Minority carrier diffusion length in proton-irradiated indium phosphide using electron-beam-induced current
The minority carrier diffusion length (L) is an important parameter in modeling the expected performance of a solar cell. Therefore, an accurate means for its measurement is essential. This work suggests that presently used values of L may be in error by as much as a factor of 3 because of the customary assumption that the edge surface-recombination velocity is infinite. To demonstrate this point, a novel electron-beam induced current (EBIC) technique for determining L was used: a scanning electron microscope (SEM) was used to generate EBIC profiles, and the approach suggested by Watanabe et al. was used to measure the edge surface-recombination velocity (V s) at numerous points along the beam scan. These values were then used in a numerical approximation to a theoretical expression derived by Donolato for the normalized EBIC. This technique was first applied to gallium arsenide (GaAs) p/n concentrator solar cells. It was found that accounting for a finite V s leads to a significant correction to the accepted value of the hole diffusion length (L p) for GaAs. Next the technique was applied to indium phosphide (InP), using gold/p-type InP Schottky barriers, and the electron dif fusion length (In) was measured for the first time taking into account the finite value of V s. For zinc-doped (1 × 10^18 cm-3) InP, L n ranged from 0.26 ?m to 1.36 ?m. Because solar cells used in space are subject to radiation damage from high-energy particles, the reported ability of InP to resist such damage from protons through self-annealing was examined for the case of 2 MeV protons. Although annealing at room temperature was not observed, the diffusion length, L n, did recover with photoinjection and forward-bias injection of minority carriers. In the course of this study, the diffusion length damage coefficient (K L) for 0.5 MeV proton-irradiated InP was measured for the first time.
School:Case Western Reserve University
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:minority carrier diffusion length proton irradiated indium phosphide using electron beam induced current
Date of Publication:01/01/1993