Progress in the Development of CdZnTe Unipolar Detectors for Different Anode Geometries and Data Corrections

Abstract

CdZnTe detectors have been under development for the past two decades, providing good stopping power for gamma rays, lightweight camera heads and improved energy resolution. However, the performance of this type of detector is limited primarily by incomplete charge collection problems resulting from charge carriers trapping. This paper is a review of the progress in the development of CdZnTe unipolar detectors with some data correction techniques for improving performance of the detectors. We will first briefly review the relevant theories. Thereafter, two aspects of the techniques for overcoming the hole trapping issue are summarized, including irradiation direction configuration and pulse shape correction methods. CdZnTe detectors of different geometries are discussed in detail, covering the principal of the electrode geometry design, the design and performance characteristics, some detector prototypes development and special correction techniques to improve the energy resolution. Finally, the state of art development of 3-D position sensing and Compton imaging technique are also discussed. Spectroscopic performance of CdZnTe semiconductor detector will be greatly improved even to approach the statistical limit on energy resolution with the combination of some of these techniques.

Airborne radiation mapping: overview and application of current and future aerial systems

“…A further advantage of CZT is that the material can be manufactured into different shapes, for example co-planar grids and small pixel detectors to optimize for differing applications. This therefore improves detection characteristics (Table 2) (Luke et al 2001;Luke 1995;Wilson et al 2011), however the co-planar grid variation produces the best energy resolution of any of the detectors previously discussed (<2.5% at 662 keV) (Chen et al 2008;Martin et al 2015;Sellin 2003;Zhang et al 2013), allowing for the production of the most resolved energy spectrum and hence the most confident identification of individual radionuclides (although Table 2 indicates that this could still be improved upon). Despite this high resolution, problems with the uniformity of the crystal structure, such as random grain boundaries, have limited its effectiveness by causing charge trapping -reducing the counting efficiency in certain applications and limiting the volume of the detectors to small sizes, i.e.…”

“…Despite this high resolution, problems with the uniformity of the crystal structure, such as random grain boundaries, have limited its effectiveness by causing charge trapping -reducing the counting efficiency in certain applications and limiting the volume of the detectors to small sizes, i.e. 1 cm 3 (Luke et al 2001;Zhang et al 2013). However, recent work into new methods of crystal manufacture through the travelling heater method (THM) process (Chen et al 2008;Wilson et al 2011) has yielded promising results to improve crystal uniformity and, therefore, allow for the volume of detectors to increase.…”

“…The material has a very high mass number (A), creating a very good counting efficiency -as the likelihood of interaction between the material with incident radiation is increased relative to other materials (e.g. air, water, and lead illustrated for comparison ( Figure 3)) and NaI/CsI scintillators (Luke Wilson et al 2011;Zhang et al 2013). A further advantage of CZT is that the material can be manufactured into different shapes, for example co-planar grids and small pixel detectors to optimize for differing applications.…”

Effect of charge trapping on effective carrier lifetime in compound semiconductors: High resistivity CdZnTe

“…High-resistivity CdZnTe (CZT) is currently one of the most promising room temperature radiation detector materials. [1][2][3] However, the inherent complexity of the crystallization and doping processes remains a significant challenge in detector development. In general, compound semiconductors including Cd-based semiconductors exhibit a high density of point defects and extended crystal imperfections.…”

“…These defects exhibit varying degrees of charge carrier trapping, which is the dominant problem that has limited energy resolution of the radiation detectors. [3][4][5] Therefore, the characterization and understanding of these recombination/trapping processes are critical for the optimization of radiation detection systems. 1,3 Consequently, improvement of the crystal growth processes requires non-contact metrologies that will allow characterization of the crystal properties without influence of contact related detrimental effects 6 such as formation of the space-charge regions or injection of charge carriers at the electrodes.…”