Characteristics of Resonant Tunneling in Nanostructures with Spacer Layers

The effect of spacer layers on electron transport through two-barrier nanostructures was studied using the numerical solution of the time-dependent Schrodinger-Poisson equations with exact discrete open boundary conditions. The formulation of the problem took into account both the active region consisting of a quantum well and barriers, as well as the presence of highly doped contact layers and spacer layers. The use of the time formulation of the problem avoids the divergence of the numerical solution, which is usually observed when solving a stationary system of the Schrodinger-Poisson equations at small sizes of spacer layers. It is shown that an increase in the thickness of the emitter spacer leads to a decrease in the peak current through the resonant tunneling nanostructures. This is due to the charge accumulation effects, which, in particular, lead to a change in the potential in an additional quantum well formed in the emitter spacer region when a constant electric field is applied. The valley current also decreases as the thickness of the emitter spacer increases. The peak current and valley current are weakly dependent on the thickness of the collector spacer. The collector spacer thickness has a strong effect on the applied peak and valley voltages. The above features are valid for all three different resonant tunneling nanostructures considered in this study. For the RTD structures based on Al0.3Ga0.7As/GaAs, the optimized peak current value Ip(max) = 5.6 x 10(9) A/m(2) and the corresponding applied voltage V-p = 0.44 V. For the RTD structures based on AlAs/In0.8Ga0.2As, Ip(max) = 14.5 x 10(9) A/m(2) (V-p = 0.54 V); for RTD structures based on AlAs/In0.53Ga0.47As, Ip(max) = 45.5 x 10(9) A/m(2) (V-p = 1.75 V).