Radiation-induced hydrogen migration was studied in hydrogenated amorphous silicon (a-Si:H) using layer-stacks of SiO2/a-Si:H/SiO2. The upper and lower SiO2 layers were deposited by magnetron sputtering at room temperature. The intermediate a-Si:H layers were deposited using plasma-enhanced chemical vapour deposition at 25, 150 or 270C. The samples were bombarded with MeV 15N ions during nuclear reaction analysis of the hydrogen concentration. It was established that the irradiation led to hydrogen migration and redistribution; which depended upon the a-Si:H deposition temperature. A symmetrical hydrogen concentration profile in the as-prepared layer-stack became asymmetrical following bombardment; due to an increase in the hydrogen concentration in the lower SiO2 layer. The H concentration in the layer-stacks decreased during the initial bombardment stage and then remained constant. On the other hand, hydrogen loss from the a-Si:H layer proceeded gradually and continuously with increasing bombardment fluence. It was suggested that hydrogen atoms liberated by the MeV ion bombardment did not recombine into molecules, and that the hydrogen migration in a-Si:H was related to the diffusion of the hydrogen atoms. A bombardment-induced asymmetry of the hydrogen profiles in the layer-stack implied that there was a difference in the diffusion parameters at the inner and outer interfaces.

Ion Beam-Induced Hydrogen Migration in a SiO2/a-Si:H/SiO2 Layer Stack. B.Pantchev, P.Danesh, B.Schmidt, D.Grambole, W.Möl: Semiconductor Science and Technology, 2009, 24[3], 035012