Study of deep-level defects and annealing effects in undoped and Sn-doped GaAs solar cells irradiated by one-MeV electrons

DLTS and C-V techniques have been employed to determine the defect energy levels and density, carrier capture cross sections, lifetimes and diffusion lengths in the Sn-doped and the undoped GaAs solar cells irradiated by one-MeV electrons under different electron fluences (10¹⁴ to 10¹⁶ cm^?2), fluxes (2 × 10⁹, 4 × 10¹⁰ e/cm²-s), and annealing conditions (150 ? T ? 230°C). The results show that density of both electron and hole traps will in general increase with incresing electron fluence and flux, and decrease with increasing annealing temperature and annealing time. Some distinct difference in defeat spectrum was observed in the undoped and the Sn-doped GaAs solar cells studied. The low temperature thermal annealing and the recombination enhanced annealing processes are found to be very effective in reducing the density of deep-level defects induced by one-MeV electrons. The results of our findings are discussed in detail in this paper.