Influences Of Indium Composition X And Temperature On The Raman Phonon Properties Of In_xGa_1-xN Alloys And GaN Quantum Dots Grown Based On Block Copolymer Lithography

Since the band gap can be consistently turned from0.7eV to6.2eV and covers the extensive spectrum range between near-infrared to ultraviolet, GaN-based semiconductors are one of the most promising materials for optoelectronic device applications. Besides, because of their excellent electrical, thermal and chemical properties, they also have great potential in the fabrication of high-temperature, high-frequency and high-power devices. All these advantages naturally make the studies of the kernel issues in the research field. Of all these methods to study GaN based semiconductors, Raman scattering is an important one to investigate the structural properties of the Ⅲ-nitride materials. Nowadays, the combination of low dimensional quantum structures and GaN based semiconductors is another hot spot research field. The development of fabrication of high quality quantum structure is of great significance. In this thesis, we focus on two issues. The first one is about the influences of Indium composition x and temperatures on the Raman phonon properties of InxGa1-xN alloy. The In composition x of InxGa1-xN samples are calculated to be from0.34to1by using Bragg diffraction angles resulted from X-ray diffraction(XRD) measurements. These InGaN alloys were first studied by Raman scattering at room temperature. It is found the peak position of both A1(LO) and E2(high) phonons shifts to low energies with the increase of composition x, which obeys the one mode behavior. The results of Raman scattering spectra under varied temperatures (93K～673K) show that the Raman shift of A1(LO) phonon decreases non-linearly with elevated temperatures, which could be attributed to the temperature dependence of crystal thermal expiation and the lattice vibration anharmonicity.In the second part, using block copolymer lithography nanopatterned GaN templates, we successfully grow GaN quantum dot(QD) arrays with high density of9.44×1010cm-2and uniform size of28±4nm in diameter by metal-organic chemical vapor deposition(MOCVD). In the PL spectra, a distinct emission around410nm is observed, which is related to the GaN QDs. In addition, according to the grazing incidence X-ray reflectivity, the height of GaN QDs are obtained.