Effect of nitrogen concentration on the performance of Ga1-xInxNyAs1-y solar cells

A study of Ga_1-xIn_xN_yAs_1-y solar cells shows that nitrogen degrades the solar cells even for very small nitrogen concentrations. By comparing the properties of p-on-n and n-on-p Ga_1-xIn_xN_yAs_1-y cells as a function of y, we find that the n-on-p cells show a more abrupt decrease in the open-circuit voltage and greater decrease of the photocurrent. The asymmetry in the performance of the cells reflects the differences observed for electrons and holes in Ga_1-xIn_xN_yAs_1-y. The electron mobility is degraded much more than the hole mobility when nitrogen is added to GaAs, implying that the electron diffusion length should be degraded more than the hole diffusion length. An electron trap (observed by deep-level transient spectroscopy) affects p-type GaN_yAs_1-y more than n-type GaN_yAs_1-y, consistent with the observation that the open-circuit voltage of n-on-p cells decreases more than that of p-on-n cells. The effect of nitrogen on GaNAs cells is shown to be much greater than expected for an isoelectronic impurity.