A comprehensive study on the photon energy response of RadFET dosimeters using the PENELOPE Monte Carlo code

Abstract

Radiation-sensing Field Effect Transistors (RadFETs or MOSFET dosimeters) with SiO2 gate dielectric have found applications in space, radiotherapy clinics, and high-energy physics laboratories. More sensitive RadFETs, which require modifications in device design, including gate dielectric, are being considered for personal dosimetry applications. This paper presents results of a detailed study of the RadFET energy response simulated with PENELOPE Monte Carlo code. Alternative materials to SiO2 were investigated to develop high-efficiency new radiation sensors. Namely, in addition to SiO2, Al2O3 and HfO2 were simulated as gate material and deposited energy amounts in these layers were determined for photon irradiation with energies between 20 keV and 5 MeV. The simulations were performed for capped and uncapped configurations of devices irradiated by point and extended sources, the surface area of which is the same with that of the RadFETs. Energy distributions of transmitted and backscattered photons were estimated using impact detectors to provide information about particle fluxes within the geometrical structures. The absorbed energy values in the RadFETs material zones were recorded. For photons with low and medium energies, the physical processes that affect the absorbed energy values in different gate materials are discussed on the basis of modelling results. The results show that HfO2 is the most promising of the simulated gate materials.