High-temperature behavior of CdTe<Cl> crystals

Petro Fochuk 1Oleg Panchuk 1L. Shcherbak 1Paul Siffert 2

1. Chernivtsi National University (ChNU), 2 Kotsubinsky Str., Chernivtsi 58012, Ukraine
2. European Materials Research Society (E-MRS), Strasbourg, France


CdTe crystals, doped by Cl, are widely used for γ-detectors manufacturing due to their high resistivity and atomic number, as well as long carriers lifetime. Up to now, their properties were investigated in details only at rather low temperatures. It is of interest to know the point defect structure of this material at high temperature where it forms, what will allow to govern the type and concentration of point defects.
CdTe<Cl> crystals were grown by THM and traditional Bridgman techniques. High temperature Hall effect measurements were carried out under well defined Cd or Te vapor pressure in temperature ranging from 300 to 900o C in sealed quartz ampoule using graphite contacts.
At room temperature all of them revealed high resistivity (ρ>108 Ohm cm) with hole mobility ~60 cm2/Vs.
In the investigated samples, the electron mobility decreases from ~500 V/cm2s at 400oC to ~170 V/cm2s at 900o C. During the first heating up to T=650oC the electron concentration did not depend on temperature or Cd pressure and was 5x1018 cm-3; it rises at higher temperatures only. After a quick cooling a rise of [e-] by 1,5-2 times comparing with initial level is observed. A similar situation is reported during the second and third heating-cooling cycle.
Under Te vapor pressure the samples demonstrated p-type conductivity from 180C(μ = 30 V/cm2s, [h+]=1016 cm-3) up to (μ =5 V/cm2s, [h+]=3x1017 cm-3). Between T=550-800oC the conductivity was bipolar and only for even high values (T>800oC) the mobility becomes really of n-type.
In this paper, the observed phenomena are explained in terms of point defect chemistry by Cl-containing precipitates dissolution in Cd saturation region and by rising both Tei- and VCd- concentrations in the Te region.

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Presentation: poster at E-MRS Fall Meeting 2004, Symposium F, by Petro Fochuk
See On-line Journal of E-MRS Fall Meeting 2004

Submitted: 2004-04-28 21:25
Revised:   2009-06-08 12:55
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