11 research outputs found
Dissipative Chaos in Semiconductor Superlattices
We consider the motion of ballistic electrons in a miniband of a
semiconductor superlattice (SSL) under the influence of an external,
time-periodic electric field. We use the semi-classical balance-equation
approach which incorporates elastic and inelastic scattering (as dissipation)
and the self-consistent field generated by the electron motion. The coupling of
electrons in the miniband to the self-consistent field produces a cooperative
nonlinear oscillatory mode which, when interacting with the oscillatory
external field and the intrinsic Bloch-type oscillatory mode, can lead to
complicated dynamics, including dissipative chaos. For a range of values of the
dissipation parameters we determine the regions in the amplitude-frequency
plane of the external field in which chaos can occur. Our results suggest that
for terahertz external fields of the amplitudes achieved by present-day free
electron lasers, chaos may be observable in SSLs. We clarify the nature of this
novel nonlinear dynamics in the superlattice-external field system by exploring
analogies to the Dicke model of an ensemble of two-level atoms coupled with a
resonant cavity field and to Josephson junctions.Comment: 33 pages, 8 figure
Far-infrared emission and absorption by hot carriers in superlattices
Some of the earliest theoretical speculation, stimulated by the growth of semiconductor superlattices, focused on novel devices based on vertical transport through engineered band structures; Esaki and Tsu promised Bloch oscillators in narrow mini-band systems and Kazarinov and Suris contemplated electrically stimulated intersubband transitions as sources of infrared radiation. Nearly twenty years later these material systems have been perfected, characterized and understood and experiments are emerging that test some of these original concepts for novel submillimetre wave electronics. The authors describe recent experiments on intersubband emission in quantum wells stimulated by resonant tunnelling currents. A critical issue at this time is devising a way to achieve population inversion. Other experiments explore 'saturation' effects in narrow miniband transport. Thermal saturation may be viewed as a precursor to Bloch oscillation if the same effects can be induced with an applied electric field