Modeling the effect of elastic strain on ballistic transport and photonic properties of semiconductor quantum structures

The recent progress in microelectronic processing techniques has made it possible to fabricate artificial materials, dedicated and tailored directly for nanoelectronics and nanophotonics. The materials are designed to achieve a confinement of electrons to nanometer size foils or grains, often called quantum structures because of the quantization of the electron energies. In this work I have developed computationalmodels for the electronic structure, photonic recombination and carrier dynamics of quantum confined charge carriers of artificial materials. In this thesis I have studied in particular the effect of elastic strain on the ballistic transport of electrons, in silicon electron wave guides; and on the electronic structure and photonic properties of III-V compound semiconductor heterostructures. I have simulated two types of elastic strain. The strain in the silicon wave guides is induced by the thermal oxidation of the silicon processing and the strain of the III-V compound semiconductor structures is a result of a pseudomorphic integration of lattice mismatched materials. As one of the main results of this work, we have shown that the oxidation-induced strain can lead to current channeling effects in electron wave guides and a doubling of the conductance steps of the wave guide. In the case of the III-V compound semiconductor heterostructures, it was shown that piezoelectric potential (which is due to the elastic strain) complicates considerably the electron-hole confinement potential of strain-induced quantum dots. This has several consequences on the optical properties of these systems. Our results are well in agreement with experimental observations and do explain a set of experiments, which have so far lacked any explanation. This work does, thereby, imply a much better understanding of both silicon electron wave guides and strain-induced quantum dots. This could have implications for both further detailed experiments and future technological applications of the studied devices.reviewe

Integrated silicon pressure sensors using wafer bonding technology

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1997.Includes bibliographical references (p. 151-156).by Lalitha Parameswaran.Ph.D

SCANNING TUNNELING MICROSCOPY STUDIES OF GROWTH MEDIUM & TEMPERATURE DEPENDENT STRUCTURAL PHASES OF ALKANETHIOL SELF-ASSEMBLED MONOLAYERS, REACTIVE SELF-ASSEMBLED MONOLAYERS, & FLAT GOLD NANOPARTICLE/INDIUM TIN OXIDE SUBSTRATES AND A SCANNING SURFAC

Self-assembled monolayers (SAMs) of alkanethiolates on Au(111) represent promising platforms to study the molecular surfaces and interfaces for applications ranging from molecular electronics, nanophotonics to biology. Understanding the effect of growth conditions on SAMs particularly on their structural features is important from both fundamental and applied points of view. Knowledge of SAM structural features and structural phase transitions provides important insights into molecular packing for the control of the molecular self-assembly.We compared SAMs grown from different media, from 1 mM C10 solution in decalin, hexadecane and triethylene glycol and from C10 vapor. We present a molecularly-resolved scanning tunneling microscopy study showing the dependence of the SAM structure on the growth conditions. We have established conditions for making samples almost vacancy islands (VI) free with very large SAM domains of (2√3 × 3)rect. superstructure and (√3 × 4√3)R30° striped phase and investigated the orientation of low-index step edges of Au(111) for normal and striped-phase SAMs. We showed that the striped phase is stable to converting to (2√3 × 3)rect. below 40 °C.We demonstrate that flat gold nanoparticles (FGNPs) supported on indium tin oxide glass (ITO) are excellent substrates for molecularly-resolved STM imaging of alkanethiol SAMs. Nanoparticles were characterized using STM, TEM, and SEM techniques. Surface treatment techniques, Ar/O2 and H2 plasma treatments, dry thermal annealing and exposures to UV/O3, were used to prepare the surfaces of FGNPs supported on ITO and Au/mica substrates for high-resolution STM imaging of alkanethiol SAMs.We developed a convergent approach to functionalize SAM surfaces. Ordered mixed monolayers comprised of alkanethiols and azidoalkanethiols islands are formed and subsequent IMesCulBr catalyzed [3+2] "click" cycloaddition reaction with substituted alkyne introduced dilute substituent onto the ordered surface.Mechanical stress is one of the major factors in current design and manufacture of very large scale integrated (VLSI) devices. Mechanical stress in deep sub-micron silicon technologies can drastically alter carrier mobility (e.g., approximately 25% dependent on device geometry). This affects the device performance. Current in-line production stress metrology is conducted only at a wafer monitor level. The available stress measurement techniques such as micro-Raman spectroscopy, nano beam diffraction (NBD), converging electron beam diffraction (CEBD) either do not have required resolution or they require complex data interpretation. We present a method for measuring mechanical stress in deep sub-micron silicon devices with high spatial resolution using scanning Kelvin probe force microscopy and scanning surface photovoltage (SSPVM) techniques