非晶态碲镉汞薄膜的射频磁控溅射生长及其晶化过程研究

在玻璃衬底上用射频磁控溅射技术进行了非晶态碲镉汞(a-HgCdTe或a-MCT)薄膜的低温生长,获得了射频磁控溅射生长a-HgCdTe薄膜的\     

非晶态碲镉汞的光学性质

采用椭圆偏振光谱技术研究了射频磁控溅射生长非晶态碲镉汞(amorphous Hg1-xCdxTe,amorphous MCT,a-MCT)薄膜的光学性质,发现非晶态碲镉汞薄膜的介电函数谱特征与晶态碲镉汞材料的明显不同,表现出与其他非晶态半导体材料类似的“波包”结构特征.基于修正的FB模型在1.0～4.0 eV的能量范围内对实验结果进行了拟合分析,得到了不同组分非晶态碲镉汞薄膜的光学带隙随组分关系.通过与单晶碲镉汞光学带隙随组分变化关系的对比研究,结果表明碲镉汞的结构从晶态向非晶态转变过程中,材料的光学待续发生了明显的“蓝移”.     

碲锌镉衬底晶向对碲镉汞薄膜表面形貌的影响

利用定向仪对原生晶片及加工后的碲锌镉衬底的晶向进行比较,观察不同晶向衬底液相外延碲镉汞薄膜的表面形貌,考察了衬底晶向偏差对液相外延碲镉汞薄膜表面形貌的影响。通过进一步的追踪碲锌镉衬底在加工过程中的晶向变化,研究衬底晶向变化的原因和解决方法。研究发现,碲锌镉晶体在初次定向切割后的加工过程中晶向会发生明显变化,而在厚度减薄较大的粗磨工艺后不会发生较大晶向偏差,因此,可将粗磨后衬底的再次定向结果作为进一步筛选碲锌镉衬底的依据,以保证液相外延碲镉汞薄膜的质量。     

非晶态碲镉汞的暗电导率和吸收边

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0.88～0.91 eV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.     

非晶态碲镉汞薄膜的射频磁控溅射生长及其结构和光学特性

在玻璃衬底上用射频磁控溅射技术进行了非晶态碲镉汞(α-HgCdTe,α-MCT)薄膜的低温生长.采用X射线衍射(XRD)和原子力显微(AFM)技术对所生长的薄膜进行分析研究,所生长的非晶态HgCdTe薄膜表面平整,没有晶粒出现,获得了射频磁控溅射生长非晶态HgCdTe薄膜的"生长窗口".采用傅里叶红外透射光谱分析技术对非晶态HgCdTe薄膜进行了光学性能研究,在1.0～2.0μm范围内研究了薄膜的透射谱线,获得了薄膜的吸收系数(～8×104cm-1),研究了其光学带隙(约0.83eV)和吸收边附近的3个吸收区域.     

非晶态碲镉汞薄膜的射频磁控溅射生长及其结构和光学特性

在玻璃衬底上用射频磁控溅射技术进行了非晶态碲镉汞(α-HgCdTe,α-MCT)薄膜的低温生长.采用X射线衍射(XRD)和原子力显微(AFM)技术对所生长的薄膜进行分析研究,所生长的非晶态HgCdTe薄膜表面平整,没有晶粒出现,获得了射频磁控溅射生长非晶态HgCdTe薄膜的"生长窗口".采用傅里叶红外透射光谱分析技术对非晶态HgCdTe薄膜进行了光学性能研究,在1.0～2.0μm范围内研究了薄膜的透射谱线,获得了薄膜的吸收系数(～8×104cm-1),研究了其光学带隙(约0.83eV)和吸收边附近的3个吸收区域.     

退火对非晶态碲镉汞薄膜微结构和光敏性的影响

对射频磁控溅射生长的非晶态碲镉汞(a-MCT)薄膜在真空状态下进行退火,并通过X射线衍射(XRD)技术指出原生及低于125℃退火后的MCT薄膜均为非晶态.采用双体相关函数g(r)和电学测试系统研究了退火对a-MCT薄膜微结构和光敏性的影响.结果表明:经110℃,115℃和120℃退火后的a-MCT薄膜短程有序畴Rs由退火前的13.9 分别增大至17.9 、20.8 和26.2 ;光敏性则由原来的1.17,分别增加至退火后的2.01、2.67和4.25.     

