Mar 25, 2009
Unraveling coupled multiscale phenomena in QD nanostructures
Coupled phenomena are ubiquitous in quantum dot (QD) nanostructures. Optoelectronic properties of quantum dots and other low dimensional nanostructures are affected by other material properties such as thermal, mechanical and electromagnetic, to name just a few. This makes the entire problem of the analysis and determination of properties of such nanostructures intrinsically coupled.
Low dimensional semiconductor nanostructures (LDSN) are multiscale complex systems, parts of which are joined together at the atomic level via interfaces to form a new structure with useful features. Due to the size of the structures and the way that they are fabricated, coupled phenomena are important as they hold the key to the properties of LDSNs and their associated devices.
In a recent study on thermo-electromechanical effects in QDs, which was published in Nanotechnology, the authors reported for the first time results based on a coupled model of thermo-electroelasticity applied to the analysis of QDs. The group has used its new data to perform a systematic analysis of the influence of thermo-electromechanical effects on bandstructures of these LDSNs.
The developed methodology can account for a practically important range of internal and external thermo-electromechanical loadings, various geometries of QDs, as well as for the wetting layer effect. It provides a general framework for studying related coupled effects including piezoelectricity, flexoelectricity, thermoelectricity, and thermoelasticity, as well as a way of accounting for nonlinear effects such as electrostriction, nonlinear strain and shape memory effects. Details are also given on how the developed methodology can be extended to account for coupled thermo-magneto-electromechanical effects.
To demonstrate their technique, the team examined typical QD systems based on GaN/AlN and CdSe/CdS, as representatives of III–V and II–VI group semiconductors, respectively. When QDs are embedded in a host material with different structural properties, in addition to accounting for lattice mismatch and residual strains, it is also important to account for the difference in thermal expansion coefficients. The study revealed a significant reduction in electronic state energies due to thermal loadings. Thus, in addition to electromechanical tuning, the operating temperature can also provide an additional tuning parameter in band-gap engineering of QDs and other LDSNs.
The coupled model formulation and the technique developed by the group can act as a foundation for the study of nanostructures in novel applications, including acousto-optoelectronic, sensor, and bionanotechnologies, where the coupling between different media such as solid and fluid/gas is essential.
About the author
The work was performed at the M2NeT Lab and was supported by NSERC, CRC, and SHARCNET Programs. The M2NeT Lab is based at the Wilfrid Laurier University in Waterloo, Canada. It consists of an interdisciplinary group of applied mathematicians, physicists, materials scientists and engineers. The group is headed by Prof. Roderick Melnik who is also Tier I Canada Research Chair in Mathematical Modeling. Dr Sunil R Patil is a Postdoctoral Fellow at the M2NeT Lab supported by SHARCNET and NSERC CRC grants. The group has active collaborations with colleagues in the US, Canada, Europe, India, Australia and China.