Intrinsic oscillations in resonant tunneling structures

The resonant tunneling diode (RTD) is an important device because it yields a negative differential resistance which can respond very rapidly to changes in applied bias. In fact, RTDs have been shown experimentally to have detection capabilities up to 2.5 THz and have been implemented as oscillators up to 712 GHz. However, RTD-based power sources have only demonstrated microwatt levels (i.e. <50 /spl mu/W) of performance above 100 GHz. Traditional RTD-based sources generate power by establishing limit-cycles which exchange energy with storage elements in the external circuit. Hence, in this implementation the amount of achievable output power will always be limited by external losses (e.g. contact resistance) and low-frequency design constraints (i.e. suppression of bias circuit oscillations). Recently, we have performed a comprehensive study of various nonlinear second-order circuit forms in an effort to reproduce the high-frequency self-oscillations observed in previous quantum-transport simulations of an RTD structure. A comparison between these two theoretical results allows one to deduce intrinsic oscillations which are free of external resonances.