p-i-n junction nuclear devices have been made using tritiated amorphous silicon in the intrinsic region. In this unique device, tritium passivates defects and at the same time is an internal source of beta particles. The beta particles traverse the i-layer and through impact ionization, electron-hole pairs are generated. These charges are separated by the built-in field of the p-i-n junction and electrical power is generated. The power from the devices is about 0.2 nW cm-2 in a device of 400 nm thickness. The decay of tritium leads to the formation of dangling bonds and strain related defects in the silicon lattice. These defects lead to a decrease in the effective width of the space charge region and thereby to an increase in the recombination rate of carriers. As a consequence the electric power decreases with time. To overcome this degradation in performance, delta layered devices were made by selectively introducing tritium into the intrinsic region by modulating the tritium gas fraction during film deposition. The electric power from devices with a delta layer have better stability.