Modeling the radiation ionization energy and energy resolution of trigonal and amorphous selenium from first principles

Abstract

Advances in the development of amorphous selenium-based direct conversion photoconductors for high-energy radiation critically depend on the improvement of its sensitivity to ionizing radiation, which is directly related to the pair production energy. Traditionally, theories for the pair production energy have been based on the parabolic band approximation and do not provide a satisfactory agreement with experimental results for amorphous selenium. Here we present a calculation of the pair creation energy in trigonal and amorphous selenium based on its electronic structure. In indirect semiconductors, such as trigonal selenium, the ionization threshold energy can be as low as the energy gap, resulting in a lower pair creation energy, which is a favorable factor for sensitivity. Also, the statistics of photogenerated charge carriers is studied in order to evaluate the theoretical value of the Fano factor and its dependence on recombination processes. We show that recombination can significantly compromise the detector's energy resolution as a result of an increase in the Fano factor.

Cascaded systems analysis of a-Se/a-Si and a-InGaZnO TFT passive and active pixel sensors for tomosynthesis

“…Where, f factor is the Fano factor (Darbandi et al 2012). It has been shown by Darbandi et al (2012), that the intrinsic value of the Fano factor in a-Se is within 0.03-0.06. However, due to recombination of charges in a-Se these values are seldom achieved.…”

“…However, due to recombination of charges in a-Se these values are seldom achieved. In fact for an electric field of 10 V µm −1 , the Fano factor approaches 0.9-1 (Darbandi et al 2012). Moreover, assuming that mean number of electron hole pairs released per x-ray photon obey a Poisson process (Kabir et al 2011), the Fano factor is determined to be 1 and the variance to be:…”

A high-resolution CMOS imaging detector for the search of neutrinoless double β decay in82Se

“…Data on the intrinsic resolution of amorphous selenium is severely lacking, with measurements and Monte Carlo simulations existing only up to 140 keV [29,30]. We adopted an average energy for the production of one electron-hole pair of 15 eV, as measured for 140 keV X-rays at an electric field of 30 V/µm [29], and a value of the Fano factor F = 0.6, as predicted at this field [31]. From the simulation of the ionizing tracks and the instrumental response, followed by clustering and track reconstruction algorithms, we obtained a FWHM of the energy response at Q ββ of 24 keV.…”