Performance Characteristics of CdTe Gamma-Ray Spectrometers
- PDF / 291,143 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 16 Downloads / 166 Views
PERFORMANCE CHARACTERISTICS OF CDTE GAMMA-RAY SPECTROMETERS MICHAEL R. SQUILLANTE, HERBERT COLE, PETER WAER, AND GERALD ENTINE Radiation Monitoring Devices, Inc., 44 Hunt Street, Watertown, MA 02172 ABSTRACT The use of cadmium telluride (CdTe) semiconductor nuclear detectors is continuing to expand into new areas because of their unique properties which include room temperature operation and high detection efficiency. In addition, they remain the material of choice in many critical applications such as nuclear medicine and1 power plant monitoring because of their reputation for reliability and long term stability . CdTe is by far the most developed of the compound semiconductors used in nuclear detector applications and it offers a number of significant benefits to researchers, clinicians and engineers who have special requirements relating to size, sensitivity and operating temperature. Recently, there have been improvements in the growth of the crystalline material and in the fabrication procedures which have resulted in better performance and in the ability to produce arrays. This article describes the physical and electronic properties of CdTe nuclear detectors, discusses how the crystal growth and device fabrication procedures can affect these properties, and compares the performance to CdZnTe detectors. INTRODUCTION The requirements for semiconductor nuclear detectors are well known. Clearly, high stopping power for efficient detection is desirable. CdTe is composed of two high atomic number 3elements (Z = 48 and 52 for Cd and Te respectively) and has a high density of 6.2 g/cm . Also, for high performance spectroscopy, the signal to noise ratio (S/N) must be good. There are two key parameters which effect S/N. By far the most important parameter is the product of the mobility and the lifetime (ATr) of both the electrons and the holes in the detector. However, a high ATir product alone is not sufficient for good performance if room temperature operation is desired. The resistivity of the material must be sufficiently high such that the thermally generated carriers do not overwhelm the signal. For example, silicon and germanium have by far the highest AT products of common semiconductors and extremely high resolution spectrometers can be made from these materials. However, the detectors must be cooled to cryogenic temperatures to be useful. The resistivity of a material is related to its bandgap, a wider bandgap results in higher resistivity and lower thermally-generated noise. Of all of the available semiconductor materials, CdTe offers the best performance in many applications because of its unique combination of high density, excellent charge carrier properties, wide bandgap and high resistivity. Electronic Properties of CdTe CdTe is a compound semiconductor with a band gap of 1.44 eV. It has many attractive properties for use as a nuclear detector material. The CdTe crystals used in nuclear detectors are almost always grown by the Travelling Heater Method (THM),2. Because of the relatively low growth tempe
Data Loading...
