Improved CdZnTe detectors grown by vertical Bridgman process
- PDF / 614,694 Bytes
- 10 Pages / 414.72 x 648 pts Page_size
- 31 Downloads / 184 Views
16056
ABSTRACT The 7 ray (57Co) and a particle (241Am) detector response of Cdl.xZnxTe crystals grown by vertical Bridgman technique was studied under both positive and negative bias conditions. Postgrowth processing was utilized to produce a high-resistivity material with improved chargecollection properties. Samples of various Zn concentrations were investigated by I-V measurements and thermally stimulated spectroscopies to determine the ionization energies of deep levels in the band gap. When the post-processing conditions were optimized the lowenergy tailing of the ,-ray photopeaks was significantly reduced and an energy resolution of under 5% was achieved for the 122 keVy-photon line in crystals with x=0.2 Zn content at room temperature. A peak to background ratio of 14:1 for the 122 keV photopeak from 57Co was observed on the best sample, using a standard planar detection geometry. The low-energy 14.4 keVX-ray line could also be observed and distinguished from the noise. INTRODUCTION Semi-insulating (SI) CdZnTe crystals have shown great potential for room-temperature radiation-detector and imaging applications [1,2]. The combination of the high efficiency and good energy resolution of CdZnTe detectors make these compounds attractive in a number of applications such as simple, low-cost, efficient, rugged, portable industrial sensors, highsensitivity radiation detectors for nuclear safeguards and imaging devices for X-ray digital radiography and 7 diagnostics. So far CdZnTe crystals grown by the high-pressure Bridgman (HPB) technique containing typically 10% Zn have shown the best detector properties and longterm stability [3,4]. The relatively poor hole transport properties of the HPB-grown CdZnTe crystals, however, result in a low-energy tailing of the photopeaks and lower energy resolution than desired. To compensate for the poor hole collection and achieve a better energy resolution single-carrier devices [5] and pulse-processing techniques [6] were developed. It would be however a tremendous advantage if the hole transport properties of SI CdZnTe could be improved and the low-energy tailing eliminated in CdZnTe radiation detectors. In this report we discuss the radiation detector performance of Cdi-.Zn Te (x-0.2, 0.1, and 0.05) crystals grown by the classical vertical Bridgman technique at Johnson Matthey Electronics (JME) and subsequently processed to obtain SI crystals with good carrier transport properties. The response of the detectors to radiation from "Co (14.4, 122, and 136 keVy rays) (shown in figure 1), from 133 Ba as well as a and 7 radiation from a 24 'Am source (shown in figure 2) under both positive and negative bias conditions was studied. In addition to the detector performance the carrier transport properties and deep electronic levels were also studied using thermoelectric effect spectroscopy (TEES) [7,8], thermally stimulated current (TSC) [9] and I-V measurements. The performances of the detectors were compared to the performance of planar and coplanar grid detectors made from commercia
Data Loading...
