Electrical properties of CdTe:Br single crystals at high temperature

Petro Fochuk 1Yevheniya Verzhak 1Roman Grill 2Oleg Panchuk 1

1. Chernivtsi National University (ChNU), 2 Kotsubinsky Str., Chernivtsi 58012, Ukraine
2. Charles University, Institute of Physics (FU UK), Ke Karlovu 5, Prague 121 16, Czech Republic

CdTe crystals, doped by chlorine, have found an application for gamma- and X-ray detector production. The possibility of CdTe:I films to “feel” radiation was shown. Bromine also can be a very interesting dopant for this purpose but there are few information concerning its behavior in CdTe. The goal of this work was to study the electrical properties and self-compensation phenomena in CdTe:Br single crystals at high temperature.

The crystals were grown by the Bridgman method and contained 3*1019 at/cm3 of Bromine in the melt. Hall effect measurements were performed under well-defined Cd/Te vapor pressure at ~600-1200 K using the 6 contacts method. Temperature, component vapor pressure and temporal dependencies of specific conductivity, charge carrier density and their mobility were studied.

The electron density ([e-]) at RT in as-grown samples varied from 1010 till 1017 cm-3 but after heating above 800 K it became essentially higher than in undoped CdTe, sometimes  exceeding 1018 cm-3 at T>1100 K. It didn’t depend on the Cd vapor pressure (PCd) till 1000 K and increased at higher temperature with PCd increasing. In heavily doped samples after heating above 900 K the [e-] was above 1017 cm-3  and constant in a wide temperature range (500-1100 K). The electron mobility in CdTe:Br crystals usually was lower comparing with undoped CdTe due to the high concentration of dopants atoms. It was impossible to reduce the [e-] sufficiently by PCd reducing or quenching. Only the treatment at Te saturation allowed decreasing the [e-] more than 6 orders of magnitude (at RT). The observed strong self-compensation phenomena are discussed in the framework of the Krogers’ quasichemical point defect theory assuming the presence in the samples of a large quantity of dopant acceptors (Bromine associates with Cd vacancies) and dopant donors (BrTe).

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Presentation: Poster at E-MRS Fall Meeting 2009, Symposium C, by Petro Fochuk
See On-line Journal of E-MRS Fall Meeting 2009

Submitted: 2009-05-11 13:52
Revised:   2009-06-07 00:48
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