衍射等，研究了退火对CdZnTe晶体质量的影响．结果表明，在Cd气氛中，700℃，退火5小时以上，能大量地去除晶片中的Te沉淀，提高其红外透射比；同时，退火也导致了晶片表面的损伤，损伤层为50～130μm．表面结构损伤的原因是，（1）Cd气氛中退火，CdZnTe晶体表面的Zn损失；（2）退火过程中，吸附在沉淀物周围的杂质，尤其是快扩散杂质，将随着沉淀相的消失而迁移到晶体的表面，从而破坏了表面的晶体结构．退火后，磨去损伤层，可将聚集在表面的这些杂质除去，更有利于外延生长或器件制备．     

高阻碲锌镉单晶体的生长及其性能观测

报道了采用富Cd原料的无籽晶垂直布里奇曼法生长高阻碲锌镉Cd0.8Zn0.2Te(CZT)单晶体的新工艺,对所生长的晶体作了X射线衍射分析、红外透过率测试、光吸收截止波长测量及电学性能测试.晶体在4400～450cm-1范围内的红外透过率达到50%,截止吸收波长为787.6nm,带隙为1.574eV,室温电阻率达到2×1010Ω·cm,已接近本征Cd0.8Zn0.2Te半导体的理论值.用该晶体制作的核探测器在室温下对241Am和109Cd放射源均有响应,并获得了比较好的241Am-59.5keV吸收谱.结果表明改进的方法是一种生长室温核辐射探测器应用的高阻CZT单晶体的简便有效的新方法.     

高阻碲锌镉单晶体的生长及其性能观测

报道了采用富Cd原料的无籽晶垂直布里奇曼法生长高阻碲锌镉Cd0.8Zn0.2Te(CZT)单晶体的新工艺,对所生长的晶体作了X射线衍射分析、红外透过率测试、光吸收截止波长测量及电学性能测试.晶体在4400～450cm-1范围内的红外透过率达到50%,截止吸收波长为787.6nm,带隙为1.574eV,室温电阻率达到2×1010Ω·cm,已接近本征Cd0.8Zn0.2Te半导体的理论值.用该晶体制作的核探测器在室温下对241Am和109Cd放射源均有响应,并获得了比较好的241Am-59.5keV吸收谱.结果表明改进的方法是一种生长室温核辐射探测器应用的高阻CZT单晶体的简便有效的新方法.     

In气氛退火对Cd0.9Zn0.1Te材料电阻率的影响研究

在不同温度条件下对Cd0.9Zn0.1Te晶片进行In气氛退火热处理,显著提高了Cd0.9Zn0.1Te材料的电阻率。通过实验测量和理论建模计算,得到了1 073、1 023和973K条件下In原子在Cd0.9Zn0.1Te晶片中的扩散系数分别为4.25×10-9 cm2·s-1、9.02×10-10 cm2·s-1和2.17×10-10 cm2·s-1,并且拟合出了1 073~973K范围内扩散系数和温度之间的函数关系表达式D(T)=2.15×exp(-1.9/k0T)及频率因子D0等数据。最后,对实验结果进行了简要的对比和分析解释。     

Cd1-xMnxTe晶体衬底的红外透过性能

研究了生长态和退火后Cd1-xMnxTe晶片的吸收边和红外透过性能.Cd1-xMnxTe晶体采用垂直Bridgman法生长,获得面积为30 mm×40 mm的(111)面Cd1-xMnxTe单晶片;晶片在Cd气氛下退火.近红外光谱表明,吸收边的截止波长反映晶片的Mn含量范围为0.1887≤x≤0.2039,其中轴向成分波动差值约为0.0152,径向成分波动差值约为0.0013;x=0.2的Cd1-xMnxTe晶体吸收边的吸收系数变化范围为2.5～55 cm-1;退火后,晶体的吸收边位置没有变化,表明晶片中Mn含量未受到退火的影响.傅里叶变换红外透射光谱表明,晶片在红外光波数为4000～500 cm-1范围的红外透过率为45%～55%;退火后,晶片的红外透过率提高到61%以上,接近理论值65%.     

