Physics Department Seminar

Wednesday, 4^th October, 1.30pm, Rm 1311HN

A MULTI-SUBBAND THEORY FOR THE ORIGINATION OF INTRINSIC OSCILLATIONS WITHIN DOUBLE-BARRIER QUANTUM-WELL SYSTEMS AND I-V CHARACTERISTICS OF THE SYSTEMS

Peiji Zhao

Department of Electrical and Computer Engineering

North Carolina State University

Resonant tunneling diode (RTD) is a simple but important nano-scale device. On one hand, with the downscaling of information processing devices, CMOS devices are approaching their scaling limits. RTD, as one of the replacements of the CMOS devices for future information processing devices, can offer speed advantages and possible reductions of circuit complexity. On the other hand, RTDs can also be used as nonlinear components for high frequency applications. For example, RTDs can be used as THz power sources, infrared photo-detectors, and terahertz switching devices. Although RTDs play important roles in modern information processing technology, our knowledge to RTD physics is incomplete. This leads to some important RTD device physics problems, such as the origin of the hyteresis of the I-V characteristics of RTDs and the origin of the current instability in a double barrier quantum well system, stood unsolved for many years. Recently, these problems were resolved by our research group. In this talk, I will present the theory accounting for the origin of the high frequency current oscillation in a double barrier quantum well system and of the hysteresis of I-V characteristics of the system. I will also show that the origin of the current oscillation and the hysteresis of the I-V characteristics is traced to the development of a dynamic emitter quantum well and the coupling of the energy levels in the double barrier quantum well system. The relationship between the oscillation frequency and the device structure will be discussed. A self-consistent, time-dependent Wigner-Poisson numerical experiment has been used to revealed remarkable intrinsic, sustained current oscillations in a double-barrier quantum well in THz frequencies. The oscillation frequency predicated by the theory shows very good agreement with the simulated oscillation frequency. Based on this theory, a new energy conversion mechanism, subband energy coupling mechanism, is suggested. This mechanism has been used to design THz oscillators with larger output powers, which is important for solving the THz-gap issue.