碲镉汞外延晶膜的输运特性

反常霍尔效应是在检测碲镉汞（ＭＣＴ）薄膜的电学性质时的一种常见现象，反常的根本原理是由于材料的不均匀。本文着讨论ＭＣＴ外延膜的电学参数的种种不均匀引起不同的电磁输运特性。     

碲镉汞薄膜的MOVPE生长和特性

报道了在水平、常压ＭＯＶＰＥ实验型生产装置中,采用互扩散多层工艺（ＩＭＰ）,用金属有机化合物ＤＭＣｄ、ＤｉＰＴｅ和元素Ｈｇ,在ＣｄＴｅ和ＧａＡｓ衬底上生长的ＨｇＣｄＴｅ薄膜,其组分和薄膜厚度的均匀性以及ｐ型电学性质,初步达到了目前红外焦平面列阵研制的要求,同时,这种薄膜的生长具有一定重复性。     

The direct determination of the vacancy concentration andP-T phase diagram of Hg0.8Cd0.2Te and Hg0.6Cd0.4Te by dynamic mass-loss measurements

A modified mass-loss measurement technique is employed, for the direct,in- situ determination of the metal vacancy formation in (Hg_1x2212;itxCd _x )_1−y Te _y (s) withx = 0.2 and 0.4. Forx = 0.2, the metal vacancy concentrations are determined between 336 and 660° C for three different compositions(y) within the homogeneity region and range from 2.4 to6.8 x 10¹⁹cm₋₃. The enthalpy of formation of a singly-ionized metal vacancy is derived to be between 0.17 and 0.45 eV depending upon the deviation from stoichiometry (compositiony). Forx= 0.4, three samples of different y-values give the metal vacancy concentrations from 1.9 to 5.5 x 10¹⁹cm⁻³ between 316 and 649° C, and the enthalpy of vacancy formation between 0.25 and 0.40 eV. Compared to the recent data on HgTe(s), these experimental results show a slight but significant decrease in the enthalpy of vacancy formation from HgTe to Hg_0.8Cd_0.2Te, which supports theoretical predictions of the bond weakening effect of Cd for the latter alloy system. Based on the simultaneously determined equilibrium Hg partial pressures within the homogeneity range, the vacancy concentration-partial pressure isotherms are constructed. The Hg partial pressures are also measured along the three-phase boundaries of the solid solutions of bothx = 0.2 and 0.4, and these are in close agreement with published data obtained by optical absorption measurements.     

Cd0.8Mn0.2Te晶体的生长及其性能

通过适当的工艺措施,采用传统布里奇曼法生长了尺寸为φ30mm×120mm的Cd0.8Mn0.2Te晶体.对晶体进行了X射线粉末衍射、X射线双晶摇摆曲线、紫外-可见光光谱、红外透过率及电阻率测试.测试结果表明,晶体结构为立方型,半峰宽较低,吸收边为720nm,对应禁带宽度为1.722eV,晶体的红外透过率和电阻率都较高.并讨论了晶体中的缺陷对红外透过率和电阻率的影响.     

Bulk growth of Hg0.8Cd0.2Te single crystals by a combined CVT-seeding technique

The growth of high quality Hg_0.8Cd_0.2Te bulk single crystals by CVT, combined with an in-situ seeding technique, is reported here for the first time. For this purpose, a temperature difference of 590° → 540° C with a gradient of 40°-50° C/cm at the solid-vapor interface, and about 0.1 atm of HgI₂ as a transport agent, were employed. The bulk crystals have the expected stoichiometry and compositional homogeneity. Etch pit densities of 10⁴-10⁵ cm⁻² on the (111) face and hitherto unreported etch pits on the (100) face were observed in this work. Possible origins of the sub-grain structure are discussed.     

