Ion beam-induced hydrogen migration in a SiO2/a-Si:H/SiO2 layer stack

The phenomenon of radiation-induced hydrogen migration has been studied in hydrogenated amorphous silicon (a-Si:H) using layer stacks of SiO2/a-Si:H/SiO2. The top and bottom SiO2 layers were deposited by magnetron sputtering at room temperature. The intermediate a-Si:H layers were deposited using plasma-enhanced chemical vapor deposition at three temperatures—room temperature, 150 °C and 270 °C. The samples were irradiated with MeV 15N ions during nuclear reaction analysis of hydrogen concentration. It has been established that the irradiation leads to hydrogen migration and redistribution, which depend on the a-Si:H deposition temperature. The symmetric hydrogen concentration profile in the as-prepared layer stack becomes asymmetric after the irradiation due to increase in the hydrogen concentration in the bottom SiO2 layer. Hydrogen concentration in the layer stacks decreases during the initial irradiation stage and then remains constant. In contrast, hydrogen loss from the a-Si:H layer proceeds gradually and continuously with increasing radiation fluence. It has been suggested that the hydrogen atoms liberated by the MeV ion irradiation do not recombine in molecules and that the hydrogen migration in a-Si:H is related to the diffusion of the hydrogen atoms. The radiation-induced asymmetry of the hydrogen profiles in the layer stack implies that there is a difference in the diffusion parameters at the inner and outer interface.