Wigner-Poisson simulation of quantum devices

An accurate understanding of quantum effects in small devices (feature length less than 100 A) is important in the design of quantum devices and future quantum integrated circuits. At this point, suitable quantum device simulators have not been developed. Part of reason for the lack of the simulators is due to several device physics problems unsolved for more than ten years, such as the origin of hysteresis and the plateau-like structure in the IN curve of resonant tunneling diodes (RTD), and the intrinsic high frequency current oscillation in RTD's. In this thesis, we mainly focus on solving the unsolved quantum device physics problems.; By numerically solving the coupled and time-independent Wigner-Poisson equations, the hysteresis and plateau-like behavior of the IN curves of the double-barrier resonant tunneling structure are simulated in the negative differential resistance region. Our simulation results show that the creation of an emitter quantum well after the current passes its maximum value is the key point in understanding the origin of the IN plateau-like structure. It is demonstrated that the plateau-like behavior of the IN curves is produced by the coupling of the energy level in the emitter quantum well with that in the main quantum well. The hysteresis is a manifestation of tills coupling, the accumulation and distribution of electrons in the emitter, and the coupling between the energy level in the quantum well and the conduction band edge or the three-dimensional continuum states in the emitter.; Furthermore, based on our self-consistent, time-dependent Wigner-Poisson simulation, intrinsically sustained electron current oscillations in a double-barrier quantum well resonant tunneling diode at Tera-Hertz (THz) frequencies have been revealed. A time-dependent energy level coupling model (TDELCM) is presented for explaining the origin of this oscillation. The origin of both the electron oscillation and the peculiar structure of the IN curve is traced to the development of a dynamic emitter quantum well and the coupling of its energy level with the level of the main quantum well. Therein evolves a complete theory of the instability and resonant tunneling through a double barrier quantum well system, and accurate prediction of the oscillation frequencies. (Abstract shortened by UMI.)...