改进的垂直布里奇曼法生长CdZnTe晶体中的成分偏离现象

采用多种测试方法,对改进的垂直布里奇曼法生长Cd0.96Zn0.04Te晶体中的成分偏离标准化学计量比现象及其对晶体性能的影响进行了研究.X射线能谱成分测试表明,在晶锭的头部即初始结晶位置,(Cd Zn)/Te比大于1;而在中部及末端,小于1.表明这种方法生长的CZT晶体仍然存在对标准化学计量比的偏离现象,开始结晶是在富Cd熔体中,生长至中后段则是在富Te条件下进行的.PL谱测试表明,富Cd的晶片内存在大量Te空位,严重富Te的晶片内Cd空位及其杂质复合体等引起的缺陷密度显著增加.晶体红外透过率测试结果表明,接近化学计量配比的CZT晶片具有高的红外透过率.     

改进的垂直布里奇曼法生长CdZnTe晶体中的成分偏离现象

采用多种测试方法,对改进的垂直布里奇曼法生长Cd0.96Zn0.04Te晶体中的成分偏离标准化学计量比现象及其对晶体性能的影响进行了研究.X射线能谱成分测试表明,在晶锭的头部即初始结晶位置,(Cd+Zn)/Te比大于1;而在中部及末端,小于1.表明这种方法生长的CZT晶体仍然存在对标准化学计量比的偏离现象,开始结晶是在富Cd熔体中,生长至中后段则是在富Te条件下进行的.PL谱测试表明,富Cd的晶片内存在大量Te空位,严重富Te的晶片内Cd空位及其杂质复合体等引起的缺陷密度显著增加.晶体红外透过率测试结果表明,接近化学计量配比的CZT晶片具有高的红外透过率.     

（英）沉积参数对射频磁控溅射制备的碲锌镉薄膜的影响

采用Cd096Zn0.04Te靶,利用射频磁控溅射制备碲锌镉薄膜,通过改变基片温度、溅射功率和工作气压,制得不同的碲锌镉薄膜.将制备的碲锌镉薄膜放置在高纯空气气氛中,在473 K温度下退火.利用台阶仪、分光光度计、XRD和SEM测试设备表征,结果表明,通过退火和改变沉积参数,可以制备出禁带宽度在1.45～2.02eV之间调节的碲锌镉薄膜.     

Thermomigration of Te precipitates and improvement of (Cd,Zn)Te substrate characteristics for the fabrication of LWIR (Hg,Cd)Te photodiodes

(Cd,Zn)Te wafers containing Te precipitates have been annealed under well defined thermodynamic conditions at temperatures below and above the melting of Te. Results of the examination of the wafers with infrared microscopy before and after the anneals indicate a substantial reduction of the Te precipitates in wafers annealed at temperatures in excess of the melting point of Te compared with those annealed at temperatures below the melting point of Te. These results confirm the thermomigration of liquid Te precipitates to be the principally operative mechanism during annealing in the elimination of these precipitates in (Cd,Zn)Te wafers. The occurrence of Te precipitates in (Hg,Cd)Te epitaxial layers grown on (Cd,Zn)Te substrates containing Te precipitates is also explained on the basis of thermomigration of these precipitates during LPE growth from the substrates to the epilayers. Absence of occurrence of Te precipitates in (Hg,Cd)Te epilayers grown on annealed (Cd,Zn)Te substrates with negligible Te precipitates is also confirmed. Usefulness of annealing (Cd,Zn)Te substrates—to eliminate Te precipitates—prior to epilayer growth is confirmed via demonstration of improved long wavelength infrared (Hg,Cd)Te device array performance uniformity in epitaxial layers grown on (Cd,Zn)Te substrates with negligible Te precipitates after annealing.     

