Investigation on electrical transport properties of CdZnTe pixel detector

Semi-insulating cadmium zinc telluride (CdZnTe or CZT) is an excellent material candidate for fabricating room-temperature nuclear radiation semiconductor detectors due to its high resistivity and good carrier transport behaviors. It is widely used in nuclear security, nuclear medicine, space science, etc. Nevertheless, the traditional CdZnTe planar detector is subjected to the effect of "hole trailing" on its hole transport characteristic, where its energy resolution and the photoelectric peak efficiency both decrease, and thus deteriorating the detection performance. In order to eliminate the effect of hole capture, the electrode with pixel structure for CdZnTe detector is designed for detecting single carriers that are only electrons. In this paper, a 10 mm x 10 mm x 2 mm wafer cut from an In doped Cd0.9Zn0.1 Te single crystal, grown by the modified vertical Bridgman method, is employed to fabricate a 4 x 4 CdZnTe pixel detector, which is composed of 16 small pixel units with an area of 2 mm x 2 mm. Each of the pixel units is linked up with ASIC multichannel preamplifier and shaping amplifier by flip chip technology. Finally, the signal is treated by an integrated sensing chip. In the first case, the electrical properties and carrier transport properties of CdZnTe pixel detector are characterized by current-voltage (I -V) measurement via an Agilent 4155C semiconductor parameter analyzer and gamma ray energy spectrum response via a standard Multi Channel Analyzer 6560 spectra measurement system, respectively. In the second case, the differences between CdZnTe planar detector and 4 x 4 pixel detector in the detection performance are discussed in detail. The results indicate that the bulk resistivity of CdZnTe pixel detector is determined to be about 1.73 x 10(10) Omega.cm by a linear fit of I -V curve. The maximum leakage current of a single pixel is less than 2.2 nA for a bias voltage of 100 V. Furthermore, the carrier transport behaviors are evaluated with the mobility-lifetime product for electron in CdZnTe detector, which is 5.41 x 10(-4) cm(2) .V-1 estimated by gamma ray energy spectroscopy response under various bias voltages from 50 to 300 V at room temperature. The energy resolutions of the two CdZnTe detectors can reflect the ability of them to distinguish different energy gays during operation. The best energy resolution of a single pixel in CdZnTe pixel detector for Am-241@59.5 keV gamma ray increases up to 5.78% under a 300 V bias voltage, whereas that of CdZnTe planar detector is only 6.85% in the same conditions. As a consequence, the detection performance of 4 x 4 CdZnTe pixel detector is better than that of the planar detector.