Direct growth of CdTe on (100), (211), and (111) Si by metalorganic chemical vapor deposition

CdTe epilayers were grown directly on (100), (211), and (111) silicon substrates by metalorganic chemical vapor deposition (MOCVD). The crystallinity and the growth orientation of the CdTe film were dependent on the surface treatment of the Si substrate. The surface treatment consisted of exposure of the Si surface to diethyltelluride (DETe) at temperatures over 600°C prior to CdTe growth. Direct growth of CdTe on (100) Si produced polycrystalline films whereas (lll)B single crystals grew when Si was exposed to DETe prior to CdTe growth. On (211) Si, single crystal films with (133)A orientation was obtained when grown directly; but produced films with (211)A orientation when the Si surface was exposed to DETe. On the other hand, only (lll)A CdTe films were possible on (111) Si, both with and without Te source exposure, although twinning was increased after exposure. The results indicate that the exposure to a Te-source changes the initial growth stage significantly, except for the growth on (111) Si. We propose a model in which a Te atom replaces a Si atom that is bound to two Si atoms.     

垂直Bridgman生长CdTe过程的数值模拟

采用 Galerkin有限元算法 ,计算了垂直 Bridgman生长 Cd Te过程中的温场分布、液体流动和固液界面的形状 ,分析了生长速率、温区分布等参数对固液界面的影响 .计算结果表明 ,较小的生长速率可以获得更为平坦的固液界面 ,适当增加结晶区域的温度梯度也是改善固液界面形状的一个有效方法 .同时 ,通过对生长系统中的热流分析 ,表明在生长过程的中间阶段 ,热量交换主要集中在梯度区附近 ,而坩埚两端与外部环境的热量交换较少     

Ge(211)衬底上分子束外延CdTe薄膜

采用分子束外延在3英寸Ge(211)衬底上生长了10 μm厚的CdTe(211)B薄膜.CdTe表面镜面光亮,3英寸范围厚度平均值9.72 μm,偏差0.3 μm;薄膜晶体质量通过X射线双晶迴摆曲线进行评价,FWHM平均值80.23 arcsec,偏差3.03 arcsec; EPD平均值为4.5×106cm-2.通过研究CdTe薄膜厚度与FWHM和EPD的关系,得到CdTe的理想厚度为8～9 μm.     

n-CdTe Schottky势垒薄膜太阳能电池中嵌入p型层对其势垒高度影响的计算机模拟

通过求解Ｐｏｉｓｓｏｎ方程，对热平衡态金属：ｐ－ｎ－ＣｄＴｅＳｃｈｏｔｋｙ势垒薄膜太阳能电池进行计算机数值模拟。嵌入的ｐ型层增大传统金属：ｎ－ＣｄＴｅ结的有效Ｓｃｈｏｔｋｙ势垒高度与ｐ型层厚度、掺杂浓度以及ｎ－ＣｄＴｅ本底电阻率有依赖关系。最后讨论嵌入ｐ型层增强ＣｄＴｅＳｃｈｏｔｋｙ势垒太阳能电池对光生载流子的收集作用。     

Growth and optical characterization of strained CdZnTe/ CdTe quantum wells

We have grown strained Cd_1-xZn_xTe(x ≈ 0.2)/CdTe single and multiple quantum wells by molecular beam epitaxy. GaAs was used as a substrate. The well widths were systematically increased until the critical thickness was exceeded. Low-temperature (liquid helium) photoluminescence (PL) spectroscopy was used to characterize the films. Two prominent PL peaks were observed: one arising from the quantum well and the other from the barrier material. The energy of the quantum well luminescence is consistent with theory when strain is included. The critical layer thickness for the CdTe quantum wells was found to be between 150 and 175 å, in agreement with the model of Matthews and Blakeslee.     

