Low Temperature Photoluminescence and Photoinduced Current Spectroscopy on CdZnTe Grown by High-Pressure Bridgman Techni
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properties makes CdTe and CdZnTe (CZT) potential semiconductor-based detectors for X- and .y -ray applications at room-temperature. The ternary compound CdZnTe elaborated by the new High Pressure Bridgman (HPB) method [3] presents some advantages over CdTe grown by standard Traveling Heater Method (THM). Its relative wider band gap offers high resistivity at room temperature and its large ingot size is at moderate cost. Besides this, CZT presents a good electron mobility-lifetime product. However, the hole mobility-lifetime product becomes reduced resulting in degradation of hole charge collection as compared to CdTe. The origin of this enhanced hole trapping in CZT has not yet been well studied and is not understood at present. It is known that the performance of a semiconductor-based detector depends on the total charge collection (hole and electron). This last is strongly influenced by the presence of electrical active defects and the crystal quality of the CZT material [4]. Therefore, the characterization of shallow and deep trapping levels is of great importance to improve the electrical properties of the CZT detectors. In this paper we present a deep level characterization of semi-insulating CZT crystals taken from different slices of the same ingot using a combination of experimental techniques. Photo-induced current transient spectroscopy (PICTS) and thermo-electric effect spectroscopy (TEES) were used to study the characteristics and the distribution of defects present in the CZT ingot. The photoluminescence (PL) has been used to control the quality of these CZT samples and to determine the zinc segregation through the ingot. Finally, we have tried to modelize the high resistivity in order to clarify the compensation mechanism in CZT material. 67 Mat. Res. Soc. Symp. Proc. Vol. 588 ©2000 Materials Research Society
GROWTH AND CHARACTERIZATION TECHNIQUES The Cd 09Zn 0jTe samples investigated in this study were grown with High Pressure Bridgman Method by eV Products. The electrical intrinsic resistivity of the as grown CZT crystals exceeds 10' 0Qcm at room temperature. So, the PICTS, TEES and PL experiments are well convenient to study the as grown CZT material. The samples were taken from the same ingot and they were lOxl0x2 mm 3 sized. The position of these samples is 1mm, 5mm, 15mm and 20mm from the top of the ingot, referenced as CZT1, CZT5, CZT15 and CZT20 respectively. These samples were etched in bromine methanol solution and rinsed in methanol. The ohmic contacts have been made by electroless deposition of gold in the front and the back face. The optical excitation source used for filling traps in the PICTS measurements was a HeNe laser (emitting at 0.631am). The applied voltage was 1OV and the pulse duration was fixed at
150ms in order to reach trap saturation. In TEES experiments, the thermoelectric current induced by the temperature difference across the sample is measured without any external applied bias. The heating rate, about 0.20.3K/s, leads to a temperature difference about 5K between the
