Deep-level impurities were studied in p+n solar cells by using deep-level transient spectroscopy. These films were grown by means of atmospheric and low-pressure metalorganic vapor-phase epitaxy. The base layer was doped with Si, and the emitter layer was Zn-doped. The samples were grown with, or without, the addition of O impurity. Two electron traps were found in all of the samples. These were E1 (Ec - 0.23eV to Ec - 0.27eV), E2 (Ec - 0.45eV) and E2* (0.77eV). Upon adding O, deep-level transient spectroscopy revealed additional traps: E3 (electron) at Ec - 0.59eV and R3 (hole) at Ev + 0.59eV. By using secondary ion mass spectroscopy, the O concentration was found to be between 2 x 1019 and 3 x 1019; or 1017/cm3. Only the samples which contained O also contained the 2 near-midgap levels: E3 and H3. These levels were associated with the O defect. As the direct-current bias voltage was changed, the E3 trap disappeared while the H3 trap appeared. The E3 and H3 trap levels had comparable capture cross-sections. This O-related trap was an effective recombination center. The Shockley-Hall-Read lifetime of this center was about 0.6μs.

Evidence of an Oxygen Recombination Center in p+-n GaInNAs Solar Cells A.Balcioglu, R.K.Ahrenkiel, D.J.Friedman: Applied Physics Letters, 2000, 76[17], 2397-9