Phase Separation And Suppression In Wurtzite InGaN

InGaN has been widely used in the fabrication of optoelectronic devices due to its wide bandgap ranges (0.7– 3.4 eV). The stringent requirement for the growth of high-quality InGaN films, which has become a major obstacle for the further developments of high-performance devices, and studies on mechanisms of light emission and phase separation (PS) have attracted intense interests. The thesis has focused on the PS-related problems of InGaN, i.e., properties of InGaN, PS mechanisms, effects of PS on light emission properties, and suppression of PS. The polarity of the Mixing Free Energies (MFEs) is determined by the mixing enthalpy and entropy. For ?2G/?x2<0, the spinodal decomposition (SD) will automatically occur, which results in PS; Inversely for ?2G/?x2<0, nucleation and growth will occur when there is a large composition fluctuation. The PS can occur in several ways including clustering, ordering and several phases with different InN mole fraction. Experimental techniques such as X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM), Selected Area Diffraction (SAD), Cathodoluminescence, and Raman have been applied to determine whether PS has occurred and the way in existence. Generally, high InN mole fraction and thick InGaN film will result in PS, which can be suppressed when the thickness of InGaN film under the substrate's strain is smaller than the critical layer thickness (CLT). On the other hand, values for CLT of InxGa1-xN within GaN/InxGa1-xN can be experimentally determined using electrical data (mobility and conductivity) and optical emission energy of the InxGa1-xN films, and can be estimated as a function of x using both the PB model and Fischer model, which both were as a function of the lattice mismatch and the film structural properties. Self-assembled In-rich quantum dots (QDs) by enhanced PS in the InGaN layer less than CLT, can be grown on a GaN layer with a rough surface. If PS happens, though it reduces the efficiency of unique photoluminescence (PL) and has bad influence on the physical properties and controls of the epi-films, the phase-separated QDs are responsible for the enhanced...