Self-sustained Current Oscillations Research Articles

Dynamics of electric field domain walls in semiconductor superlattices

A self-consistent microscopic model of sequential tunneling in superlattices is employed to investigate self-sustained current oscillations. Current spikes – high-frequency modulation due to well-to-well hopping of charge monopole domain walls – are naturally reproduced. Moreover, as the contact doping shrinks, the recycling and motion of charge dipoles resulting in a lower-frequency oscillatory mode is predicted. For low contact doping, this mode dominates and monopole oscillations disappear. At intermediate doping, hysteresis between both the oscillatory modes may be possible.

Time-dependent current oscillations through a quantum dot

Time dependent phenomena associated to charge transport along a quantum dot in the charge quantization regime is studied. Superimposed to the Coulomb blockade behaviour the current has novel non-linear properties. Together with static multistabilities in the negative resistance region of the I-V characteristic curve, strong correlations at the dot give rise to self-sustained current and charge oscillations. Their properties depend upon the parameters of the quantum dot and the external applied voltages.

Dynamical Instabilities in Resonant Tunneling

Time dependent phenomena associated to charge transport along double barrier heterostructures are studied. Systems in 3D under the effect of an external magnetic field along the current and 1D systems are analyzed. Together with static multistabilities in the negative resistance region of the I–V characteristic curve, we found self-sustained time dependent current and charge oscillations. The nature of this oscillatory behavior depends upon the parameters that define the system.

Dynamical Instabilities in Resonant Tunneling

Time dependent phenomena associated to charge transport along double barrier heterostructures are studied. Systems in 3D under the effect of an external magnetic field along the current and 1D systems are analyzed. Together with static multistabilities in the negative resistance region of the I–V characteristic curve, we found self-sustained time dependent current and charge oscillations. The nature of this oscillatory behavior depends upon the parameters that define the system.

Current self-oscillations, spikes, and crossover between charge monopole and dipole waves in semiconductor superlattices

Self-sustained current oscillations in weakly-coupled superlattices are studied by means of a self-consistent microscopic model of sequential tunneling including boundary conditions naturally. Well-to-well hopping and recycling of charge monopole domain walls produce current spikes (high frequency modulation) superimposed on the oscillation. For highly doped injecting contacts, the self-oscillations are due to dynamics of monopoles. As the contact doping decreases, a lower-frequency oscillatory mode due to recycling and motion of charge dipoles is predicted. For low contact doping, this mode dominates and monopole oscillations disappear. At intermediate doping, both oscillation modes coexist as stable solutions and hysteresis between them is possible.

Self-sustained current oscillation above 100 GHz in a GaAs/AlAs superlattice

A GaAs/AlAs superlattice with a large miniband (120 meV) showed self-sustained current oscillation at a frequency of 103 GHz giving rise to microwave emission (power 0.5 mW). The emission line had a linewidth of about 1 MHz and was tuneable by about 800 MHz. An analysis suggests that the transport in the superlattice was mainly due to electrons in the lowest miniband and that the oscillation was caused by traveling dipole domains. We also observed frequency locking of the current oscillation attributed to a synchronization of domain propagation by the external high-frequency field.

Suppression of Self-Sustained Field Domain Oscillation in GaAs/AlAs Superlattice by Hydrostatic Pressure at Room Temperature

The behavior of room temperature self-sustained current oscillations resulting from sequential resonance tunneling in a doped weakly-coupled GaAs/AlAs superlattice (SL) is investigated under hydrostatic pressure. From atmosphere pressure to 6.5 kbar, oscillations exist in the whole plateau of the I-V curve and oscillating characteristics are affected by the pressure. When hydrostatic pressure is higher than 6.5 kbar, the current oscillations are completely suppressed although a current plateau still can be seen in the I-V curve. The plateau disappears when the pressure is close to 13.5 kbar. As the main effect of hydrostatic pressure is to lower the X point valley with respect to Γ point valley, the disappearance of oscillation and the plateau shrinkage before Γ - X resonance takes place are attributed to the increases of thermoionic emission and nonresonant tunneling components determined by the lowest Γ - X barrier height in GaAs/AlAs SL structure.

Microwave generation by a self-sustained current oscillation in an InGaAs/InAlAs superlattice

We observed a self-sustained current oscillation in an InGaAs/InAlAs superlattice at room temperature. The oscillation gave rise to microwave generation at a fundamental frequency around 2GHz and higher harmonics. The power at the first harmonic was 0.1 mW, corresponding to an efficiency (i.e. ratio of microwave power to dc power) of 3.5%. We attribute the current oscillation to travelling dipole domains.

Millimeter wave generation by a self-sustained current oscillation in an InGaAs/InAlAs superlattice

We report millimeter wave generation by a self-sustained current oscillation in a doped InGaAs/InAlAS wide miniband superlattice. The superlattice (miniband width 160 meV) showed, at room temperature, a current voltage characteristic with negative differential conductance. Coupled to a high-frequency circuit, the superlattice generated millimeter waves, at a frequency (55 GHz) which was tunable by half a percent by changing the bias voltage. The power (0.3 mW) corresponded to an efficiency (i.e., ratio of microwave power to dc power input) of 0.3%. We attribute the microwave generation to a current oscillation caused by traveling dipole domains.

Magnetic-field-induced bistability in resonant tunneling

We report an unusual magnetic-field-induced bistability in the current-voltage characteristic of an asymmetric double-barrier resonant tunneling structure. It is suggested that this bistability is the experimental manifestation of self-sustained current oscillations that have recently been predicted by Orellana, Anda, and Claro [Phys. Rev. Lett. 79, 1118 (1997)].

