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1

Physics of Resonant Tunnelling

100%

Sheard F., Fromhold T.

Acta Physica Polonica A

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1992

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vol. 82

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issue 4

523-538

EN

A description is given of resonant tunnelling processes in double-barrier semiconductor heterostructures from the point of view of sequential theory. If a magnetic field is applied in the plane of the barrier interfaces, the energy and transverse momentum of the electrons injected into the quantum well through the emitter tunnel barrier can be varied independently by changing the applied voltage and magnetic field. This technique can be used to probe the energy and momentum spectrum of the subband states in a quantum well. In n-type wide-well structures, a detailed interpretation of magneto-oscillations in the tunnel current has been given in terms of semiclassical orbits of electrons in the well. In p-type structures with narrow wells, the dispersion curves of hole subbands, which are complicated by the strong mixing of light hole and heavy hole states, have been directly studied. Resonant tunnelling into the bound state of single donor atoms in a quantum well has recently been observed. The magnetic field dependence of the tunnel current then gives a measure of the transverse momentum distribution and hence lateral extent of the donor wave function.

2

Resonant Tunnelling Studies of Chaos in Quantised Systems

81%

Eaves L., Fromhold T., Wilkinson P., Sheard F.

Acta Physica Polonica A

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1997

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vol. 92

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issue 4

609-619

EN

This paper gives a brief introductory overview of quantum chaology, with particular reference to recent experimental work involving the use of semiconductor heterostructures. In the presence of a tilted magnetic field, a double-barrier resonant-tunnelling device incorporating a quantum well produces a chaotic stadium for electron motion. The basic properties of this system are described. It is shown how resonant magnetotunnelling spectroscopy provides firm experimental evidence for the effect of scarred wave functions on a physically-measurable property, in this case the measured current-voltage characteristics of the device. The paper concludes with some speculations concerning for the development of this field.

3

Theory of Magnetotunnelling through Donors in the Quantum Well of Double-Barrier Resonant-Tunnelling Structures

81%

Fromhold T., Sheard F., Eaves L.

Acta Physica Polonica A

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1992

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vol. 82

|

issue 5

737-740

EN

The tunnel current from a two-dimensional electron gas (2DEG) into donor impurities in the quantum well of a double-barrier heterostructure is studied using the Bardeen Transfer-Hamiltonian formalism. Resonant tunnelling occurs when the donor level lies within the energy range of occupied 2DEG states. It is shown that in the presence of a magnetic field B normal to the current flow, the magnetocurrent J(B) is determined by the Fourier probability density of the donor wave function corresponding to the momentum p0 transferred to the tunnelling electrons by the Lorentz force. Then experimental J(B) curves, in principle, directly measure the donor wave function. The magnetocurrent is quenched when p0 greatly exceeds the width of the distribution of momentum Fourier components of the donor wave function.

4

Stochastic Carrier Dynamics in Semiconductor Superlattices

42%

Fromhold T., Bujkiewicz S., Patanè A., Stapleton S., Sherwood D., Fowler D., Cooper J., Eaves L., Belyaev A., Krokhin A., Neumann A., Wilkinson P., Sankeshwar N., Henini M., Sheard F.

Acta Physica Polonica A

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2006

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vol. 109

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issue 1

43-52

EN

We explore a new regime of hot carrier dynamics, in which electrons in a superlattice miniband exhibit a unique type of stochastic motion when a magnetic field is tilted at an angleθ to the superlattice axis. Remarkably, the dynamics of a miniband electron in a tilted magnetic field reduce to a one-dimensional simple harmonic oscillator, of angular frequencyω_C cosθ, whereω_C is the cyclotron frequency, driven by a time-dependent plane wave whose angular frequency equals the Bloch frequencyω_B. At bias voltages for whichω_B=nω_C cosθ, where n is an integer, the electron orbits change from localised Bloch-like trajectories to unbounded stochastic orbits, which diffuse rapidly through intricate web patterns in phase space. To quantify how these webs affect electron transport, we make drift-diffusion calculations of the current-voltage curves including the effects of space-charge build up. When the magnetic field is tilted, our simulations reveal a large resonant peak, which originates from stochastic delocalisation of the electron orbits. We show that the corresponding quantised eigenstates change discontinuously from a highly localised character when the system is off resonance to a fully delocalised form when the resonance condition is satisfied.

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Physics of Resonant Tunnelling

Resonant Tunnelling Studies of Chaos in Quantised Systems

Theory of Magnetotunnelling through Donors in the Quantum Well of Double-Barrier Resonant-Tunnelling Structures

Stochastic Carrier Dynamics in Semiconductor Superlattices