Polar and Nonpolar Gallium Nitride and Zinc Oxide based thin film heterostructures Integrated with Sapphire and Silicon

This dissertation work explores the understanding of the relaxation and integration of polar and non-polar of GaN and ZnO thin films with Sapphire and silicon substrates.;Strain management and epitaxial analysis has been performed on wurtzitic GaN(0001) thin films grown on c-Sapphire and wurtzitic non-polar a-plane GaN(11-20) thin films grown on r-plane Sapphire (10-12) by remote plasma atomic nitrogen source assisted UHV Pulsed Laser Deposition process. It has been established that high-quality 2-dimensional c-axis GaN(0001) nucleation layers can be grown on c-Sapphire by PLD process at growth temperatures as low as ∼650°C. Whereas the c-axis GaN on c-sapphire has biaxially negative misfit, the crystalline anisotropy of the a-plane GaN films on r-Sapphire results in compressive and tensile misfits in the two major orthogonal directions. The measured strains have been analyzed in detail by X-ray, Raman spectroscopy and TEM. Strain relaxation in GaN(0001)/Sapphire thin film heterostructure has been explained by the principle of domain matched epitaxial growth in large planar misfit system and has been demonstrated by TEM study. An attempt has been made to qualitatively understand the minimization of free energy of the system from the strain perspective. Analysis has been presented to quantify the strain components responsible for the compressive strain observed in the GaN(0001) thin films on c-axis Sapphire substrates. It was also observed that gallium rich deposition conditions in PLD process lead to smoother nucleation layers because of higher ad-atom mobility of gallium.;We demonstrate near strain relaxed epitaxial (0001) GaN thin films grown on (111) Si substrates using TiN as intermediate buffer layer by remote nitrogen plasma assisted UHV pulsed laser deposition (PLD). Because of large misfits between the TiN/GaN and TiN/Si systems the TIN buffer layer growth occurs via nucleation of interfacial dislocations under domain matching epitaxy paradigm. X-ray and Raman characterization confirmed the GaN thin films grew nearly relaxed. The chemistry between the TiN and GaN permits two-dimensional growth which has been confirmed by RHEED and AFM. The planar misfit for the GaN growth on TiN is ∼6.48%. TEM characterization was performed and mechanism of relaxation via planar matching was investigated. In addition, TiN being a strong Si diffusion barrier reduces the GaN stress occurring due to unintentional Si doping which is typically observed in AlN system and therefore eliminates the requirement of complex strain management techniques. This work demonstrates the thermal strain engineering coupled with large lattice mismatch and strong diffusion barrier properties in the case of TiN as buffer layer can be used to grow good quality 2-dimensional relaxed GaN thin films on Si(111).;Epitaxial growth of c-plane ZnO(0001) has been demonstrated on the Si(001) by using TiN as an intermediate buffer layer. Because of different out of plane symmetry of the substrate (Si/TiN) and the film (ZnO), two orientation of ZNO domains were obtained and the ZnO film growth is of bi-epitaxial nature. The ZnO thin film was observed to be nearly strain relaxed from X-ray and Raman measurements. The interface between the ZnO and TiN was investigated by TEM. Reaction at ZnO/TiN interface at higher growth temperature causing zinc titanate formation was observed. The grain boundary structure between the observed domains investigated by STEM, revealed the ZnO (0001) planes to be contiguous across the grain boundary which is significant from the perspective of conduction electron scattering. In this configuration the TiN (being electrically conductive) can be effectively used as an electrode for novel device applications (like LEDs) integrated on Si(100) substrate.;Non-polar orientation of m-plane (10-10) ZnO and GaN thin films have been successfully integrated with technologically important Si(001) substrate using MgO and TiN buffer layers. The epitaxy of the ZnO(10-10) on MgO(001) has been established by the X-ray and the TEM analysis. The non-polar m-plane ZnO has further been demonstrated as a suitable template for m-plane GaN (10-10) growth which paves the way for GaN integration with Si(001) substrate. The mentioned non-polar orientation of ZnO exhibits four types of rotational domains. Raman spectroscopy revealed that the ZnO thin film grows uniaxial strained in [0001] ZnO direction and is relaxed in the orthogonal [11-20] direction because of the large planar misfit which can be explained under the domain matching epitaxy paradigm. Growth of GaN (10-10) on ZnO causes further compressive strain in ZnO and tensile strain in GaN because of the smaller lattice parameter of GaN and the planar misfit between ZnO/GaN being small. (Abstract shortened by UMI.)...