Thermal-Equilibrium Defect Processes in Hydrogenated Amorphous Silicon

The first experimental evidence for a thermal-equilibrium defect density in undoped hydrogenated amorphous silicon, a metastable material, is presented. The defect density is in thermal equilibrium at temperatures above 200°C; the defects measured at room temperature are largely those frozen in during cooling from the equilibrium regime. Rapid quenching reversibly increases defect density. The defect density can be reversibly decreased by shunting of the defect-generation process during cooling. This latter technique has important implications for $a$-Si:H-based solar cells.