GaAs/AlₓGa₁₋ₓAs Quantum Well Lasers Grown on GaAs and Si by Molecular Beam Epitaxy

Molecular beam epitaxy (MBE) has been known as a "black art" since its invention in the early 1970's. The main goal of this thesis is to present practical techniques used daily MBE experts which have never been discussed in the literature. If this thesis can make a small step toward a better understanding and utilization of this technology, the author is more than satisfied. The following is a summary of experimental and theoretical work of GaAs-on-GaAs and GaAs-on-Si material growth by MBE. Except for the relatively new GaAs-on-Si research, background information is presented at a minimum level. Emphasis is made on both theoretical and experimental techniques rather than on general discussions which exist in the literature. The thesis begins with an introduction, in Chapter 1, to activities in molecular beam epitaxy and related crystal growth methods as well as their applications in the field of optical interconnects using low-threshold lasers and high-speed photodetectors. In Chapter 2, a Green's function formulation of interface matching problems is presented. A very simple equation can be derived, which can provide some support to a very controversial, yet highly successful and very popular quantum dipole model for Schottky barriers and heterojunctions by J. Tersoff. A simplified model can be obtained, which eliminates the uncertainties in Tersoff's scheme and predicts very well the band offsets for several important semiconductor heterosystems including GaAs/AlAs. The theory is found to be in excellent agreement with a photoelectric measurement on the band offsets of the GaAs/AlGaAs system. Chapter 3 deals with details of MBE growth of GaAs/AlGaAs quantum well laser material on GaAs substrates. Various growth techniques and substrate orientations are discussed. The dependence of threshold current density of a GaAs/AlGaAs GRINSCH laser on quantum well thickness is experimentally studied. The experimental results are in good agreement with a qualitative analysis. A theoretical discussion of the effect of quantum well thickness on the threshold current density is used to explain the experimental results. Furthermore, this study has achieved for the first time, threshold current densities below 100 A/cm² in any semiconductor laser. The transparency current density obtained in this study, 60 A/cm², is very close to the theoretical prediction of 63 A/cm². It also establishes a record of lowest threshold current density for any semiconductor lasers. Chapter 4 presents some important issues in GaAs-on-Si research. Both the potentialities and limitations of GaAs-on-Si technology are discussed. The main advantage of GaAs-on-Si technology is the special features of Si substrates not available in GaAs substrates. Chapter 5 discusses the experimental aspects of GaAs-on-Si laser growth by MBE. The formation and prevention of antiphase domains (APDs) are discussed. Various methods to reduce defect density are presented. The first low threshold current density GaAs-on-Si laser growth by MBE, and the first room temperature continuous wave (CW) operation are described in detail. Important applications such as high-speed modulation of GaAs-on-Si stripe lasers and high-speed GaAs-on-Si p-i-n photodiodes are also presented. Appendix I summarizes the operation and maintenance of a Riber 2300 MBE system from a practical point of view. Only several components in this MBE system are absolutely needed to grow high quality materials. It also discusses the routine material calibrations performed. Appendix II, III, IV, V, and VI deal with the details of material processing and device fabrication.