Relocation time of the domain boundary in weakly coupled GaAs/AlAs superlattices

Abstract

Static domain formation in doped semiconductor superlattices results in many branches in the currentvoltage characteristic separated by a discontinuity in the current. The transition process from one branch to the next has been studied experimentally by adding an ac bias with different amplitudes to a dc bias close to a discontinuity and recording the time-resolved current. The relocation time of the domain boundary depends exponentially on the difference between the final static current and the maximum or minimum current value of the corresponding branch, which is reached before the relocation of the domain boundary takes place. A universal relationship between the relocation time and the current difference has been observed. ͓S0163-1829͑98͒50812-0͔The current-voltage (I-V) characteristic of doped, weakly coupled superlattices ͑SL's͒ exhibits-under formation of static electric-field domains-many sharp branches, which are separated by a discontinuity in the current. Under domain formation, the electric field in the SL's breaks up into two regions of constant field, which are separated by a domain boundary. The domain boundary is formed by a charge accumulation layer, which is confined to one or several SL periods, i.e., one or several quantum wells of the SL. When the applied bias voltage is swept from one current branch to the next across a discontinuity, the domain boundary moves exactly by one SL period. 1 Although there has been previously a large amount of investigations on static domain formation, 2-7 dynamical processes such as the domain formation time have only been studied recently. 8,9 However, the actual motion of the domain boundary, which occurs during a current jump from one branch to the next, remains unclear.In this paper, we determine the relocation time of the domain boundary in a weakly coupled SL by fixing the dc bias (V dc ) near a discontinuity of the I-V characteristic and adding an ac square pulse voltage with different amplitudes (V ac ). The transient behavior of the current is measured as a function of V ac . When the total applied bias sweeps across a current jump, e.g., from one branch to the next, the current response exhibits a delay, which becomes faster with increasing V ac . The delay time depends exponentially on the difference between the final stabilized current and the maximum or minimum current of the initial current branch. A universal relationship between the decay time and the current difference has been observed for all cases.The investigated sample consists of a 40-period, weakly coupled SL with 9.0 nm GaAs wells and 4.0 nm AlAs barriers grown by molecular beam epitaxy on a ͑100͒ n ϩ -GaAs substrate. The central 5 nm of each well are n doped with Si at 3.0ϫ10 17 cm Ϫ3 . The SL is sandwiched between two highly Si-doped Al x Ga 1Ϫx As contact layers forming an n ϩ -n-n ϩ diode. The sample is etched to yield mesas with a diameter of 120 m. The experimental data are recorded in a He-flow cryostat at 5 K using high-frequency coaxial cables with a bandwidth of 20 GHz. The ti...

Nonlinear stochastic discrete drift-diffusion theory of charge fluctuations and domain relocation times in semiconductor superlattices

“…These figures are qualitatively similar to the corresponding ones depicted from experimental data in Refs. [9] and [5]. Quantitative differences are due to the above mentioned discrepancies in F M , the tunneling current and the shot noise amplitude.…”

“…In Ref. [5] it was claimed that the time delay depends exponentially on the difference between the final value of the stabilized current, I, and the maximum value of the current (or mimimum value in the case of a down switch) at the initial branch, I m . Then the relocation time (measured in units of 1.021 ns) depends exponentially on the current difference I − I m , i.e.,…”

“…Branches exhibit hysteresis cycles due to coexistence of two or more stable electric field profiles at a given value of the voltage. Many interesting dynamical phenomena are associated to these SL: (i) response of the SL to sudden changes in bias (which may force relocation of electric field domains [3][4][5][6]), and (ii) self-sustained oscillations of the current provided temperature is raised or doping is lowered [7,8]. Motivated by recent experimental evidence [9,10], we shall present in this paper a stochastic theory of domain relocation in highly doped SL.…”

“…In relocation experiments [5,9,11], a doped SL displaying a multistable I-V characteristic is biased (typically) on the first plateau, say in the middle of a branch. The corresponding field configuration has two domains separated by a domain wall which is an accumulation layer.…”

Lifetime of metastable states in resonant tunneling structures

“…[7]. Recent experiments [8,9] with such devices have demonstrated that near the boundary of the bistable region one of the two states is metastable, and its lifetime has been studied by measuring current as a function of time at different voltages. Thus, these devices provide an ideal experimental system for studying the decay of metastable states in real time.…”