h1

%0 Thesis
%A Mauder, Christof
%T Physics, MOVPE growth, and investigation of m-plane GaN films and InGaN/GaN quantum wells on gamma-LiAlO 2 substrates
%C Aachen
%I Publikationsserver der RWTH Aachen University
%M RWTH-CONV-125845
%P 132 S. : Ill., graph. Darst.
%D 2011
%Z Prüfungsjahr: 2011. - Publikationsjahr: 2012
%Z Aachen, Techn. Hochsch., Diss., 2011
%X The growth of InGaN/GaN quantum well structures along a nonpolar orientation avoids the negative effects of the so-called "Quantum Confined Stark Effect" and is therefore considered as promising approach to improve wavelength stability and efficiency of future optoelectronic devices. This work describes physical principles and experimental results on metal-organic vapor phase epitaxy and characterization of GaN layers and InGaN/GaN quantum well structures, which grow along the nonpolar (1-100) m-plane on (100) lithium aluminum oxide (LiAlO2) substrates. The limited thermal and chemical stability of the LiAlO2 substrate can be improved by a nitridation step, which causes the formation of a thin (1-100) AlN layer on the surface of the LiAlO2. This enables the phase-pure deposition of high-quality and smooth (1-100) GaN layers. The low lattice mismatch of (1-100) GaN to (100) LiAlO2 allows for a coherent growth of thin films, which show strong in-plane compressive strain. Due to the absence of a suitable slip plane, this strain relaxes only partly for layer thicknesses up to 1.7 µm. Low densities of line and planar defects compared to other heteroepitaxially deposited nonpolar GaN layers were assessed by X-ray diffraction (XRD), transmission electron microscopy (TEM) and electron channelling contrast imaging microscopy (ECCI). The surface of the GaN layers is dominated by macroscopic hillocks, which are elongated along the c-axis direction and result in an average root mean square (RMS) roughness of   20 nm in a 50 • 50 µm2 scan area. Spiral growth around line defects is seen as most likely cause for this effect. In a microscopic scale, one can detect a stripe pattern, which is formed by 2 - 3 nm high steps aligned parallel to the c-axis. An anisotropic growth mode is assumed responsible for this appearance. Between these steps, much smoother areas with typical RMS roughness of 0.2 nm (for a 0.5 • 0.5 µm2 scan) is found, which is also an indication for high quality on this small scale. As a consequence of the anisotropic growth mechanism, the line widths of XRD omega-scans taken with the incident direction perpendicular to the c-axis are strongly broadened compared to the perpendicular direction. The larger extension of coherent crystal regions along the c-axis is also reflected in the electron mobility, which is on average by 13
%K Galliumnitrid (SWD)
%K MOCVD-Verfahren (SWD)
%K Quantenwell (SWD)
%K Photolumineszenz (SWD)
%K Röntgendiffraktometrie (SWD)
%K Polarisation (SWD)
%F PUB:(DE-HGF)11
%9 Dissertation / PhD Thesis
%U https://publications.rwth-aachen.de/record/64546