On-chip characterization devices have been used to extract the Young’s modulus, average stress and stress gradient of polysilicon doped with phosphorus using thermal diffusion. Devices for extracting the Young’s modulus, average stress and stress gradients have been designed to work within the range of expected material property values. A customized fabrication process was developed and the devices were fabricated. Static and resonant tests were performed using clamped-clamped and cantilever beams in order to extract material properties. The experimental setup and detailed experimental results and analysis are outlined within. Several doping concentrations have been studied and it has been concluded that the Young’s modulus of polysilicon doped for 2 hours increases by approximately 50GPa and the average stress of polysilicon doped for 2.5 hours becomes more tensile by approximately 63 MPa. It has also been found that short doping times can introduce a large enough stress gradient to create a concave up curvature in free-standing structures. This work was performed in order to determine the usability of doping as a means to increase the sensitivity of temperature and pressure sensors for harsh environments. It has been concluded that doping is a promising technique and is worth studying further for this purpose.

The operating characteristics of non-volatile memory for modern requirement are high-density , low power consumption, fast read and write speed, and good reliability. The floating gate memory generated leakage path in the tunnel oxide during the trend of scaling down, which will result in the loss of all stored charge to the silicon substrate. As the data retention time and endurance are taken into consideration, the thickness of tunnel oxide exist a physical limit, owing to the demand of high-density capacities. RRAM is offered as an option in the next generation non-volatile memories, due to the following advantages: (1) simple structure and easy to process, and low cost ; (2) less restrictive in the scaling-down process; (3) with the multi-bit data storage features; (4) high speed operation; (5) Repeat write and read is more than one million. In the thesis, we use a simple and low-temperature process to form the silicon germanium oxide (Si-Ge-O) RRAM and silicon germanium oxide RRAM with nitrogen doping between the electrode and silicon-germanium oxide interface. By sputtering at argon and oxygen (Ar/O2), and sputtering at argon and ammonia (Ar/NH3) with silicon-germanium target to form silicon germanium oxide RRAM and silicon germanium oxide (Si-Ge-O)/silicon germanium oxnitride (Si-Ge-O-N) RRAM. By informing a SiGeON layer between the interface of electrode and silicon-germanium oxide improve the stability of write voltage and endurance reliability. In addition, both silicon and germanium are useful as materials in the optoelectronics industry and extensively studied in material science. Based on the two materials, the smiting characterizations of RRAM will be improved in the read-write stability and operation reliability.

The purpose of this thesis is to fabricate 12-layer InxGa1-xAs quantum dots grown on 2-nm In0.1Ga0.9As quantum wells (DWell) laser structures grown by molecular-beam epitaxy (MBE) on GaAs substrats. We expect to optimum the lasers performance by tune the epitaxial recipe and fabrication condition. For the carrier injection efficiency, DWell structure of quantum dots grown on quantum wells is proposed to enhance the carrier capture rate. So we analyze a series of DWell structure in this work. In the epitaxial recipe, we investigate the influences of p-type doping and change the quantum wells growth temperature for the laser structures. In the laser fabrication, to transport the light wave in smaller dispersion loss single mode waveguide, dry etching photolithography processes are adapted in this study to fabricate 2.2mm width ridge waveguide. The as-cleaved facets are used as Fabry-Perot laser mirrors in ridge waveguide lasers. The pattern can be transferred effectively with less under-cut by dry etching compare with wet etching. Finally, the P-type doping DWell laser exhibits high power/facet of 24mW, slope efficiency of 0.209W/A. The maximum power/facet of PWell580 laser reach to 24mW, slope efficiency of 0.238W/A after raising the growth temperature to 580oC.

