Probing Local Structure Evolution in Amorphous Selenium and Se–Te Alloys via Temperature-Dependent EXAFS

Amorphous selenium (a-Se) is a promising photoconductor for X-ray, UV, and visible light detection due to its low dark current, ease of fabrication, and broad spectral sensitivity extending from the vacuum ultraviolet (VUV) to X-ray energies. Despite its extensive use, fundamental questions remain about its atomic structure and stability, particularly under cryogenic conditions. Understanding these behaviors is vital for emerging applications in liquid noble–based particle detectors, where selenium-based photodetectors have been proposed. To investigate temperature-dependent local structure, we performed Extended X-ray Absorption Fine Structure (EXAFS) measurements on amorphous selenium and Se/Te alloys at the QAS beamline at Brookhaven National Laboratory. EXAFS provides element-specific insight into short-range order by resolving bond lengths and coordination environments through oscillations above the absorption edge. Our measurements span a broad temperature range, revealing subtle rearrangements linked to thermal relaxation and potential phase transitions. Additionally, we conducted in-situ optical illumination studies using a 625 nm LED to examine photo-induced modifications in the local bonding network. Together, these results provide new insight into how temperature and optical excitation jointly influence structural dynamics and inform the design of future cryogenic detector materials.