Future Trends in Microelectronics: From Nanophotonics to Sensors to Energy

Semiconductor Gamma Radiation Detectors: Band Structure Effects in Energy Resolution

Arsen Subashiev and Serge Luryi

Dept. of Electrical and Computer Engineering, SUNY-Stony Brook Stony Brook, NY 11794-2350, U.S.A.

1.   Introduction

Energy spectroscopy in semiconductor γ-detectors is based on registration of the total number of electron-hole (e-h) pairs produced by a single γ-photon after a cascade of various processes. These include Compton scattering events, photo-absorption, deep core level excitation, core vacancy relaxation, emission of plasmons by the secondary electrons (holes), plasmon decay into e-h pairs and impact ionization events. At each stage, the cascade is accompanied by sequential energy branching between secondary particles, resulting in a nearly random energy distribution in a cloud of secondary electrons and holes in the final state. The branching is terminated when the energy of a secondary electron or hole is below the impact ionization threshold. Importantly, to a very high precision and in a broad energy range, the number of created pairs N is just proportional to the initial energy E = hv of the γ-photon, N = E/ε, where ε is the average excitation energy of a single pair (referred to as the pair excitation energy). For semiconductor materials, the pair excitation energy ε is about 3E_G, where E_G is the band gap energy and is typically about 2EM, i.e. twice the minimal energy required for an electron to produce a pair by impact ionization in a process with ...