I.2.Electronic Structure and Response of Confined Systems
Understanding, through modeling, calculations and measurements, the
electronic energy level structure and the electrical and optical behavior of low dimensional quantum structures, including those we synthesize as
noted in Sec.I.1, has been an integral part of the Madhukar groups endeavors. These have resulted in the introduction of several ideas and
uncovering a few important results. A brief summary of some work on quantum wells is followed below by some examples of contributions to the
subject of quantum dots.

Heterojunctions and Quantum Wells
Some
firsts in the area of heterojunctions, quantum wells,
and superlattices include: introduction of the concept
of structure-induced charge transfer (SICT) in atomic
networks and its use to explain the distributed ring
nature of amorphous SiO2 (glassy material) and the role
of stress at the Si/SiOx interface in Si CMOS [1,2];
the earliest calculations of the electronic structure
of the nine (Ga,Al,In)(As,Sb,P) binary semiconductor
surfaces employing tight binding (TB) modeling and surface
Greens function techniques [3,4];
the first calculations of the electronic band structure
of the InAs/GaSb heterojunction and superlattices to
explain the semiconductor to semi-metallic transport
behavior expected from the unusual band line up of this
system [5,6]; prediction
of the possibility of a direct band gap superlattice
arising from the combination of indirect band gap bulk
materials such as GaP/Si or GaP/AlP [7,8];
prediction of resonant coupling of confined quantum
well electronic states with phonon modes [9]
and its subsequent experimental demonstration [10];
prediction of coupled plasmon modes in spatially separated
interacting two-dimensional plasmas [11];
prediction and experimental demonstration of the dominance
of quantum well depth fluctuations in controlling the
exciton radiative recombination life time (rather than
the prevailing models of quantum well width fluctuations)
in high quality quantum wells (QWs) involving alloy
barrier layers (such as the ubiquitous GaAs/AlGaAs QWs)
[12];

Self-Assembled Quantum Dots: Electronic Properties

For the SAQD field, our primary current focus, some significant contributions include:

The
first demonstration of PLE (photoluminescence excitation)
spectroscopy as a probe to reveal the excited electronic
states of semiconductor epitaxical quantum dots [13]
and its usage for size-selective spectroscopy [14];
the first measurement of the exciton-phonon coupling
in an island quantum dot system, the InAs/GaAs self-assembled
QD system [15]; the first
study of excitation transfer between asymmetric SAQDs
with controlled variation of coupling [16];
systematic and multi-pronged examination leading to
the first determination of the dominant intra- and inter-band
transitions in large pyramidal SAQDs [17,18];
and the first selective manipulation of SAQD wavefunctions
through manipulation of the lateral confinement potential
[19,20].

Additional information on selected examples from the SAQD studies can be found by clicking on the bullets below:

Excitation transfer between coupled asymmetric SAQDs

Exciton-phonon coupling in InAs/GaAs SAQDs.

Large InAs/GaAs SAQD electronic structure

Inter- and Intra-band Transition Dipoles in SAQDs

SAQD wavefunction manipulation

Current
Research Focus
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