Microstructural and optical properties of InAs-based quantum dot structures

Abstract

The physical properties of self-assembled quantum dots (SAQDs) formed by using the Stranski-Krastanow (S-K) growth mode have been studied for several years because of their potential applications to optoelectronic devices. Since the microstructural properties of SAQDs can significantly affect their electrical and optical properties, studies on microstructural properties of SAQDs must be preceded before understanding of operation of optoelectronic devices based on quantum dot structures. Therefore, in this dissertation, we have studied the microstructural and the optical properties of various SAQD structures grown by molecular beam epitaxy (MBE). In the chapter 3, we have studied the formation process of InAs QDs grown on a GaAs substrate by using reflection high-energy electron diffraction (RHEED) and transmission electron microscopy (TEM). The growth process of the InAs layer during the initial stage is clearly divided into 2D growth and QD formation. The in-plane surface lattice parameter of the InAs layer was measured to investigate the strain relaxation behaviors of the InAs QDs. A schematic diagram of a strained InAs/GaAs QD was presented on the basis of high-resolution TEM results. The dependence of the microstructural and the optical properties on the growth times for vertically stacked InAs/GaAs QDs has been studied. The sizes of the QDs increased with increasing number of stacking layers when the growth time of the InAs layer was constant. However, the results of TEM and photoluminescence (PL) measurements showed that a narrow size distribution of vertically stacked InAs QD arrays inserted into GaAs barriers could be achieved when the growth time of InAs QDs gradually decreased with increasing number of stacking layers. In the chapter 4, we have investigated the microstructural and the optical properties of doped SAQD structures. In the case of high-quality Si-doped InAs QD arrays embedded into GaAs barriers, PL measurements showed that the dominant...