Light-induced hydrogen evolution from hydrogenated amorphous silicon: Hydrogen diffusion by formation of bond centered hydrogen

The light-induced hydrogen evolution (LIHE) from amorphous (a-) Si:H by the order of at. % is observed during white light soaking (WLS) of 100–400 mW/cm2 at 350–500 K or ultra violet light soaking (UVLS) of 30–120 mW/cm2 at 305–320 K in a vacuum. The thermal desorption spectroscopy indicates that LIHE originated from bonded hydrogen takes place through the diffusion of light-induced mobile hydrogen (LIMH) with the activation energy of 0.5 eV. LIMH is assigned to bond centered hydrogen and the hydrogen diffusion process becomes prominent when LIMH can leave from a-Si:H such under light soaking in a vacuum above room temperature. For H2 in microvoids, the hydrogen evolution rate is governed by the surface barrier and its activation energy of 1.0 eV in dark decreases to 0.4 eV under WLS or UVLS.