In this work, Mn atoms are doped into GaN nanorods by two doping types, homogeneous and delta doping, and GaN nanorods are grown on Si (111) substrate using plasma-assisted MBE. The GaMnN nanorods are characterized by scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), high-resolution x-ray diffraction (HR-XRD), Raman scattering, Transmission electron microscopy (TEM), superconducting quantum interference device (SQUID), and x-ray photoelectron spectroscopy (XPS). The Mn delta-doping GaN nanorods with Ga/Mn growth time ratio 20 are approximately 1500 nm in height, grown along the c-axis. The Mn concentration in nanorods is determined to be 0.83% by EDS, without secondary phase formation. The Mn atoms substitute Ga sites in the GaN wurtzite hexagonal structure and, according to the results of Raman, there is no observable Mn-N cluster formation existed. The delta-doping structure, without secondary phase inclusions, can be observed under TEM imaging of the nanorods. The nanorods appear to show ferromagnetic behavior at room temperature, as judged by the M-H with hysteresis curve, however the small the loops are. The delta-doping is adopted in this thesis work to fabricate GaMnN DMS nanorods without secondary phase formation.

Nearly dislocation-free vertical GaN pillars in nanoscale were grown on Si (111) surface through self-assembly by molecular-beam epitaxy. No extra catalytic or nanostructural assistance has been employed. These nanorods have a lateral dimension from 10 nm to ~ 800 nm and a height of 50 nm to 3

In this thesis, we study high quality InN films grown on sapphire (0001) by plasma-assisted molecular beam epitaxy (PAMBE). We used double layers methods to reduce lattice mismatch successfully. In this experiment, we have two series of samples, about series of A use low temperature GaN (LT-GaN) as the buffer layer as compared with series of B use high temperature AlN (HT-AlN) as the buffer layer. By in situ reflection high-energy electron diffraction (RHEED), we got film¡¦s surface situation. Surface morphology of the samples was observed by atomic force microscope (AFM). By high resolution X-ray diffraction (HR-XRD) methods was analyzed quality and composition of InN films. Van der Pauw method (Hall) was used to determine carrier concentration and mobility. The optical properties of InN films under different growth conditions were investigated by photoluminescence (PL). By changing growth temperature of these samples, we found the series of A having some fine characters as the InN(0002) rocking curve was 343 arcsec and InN(10-12) rocking curve was nearly 1000 arcsec. The mobility and carrier density of these samples were approximately 1000 cm2/Vs and 3 x 1018 cm-3 by Van der Pauw method.

This study presents the GaSb epitaxial grown by molecular beam epitaxy (MBE) on the semi-insulating GaAs substrate and n+-GaAs substrate. Investigations are made to the effect of Sb4/Ga beam equivalent pressure (BEP) ratios on the current-voltage characteristics of the p-n hetero-junction and the metal-GaSb semiconductor Schottky contact for various metals deposited on n-type GaSb layers. Several growth conditions were taken to improve the quality of GaSb epitaxial films. The structure of GaSb epitaxial layers are characterized by the X-ray diffraction, and the optimum growth conditions 500¢J of substrate temperature and the Sb4/Ga flux ratio about 2~3 have been obtained. From the I-V curve of GaSb Schottky diodes, we know that the higher Sb4/Ga ratio will induce the lower breakdown voltage. Hence, the interface properties of hetero-junction between the GaSb/GaAs and metal/GaSb can be investigated by the current-voltage characteristics, in which the current leakages and the surface state density are strongly dependent on the ratio of Sb4/Ga BEP. Based on the thermionic emission theory, the barrier height obtained was decrease with the Sb4/Ga ratio increases. After metal deposited on the GaSb epitaxial film to form the Schottky diode, the density of surface states can be calculated from the relationship of metal work-function and barrier height, which were obtained from the current-voltage characteristics of Schottky diode measurement, and then it also found that the density of surface states show decrease as the Sb4/Ga ratio increase.

This research is related to the molecular beam epitaxy (MBE ) to grow GaSb . The fabrication of GaSb/InGaSb strained quantum well and superlattice structures are used for photodetection . They are carefully investigated to obtain high quality of GaSb films. The growth mechanisms related to the major factors of (1) Subtrate temperature (2) Beam flux ratio(V/III). The properties of GaSb epilayers are characterized by different methods such as the X-ray diffraction , I-V curve and Raman spectra . The optimum growth conditions 500¢J of substrate temperature and the V/III flux ratio about 2~3 have been obtained. On the basis of structure, the best growth conditions is identified by the peak intensity and FWHM related to the quality of the GaSb films by the X-ray diffraction. On the basis of electrical property, the best growth conditions is identified by the lowest leakage current for the p-n junction related to the quality of the GaSb films by the I-V curve. On the basis of optical property, the best growth conditions is identified by the LO mode phonon intensity related to the quality of the GaSb films by the Raman spectra. Based on the GaSb growth studied here, the study will be focused in the quantum well and quantum dot laser devices furtherly by us.

