Fabrication and Characterization of Thin Amorphous Selenium Films for Integrated Charge plus Light Sensors

Amorphous selenium (a-Se) is a promising material for direct light sensing in time projection chambers (TPCs) due to its strong absorption of vacuum ultraviolet light and low dark current. In this work, thin a-Se films were fabricated using a custom built thermal vapor deposition system under high vacuum to explore their suitability as large-area photodetector layers. Deposition parameters, including: temperature, deposition rate, and film thickness, were varied to optimize film uniformity and electrical properties. Surface morphology and uniformity of the a-Se films were characterized using scanning electron microscopy, while Raman and x-ray diffraction spectroscopy confirmed the amorphous nature of the deposited layers. Additionally, the film's electrical response to UV light was characterized. We will present details of the thermal evaporation system, characterization of the films, and the demonstration of constructed sensors using these films. Our work lays the foundation for the design and implementation of a-Se sensors within a TPC in a novel pixelated layout integrating both charge and light sensors.