Investigating the performance of various hole-blocking materials for amorphous selenium-tellurium photodetectors

The material properties of amorphous selenium (a-Se), which demonstrates low dark currents, the ability to undergo an avalanche process at relatively lower electric fields compared to amorphous silicon, and uniform deposition over large areas, make it a promising semiconductor for X-ray detection and related applications. Additionally, alloying and doping a-Se has been shown to allow for tuning of material properties depending on the target application. In this work, we investigated alloying tellurium with a-Se for the desired application of indirect conversion X-ray detectors. Alloying Te lowers the bandgap of a-Se allowing for increased absorption of green light emitted by scintillating materials commonly used in commercial detectors. However, alloying Te also lowers the resistivity of a-Se, leading to elevated dark currents in a-Se-Te, which we aimed to minimize by adding hole-blocking layers (HBLs). We evaluated the performance of a-Se-Te devices with various HBLs in (1) their ability to suppress dark current and (2) their ability to maintain high conversion efficiencies. We observed that devices with SiO₂ and Al₂O₃

HBLs showed promisingly low dark currents, close to the ideal limit of 10 pA/mm², while also showing high conversion efficiencies.