Influence of disorder on the vertical transport in wide barrier superlattices

We report a combined theoretical and experimental study of vertical electron transport in wide barrier superlattices. The proposed microscopic transport model is applied to a parabolic ${\mathrm{Al}}_{0.4}{\mathrm{Ga}}_{0.6}\mathrm{A}\mathrm{s}/\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}$ structure and to a \ensuremath{\delta}-doped GaAs superlattice. Taking into account the structure-dependent deviations from the ideal case, i.e., interface roughness in the first case and doping-induced disorder in the second case, we obtain quantitative agreement between calculated and measured current-voltage characteristics for both superstructures. While negative differential conductivity persists up to intermediate temperatures in the parabolic sample, the doping superlattice exhibits no fine structure of the current-voltage characteristics even at low temperatures. These findings are explained by comparing the inhomogeneous broadening of electronic states due to interface roughness $(\ensuremath{\sim}10 \mathrm{meV})$ and doping-induced disorder $(\ensuremath{\gtrsim}50 \mathrm{meV}).$ An analysis of photoluminescence spectra and current-voltage characteristics of the doping superlattice is used as an additional tool to verify the structure parameters, i.e., doping densities and period.