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I.Self-Assembled Semiconductor Epitaxical Nanostructures  >> 2.Electronic Structure and Response of Confined Systems
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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