We have investigated the polarization effect of optical process in the vertically coupled InGaAs quantum dots (QDs) triple layers by varying the thickness of GaAs spacer layer. The TE/TM ratio for the ground state emission decreases from near 4 to 1.5 as the spacer thickness (d) decreases from 40 nm to 5 nm. And, the TE polarization (in-plane polarization) is anisotropic with a stronger component along [01-1] direction. P-type modulation doping further decreases the TE/TM ratio to r = 1.2 for the strong vertical coupling QDs structure of 5-nm spacer. Then, using a cross-sectional transmission electron microscopy directly reveals the InGaAs QDs of 5-nm spacer well aligned along the growth direction. From the electroluminescence (EL) and differential absorption (£G£\) experiments, the higher optical gain and absorption change for the excited state suggest that the e2-hh transition has higher oscillator strength for the vertically coupled QDs. We also investigate for the triple-layer InGaAs vertically coupled quantum dots (VCQDs) by adding modulation doping (MD) in the 5-nm GaAs spacer layers. In addition to the QDs fundamental and excited transitions, a coupled-state transition is observed for the VCQDs. For the VCQDs of p-type MD, the optical transitions at ground state and coupled state are enhanced by the improvement of hole capture for the valence subbands. For the VCQDs of n-type MD, the main absorption change occurs at the coupled state, consistent with the dominant emission peak observed in EL spectra. For GaAs-based solar cells application, in order to enhance absorption at infrared range for GaAs-based solar cells, multi-stack InGaAs VCQDs of 5-nm GaAs spacers are grown in the active region. Due to the strong vertical coupling between QDs would promote quantum efficiency. We have investigated the photovoltaic response for the solar cells by increasing the layer numbers of VCQDs. The device of nine-layer InGaAs VCQDs shows an enhanced short-circuit current density (Jsc) of 10.5 mA/cm2. The value is increased by 42% compared to GaAs reference device. However, the open-circuit voltage (Voc) is reduced from 0.88 V to 0.54 V. Then, we change the GaAs spacer thickness of coupled In0.75Ga0.25As QDs, and investigated the effects on photovoltaic response. For the sample of d =10 nm shows the best performance of current density (Jsc~24 mA/cm2) and efficiency (h~10.6%). The Jsc and h are increases by 55% and 112% more than the device without QDs, respectively.

Nanotechnology comprises of the understanding and control of materials and processes at the nanoscale. Among various nanostructured materials, semiconducting nanowires attract much interest for their novel physical properties and potential device applications. The unique properties of these nanowires are based on their high surface to volume ratio and quantum confinement effect. Zinc oxide, having a direct, wide bandgap and large exciton binding energy, is highly appealing for optoelectronic devices. Due to excellent optical and electrical properties, zinc oxide nanowires have been utilized to fabricate various devices such as solar cells, light emitting diodes, transistors and photodetectors. Furthermore, zinc oxide, in its natural state exhibits n-type conductivity. Addition of impurities often leads to remarkable changes in their electrical and optical properties, which open up new application areas. Among the many synthesis methods for zinc oxide nanowires, hydrothermal method is an attractive one due to its easy procedure, simple equipment and low temperature requirements. In this thesis, zinc oxide nanowires were grown and doped by hydrothermal method. Different metal dopants such as copper, silver and aluminum were used for this purpose. These metals were selected as dopants due to their effect on magnetic properties, p-type conduction and electrical conductivity of ZnO nanowires, respectively. Doped nanowires were fully characterized and the changes in their physical properties were investigated. In addition, hydrothermally synthesized pure and aluminum doped zinc oxide nanowires were used as the electrically active components in ultraviolet photodetectors. Silver nanowires were utilized as transparent electrodes. Optoelectronic properties of the detectors were examined. Effect of in-situ annealing and nanowire length was investigated. Short recovery time, around 4 seconds, with a decent on/off ratio of 2600 was obtained. This design provides a simple and cost effective approach for the fabrication of high performance ultraviolet photodetectors.

ETH, Diss.--Zürich, 2007.

Thesis (Ph. D.)--University of Missouri-Columbia, 1999. / Typescript. Vita. Includes bibliographical references (leaves 147-152). Also available on the Internet.

Thesis (M.S.)--West Virginia University, 2002. / Title from document title page. Document formatted into pages; contains xi, 105 p. : ill. Includes abstract. Includes bibliographical references (p. 100-105).

Thesis (Ph. D.)--Mississippi State University. Department of Electrical and Computer Engineering. / Title from title screen. Includes bibliographical references.

Thesis (M. Phil.)--University of Hong Kong, 2002. / Includes bibliographical references (leaves 75-77).