Experimental demonstration of resonant-tunneling-diode operation beyond quasibound-state-lifetime limit

Abstract

Abstract. We show, first, that the charge relaxation (response) time of resonant-tunneling diode (RTD) can be significantly shorter or longer than the resonant-state lifetime, depending on RTD operating point and RTD parameters. Coulomb interaction of electrons is responsible for the effect. Second, we demonstrate that the operating frequencies of RTDs are limited neither by resonant-state lifetime, nor by relaxation time; particularly in the RTDs with heavily doped collector, the differential conductance can stay negative at the frequencies far beyond the limits imposed by both time constants. We provide experimental evidences for both effects. IntroductionResonant-tunneling diodes (RTDs, see Fig. 1) are the most simple structures with resonant tunneling. Such structures were intensively studied in the last several decades, they are used for studies of fundamental aspects of tunneling and they are also attractive for practical applications. E.g., RTDs belong to the fastest [1] operating devices nowadays and their negative differential conductance (NDC) is useful for high-frequency oscillators [2,3]. The question that arises in connection with any electronic device: what is limiting its response time and its operating frequencies? The response of RTD is connected to population and depopulation of the resonant states in the quantum well (QW) of the diode. Therefore, it is typically accepted [4,5] that the inherent response-time limitation of such structures should be determined by the resonantstate lifetime (τ ). Also it is intuitively expectable [5] that the current and conductance of the structure should tend to zero, when ωτ ≫ 1.One of us has shown theoretically previously that the intuitive picture is not generally correct [6,7,8]. The objective of the present work is to demonstrate that experimentally. We show that the response time or, equivalently, the time constant of charge-relaxation processes (τ rel ) can be significantly shorter than τ . Such behavior is the consequence of the Coulomb interaction between the charge carriers in the structures [6,7]. We also show that, under certain conditions, the Coulomb interaction can lead to the opposite effect, when τ rel becomes longer than τ . Additionally, we demonstrate that, as predicted [8], the resonant-tunneling conductance can