Numerical simulation of intrinsic bistability and high-frequency current oscillations in resonant tunneling structures

Abstract

Intrinsic high-frequency oscillations (^2.5 THz) in current and corresponding quantum-well density have been simulated for the first time for a fixed-bias voltage in the negative differential resistance (NDR) region of the current-voltage (I-V) characteristics of a resonant tunneling diode. Scattering and self-consistency are included. Hysteresis and "plateaulike" behavior of the time-averaged I-V curve are simulated in the NDR region. Intrinsic bistability is manifested by the phenomenon of unstable electron charge buildup and ejection from the quantum well.PACS numbers: 73.40.Gk The resonant tunneling of electrons through doublebarrier structures is known to produce a region of negative differential resistance (NDR) in the I-V relationship. This has been well established experimentally, 1 " 5 and a simple understanding of the phenomena may be obtained through analyzing the transmission coefficient of the one-dimensional resonant tunneling diode (RTD) profile. 6 " 9 Transmission-coefficient-based calculations can include self-consistency and duplicate gross features of RTD I-V curves, but they are impractical for simulating time-dependent nonlinear effects, such as occur when the bias is suddenly switched (transient response or frequency-dependent behavior) and other time-dependent nonlinear phenomena such as the high-frequency oscillations at fixed bias in the NDR region simulated in this paper.As the full characterization of RTD devices requires simulating a time-evolving system, the Wigner distribution function 10 (WDF) approach has emerged as the most promising method. 11 " 15 Scattering within the device and self-consistency 13,15 " 17 may be included, and the WDF approach has the added advantage of lending itself to a "particle" interpretation. 15,16 ' 18 We present here a more accurate and fully time-dependent and self-consistent quantum transport simulation 15 which includes scattering as a function of temperature and which demonstrates current oscillations at a fixed bias. We note, however, that other time-dependent and selfconsistent scattering calculations have been reported prior to the current work, 12 " 14 but they differ from ours in some key respects. 19 The method we have chosen to incorporate self-consistency and scattering allows us to address more accurately the controversial "bistability" issue reported 4,20 and challenged 21 previously.The experimentally reported I-V curves exhibit a characteristic "plateaulike" behavior 5,22 and hysteresis. 20,21 The first view proposed by Goldman, Tsui, and Cunningham 4 attributed this entire behavior to "intrinsic bistability," that is, charge is dynamically built up and ejected from the well, and through an electrostatic feedback mechanism, two current states exist. Sollner, 21 who represents the second view, disagrees, claiming that instead of Goldman's hysteresis being due to a charging of the well, it is due to external circuit-induced oscillations of the current in the NDR region of the device. We have observed intrinsic oscillations (which have a f...

An Approach to Quantum Transport Based on Reduced Hierarchy Equations of Motion: Application to a Resonant Tunneling Diode

“…A similar I-V curve was obtained by Jensen and Buot. 24) However, while they observed only one plateau region, our results indicate the existence of two plateau regions. In addition, while the oscillation they found does not decay, the oscillation found here does besides the cases in the upper plateau.…”

“…23) Jensen and Buot developed a numerical scheme to treat systems of the same kind and reported that current oscillation and plateau-like behavior arise from intrinsic bistability. 24,25) In the previous studies, dissipative effects of electron transport have been taken into account by using the Boltzmann equation. The quantum version of the Boltzmann equation, however, employs several approximations, and it does not satisfy the fluctuation-dissipation theorem.…”

“…We set the parameters used in the HEOM as ¼ 12:1 THz ( À1 ¼ 8:27 fs), ¼ 72:5 GHz ( À1 ¼ 13:8 ps), and T ¼ 300 K to create conditions close to those used in previous theoretical studies. [21][22][23][24][25] The depth of the hierarchy and the number of Matsubara frequencies were chosen as N 2 f2; 3; 4; 5; 6g and K 2 f1; 2; 3g, respectively. The third-order up-wind and down-wind difference schemes respectively were used in the positive and negative p regions to approximate the spatial derivative of the kinetic term, Àðp=mÞ@=@q, in order to facilitate implementation of the inflow and outflow boundary conditions.…”

Coulomb-driven terahertz-frequency intrinsic current oscillations in a double-barrier tunneling structure

“…Theoretical work by several other groups predicted the same phenomenon [13][14][15][16] . It has been suggested that the RTD intrinsic current oscillations could circumvent the low-power problem and lead to THz-frequency power in the milli-watt range 12 .…”

“…Intrinsic current oscillations in dc-biased RTDs were first observed in numerical calculations by Jensen and Buo 13 , who found that the oscillations were persistent (did not decay over time). Theoretical work by several other groups predicted the same phenomenon [13][14][15][16] .…”