Quantum transport simulation of the resonant-tunneling diode

The quantum-well resonant-tunneling diode is modeled by calculation of the Wigner distribution function. Boundary conditions applied to the Wigner function model the Ohmic contacts to the device and provide the required dissipative behavior. The Liouville equation is solved to obtain the steady-state response, or integrated to obtain the transient response. The steady-state I-V curves show the expected negative resistance, though the calculated peak-to-valley current ratio is smaller than that obtained from more conventional calculations and is smaller than the better experimental devices at low temperatures. The calculations of the detailed transient response are the first reported for a tunneling device, and resolve the question of the response time of the tunneling current. For a structure with 2.8 nm AlGaAs barriers, the current switches from its peak to its valley value in about 0.2 ps. The response time increases with the thickness of the barriers.