Origins of Persistent Photoconductivity in GaAsN Alloys

In GaAs$_{\mathrm{1-x}}$N$_{x}$ alloys, we observe significant persistent photoconductivity (PPC) at cryogenic temperatures for $x$ \textgreater\ 0.006, with the PPC strength increasing with increasing $x$ and decreasing upon rapid-thermal annealing (RTA). Since the RTA-induced suppression is accompanied by a reduction of the interstitial N fraction, the N-induced donor state is likely associated with N pairs. PPC is attributed to the promotion of carriers from a ground N-pair state to the conduction band edge, inducing modifications in the N-pair molecular bond configuration. When illumination is terminated, an energy barrier hinders the return of carriers to the N-pair induced complex. With the addition of thermal energy, the original N-pair configuration is restored and the N-pair induced complex is then able to accept carriers. We use PPC at cryogenic temperatures to go through a metal-insulator transition in GaAsN by increasing the carrier density with illumination. For different illumination durations we determine the minimum metallic conductivity, giving us the critical carrier density, $n_{c}$, at the transition point. We then determine the effective mass, $m*$, using the Mott criterion $n_{c}^{1/3}a_{H} = $ 0.26 where $a_{H} = $ (4$\pi \varepsilon $h$^{2})$/($e^{2}m$*) is the Bohr radius. We use PPC to induce a metal-insulator transition in GaAsN. We will discuss the effective mass as a function of N concentration and compare to the predictions of the band anticrossing model.