Defect-assisted tunneling in the resonant tunneling diode

The major goal of this research is to understand the current transport mechanisms of the RTD (Resonant Tunneling Diode). A significant discrepancy exists between the predicted and measured values of the RTD current in the off-resonance region. Theory consistently predicted lower off-resonant currents than are observed. To model this underestimated valley current, defect states are introduced that perturb the conduction band profile. The results of model simulations are compared to measurements on real devices.; In this dissertation, the current-voltage characteristics of the resonant tunneling diode (RTD) were based on the Thomas-Fermi model. The dependency on the structural parameters was studied by varying parameters of interest in simulation of model devices. The electrical parameters of the RTD necessary for circuit applications can be controlled by proper selecting of structural parameters.; In order to better understand the overestimated peak-to-valley current ratios (PVCR) of double barrier resonant tunneling diodes, a defect-assisted tunneling mechanism through defect states inside the barriers is proposed and analyzed. For simplicity a one-dimensional {dollar}delta{dollar} function potential to describe the defect states is used to model defect state. The transmission coefficients are calculated using a transfer matrix method. The shape of the transmission coefficient is broadened and greatly increased in the off-resonance region compared to devices without such defects. The simulation results shows that the increase of the transmission coefficient in the off-resonance energy level contributes to an increase of the valley current and thus a reduction of the PVCR. A strong temperature dependence is observed due to the broadness and enhancement in the off-resonance transmission coefficient.; The temperature dependence at a different bias was studied using the Arrhenius plots. Below the peak voltage, the slope of high temperature region is reduced as the bias approaches the peak voltage. Then in the valley region, the slope is reduced with increasing bias. The measured current-voltage characteristics show the same trend as the predicted one.; The current-voltage characteristics are fitted by changing the defect well depth and adding a parasitic resistance of ohmic contact to the bulk region. The measured and simulation results shows a good agreement with a proper choice of defect well and parasitic resistance. The defect-assisted tunneling mechanism contributed clearly to the current path showing a non-ideal transport through the double barrier. The strong temperature dependence is observed for the model contains defect state inside the barrier.