Spatiotemporal propagation of a non-linear electrochemical reaction over an iron electrode

Propagation of the reaction front of oxide formation and reduction along an iron electrode has been investigated when a self-sustained non-linear current oscillation is proceeding. It has been observed that a resistance inserted between the electrode and the potential source changes the oscillation waveform and the propagation speed of the reduction. This finding shows a coupling between the ohmic potential drop in the solution and the reaction propagation along the electrode.

Frequency-locked GaAs/AlAs superlattice oscillator for tunable narrowband microwave generation

We observed frequency locking of a wide-miniband GaAs/AlAs superlattice oscillator. The oscillator showed a free self-sustained current oscillation giving rise to microwave generation (power 100 μW) at a natural frequency (near 5 GHz) and ultraharmonics. A narrowband driving field locked the oscillator and caused a drastic narrowing (from 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> Hz to less than 10 Hz) of the halfwidths of the microwave lines, now centered at the driving frequency and its harmonics; at a driving power of 10 μW we obtained a locking range of 1% around the natural frequency. Our experiment, performed with a superlattice integrated in a planar microwave circuit, shows that a locked superlattice oscillator is suitable for tunable narrowband generation of high-frequency radiation.

Current Self-Oscillations in Undoped, Photoexcited GaAs/AlAs Type-I Superlattices

Self-sustained current oscillations have been observed in undoped, photoexcited GaAs/AlAs type-I superlattices with different well and barrier thicknesses. The oscillations originate from a periodic motion of a space charge layer forming the boundary between low- and high-field regions of electric-field domains. When undamped photocurrent oscillations are detected, the high-field domain is found to originate from Γ–X resonant transfer. This observation implies that through the Γ–X resonance the recombination lifetime for electrons and holes is prolonged so that undamped photocurrent oscillations in the MHz regime can even be observed in undoped type-I superlattices.

Dynamics of the single barrier heterostructure hot electron diode

The dynamics of the bistable and oscillatory behavior of a heterostructure hot electron diode is investigated both theoretically and experimentally. Monte Carlo simulations are performed accounting for the scattering to subsidiary conduction band valleys of GaAs and AlGaAs. S-shaped current-voltage characteristics and self-sustained current oscillations in an external cavity are obtained in good agreement between theory and experiment.

Dynamic Instabilities in Resonant Tunneling Induced by a Magnetic Field

We show that the addition of a magnetic field parallel to the current induces self-sustained intrinsic current oscillations in an asymmetric double barrier structure. The oscillations are attributed to the nonlinear dynamic coupling of the current to the charge trapped in the well, and the effect of the external field over the local density of states across the system. Our results show that the system bifurcates as the field is increased, and may transit to chaos at large enough fields.

Current-voltage characteristic and stability in resonant-tunneling n-dopedsemiconductor superlattices

We review the occurrence of electric-field domains in doped superlattices within a discrete drift model. A complete analysis of the construction and stability of stationary field profiles having two domains is carried out. As a consequence, we can provide a simple analytical estimation for the doping density above which stable domains occur. This bound may be useful for the design of superlattices exhibiting self-sustained current oscillations. Furthermore we explain why stable domains occur in superlattices in contrast to the usual Gunn diode.

Quenching of the spontaneous current oscillations in GaAs/AlAs superlattices under domain formation

Self-sustained current oscillations in a dc biased GaAs/AlAs superlattice exhibiting domain formation can be quenched by applying an external ac driving voltage with a large amplitude. The frequency of the driving voltage has to be much larger than the oscillation frequency and the well-to-well hopping frequency of the domain boundary. Under this condition, the oscillations of the domain boundary cannot follow anymore the ac driving signal. Consequently, for a fixed dc bias voltage the accumulated charge forming the domain boundary is confined within a single quantum well resulting in stationary domains.

High-frequency self-sustained current oscillation in an Esaki-Tsu superlattice monitored via microwave emission

We report the observation of a high-frequency self-sustained current oscillation in an n doped GaAs AlAs superlattice (at room temperature) that shows a negative differential conductance (Esaki-Tsu superlattice). The superlattice biased in the region of the negative differential conductance emitted microwave radiation at a fundamental frequency of about 6 GHz and at harmonics. We attribute the oscillation to space charge instabilities inside the superlattice caused by Bragg reflection of electrons in the lowest, wide miniband.

Chaotic dynamics of electric-field domains in periodically driven superlattices.

Self-sustained time-dependent current oscillations under dc voltage bias have been observed in recent experiments on n-doped semiconductor superlattices with sequential resonant tunneling. The current oscillations are caused by the motion and recycling of the domain wall separating low- and high-electric-field regions of the superlattice, as the analysis of a discrete drift model shows and experimental evidence supports. Numerical simulation shows that different nonlinear dynamical regimes of the domain wall appear when an external microwave signal is superimposed on the dc bias and its driving frequency and driving amplitude vary. On the frequency-amplitude parameter plane, there are regions of entrainment and quasiperiodicity forming Arnol'd tongues. Chaos is demonstrated to appear at the boundaries of the tongues and in the regions where they overlap. Coexistence of up to four electric-field domains randomly nucleated in space is detected under ac+dc driving. \textcopyright{} 1996 The American Physical Society.

Self-Oscillations of the Current in Doped Semiconductor Superlattices

Self-sustained current oscillations have been found in doped GaAs-AlAs superlattices and are investigated experimentally and theoretically. The electric-field distribution in doped superlattices becomes unstable if the carrier density is not sufficiently large to form stable domains. The instability results in self-oscillations of the current, which are due to an oscillatory motion of the domain boundary in the superlattice. A discrete drift model taking into account several regions of negative differential velocity and a large electron density clearly establishes the origin of these oscillations.