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1.
L. Verger J. P. Bonnefoy F. Glasser P. Ouvrier-Buffet 《Journal of Electronic Materials》1997,26(6):738-744
There has been considerable recent progress in II-VI semiconductor material and in methods for improving performance of the
associated radiation detectors. New high resistivity CdZnTe material, new contact technologies, new detector structures, new
electronic correction methods have opened the field of nuclear and x-ray imaging for industrial and medical applications.
The purpose of this paper is to review new developments in several of these fields. In addition, we will present some recent
results at LETI concerning first the CdTe 2-D imaging system (20 × 30 mm2 with 400 × 600 pixels) for dental radiology and second the CdZnTe fast pulse correction method applied to a 5 × 5 × 5 mm3 CdZnTe detector (energy resolution = 5% for detection efficiency of 85% at 122 keV) for medical imaging. 相似文献
2.
M. S. Han S. R. Hahn H. C. Kwon Y. Bin T. W. Kang J. H. Leem Y. B. Hou H. C. Jeon J. K. Hyun Y. T. Jeoung H. K. Kim J. M. Kim T. W. Kim 《Journal of Electronic Materials》1998,27(6):680-683
Double-crystal x-ray rocking curve (DCRC) and secondary-ion mass-spectroscopy (SIMS) measurements have been performed to investigate the effect of rapid thermal annealing on the interdiffusion behavior of Hg in HgTe/CdTe superlattices grown on Cd0.96Zn0.04Te (211)B substrates by molecular beam epitaxy. The sharp satellite peaks of the DCRC measurements on a 100-period HgTe/CdTe (100Å/100Å) superlattice show a periodic arrangement of the superlattice with high-quality interfaces. The negative direction of the entropy change obtained from the diffusion coefficients as a function of the reciprocal of the temperature after RTA indicates that the Hg diffusion for the annealed HgTe/CdTe superlattice is caused by an interstitial mechanism. The Cd and the Hg concentration profiles near the annealed HgTe/CdTe superlattice interfaces, as measured by SIMS, show a nonlinear behavior for Hg, originating from the interstitial diffusion mechanism of the Hg composition. These results indicate that a nonlinear interdiffusion behavior is dominant for HgTe/CdTe superlattices annealed at 190°C and that the rectangular shape of HgTe/CdTe superlattices may change to a parabolic shape because of the intermixing of Hg and Cd due to the thermal treatment. 相似文献
3.
Thin CdTe films were deposited by hot-wall epitaxy (HWE) on (111) HgCdTe and CdZnTe substrates at temperatures from about 140 to 335°C. X-ray rocking curves were used to show that crystal quality of the CdTe (111)B films improved as substrate temperature increased from 140 to about 250°C. Rocking curve values for full width at half maximum (FWHM) decreased from 2–4 degrees at 140–150°C to less than 100 arc-s at 250°C, and a FWHM of 59 arc-s was the lowest value observed near 250°C. The FWHM of the HWE CdTe was found to be insensitive to growth rate below about 400Å/min, but increased to four degrees at 1250Å/min. X-ray diffraction confirmed that films grown on the B-face at higher temperatures were epitaxial, but contained a significant volume fraction, 35% to 50%, of rotational in-plane twins. Electron microscopy confirmed a coarse twin density, and photoluminescence spectra showed an absence of excitonic emission in the HWE films. Simultaneous growth on two (111) HgCdTe substrates with different surface polarities between 230°C and 335°C showed that deposition rate on the A-face decreased relative to that on the B-face as temperature increased. Films grown on the B-face exhibited better surface morphologies than those grown on the A-face. 相似文献
4.
Strategies to increase CdTe solar-cell voltage 总被引:1,自引:0,他引:1
There is a significant difference in performance between today's highest efficiency of CdTe solar cells and single-crystal cells of comparable band gap. The largest contribution to this difference is the voltage, where the values for the best CdTe cells are about 230 mV below the best GaAs cells when an appropriate adjustment is made for band gap. CdTe voltage and fill-factor are currently compromised by low recombination lifetime (near 1 ns), low hole density (near 1014 cm− 3), and in some cases an excessive back-contact barrier. Numerical simulation is used to evaluate how combinations of lifetime, carrier density, back electron reflection, and interfacial properties affect voltage and cell performance. Two different strategies for improving voltage and performance are explored. 相似文献
5.
We have performed selective area epitaxy (SAE) of CdTe layers grown by molecular beam epitaxy using a shadow mask technique.
This technique was chosen over other SAE techniques due to its simplicity and its compatibility with multiple SAE patterning
steps. Features as small as 50 microns × 50 microns were obtained with sharp, abrupt side walls and flat mesa tops. Separations
between mesas as small as 20 microns were also obtained. Shadowing effects due to the finite thickness of the mask were reduced
by placing the CdTe source in a near normal incidence position. Intimate contact between the mask and the substrate was essential
in order to achieve good pattern definition. 相似文献
6.
7.
