Characterization of Thick Selenium Layers for Dual-Layer X-ray Imaging

Amorphous selenium (a-Se) as a direct conversion X-ray photoconductor has many desirable properties in X-ray imaging, due to its high spatial resolution, low dark current, high absorption efficiency, and large area fabrication. We present the fabrication and performance evaluation of thick a-Se layers for a cost-effective dual-layer X-ray flat-panel detector (DL-FPD). Building on a Cascaded Linear Systems Model that identifies 200-400 μm as the optimal a-Se thickness for the top layer detector, we manufactured 253 μm and 414 μm a-Se samples with a polyimide hole-blocking contact to suppress dark current to below 10 pA/mm² at electric fields up to 10 V/μm. Under low-energy X-ray irradiation, both devices demonstrated increasing response to increasing tube energy, with the 414 μm layer achieving higher photocurrent due to increased photon absorption. Temporal lag analysis revealed more pronounced signal persistence in the thicker sample at a lower bias, consistent with increased carrier trapping for greater thicknesses. These measurements provide critical metrics such as leakage, photoresponse, and lag for guiding the design of readout electronics in future direct/indirect DL-FPD arrays.