Origin of Persistent Photoconductivity Effect in GaAsN Alloys

(In)GaAsN alloys with a few percent nitrogen have potential applications in many long wavelength optoelectronic devices. However, the formation of point defects, such as N interstitials and Si-N complexes, has been predicted to substantially limit the optical emission efficiency and minority carrier transport of (In)GaAsN. Here, we report a persistent photoconductivity (PPC) effect associated with N interstitial-related defects in GaAsN films. In our GaAsN films, PPC was observed up to 160K, with a photo-capture barrier of 350 - 400 meV. Meanwhile, low $T$ transport measurements reveal two regimes of carrier concentration, $n$, a $T$-independent regime above 150K and a thermally-activated regime below 150K. These two phenomena are reminiscent of the behavior of n-type AlGaAs due to the presence of DX-center levels, suggesting the presence of similar N-induced defect levels in GaAsN. Furthermore, after annealing, the PPC effect is suppressed and $n$ increases substantially. Our recent nuclear reaction analysis revealed that the interstitial N concentration is decreased by RTA. Therefore, the RTA-induced suppression of the PPC and the increase of $n$ in GaAsN suggest their association with N interstitials.