K. Yasuda Y. Tomita Y. Masuda T. Ishiguro Y. Kawauchi H. Morishita Y. Agata 《Journal of Electronic Materials》2002,31(7):785-790
Iodine doping of CdTe layers grown on (100) GaAs by metal-organic vapor phase epitaxy (MOVPE) was studied using diethyltelluride
(DETe) and diisopropyltelluride (DiPTe) as tellurium precursors and ethyliodine (EI) as a dopant. Electron densities of doped
layers increased gradually with decreasing the growth temperature from 425°C to 325°C. Doped layers grown with DETe had higher
electron densities than those grown with DiPTe. When the hot-wall temperature was increased from 200°C to 250°C at the growth
temperature of 325°C, doped layers grown with DETe showed an increase of the electron density from 3.7×1016 cm−3 to 2.6×1018 cm−3. On the other hand, such an increase of the electron density was not observed for layers grown with DiPTe. The mechanisms
for different doping properties for DETe and DiPTe were studied on the basis of the growth characteristics for these precursors.
Higher thermal stability of DETe than that of DiPTe was considered to cause the difference of doping properties. With increasing
the hot-wall temperature from 200°C to 250°C, the effective ratio of Cd to Te species on the growth surface became larger
for layers grown with DETe than those grown with DiPTe. This was considered to decrease the compensation of doped iodine and
to increase the electron density of layers grown with DETe. The effective ratio of Cd to Te species on the growth surface
also increased with decreasing growth temperature. This was considered to increase the electron density with decreasing growth
temperature. 相似文献
8.
T. D. Dzhafarov S. S. Yesilkaya N. Yilmaz Canli M. Caliskan 《Solar Energy Materials & Solar Cells》2005,85(3):371-383
The effective diffusion coefficients of Cu for thermal and photodiffusion in the CdTe films have been estimated from resistivity versus duration of thermal or photoannealing curves. In the temperature range 60–200°C the effective coefficient of thermal diffusion (Dt) and photodiffusion (Dph) are described as Dt=7.3×10−7exp(−0.33/kT) and Dph=4.7×10−8exp(−0.20/kT).It is found that the diffusion doping of CdTe thin films by Cu at 400°C results in a sharp decrease of resistivity up to 7 orders of magnitude of p-type material, depending on thickness of Cu film. The comparative study of performance of CdTe(Cu)/CdS and CdTe/CdS cells has been studied. It is shown that the diffusion doping of CdTe film by Cu increases efficiency of CdTe(Cu)/CdS cells from 0.9% to 6.8%. The degradation of photovoltaic parameters of CdTe(Cu)/CdS cell, during testing under forward and reverse bias at room temperature, proceeds at a larger rate than those of CdTe/CdS cell without Cu. The degradation of performance of CdTe(Cu)/CdS cells is tentatively assigned to electrodiffusion of Cu in CdTe, resulting in redistribution of concentration of Cu-related centers in CdTe film and heterojunction region. 相似文献
9.
M. Hädrich N. Lorenz H. Metzner U. Reislöhner S. Mack M. Gossla W. Witthuhn 《Thin solid films》2007,515(15):5804-5807
In this paper, we describe our new baseline for CSS-CdTe-CdS solar cells on 10 × 10 cm2 substrates. The deposition of the p-n junction and all the following steps were performed at the Institut für Festkörperphysik (IFK) in Jena. Using the new baseline, we are already able to produce solar cells with similar properties as commercial ones. In the batch type process, all manufacturing steps can be investigated separately. We employ Rutherford backscattering spectrometry (RBS), X-ray diffraction (XRD) and external quantum efficiency (EQE) measurements to characterise the structure of the bulk materials and interfaces. It is demonstrated that by RBS the front contact becomes accessible for thinned CdTe films. At the back contact, RBS spectra show a tellurium accumulation which is due to etching. This tellurium rich layer is confirmed by XRD with Rietveld refinement. The intermixing at the CdS-CdTe interface caused by the activation step is quantified by a bandgap determination based on EQE measurements. From the bandgap energy of the CdTe1 − xSx compound, we calculated the sulphur fraction x at the interface. XRD measurements imply that the activation step induces a (111) texture in CdTe. With regard to an improved manufacturing process, our cells are compared to industrial cells produced by Antec Solar Energy. 相似文献
10.
Atomic layer epitaxy or ALE has proven to be useful for the growth of epitaxial layers of high uniformity, good quality, and
well-controlled thickness. In this study, we have carried out in-situ monitoring during the atmospheric pressure ALE of CdTe on GaAs (100) substrates using spectroscopic ellipsometry (SE). The
susceptor temperature, reactant partial pressures, as well as the flow and flush duration for each precursor are crucial process
variables for ALE growth. Growth was carried out for 20–25 cycles under different sets of these process conditions during
the experiment and in-situ SE was used to verify the presence of layer-by-layer growth, which enabled the quick determination of the process window.
We observed ALE growth of CdTe at 300°C, supporting the explanation that the growth of CdTe occurs via a surface catalyzed
decomposition of the Te precursor di-isopropyltelluride (DIPTe). Investigation of ALE mode growth behavior for different susceptor
temperatures and DIPTe flush times indicated that the growth was limited by competition between desorption and reaction of
the adsorbed DIPTe species on the Cd terminated surface. 相似文献