Plasma Passivation Etching for HgCdTe

Inductively coupled plasmas (ICP) are the high-density plasmas of choice for the processing of HgCdTe and related compounds. Most dry plasma process works have been performed on HgCdTe for pixel delineation and the p-to-n-type conversion of HgCdTe. We would like to use the advantages of “dry” plasma processing to perform passivation etching of HgCdTe. Plasma processing promises the ability to create small vias, 2 μm or less with excellent uniformity across a wafer, good run-to-run uniformity, and good etch rate control. In this study we developed processes to controllably etch CdTe, the most common passivation material used for photovoltaic-based HgCdTe devices. We created a process based on xenon gas that allows for the slow controllable CdTe etch at only 0.035 μm/min, with smooth morphology and rounded corners to promote further processing.     

Semi-insulating CdTe with a minimized deep-level doping

The possibility to prepare semi-insulating CdTe with a deep-level doping below the limit 10¹³ cm⁻³ demanded in detector industry is studied theoretically within quasi-chemical formalism. We show that proper thermal treatment, including low temperature (ca 200°C) dwell, allows fulfillment of this demand also in 7N or less purity materials. The procedure is demonstrated in Te-rich CdTe doped with a shallow donor. Its principle is based on enhanced defect selfcompensation, which affords at sufficiently low temperature extremely high compensation of shallow defects. New high-temperature transport data are used to refine on previous native defect properties for the modeling. The analysis of diffusion rates at lowered temperature approves the model for a real-time experimental verification.     

Improving optical properties of CdTe quantum dots by a new multidentae biopolymer based on salep

In this work, we have successfully modified aqueous CdTe quantum dots (QDs) by a biopolymer based on poly (2-hydroxyethyl methacrylate) grafted onto salep via a facile method at room temperature. The obtained QDs were characterized using Fourier transform infrared spectroscopy (FT-IR), thermo-gravimetric analysis (TG), X-ray diffraction (XRD), and transmission electron microscopy (TEM). The size of the prepared QDs was estimated around 1.5 nm by TEM and XRD. Optical properties of modified QDs were monitored by absorption and fluorescence spectrophotometers. It was found that the fluorescence intensity of CdTe QDs was enhanced after coating by biopolymer. Finally, the fluorescence intensity of CdTe QDs was investigated at different temperatures and times.     

Specific contact resistivity of indium contacts to n-type CdTe

Indium alloyed to n-type CdTe of about 10¹⁶ cm^-3 electron concentration provides a contact resistivity of about 7 x 10^-3 ohm cm². This is achieved by alloying for 10 minutes at 150-450‡C in a sealed ampoule with an overpressure of cadmium. If the alloying is done in an open tube H₂ flow without a Cd vapor overpressure, alloying temperatures above 250‡C cause the contact resistance to rise as cadmium vacancies increase the compensation in the CdTe. Further improvement of the contact resistivity to 1 x 10^-3 ohm cm is obtained by a 900‡C diffusion of In into the n-CdTe (electron concentration 10¹⁶ cm^-3 before the diffusion).     

Manufacturing of CdTe thin film photovoltaic modules

The technology to fabricate CdTe/CdS thin film solar cells can be considered mature for a large-scale production of CdTe-based modules. Several reasons contribute to demonstrate this assertion: a stable efficiency of 16.5% has been demonstrated for 1 cm² laboratory cell and it is expected that an efficiency of 12% can be obtained for 0.6 × 1.2 m² modules; low cost soda lime float glass can be used as a substrate; the amount of source material is at least 100 times less than that used for single crystal modules and is a negligible part of the overall cost. The fabrication process can be completely automated and a production yield of one module every 2 min can be obtained, which implies a production cost substantially less than 1€/W_P. A further cost reduction will render this kind of energy production competitive with the energy obtained from fossil fuels by approaching the so-called grid-parity. Some new companies have recently announced the start of production or plan to do so in the near future. Many of these plants are located in Germany, some in the USA. In Italy, a new company has been constituted in 2008, with the aim of building a factory with a capacity of 18 MW/year. In this article, we will describe and compare the basic principles of CdTe solar cells and modules. We will include an overview of the potentials of these technologies and of the R&D issues under investigation. This paper describes how the large-area mass production of CdTe solar modules is realized in the Italian factory and presents a worldwide overview of the current production activities.     

Study of polarization phenomena in Schottky CdTe diodes using infrared light illumination

Schottky CdTe diode detectors suffer from a polarization phenomenon, which is characterized by degradation of the spectral properties over time following exposure to high bias voltage. This is considered attributable to charge accumulation at deep acceptor levels. A Schottky CdTe diode was illuminated with an infrared light for a certain period during a bias operation, and two opposite behaviors emerged. The detector showed a recovery when illuminated after the bias-induced polarization had completely progressed. Conversely, when the detector was illuminated before the emergence of bias-induced polarization, the degradation of the spectral properties was accelerated. Interpretation of these effects and discussion on the energy level of deep acceptors are presented.     

基于MBE替代硅衬底的材料综述

主要介绍了几种用MBE技术生长HgCdTe/CdTe的Si衬底的替代性衬底材料的基本参数,以及不同材料的最新生长过程及结果,和对它们的生长结果的比较分析,以此来选择较为适合替代Si衬底来生长HgCdTe/CdTe的衬底。本文通过一系列的对比,得出目前最有发展前景的替代衬底是GaSb衬底,是未来发展的方向。     

Properties and mechanism of solar absorber CdTe thin film synthesis by unipolar galvanic pulsed electrodeposition

Electrochemical deposition of CdTe semiconductor thin films over transparent conducting glass substrates by sequential unipolar current pulses is described. The magnitude of pulsed current and pulse periodicity affects the crystalline structure, morphology, optical absorbance and composition of CdTe films. CdTe films formed under high magnitude pulsed current density ~5–15 mA cm⁻² are crystalline with dominant cubic structure having (111) plane oriented parallel to the substrate. Stoichiometric CdTe film growth occurs with current pulses of short 25–300 ms periodicity and 3–50 ms duration. A mechanism of the CdTe growth involving in situ cathodic tellurization process step involving H₂Te formation and reaction with electrochemically deposited Cd monolayer is described. CdTe film growth in the pulsed electrodeposition occurs under mass transport conditions under strong influence of high magnitude pulsed current. This results in much higher growth rates ~5–8 μm h⁻¹ for CdTe films which is attractive for CdTe solar cells in a production environment.