Doctor of Philosophy (PhD), Ohio University, 2005, Physics (Arts and Sciences)

MnGaN and CrGaN thin films were grown by molecular beam epitaxy on MOCVD GaN(0001)/sapphire(0001) and sapphire(0001) substrates respectively. Dependence of structural and magnetic properties of MnGaN and CrGaN samples on Ga/N flux ratios were investigated. Scanning tunneling microscopy studies of c-GaN(001) were performed to understand the surface reconstructions of this material, as Mn doped c-GaN has been predicted to have a Curie temperature about 6% higher compared to Mn-doped wurtzite GaN. MnGaN samples were grown on MOCVD GaN(0001)/sapphire(0001) at substrate temperature of 550 °C under different Ga/N flux ratios leading to 4 different growth regimes: N-rich, slight metal-rich, metal-rich, and Ga-rich. Mn incorporation and hence magnetic properties clearly depend on the growth conditions. The N-rich grown sample exhibits much larger magnetization compared to the other samples. Ga-rich magnetization is attributed to accumulates, but N-rich magnetization is attributed to carrier-mediated ferromagnetism and/or ferromagnetism due to clusters. Influence of the growth conditions for CrGaN grown on sapphire(0001) using radio frequency N plasma-assisted molecular beam epitaxy has been investigated. CrGaN samples are grown under different Ga/N flux ratio of 65% to 100% at substrate temperatures of 650 and 700 °C. The Cr/Ga flux ratio is set to either 3% or 5%. These growth parameters allow to vary over a range of growth conditions from N-rich to Ga-rich. Surface conditions during growth influence the surface morphology and magnetic properties of CrGaN films. In particular, we show that N-rich and metal-rich growth conditions result in room temperature ferromagnetism. Scanning tunneling microscopy studies have been performed on c-GaN(001) grown by rf N-plasma molecular beam epitaxy. Scanning tunneling microscopy studies of c-GaN (001) reveal several surface reconstructions including 4×11, c(4×20), 4×9, c(4×16), 4×7, and c(4×12). These reconstructions depend on the surfa (open full item for complete abstract)

Committee: Arthur Smith (Advisor) Subjects: Physics, Condensed Matter