A complete quantitative model of the isothermal vapor phase epitaxy of (Hg,Cd)Te

A quantitative model of isothermal vapor phase epitaxy is proposed. It can be applied to both closed and open tube systems. This model enables the prediction of compositional profiles of the layers grown by isothermal vapor phase epitaxy with dependence on the growth parameters and thermodynamical data of the (Hg,Cd)Te system. The dependence of compositional profiles of the ISOVPE layers on temperature and time of deposition, source to substrate spacing, mercury and inert gas pressures are discussed for both solid and liquid sources. Modification of the compositional profiles by the postgrowth annealing has also been studied. The proper choice of growth and annealing parameters makes the optimization of the profiles possible. The calculated profiles are compared with the experimental data and a satisfactory quantitative fit is found in most cases. The possible reasons for remaining discrepancies are discussed.     

分子束外延Hg0.68Cd0.32Te薄膜光致发光和喇曼散射的研究

对利用ＭＥＢ技术生长的Ｈｇ０．６８Ｃｄ０．３２Ｔｅ薄膜进行了光致发光和喇曼光谱的研究，拟合薄膜光致发光谱得到的禁带宽度，与红外透射谱得到的薄膜带宽相近；其半宽仅为５ｍｅＶ，带尾能量小于１．３ｍｅＶ，显示了较高的薄膜质量。     

剩余杂质对Hg_(0.8)Cd_(0.2)Te晶体光吸收的影响

研究了Hg_(0.8)Cd_(0.2)Te晶体经吸除工艺处理前后的透射光谱,发现样品经吸除处理后的光吸收发生明显变化,分析认为因吸除工艺降低了样品内的剩余杂质含量,从而减少了杂质参与的光吸收,利用受主“掺杂”实验进一步验证了上述解释。     

As Doping in (Hg,Cd)Te: An Alternative Point of View

Acceptor doping of many II–VI compound semiconductors has proved problematic and doping of epitaxial mercury cadmium telluride (MCT, Hg_1−x Cd _x Te) with arsenic is no exception. High-temperature (>400°C) anneals followed by a lower temperature mercury-rich vacancy-filling anneal are frequently required to activate the dopant. The model frequently used to explain p-type doping with arsenic invokes an amphoteric nature of group V atoms in the II–VI lattice. This requires that group VI substitution with arsenic only occurs under mercury-rich conditions either during growth or the subsequent annealing and involves site switching of the As. However, there are inconsistencies in the amphoteric model and unexplained experimental observations, including arsenic which is 100% active as grown by metalorganic vapor-phase epitaxy (MOVPE). A new model, based on hydrogen passivation of the arsenic, is therefore proposed.     

The direct determination of the vacancy concentration and P-T phase diagram of Hgin0.8Zn0.2Te by dynamic mass-loss measurements

A modified mass-loss measurement technique is employed, for the first time, for the direct, in-situ determination of the metal vacancy formation in (Hg_0.8Zn_0.2)_1-yTe_y,(s). The metal vacancy concentrations are determined between 350 and 650° C for four different compositions(y) within the homogeneity region and range from 1.7 to 6.6 × 10¹⁹ cm^-3. The enthalpy of formation of a singly-ionized metal vacancy is derived to be between 0.32 and 0.72 eV depending upon the deviation from stoichiometry (compositiony). Com-pared to the recent data on HgTe(s), these experimental results show a slight but sig-nificant increase in the enthalpy of vacancy formation from HgTe to Hg_0.8Zn_0.2Te. These data provide the first, direct experimental evidence, in terms of vacancy formation en-ergy, supporting theoretical predictions of the bond strengthening effect of Zn for the latter alloy system. Based on the simultaneously determined equilibrium Hg partial pressures within the homogeneity range, the vacancy concentration-partial pressure iso-therms are constructed. The Hg partial pressures are also measured along the three-phase boundaries of the solid solutions, and these are in close agreement with published data obtained by optical absorption measurements. A considerable part of the P-T phase diagram is, thus, established in this work.