Simulation and Experimental Validation of the Uniformity of Thermally Evaporated Amorphous Selenium Films for Large-Area Imaging and Radiation Detection Applications

Amorphous selenium is one of the best photoconductors with a wide range of applications, from its early use in the photocopy industry to its present application in X-ray imaging. Low melting point and high vapor pressure of amorphous selenium enable uniform and economical deposition of this photoconductive material up to few millimeters thick. However, there is a tradeoff between deposition rate and film uniformity. In this article, a thermal evaporation system for amorphous selenium deposition was developed. The system geometry was simulated to determine the optimized source-substrate throw distance for uniform film thickness of amorphous selenium (a-Se) on a substrate with up to 4-in diameter. Boat and crucible source configurations of equal volume (100 cc) were tested. The film was fabricated, characterized, and the uniformity and thickness were measured and compared with simulation results.