Beta Irradiation of Silicon Junction Devices: Effects on Diffusion Length

This is the authors' abstract. We don't add key points for this paper.

The effects of electron irradiation on the minority carrier diffusion length in silicon devices has been studied by utilizing Pm-147 and Kr-85 beta sources. The beta spectra of Pm-147 and Kr-85 are characterized by maximum beta-particle energies of 230 and 670 kev, respectively. Short-circuit current for Li-doped p+n and n+p cells has been measured while the devices are continually irradiated. All devices have approximately 2 Ω-cm bases. The minority carrier diffusion length of the base region was deduced from the calculated betavoltaic collection efficiency. Finally, the diffusion damage coefficient has been calculated for each case. Kr-85 beta irradiated, Li-doped p+ n cells exhibit a much smaller damage rate for the first few months of testing than n+p cells. After decreasing from approximately 100 to 40 μm, the minority carrier diffusion length for the Li-doped cells began increasing until after 1.5 years of irradiation, it exceeded the initial value. Pm-147 beta-irradiated n+ p devices show only a small anmount of radiation effects. For example, typical values obtained for the damage coefficient are initially 10-13 compared to 10-11 for Kr-85 beta-irradiated n+p cells. Values of approximately 10-7 have been previously reported for n+p cells coupled to 0.5 Mev electrons.