Capacitance-spectroscopy identification of a key defect in N-degraded GalnNAs solar cells

We report a study comparing the device performance and the deep-level transient spectroscopy spectra of Ga1-yInyNxAs1-x diodes. It is found that a transient capacitance signal, which corresponds to a trap 0.18 to 0.25 eV below the conduction-band edge, is observed near 140 K in the nitrogen-containing samples. The existence of this transient correlates with higher dark current [lower open-circuit voltage (V-oc)] and the size of the transient increases with x for x <= 0.6%. The abrupt decrease of the V-oc with the addition of nitrogen is explained by the hypothesis that a close approach of the electron quasi-Fermi level to the conduction-band edge is arrested by the electron trap. The N-induced trap level reduces V-oc as if it were a new conduction-band edge. (C) 2005 American Institute of Physics.