Native defects and oxygen and hydrogen-related defect complexes in CdTe: Density functional calculations J. Appl. Phys.
Room-temperature radiation detectors have been fabricated on high-resistivity, indium-doped Cd 0.90 Zn 0.10 Te crystals grown under different amounts of excess Te. The effects of the excess Te on the properties of the detectors are explained by a simple model using only three parameters: the density of Cd vacancies, the density of Te antisites (Te at Cd sites), and the deep level of doubly ionized Te antisites. The best detectors, which can resolve the low-energy Np-L and Te-K peaks as well as Cd and Te escape peaks of 241 Am, are produced from crystals grown with 1.5% excess Te. The detectors fabricated from crystals grown without excess Te are unable to resolve any characteristic-radiation peaks of 241 Am and 57 Co. This result is explained by a model of networked p-type domains in an n-type matrix or vice versa, which is caused by the lack of sufficient deep-level Te antisites. Such conduction-type inhomogeneity causes massive electron and hole trapping. As for the detectors fabricated from Cd 0.90 Zn 0.10 Te crystals grown with 2% and 3% excess Te, they are able to resolve the 241 Am 59.5-keV, 57 Co 122-keV, and 57 Co 136-keV radiation peaks. However, the full-width at half-maximum (FWHM) values of these peaks are broadened, especially the high-energy 57 Co peaks. These phenomena are attributed to the hole and, possibly, electron trapping by Cd vacancies and Te antisites, respectively. The result of the analysis indicates that sufficient Te antisites and a low density of carrier traps in Cd 0.90 Zn 0.10 Te are essential for producing high-quality radiation detectors. In the analysis, it was discovered that most of the excess Te, on the order of 1-2 × 10 20 cm −3 , remain electrically inactive. A possible explanation for this phenomenon is that the excess Te atoms form neutral Te-antisite and Cd-vacancy complexes, such as Te Cd ·(V Cd ) 2 , during the post-growth cooling process.
A surface region about 0.22 μm thick of cadmium-annealed undoped n-type CdTe single crystal was converted to p type by implantation of 60-keV As+ ions followed by a cadmium annealing. The electrical properties of the p-type layer were measured as well as the photovoltaic properties of the p-n junction formed in this way. For illumination by sunlight an open-circuit voltage of 0.84 V was found in a cell with a solar efficiency of 3.0%. The parameters of the junction were determined using a model designed to describe the spectral response of the cell.
Epitaxial layers of mercury cadmium telluride false(Hg1−xCdxnormalTefalse) with Cd composition ( x value) from 0.17 to 1.0 have been grown in Te solution by a liquid phase epitaxial (LPE) technique. The layers are grown on normalCdTe substrates with (100), (110), (111)Cd, and (111)Te orientations. The best surface is obtained on the (111)Cd surface. Typical hole concentration of normalHgCdTe layers with Cd composition of 0.2 is on the order of 5×1016/cm3 with a Hall mobility of 400 cm2/Vsec at 77°K. X‐ray topographic analysis indicates that these epilayers have as good a crystalline structure as that of the substrates.
This letter presents a simple model developed for calculating the Hall coefficient and Hall mobility in inhomogeneous narrow-band-gap semiconductors, including inclusions with opposite conduction type. The model is based on one assumption that the current density is a uniform constant in the sample in spite of the inhomogeneities. This assumption is supported by a variational calculation based on the principle of least entropy production rate. The model is then applied to explain the anomalous Hall data in the n-type Hg0.8Cd0.2Te, and a good fit is obtained when p-type Hg0.8Cd0.2Te is considered to be the inclusions. The results show that some assumptions in a previous layer model are not necessary in order to explain the observed phenomena. By using this simplified treatment of material inhomogeneity, it will be easier to design experiments to investigate the cause of such inhomogeneity.
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