Bistability In Structures Research Articles

Optical bistability in semiconductor periodic structures

A theoretical demonstration of optical bistability in periodic layered media, particularly in long-period GaAs/AlAs superlattices is presented. The proposed structure consists of a periodic multilayer system, as opposed to previously demonstrated nonlinear bistable devices which employed Fabry-Perot etalons. The optical resonance effect which is essential for bistable devices is, in this case, induced by a refractive index modulation. The nonlinear active medium is distributed in the whole structure rather than placed between the two mirrors of a Fabry-Perot cavity. It is shown by a complete calculation of wave propagation in the periodic nonlinear medium that a multiple valued feature appears in the structure's nonlinear reflectivity spectrum. The input/output characteristics of the structure exhibit bistable hysteresis similar to that of a nonlinear Fabry-Perot etalon. >

Sequential tunnelling and magnetically enhanced bistability in double barrier resonant-tunnelling structures

A brief overview of resonant tunnelling is given. It is shown that the resonant buildup of electron space charge can be enhanced in appropriately designed devices to give intrinsic bistability in the I(V) characteristics. Evidence is provided for the sequential model of resonant tunnelling. At high magnetic fields, the intrinsic bistability effect is greatly enhanced due to the high density of states available in a Landau level.

Intrinsic bistability in resonant-tunneling structures.

We calculate in the effective-mass approximation the current-voltage characteristic for an ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As-GaAs-${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As heterostructure. Our calculation includes the effect of electron-electron interaction in a self-consistent way. We show that charge accumulation in the quantum well is large enough to produce a bistability in the negative-differential-resistance region of the current-voltage curve.

Electrical and spectroscopic studies of space-charged buildup, energy relaxation and magnetically enhanced bistability in resonant-tunneling structures

Photoluminescence measurements and magnetoquantum oscillations in the differential capacitance are used to measure space-charged buildup and study electron thermalization in a double-barrier resonant tunneling structure based on n-type (AlGa)As. The intrinsic bistability observed in the I(V) characteristics is also seen in the linewidth and photon energy of the photoluminescence. The spectroscopic data reveal clearly the importance of intersubband transitions in the voltage range at which electrons tunnel resonantly into the second bound state of the quantum well. A novel field-induced enhancement of the intrinsic bistability effect is reported for B ‖ J .

Validity of the long-wavelength approximation applied to a superlattice on a nonlinear substrate

Optical bistability in superlattice structures on a nonlinear substrate is studied theoretically using an attenuated total-reflection configuration. It is shown that even up to Λ/λ ≅ 0.2 (where Λ is the period of the superlattice and λ is the radiation wavelength) the superlattice structure and its equivalent (in the long-wavelength limit) anisotropic layer have almost identical nonlinear behavior although the linear properties may differ significantly.

Magnetic field and capacitance studies of intrinsic bistability in double-barrier structures

Intrinsic bistability is observed in the current-voltage and capacitance-voltage characteristics of double-barrier resonant tunnelling structures. Analysis of the C(V) measurements and the magneto-oscillations in both I(V) and C(V) is used to determine the resonant charge build-up in the well which gives rise to the intrinsic bistability.

Simulation of extrinsic bistability of resonant tunneling structures

A simple biasing circuit for measuring current-voltage characteristics of resonant tunneling double-barrier structures exhibits extrinsic bistabilities due to oscillations, which we show through large-signal simulations.

Space-charge buildup and bistability in resonant-tunneling double-barrier structures

Using the sequential theory of resonant tunneling, the dc current-voltage characteristic of a double-barrier structure is calculated, taking into account the effect of space charge in the quantum well. A region of current bistability is found over a voltage range which is determined by the maximum space charge and the capacitance of the structure. These parameters are directly related to the periodicity of magnetoquantum oscillations in the current.

Comment on "Observation of intrinsic bistability in resonant-tunneling structures"

It is suggested that the intrinsic bistability observed by Goldman et al. (1987) occurred not because of charging of the well, as is claimed, but because of oscillations in the negative-resistance region. A typical I-V curve for a double-barrier resonant-tunneling (DBRT) diode which is known to be oscillating is presented. In a reply to this comment, Goldman et al. show that the series resistance (of about 100 ohms) in Sollner's sample leads to extrinsic, rather than intrinsic, bistability. It is furthermore suggested that the mere presence of an oscillation does not in itself exclude intrinsic bistability in a DBRT structure. It is also noted that the intrinsic bistability and buildup of negative charge-space in a DBRT structure well has been demonstrated experimentally by Payling et al. (1987).

Observation of intrinsic bistability in resonant tunneling structures.

A simple quantum system, the semiconductor-based double-barrier resonant-tunneling structure, exhibits intrinsic bistability which we attribute to the feedback dependence of the energy of the electronic states in the well on the tunneling current density.

Pressure-induced cubic to tetragonal transition in CsI.

First-principles self-consistent total-energy calculations within the local-density approximation show, in agreement with experiments, that CsI undergoes a transition from the cubic (CsCl) structure to a tetragonal structure at a pressure ${P}_{t}\ensuremath{\simeq}40$ GPa. The calculated volume at the transition is \ensuremath{\sim} 53% of the zero-pressure volume. We find that the phase transition is driven by an "intercellular" electrostatic interaction. A structural bistability is found around the transition.