The hard X-ray performance of pixelated CdTe-based detectors using Monte Carlo and ab initio simulations

The performance of pixelated semiconductor radiation detectors based on cadmium telluride (CdTe) were investigated using experimental, Monte Carlo and ab initio methods for their detection of hard X-rays while operating at room temperature.

To achieve the imaging, photon-counting and energy-resolving requirements of CdTe-based detector applications, pixelated detector designs are commonly used. Charge sharing and fluorescence interference as a result of pixelation, and distortions of the electric field profile, severely impact the performance in these detectors. Inhomogeneities and defects in the crystals due to on-going growth challenges of CdTe also limit performance.

The photon-counting and spectral performance of a novel high-flux capable CdZnTe (HFCdZnTe) is measured at photon energies 6 to 140 keV and compared with a gold-standard CdTe detector. Factors contributing to the energy resolution of charge sharing events such as charge loss and fluorescence are quantified. A fully spectroscopic Monte Carlo (MC) detector model is developed and shown to accurately predict the rate of charge sharing in these detectors. By comparing experimental and MC simulated data, a number of quantities related to performance such as the size of the electron charge clouds, the strength of the electric field and the Zn concentration in the HF-CdZnTe material are estimated.

Using density functional theory (DFT), alloys of CdTe that are in early stages of development for radiation detection are studied from ab initio. The formation of the cadmium vacancy defect (VCd) in Cd1−xMnxTe and Cd1−xMgxTe crystals is studied and compared with the more well established Cd1−xZnxTe system. The VCd formation energy as a function of alloy concentration x is calculated to help understand the defect concentrations and resistivity in these alloys. The effect the addition of Mn and Mg have on the physical properties of CdTe, including phase transitions of their lattices, are also determined.