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Title: Growth and Characterization of ZnO and ZnO-Based Alloys MgxZn1-xO and MnxZn1-xO
Authors: Jin, Chunming
Advisors: Robert M. Kolbas, Committee Member
Carl C. Koch, Committee Member
Jagdish Narayan, Committee Chair
Ronald O. Scattergood, Committee Member
Keywords: epitaxial growth
ZnO thin film
pulsed laser deposition
cubic phase ZnMgO thin film
MnZnO thin film
MgZnO thin film
Issue Date: 19-Nov-2004
Degree: PhD
Discipline: Materials Science and Engineering
Abstract: The goals of this work were to synthesize ZnO and ZnO based alloy thin films by using PLD and to study the structural, stoichiometric, optical and electrical properties of these films. Epitaxial hexagonal MgZnO thin films have been grown on sapphire (0001) with domain-matching epitaxy by using PLD. The films show the high single-crystalline quality and bright excitonic luminescence. The maximum Mg concentration was found to be 34 at. %, which is almost ten times of the value allowed by the phase diagram. The bandgap of MgZnO alloy film can be tuned from 3.40 eV to 4.19 eV. Epitaxial ZnMgO thin films with cubic (NaCl) structure were also synthesized on MgO (001) sapphire (0001) and TiN/Si(001) by using PLD. The maximum Zn concentration in these cubic alloy films was 18 at. %. The epitaxial growth of cubic ZnMgO on Si(001) substrate is of significant importance for integrating ZnO-based alloys to the Si-based electronics. The phase stability of MgZnO/ZnO/MgZnO superlattice structures was studied using XRD and HRTEM methods. The diffusion of Mg from the MgZnO barrier to the ZnO well was observed by using the HRTEM and optical measurements. The cubic nanoinclusions were also observed with HRTEM. Epitaxial MnZnO thin films were synthesized on sapphire (0001) substrates. The maximum Mn concentration was 35 at. %. The bandgap of these films shifts to the higher energy side with increasing Mn content. Magnetic investigations indicate that these films are paramagnetic. Epitaxial ZnO films have been grown on Si (111) substrates by using PLD with two different heterostructures, ZnO/AlN/Si(111) and ZnO/MgO/TiN/Si(111). These thin films show the excellent single crystalline quality and extremely bright excitonic emission. C-axis orientated ZnO thin films have been grown on the amorphous silica substrates. The PL characteristics of these films are comparable to that of the films grown on the sapphire substrates. An ultraviolet illumination-enhanced luminescence effect was observed. This new phenomenon is attributed to the oxygen desorption on the surface. A phenomenological model was proposed to explain this new effect.
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