Morphological evolution,growth mechanism,and magneto-transport properties of silver telluride one-dimensional nanostructures

Single crystalline one-dimensional (1D) nanostructures of silver telluride (Ag₂Te) with well-controlled shapes and sizes were synthesized via the hydrothermal reduction of sodium tellurite (Na₂TeO₃) in a mixed solution. The morphological evolution of various 1D nanostructures was mainly determined by properly controlling the nucleation and growth process of Ag₂Te in different reaction times. Based on the transmission electron microscopy and scanning electron microscopy studies, the formation mechanism for these 1D nanostructures was rationally interpreted. In addition, the current–voltage (I-V) characteristics as a function of magnetic field of the highly single crystal Ag₂Te nanowires were systematically measured. From the investigation of I-V characteristics, we have observed a rapid change of the current in low magnetic field, which can be used as the magnetic field sensor. The magneto-resistance behavior of the Ag₂Te nanowires with monoclinic structure was also investigated. Comparing to the bulk and thin film materials, we found that there is generally a larger change in R (T) as the sample size is reduced, which indicates that the size of the sample has a certain impact on magneto-transport properties. Simultaneously, some possible reasons resulting in the observed large positive magneto-resistance behavior are discussed.     

Photoluminescence of CdTe quantum dots ligated with caprylic acid synthesized at low temperature

Photoluminescent semiconductor nanocrystals or quantum dots (QDs) are usually produced using expensive ligands and solvents at high temperature above 280°C to ensure high-quality optical properties, particularly the photoluminescence of QDs. The reproducibility of highly stable photoluminescence in QD preparation, in most cases, varies depending on many effects, such as the ligand used and temperature. Here a facile preparation of photoluminescent semiconductor CdTe nanocrystals or quantum dots (QDs) is conducted in the presence of caprylic acid at moderate temperatures between 80–140°C, which are much lower than the high temperatures used in conventional organic-phase preparation of CdTe QDs. The results show that the optical properties of CdTe QDs depend considerably on the reaction time, temperature and ligand used.     

Defects in PbTe doped with telluride VTe2: Positron spectroscopy study

Undoped and vanadium-doped lead telluride crystallic samples were studied by positron spectroscopy. It was shown that in undoped samples lead vacancies form large clusters at high temperatures and small clusters at low temperatures. In V-doped samples there are associates of 2 vacancies at all studied temperatures. Vacancy concentration is two orders lower than the concentration of vanadium atoms in PbTe(V) samples.     

Thermoelectric properties of the 0.05 wt.% SbI3-Doped n-Type Bi2(Te0. 95Se0. 05)3 alloy fabricated by the hot pressing method

Thermoelectric properties of the 0.05 wt.% SbI₃-doped n-type Bi₂(Te_o.95Se_o.o5)₃ alloy, fabricated by hot pressing at temperatures ranging from 350°C to 550°C, were characterized. The electron concentration of the alloy decreased as the hot pressing temperature increased due to the annealing-out of the excess Te vacancies. When hot pressed at 350°C, a figure-of-merit of 0.75x10^-3/K was obtained due to the low Seebeck coefficient of -145 μV/K and relatively high electrical resistivity of 2.05 mΩ-cm. Upon increasing the hot pressing temperature, however, the figure-of-merit was improved mainly due to the increase of the Seebeck coefficient. A maximum figure-of-merit of 2.1x10^-3/K was obtained by hot pressing at 550°C.     

CdTe thin film solar cells: Interrelation of nucleation, structure, and performance

The performance of CdTe solar cells as prototype of thin film solar cells strongly depends on film morphology. The needs for high solar cell performance using thin film materials will be addressed covering nucleation and growth control of thin film materials. In order to understand the basic growth mechanisms and their impact on cell performance, we have systematically investigated the growth of CdTe thin films by Close Spaced Sublimation (CSS) using the integrated ultra-high vacuum system DAISY-SOL. CdTe thin films were deposited on TCO/CdS substrates (transparent conductive oxide) held at 270 °C to 560 °C. The properties of the films were determined before and after CdCl₂ treatment using X-ray diffraction and electron microscopy. In addition, solar cells were prepared to find correlations between material properties and cell efficiency. At low sample temperature the films tend to form compact layers with preferred (111) orientation which is lost at elevated temperatures above 450 °C. For CdS layers without (0001) texture there is in addition a low temperature regime (350 °C) with (111) texture loss. After activation treatment the (111) texture is lost for all deposited layers leading to strong recrystallisation of the grains. But the texture still depends on the previous growth history. The loss of (111) texture is evidently needed for higher performance. A clear correlation between cell efficiency and the texture of the CdTe film is observed.     