Infrared absorption behavior in CdZnTe substrates

Infrared (IR) optical transmission measurements of polished CdZnTe wafers can provide useful information about excess impurities, stoichiometry, and inhomogeneities (precipitates and inclusions). We have investigated the IR transmission behavior of Cd_0.96Zn_0.04Te between 8 m and 20 m at room temperature. The measurements were made before and after thermal treatments involving control of the Cd and Zn overpressures, which served to minimize the Cd (cation) vacancy population. Our results support the polar optical phonon scattering theory of Jensen, according to which the absorption in donor dominated CdZnTe varies as^m with m=3. For material dominated by acceptors, we show that the theoretical absorption by inter-valence band transitions can be approximated by a similar power law with exponent m=1, and that Cd-vacancy dominated wafers are in reasonable agreement with this. We find some wafers in which the asgrown condition exhibits partial compensation of impurity donors by Cd vacancy acceptors, and demonstrate removal of the compensation by annealing to fill the vacancies. In a separate group of wafers, we find that an observed increase in absorption occurring during growth of a HgCdTe layer by liquid phase epitaxy can be explained in terms of an increase in Cd vacancies caused by diffusion of Cd to Te precipitates. This effect can be reversed by annealing in Cd−Zn vapor, which fills vacancies and eliminates some precipitates. Impurity concentrations were measured by glow discharge mass spectrometry (GDMS).     

非晶态碲镉汞的暗电导率和吸收边(英文)

研究了非晶态碲镉汞(x=0.2)薄膜的暗电导率随温度变化关系,发现非晶态结构的碲镉汞材料具有明显的半导体特性,其室温禁带宽度在0.88～0.91eV之间,与通过光学方法获得的结果相符。在80～240K的温度区间非晶态碲镉汞(x=0.2)的暗电导率从1×10—8Ω—1.cm—1缓慢增大到5×10-8Ω—1.cm—1,温度大于240K时,其电导率剧烈增大到1×10—5Ω—1.cm—1,说明在240K附近非晶态碲镉汞材料的导电机制发生了变化,这对非晶态碲镉汞材料的应用研究具有重要意义。还研究了退火过程对非晶态碲镉汞薄膜电导率的影响,结果表明140℃退火后非晶态碲镉汞薄膜发生了部分晶化。     

Reduction of CdZnTe substrate defects and relation to epitaxial HgCdTe quality

We have conducted annealing experiments on CdZnTe wafers to restore stoichiometry, eliminate or reduce second-phase (Cd or Te) inclusions, and investigate effects on the quality of epitaxial HgCdTe grown on the thermally treated substrates. Two categories of second phase features were revealed in these materials. Category 1 has a star-like shape with sixfold symmetry (as seen by infrared transmission microscopy) and a central core consisting of cadmium. These stars were observed only in the more stoichiometric materials (having good infrared transmission characteristics). Category 2 consists of triangular, hexagonal, and irregular shaped tellurium inclusions which are present in the off-stoichiometry materials (which exhibit strong IR absorption). Substrates were annealed at temperatures ranging from 500 to 700°C for one to seven days, in vapor derived from elemental Cd or Cd_1-xZn_x alloy (x = 0.005). These anneals were able to eliminate the excess IR absorption and decrease the apparent sizes of both categories of second-phase features. It was found that pinhole-like morphological defects on the surface of a HgCdTe layer grown by liquid phase epitaxy can be caused by Cd and Te inclusions located within the CdZnTe substrate near the interface. Additionally, measurement and spatial mapping of copper concentration by sputter initiated resonance ionization spectroscopy showed 10 to 100 times higher Cu concentration in the inclusions than in the surrounding matrix areas.     

