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

Introduction
thesis a detailed study of the growth and characterization of InAs and InGaAs
QDs embedded in Si matrix as well as in GaAs matrix will be presented. The
careful optimization of dierent growth parameters led to controlled QDs formation
in density, shape and size. Generally, this thesis deals with main aspects
of the current understanding of the fundamental physical mechanisms that control
the epitaxial formation of III-V nanostructures (quantm dots and dashes) on
Si substrates and presents the basic investigations for improving the structural
characteristics of such heterostructures (HSs).
1.1 Monolithic Integration of III-V Semiconductor
on Silicon
The most convincing approach for a low-cost mass production of optoelectronic
devices is the monolithic integration of III-V heterostructures with silicon microelectronics,
which in turns employ the direct epitaxial growth of III-V semiconductor
compounds layers on the Si wafers.
1.1.1 Status of Current Research and Challenges
Growth of III-V materials on silicon results in highly strained III-V lms due to
the large lattice and thermal mismatch between the lm and the substrate. The
system of InAs QDs embedded in silicon matrix has been under investigations
over the past decade [3, 4]. At a substrate temperature of 370 ◦ C, the formation
of InAs QDs were observed by RHEED at an InAs coverage of 1.7 MLs and independent
of the As/In ux ratios [3]. In addition, the thermal mismatch caused
by the dierent thermal expansion coecients of III-V lm and substrate, results
in an additional strain by cooling down the material from growth to room temperature.
Typical values for the thermal expansion coecients for InAs and Si
are 4.52 × 10 −6 k −1 and 2.6 × 10 −6 k −1 , respectively [5]. Introduction of mismatch
dislocations in the strained lm relieves lattice strain at layer thicknesses
above the critical thickness of the materials. It was also experimentally observed,
2