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I.Self-Assembled Semiconductor Epitaxical Nanostructures  >> 1. Nanostructure Synthesis and Structure: Concepts and Implementation

I.1. Nanostructure Synthesis and Structure: Concepts and Implementation

     A large part of the Madhukar group's research in the past two decades has focused on the molecular beam epitaxical synthesis and structure of compound semiconductor (InGaAlAs) heterojunction based low dimensional quantum structures such as quantum wells, superlattices, quantum wires, and quantum dots. A number of concepts and methodologies, most of which have become common practice, were introduced in our work. These include:

     Use of RHEED intensity behavior of static GaAs surface for reproducible high quality in-situ preparation of buffer layers for subsequent growth [I.1.9,12]; Growth interruption [I.1.18] for realizing atomic level perfection in interfaces; Alternate shuttering of molecular beams [I.1.33,34] (later dubbed migration enhanced epitaxy, MEE) for realizing high quality epitaxy at low growth temperatures;

     Substrate-encoded size-reducing epitaxy (SESRE) [I.1.46,53,54,55] for realizing quantum wire and box arrays of lattice matched systems on structurally patterned substrates via engineered surface stress directed self-assembly; Intrinsic defect reduction in lattice mismatched epitaxy via strain relief in growth over patterned substrates (i.e.mesas) [I.1.35,36,53];

     Discovery of the existence of coherent (i.e. defect-free) three-dimensional islands as a pathway for relief of strain in highly strained epitaxy, the basis of the field dubbed self-assembled quantum dots (SAQDs) [I.1.61]; Low temperature (<350°C) capping of islands using MEE [I.1.66]; Improved SAQD size uniformity via punctuated island growth (PIG) [I.1.75]; Stress-directed vertically self-organized growth of SAQDs [I.1.69]; Variable deposition approach (VDA) for independent manipulation of SAQD density and size [I.1.73]; Controlled creation of coupled asymmetric SAQDs [I.1.74];

     Engineered surface stress driven spatially-selective self-assembly of countable ensembles of lattice mismatch stress-induced island quantum dots [I.1.85,86,87].

     The above noted semiconductor nanostructure synthesis research in the Madhukar group utilizes the power of a unique all-UHV interconnected system of six chambers comprising growth, in-situ patterning, etching, and characterization.

     To learn more about the above noted contributions and continuing nanostructure synthesis research, click on the bullets below. Or, go to Electronic Structure or Devices.

I.1(a) Atomic Scale Understanding of Lattice-Matched and Mismatched Epitaxy.

I.1(b) Growth-Controlled Self-Assembly of Epitaxical Nanostructures.

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Coherent Island
TEM of Q-box
Coherent Island
QD on stripe