The annealing of Cd1−xZnxTe in CdZn vapors

As-grown CdZnTe usually contains defects, such as twins, subgrain boundaries, dislocations, and Te precipitates. It is always important to anneal CdZnTe slices in Cd vapor to eliminate these defects, especially Te precipitates. The exchange of Zn atoms between the slices and the vapor plays an important role during the annealing process. In this paper, the effects of Zn partial pressure on the properties of the annealed slices are studied carefully by measuring the concentration profiles, the infrared (IR) transmission spectra, and the x-ray rocking curves. It was found that a surface layer with different compositions and possibly different structure from the bulk crystal formed during the annealing of CdZnTe samples in the saturated Zn vapor. The accumulation of excess Te in the surface layer helps to increase the IR permeability of the bulk crystal greatly. To improve the crystallization quality, a lower Zn-pressure annealing should be used following the high Zn-pressure annealing. The diffusion of Zn in the bulk crystal has also been analyzed at the temperatures of 700°C and 500°C. Calculations determined that D_Zn (700°C)=4.02 × 10⁻¹² cm²s⁻¹ and D_Zn (500°C)=1.22 × 10⁻¹³ cm²s⁻¹.     

"神舟3号"上生长Cd1-xZnxTe晶片Zn组分分布的显微荧光研究

用显微荧光(μ-PL)方法对在我国"神舟3号"上空间生长的CdznTe晶片中zn组分分布的研究.对晶片的单晶"壳"区及未完全熔化的"芯"区中的小结晶区域进行了逐点PL测量.对测得每一点的PL谱进行了拟合,得到测量点的禁带宽度参数Eg,其分布对应于CdznTe中zn的组分分布.测量结果给出了空间生长晶片zn组分布的变化趋势和统计规律.作为比较,测量并分析了一块采用相同方法在地面生长的CdznTe晶片.     

根据红外透过率推断CdZnTe晶片的性能

采用傅里叶变换红外光谱仪测试了性能各异的多个CdZnTe晶片的红外透过率．研究表明，红外透过率的大小可以定性反映CdZnTe晶片的性能：红外透过率越高的晶片，其成分偏离越小，位错密度越低，电阻率越高．根据红外透过率大小随着波数的变化，红外透过率图谱可以分为4种，每一种图谱对应着具有不同性能的CdZnTe晶片，从晶片对红外光的吸收机理出发，对实验结果进行了初步分析。     

Annealing experiments in heavily arsenic-doped (Hg,Cd)Te

Arsenic doped molecular beam epitaxy (MBE) (Hg,Cd)Te films were grown on (Cd,Zn)Te substrates. The concentration of arsenic was varied from 5 x 10¹⁸ cm^-3 to 1 x 10²⁰ cm^-3. After the growth, the epitaxial layers were annealed at various partial pressures of Hg within the existence region of (Hg,Cd)Te at temperatures ranging from 400 to 500°C. Hall effect and resistivity measurements were carried out subsequent to the anneals. 77K hole concentration measurements indicate that for concentrations of arsenic <10¹⁹ cm⁻³, most of the arsenic is electrically active acting as acceptors interstitially and/or occupying Te lattice sites at the highest Hg pressures. At lower Hg pressures, particularly at annealing temperatures of 450°C and higher, compensation by arsenic centers acting as donors appears to set in and the hole concentration decreases with decrease in Hg pressure. These results indicate the amphoteric behavior of arsenic and its similarity to the behavior of phosphorus in (Hg,Cd)Te previously inferred by us. A qualitative model which requires the presence of arsenic occupying both interstitial and Te lattice sites along with formation of pairs of arsenic centers is conjectured.     

CdZnTe晶片的性能测试

测试了多个Cd0．9Zn0．1Te晶片的性能，包括红外透过率、成分分布、位错密度、Te沉淀／夹杂密度以及电阻率。研究表明，红外透过率与性能有着密切的联系：红外透过率的大小及红外透过率图谱的形状可反映晶片的成分分布、位错密度以及电阻率的情况。从晶片对红外光的吸收机理出发，对这些联系进行了详细的分析。