We present an experimental study of thin films of SrAl₄ on a LaAlO₃ substrate, with special emphasis on the Zintl-Klemm-type properties of the thin films that we grow using molecular beam epitaxy. We quantify the orientation and stoichiometry of the films and the surface morphology using reflection high energy electron diffraction (RHEED), x-ray diffraction (XRD) and atomic force microscopy (AFM). Furthermore, we present measurements of electronic properties using x-ray photoelectron spectroscopy (XPS) and ultraviolet spectroscopy (UPS). We determine the core level shifts due to the chemical environment in SrAl₄-films, which will underline the Zintl-Klemm character of the material. We measure the work function of (001)-oriented SrAl₄. Additionally we analyze the electronic transport properties of the grown thin films including the resistivity, carrier density and mobility. / text

The growth, electronic structure and doping of the semiconductor InN has been explored and analysed. InN thin films were grown by plasma assisted molecular beam epitaxy. The significance of the relative fluxes, substrate temperature and buffer layers was explored and related to the electrical and structural properties of the films. An exploration of the effect of active nitrogen species on InN films found that excited molecular nitrogen was preferred for growth over atomic and ionic species. An optimised recipe for InN was developed incorporating all explored parameters. The bandgap of InN was explored using the techniques of optical absorption, photoluminescence and photoconductivity. All three techniques identified a feature near 0.67 eV as the only dominant and reproducible optical feature measurable from InN thin films. No evidence for any optical features above 1 eV was discovered. The effect of the Burstein-Moss effect is discussed and the debate over the relative impact of the effect is related to problems with precisely measuring electron concentrations. Photoluminescence from mixed phase InN films containing significant zincblende content is presented, with tentative evidence presented for a zincblende band gap near 0.61 eV. Native defects within InN were studied by near edge X-ray absorption fine structure spectroscopy. Nitrogen related defects were found to be unlikely candidates for the high as-grown n-type conductivity. The most likely candidate remains nitrogen vacancies. Ion implantation was shown to cause substantial damage to the InN lattice, which could not be fully repaired through annealing. The limitation on annealing temperatures may limit the use of implantation as a processing tool for InN. Mg was shown to exhibit great promise as a potential p-type dopant. Photoluminescence from Mg doped films was found to quench at high Mg concentrations, consistent with a depletion region near the surface. The potential dilute magnetic semiconductor In1-xCrxN was explored. All of the In1-xCrxN films were found to be ferromagnetic at room temperature and exhibited saturated magnetic moments of up to 0.7 emu/g. An interesting correlation between background electron concentration and remnant moment is presented and the consequences of theoretical exchange models discussed. The bandgap of chromium nitride was also investigated and found to be an indirect gap of 0.7 eV.

No description available.

The fields of telecommunications and optoelectronics are under constant pressure to shrink devices and reduce power consumption. Micro-scale photonic and plasmonic structures can trap light and enhance the brightness of active emitters; thus, these types of structures are promising avenues to accomplishing the goals of miniaturization and efficiency. A deeper understanding of specific structures is important in order to gauge their suitability for specific applications. In this dissertation, two types of microstructures are explored: one-dimensional silicon photonic crystals and self-assembled indium islands. This dissertation will provide novel characterization of these structures and a description of how to utilize or compensate for the observed features. A photonic crystal can act as a tiny resonator for certain wavelengths, making it a promising structure for applications that require extremely small lasers. However, because of silicon’s indirect bandgap, a silicon photonic crystal cavity would require the addition of an active emitter to function as a light source. Attempts to incorporate erbium into these cavities, and the observation of an unusual coupling phenomenon, will be discussed. Self-assembled indium islands are plasmonic structures that can be grown via molecular beam epitaxy. In theory, these islands should be pure indium nanoantennas on top of a smooth gallium arsenide substrate. In practice, the component materials are less segregated than predicted, giving rise to unexpected hollow dome shapes and a sub-surface indium layer. Although these features were not an intended result of indium island growth, they provide information regarding the island formation process and potentially contribute additional applications.

This thesis mainly aims at application of principles of engineering technology in the field of molecular beam epitaxy (MBE). MBE is a versatile technique for growing epitaxial thin films of semiconductors and metals by impinging molecular beams of atoms onto a heated substrate under ultra-high vacuum (UHV) conditions. Here, a LabVIEW® (laboratory virtual instrument engineering workbench) software (National Instruments Corp., http://www.ni.com/legal/termsofuse/unitedstates/usH) program is developed that would form the basis of a real-time control system that would transform MBE into a true-production technology. Growth conditions can be monitored in real-time with the help of reflection high energy electron diffraction (RHEED) technique. The period of one RHEED oscillation corresponds exactly to the growth of one monolayer of atoms of the semiconductor material. The PCI-1409 frame grabber card supplied by National Instruments is used in conjunction with the LabVIEW software to capture the RHEED images and capture the intensity of RHEED oscillations. The intensity values are written to a text file and plotted in the form of a graph. A fast Fourier transform of these oscillations gives the growth rate of the epi-wafer being grown. All the data being captured by the LabVIEW program can be saved to file forming a growth pedigree for future use. Unattended automation can be achieved by designing a control system that monitors the growth in real-time and compares it with the data recorded from the LabVIEW program from the previous growth and adjusts the growth parameters automatically thereby growing accurate device structures.