Dependence of carrier lifetime on Cu-contacting temperature and ZnTe:Cu thickness in CdS/CdTe thin film solar cells

Cu diffusion from a ZnTe:Cu contact interface can increase the net acceptor concentration in the CdTe layer of a CdS/CdTe photovoltaic solar cell. This reduces the space-charge width (W_d) of the junction and enhances current collection and open-circuit voltage. Here we study the effect of Cu concentration in the CdTe layer on carrier lifetime (τ) using time-resolved photoluminescence measurements of ZnTe:Cu/Ti-contacted CdTe devices. Measurements show that if the ZnTe:Cu layer thickness remains constant and contact temperature is varied, τ increases significantly above its as-deposited value when the contacting temperature is in a range that has been shown to yield high-performance devices (~ 280° to ~ 320 °C). However, when the contacting temperature is maintained near an optimum value and the ZnTe:Cu thickness is varied, τ decreases with ZnTe:Cu thickness.     

分离富集金、铂、钯的碲共沉淀物研究

利用不同酸溶解Au,Pt,Pd的碲共沉淀产物的方法,推断其化学成分;并用X射线衍射(XRD)对沉淀产物的成分进行进一步分析确认,从中研究碲共沉淀分离富集Au,Pt,Pd的机理。研究结果表明,在碲共沉淀中,Au主要以单质的形式,Pt和Pd以碲化物形式与Te一起沉淀,为微量或痕量贵金属的分离富集过程提供了理论依据。     

Characterization of HgCdTe Diodes on Si Substrates Using Temperature-Dependent Current-Voltage Measurements and Deep Level Transient Spectroscopy

Reverse current in diodes can be dominated by generation processes, depending exponentially on temperature according to the rate-limiting step in the generation process. In this report, the current-voltage-temperature (IVT) relationship is analyzed for several midwave infrared and long-wave infrared (MWIR x = 0.295, LWIR x = 0.233) Hg_1−x Cd _x Te (MCT) diodes. The energy varied from diode to diode. At high reverse biases, the energy tends toward the band gap energy. Close to zero bias, the energy ranged from 0.06 to 0.1 eV. Deep level transient spectroscopy (DLTS) showed a broad peak centered at 55–80 K for the MWIR MCT. Comparison of the DLTS spectrum to a simulation based on the energy and capture cross section from a rate window analysis shows that the peak is a band of traps. The capacitance transient amplitude increased as the filling pulse increased from 1 μs to 0.1 s, consistent with capture at a dislocation. A shift to lower temperatures for the peak was also observed when the diodes are cooled under forward bias. The shift is reversible, indicating that the traps consist at least partially of a bistable defect.     

高光谱红外探测器组件的研究进展

描述了国外高光谱红外焦平面探测器组件的发展状况和工程应用情况,并介绍了国内高光谱红外焦平面探测器组件的研究进展。通过分析高光谱红外焦平面探测器的性能特点,提出了高光谱红外焦平面探测器的研究重点。     

分子束外延碲镉汞探测器的变结面积I-V测试研究

碲镉汞红外探测器的表面钝化处理对器件暗电流有较大影响,决定了器件的探测性能。为了研究表面钝化层不同生长方式对暗电流的抑制效果,使用分子束外延(Molecular Beam Epitaxy, MBE)系统在Si基衬底上生长碲镉汞材料,分别通过磁控溅射和原位钝化方法生长CdTe/ZnS钝化膜层。采用半导体工艺在碲镉汞材料上制备了变面积光伏探测器。通过测试不同钝化膜层器件的暗电流,分析零偏电阻和面积乘积(R₀A)与周长面积之比(p/A)的关系。结果表明,磁控溅射生长钝化层的Si基碲镉汞器件存在较大的隧穿电流,而原位钝化生长钝化层的Si基碲镉汞器件能更有效地抑制表面漏电流。拟合器件R₀A因子随PN结面积的变化,得出原位生长钝化层的器件具有更好的钝化效果。变面积器件的制备和测试能够有效且直观地反映器件性能。