Molecular beam epitaxial growth of Cd<Subscript>1−y</Subscript>Zn<Subscript>y</Subscript>Se<Subscript>x</Subscript>Te<Subscript>1−x</Subscript> on Si(211)

We report on the first successful growth of the quaternary alloy Cd_1−yZn_ySe_xTe_1−x(211) on 3-in. Si(211) substrates using molecular beam epitaxy (MBE). The growth of CdZnSeTe was performed using a compound CdTe effusion source, a compound ZnTe source, and an elemental Se effusion source. The alloy compositions (x and y) of the Cd_1−yZn_ySe_xTe_1−x quaternary compound were controlled through the Se/CdTe and ZnTe/CdTe flux ratios, respectively. Our results indicated that the surface morphology of CdZnSeTe improves as the Zn concentration decreases, which fits well with our previous observation that the surface morphology of CdZnTe/Si is poorer than that of CdSeTe/Si. Although the x-ray full-width at half-maximums (FWHMs) of CdZnSeTe/Si with 4% of Zn + Se remain relatively constant regardless of the individual Zn and Se concentrations, etched-pit density (EPD) measurements exhibit a higher dislocation count on CdZnSeTe/Si layers with about 2% Zn and Se incorporated. The enhancement of threading dislocations in these alloys might be due to an alloy disorder effect between ZnSe and CdTe phases. Our results indicate that the CdZnSeTe/Si quaternary material with low Zn or low Se concentration (less than 1.5%) while maintaining 4% total Zn + Se concentration can be used as lattice-matching composite substrates for long-wavelength infrared (LWIR) HgCdTe as an alternative for CdZnTe/Si or CdSeTe/Si.     

Dual-band infrared detectors made on high-quality HgCdTe epilayers grown by molecular beam epitaxy on CdZnTe or CdTe/Ge substrates

In this paper, we present all the successive steps for realizing dual-band infrared detectors operating in the mid-wavelength infrared (MWIR) band. High crystalline quality HgCdTe multilayer stacks have been grown by molecular beam epitaxy (MBE) on CdZnTe and CdTe/Ge substrates. Material characterization in the light of high-resolution x-ray diffraction (HRXRD) results and dislocation density measurements are exposed in detail. These characterizations show some striking differences between structures grown on the two kinds of substrates. Device processing and readout circuit for 128×128 focal-plane array (FPA) fabrication are described. The electro-optical characteristics of the devices show that devices grown on Ge match those grown on CdZnTe substrates in terms of responsivity, noise measurements, and operability.     

CdTe/CdS thin film solar cells grown in substrate configuration

The ability to grow efficient CdTe/CdS solar cells in substrate configuration would not only allow for the use of non‐transparent and flexible substrates but also enable a better control of junction formation. Yet, the problems of barrier formation at the back contact as well as the formation of a p–n junction with reduced recombination losses have to be solved. In this work, CdTe/CdS solar cells in substrate configuration were developed, and the results on different combinations of back contact materials are presented. The Cu content in the electrical back contact was found to be a crucial parameter for the optimal CdCl₂‐treatment procedure. For Cu‐free cells, two activation treatments were applied, whereas Cu‐containing cells were only treated once after the CdTe deposition. A recrystallization behavior of the CdTe layer upon its activation similar to superstrate configuration was found; however, no CdTe–CdS intermixing could be observed when the layers were treated consecutively. Remarkably high V_OC and fill factor of 768 mV and 68.6%, respectively, were achieved using a combination of MoO₃, Te, and Cu as back contact buffer layer resulting in 11.3% conversion efficiency. With a Cu‐free MoO₃/Te buffer material, a V_OC of 733 mV, a fill factor of 62.3%, and an efficiency of 10.0% were obtained. Copyright © 2012 John Wiley & Sons, Ltd.     

CdTe and HgTe surface growth kinetics for molecular and metalorganic molecular beam epitaxy

The surface growth kinetics of CdTe and HgTe have been investigated during molecular and metalorganic molecular beam epitaxy. The surface growth kinetics was studied through in-situ measurements of the growth rate as a function of flux ratio and substrate temperature on the (001), (111)B, and (211)B CdTe surface orientations. For the (001) and (111)B CdTe growth kinetics, the existence of low binding energy surface precursor sites was proposed for both molecular and atomic growth species before lattice incorporation. Intensity oscillations were observed during HgTe growth on misoriented (111)B surfaces and during CdTe growth on the (211)B orientation. The (211)B surface reconstructions displayed both vicinal and singular surface characteristics, depending on the growth flux ratio.