Nanopattern multi-well avalanche selenium detector for TOF-PET

For the first time, we propose using amorphous selenium (a-Se) as the photoconductive material for time-of-flight (TOF) detectors. Advantages of avalanche-mode a-Se are having high fill factor, low excess noise due to unipolar photoconductive gain, band transport in extended states with the highest possible mobility, and negligible trapping. The major drawback of a-Se is its poor single-photon time resolution and low carrier mobility due to shallow-traps, problems that must be circumvented for TOF applications. We propose a nanopattern multi-well a-Se detector (MWSD) to enable both impact ionization avalanche gain and unipolar time-differential (UTD) charge sensing in one device. Our experimental results show that UTD charge sensing in avalanche-mode a-Se improves time-resolution by nearly 4 orders-of-magnitude. In addition, we used Cramér-Rao lower bound analysis and Monte Carlo simulations to demonstrate the viability of our MWSD for low statistics photon imaging modalities such as PET despite it being a linear-mode device. Based on our results, our device may achieve 100 ps coincidence time resolution in TOF PET with a material that is low cost and uniformly scalable to large area.