High-frequency simulation of resonant tunneling diodes

The small and large-signal response of the resonant tunneling diode at high-frequencies is studied using a quantum simulator. The Poisson and Schrodinger equations are solved self-consistently for each harmonic using the harmonic balance technique. This ensures that the total current consisting of the displacement plus conduction currents, is conserved across the device for each harmonic. A reduced cut-off frequency for the conductance is obtained when both DC and AC self-consistency is used instead of only DC self-consistency. The RTD exhibits an increased capacitance in the negative differential conductance (NDC) region due to the discharging of the well in agreement with experimental data. The derivation of the RTD capacitance from a quasi-static analysis using the differential variation of the DC charge in the RTD is shown to be incorrect because the RTD charges through the cathode but discharges through the anode. The frequency dependence of the conductance, susceptance or capacitance is similar to reported experimental data. A large frequency dependence of the admittance is only observed when the RTD is biased in the negative differential conductance (NDC) region. Due to the simultaneous reduction of both the conductance and the capacitance at high-frequency in the NDC region the maximum frequency of oscillation does not differ much from its estimate using the low frequency conductance and capacitance. The large signal response at high frequency of a RTD biased in the negative differential region is also presented in this thesis. The negative conductance is shown to decrease with both increasing frequency and AC voltage. An oscillation circuit based on the RTD is also analyzed. It shows the oscillator can have stable oscillation only within a narrow frequency range.