Tritiated hydrogenated amorphous Si (a-Si:H:T) thin films were deposited onto crystalline Si and high resistivity glass substrates. The time evolution of the density of defect states in these films was studied using the constant photocurrent method and isothermal capacitance transient spectroscopy. The density of defect states was found to change with time and to recover upon thermal annealing. The isothermal capacitance transient spectroscopy results revealed that, following thermal annealing, in a sample with approximately 1at%T, the concentration of positively charged dangling bonds (D+) decreased by more than an order of magnitude over a period of 300h. The constant photocurrent method results showed that, over the same period of time, the concentration of negatively charged dangling bonds (D−) increased by over 2 orders of magnitude. The D+ and D− concentrations followed exponential functions of time, but the rate was different than that of tritium decay. At the same time, the Urbach energy was found to decrease with time to about 1/2 of its post-annealing value. The change in the D+ and D− concentrations was primarily the result of capture of the beta particle generated electrons in dangling bonds and weak bonds, with steady state achieved through the development of a balance between carrier generation and carrier capture processes. The role of excess carriers was confirmed by constant photocurrent method experiments under electrical bias.

Time Evolution of Charged Defect States in Tritiated Amorphous Silicon. S.Costea, N.P.Kherani, S.Zukotynski: Journal of Applied Physics, 2007, 102[10], 103715