Molecular beam epitaxial growth of III-V semiconductor ... - KOBRA

Theoretical Background of Semiconductor Nanostructures
level can enhance material functions and characteristics, leading to considerable
energy savings and environmental load reduction. However, according to this
approach which is based on the monolithic integration of nanostructures semiconductor,
such as (quantum dots QDs, quantum wells QWs, etc.) on silicon
substrates. Nanostructures, such as quantum dots (QDs), can be fabricated with
either a top-down technique or bottom-up technique. Top-down techniques are
great for generating a uniform distribution of diameters. Unfortunately, top-down
approaches like lithography are limited by the diraction limit and implies material
damage and defects. The most common way to create a QD is through a
bottom-up approach. This can be done either with metal-organic chemical vapor
deposition (MOCVD) or MBE. Self-assembled quantum dots (SAQDs) nucleate
spontaneously under certain conditions during MBE and metal-organic vapor
phase epitaxy (MOVPE), when a material is grown on a substrate to which
it is not lattice-matched. The resulting strain produces coherently strained islands
on top of a two-dimensional wetting layer. This growth mode is known as
Stranski-Krastanov (SK) growth (like InAs QDs on GaAs system). The islands
can be subsequently buried to form the quantum dot. Therefore, the fundamental
understanding of low-dimensional semiconductor physics and the electronic con-
nement inside these structures is essential for the growth and characterization
of these systems including their new structural and optical properties, etc. The
next section will bring the focus on the underlaying physics, which explains these
interesting nanostructures.
2.3 Low-Dimensional Semiconductor (Nanostrtuctures)
With the advent of epitaxial growth techniques like molecular beam epitaxy
(MBE), the realization of low-dimensional structures became feasible. However,
when one of the three spatial dimensions of a bulk solid, like in semiconductor
material, is of a size comparable to de Broglie wavelength (λ B ) (Eq. 2.1) of the
electrons or smaller, this means we are dealing with a material or a structure
of low-dimensionality (nanostructure) [18], which is referred as two-dimension
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