Deep level transient spectroscopy reveals that the main electron traps for one-MeV electron irradiated GaAs cells are E9c)-0.31, E(c)-0.90 eV, and the main hole trap is due to the level. Electron trap density was found to vary from 3/tens-trillion ccm for 2/one quadrillion cm 3/3.7 quadrillion cm for 21 sextillion cm electron fluence for electron fluence; a similar result was also obtained for the hole trap density. As for the grown-in defects in the Al(x)Ga(1-x)As p-n junciton cells, only two electron traps with energies of E(c)-0.20 and E(c)-0.34 eV were observed in samples with x = 0.17, and none was found for x 0.05. Auger analysis on the Al(x)Ga(1-x) As window layer of the GaAs solar cell showed a large amount of oxygen and carbon contaminants near the surface of the AlGaAs epilayer. Thermal annealing experiment performed at 250 C for up to 100 min. showed a reduction in the density of both electron traps.

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.

The deep-level defects and recombination mechanisms in the one-MeV electron irradiated (AlGa)As-GaAs solar cells under various irradiation and annealing conditions are discussed. Deep-level transient spectroscopy (DLTS) and capacitance-voltage (CV) techniques were used to determine the defect and recombination parameters such as energy levels and defect density, carrier capture cross sections and lifetimes for both electron and hole traps as well as hole diffusion lengths in these electron irradiated GaAs solar cells. GaAs solar cells used in this study were prepared by the infinite solution melt liquid phase epitaxial (LPE) technique at Hughes Research Lab., with (Al0.9Ga0.1)-As window layer, Be-diffused p-GaAs layer on Sn-doped n-GaAs or undoped n-GaAs active layer grown on n(+)-GaAs substrate. Mesa structure with area of 5.86x1000 sq cm was fabricated. Three different irradiation and annealing experiments were performed on these solar cells.

The objective of this work is to investigate the deep-level defects induced by one-MeV electron irradiation in the (AlGa) As-GaAs solar cells subject to different irradiation and annealing conditions. Both undoped and Sn-doped GaAs cells were fabricated for this study. For Sn-doped GaAs cells, electron irradiation was performed for fluences of 1 X 10/sup 14/, 1 X 10/sup 15/, and 2 X 10/sup 16/ e/cm/sup 2/, and subsequently annealed at 230 /sup 0/C for 10, 20, 30, and 60 minutes. In addition, irradiation was also made on Sn-doped cells with flux rates of 4 X 10/sup 10/ and 2 X 10/sup 9/ e/cm/sup 2/-s and at cell's temperatures of 150 and 200 /sup 0/C. For undoped cells, irradiation was made at 200 /sup 0/C for two fluences (1 X 10/sup 14/ and 1 X 10/sup 15/ e/cm/sup 2/). DLTS and C-V measurements were performed on these cells to determine the defect and recombination parameters. Details of the results are presented in this paper.