Self-Irradiation Enhanced Tritium Solubility In Hydrogenated Amorphous And Crystalline Silicon

Experimental results on tritium effusion, along with the tritium depth profiles, from hydrogenated amorphous silicon (a-Si:H) and crystalline silicon (c-Si) tritiated in tritium (T-2) gas at various temperatures and pressures are presented. The results indicate that tritium incorporation is a function of the material microstructure of the as-grown films, rather than the tritium exposure condition. The highest tritium concentration obtained is for a-Si: H deposited at a substrate temperature of 200 degrees C. The tritium content is about 20 at. % on average with a penetration depth of about 50 nm. In contrast, tritium occluded in the c-Si is about 4 at. % with penetration depth of about 10 nm. The tritium concentration observed in a-Si: H and c-Si is much higher than the reported results for the post-hydrogenation process. beta irradiation appears to catalyze the tritiation process and enhance tritium dissolution in the silicon matrix. The combination of tritium decay and beta-induced ionizations results in formation of reactive species of tritium (tritium atoms, radicals, and ions) that readily adsorb on silicon. The electron bombardment of the silicon surface and subsurface renders it chemically active thereby promoting surface adsorption and subsurface diffusion of tritium, thus leading to tritium occlusion in the silicon matrix. Gaussian deconvolution of tritium effusion spectra yields two peaks for a-Si: H films tritiated at high temperature (250 degrees C), one low temperature (LT) peak which is attributed to tritiated clusters and higher order tritides, and another high temperature peak which is attributed to monotritides. Activation energy of 2.6-4.0 eV for the LT peak was found. (C) 2011 American Institute of Physics. [doi:10.1063/1.3549145]