Biomedical Engineering Reference
In-Depth Information
Chapter 2
InP Ring-Shaped Quantum Dot Molecules
by Droplet Epitaxy
Wipakorn Jevasuwan, Somchai Ratanathammapan, and Somsak Panyakeow
Abstract
Droplet epitaxy technique is a key fabrication method to create
ring-shaped nanostructures. InP ring-shaped quantum dot molecules are grown
on In0.5Ga0.5P/GaAs(0 0 1) due to lattice mismatch of 3.8% between InP and
In0.5Ga0.5P and isotropic migration property of In atoms during the crystallization
step of In droplets on In0.5Ga0.5P. The ring shape, density of the ring and number
of dots on the ring are controlled by various growth parameters such as deposition
and crystallization temperatures, In deposition rate and thickness. InP ring-shaped
quantum dot molecules provide photoluminescence peak at 740 nm (1.66 eV) with
FWHM of 45 meV at 20 K. Potential applications of ring-shaped quantum dot
molecules in quantum cellular automata are discussed.
2.1
Introduction
Quantum dot molecules (QDMs) are equivalent to artificial molecules while
quantum dots (QDs) are considered as artificial atoms. QDMs hence possess more
variety of properties and functionalities than a single quantum nanostructure like
an individual quantum dot. Their fundamental characteristics and performances
are based on how the QDMs are formed in terms of number of quantum dots
in each QDM and in terms of their configurations and shapes of QDMs. QDMs
are packages of QDs either in vertical or in lateral configuration. Multi-stacks of
QDs with narrow spacers grown by residual strain of underneath QD layers are a
typical vertical alignment of QDs in this type of QDMs [
1
]. Multi-stacked QDMs
are key nanostructures for laser and solar cell applications [
2
-
5
] because of their
high dot density and intermediate band formation due to uniform dot size. However,
W. Jevasuwan S. Ratanathammapan S. Panyakeow (
)
Faculty of Engineering, The Semiconductor Device Research Laboratory, Electrical Engineering
Department, Chulalongkorn University, Bangkok 10330, Thailand
