Effects of excess tellurium on the properties of CdZnTe radiation detectors

Abstract

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.

Solution growth of In-doped CdMnTe crystals by the vertical Bridgman method with the ACRT technique

“…The current-voltage (I-V) curve of the device measured at room temperature presented good linear behavior, as shown in [16], the Te solution vertical Bridgman method firstly incorporated sufficient Te Cd caused by the Te-rich alloy into CdMnTe crystals to compensate the native points defects V Cd , and then used the shallow-donor impurity indium to compensate the residual Cd vacancies. The efficient compensation Cd vacancies make the free carrier density decrease and the resistivity increase.…”

New Approaches for Making Large-Volume and Uniform CdZnTe and CdMnTe Detectors

“…exhibit high resistivity and, subsequently, good detector performance. The possible explanation of this Te-rich requirement is that excess Te might be involved in the generation of Te antisite Te defects that are believed to play a role in pinning the Fermi level near the middle of the band-gap [8]. However, it is very hard to grow Te-inclusions-free CZT detectors in an excess Te environment.…”

Characterization of detector-grade CdZnTe:Al crystals obtained by annealing

“…This indicates that the annealed CZT:Al crystals can be used to fabricate radiation detectors. In the growing process of high-resistivity CZT crystals [14], the method is to firstly incorporate sufficient Te Cd into the crystals and then to use the shallow-donor impurities, such as indium or aluminum, to compensate the residual-Cd vacancies. On the contrary, in our case, Te antisites are used to compensate the residual-Cd vacancies in the annealing process because Al atoms have already compensated partial Cd vacancies in the growing process.…”

“…The mt value of the detector fabricated by 240 h annealed CZT:Al crystal is lower than that fabricated by 120 h annealed CZT:Al crystal. The reason may be that longer annealing time results in overfull Te Cd , which can trap more electrons [14]. According to the above discussions, annealing is an essential upgrade method to change the useless sample with bad crystal quality into the useful one for radiation detector.…”