Instabilities in n-GaAs including chaos and period 3 simulated by numerical computation

In studying current instabilities and chaos in semiconductor n-GaAs under weak photoexcitation, we pay special attention to influences from the carrier diffusion, arising from the space charges trapped near the injecting contacts. We extend the well-accepted two-impurity-level model by including the diffusion current δJ formed by such space charges near the negative contact. Without this δJ, one sees the prototype of period-doubling bifurcation (Feigenbaum scenario) but with unbound and exploding phenomena as the control parameter beyond 10.58 V/cm. Adding δJ in, we remove the unreasonable explosion and have the bifurcation routes to chaos of a current filament interrupted by a stable period 3 near E^[3]₀. Our simulations accurately reproduce the location of E^[3]₀ and the Feigenbaum number. From our results, we see that δJ plays the role of providing strong friction and preventing the further increase of the conduction electron concentration from exploding.