Molecular beam epitaxy of gallium nitride and gallium nitride-manganese

Group III nitrides have been extensively studied for their optical properties that are suitable for blue lasers. Recently transition metals, such as Mn, doped GaN are receiving increasingly more attention as they may exhibit ferromagnetic order at above 300K. This dissertation presents studies on the spiral formation during molecular beam epitaxy (MBE) growth of GaN, the suppression of spiral growth by using vicinal substrates, the adsorption of Mn on GaN (0001), and the MBE growth of single phase Ga_1−xMn_xN with x as high as 0.12.; The morphology of GaN on nominally flat 6H-SiC(0001) substrates at different film thickness was studied by scanning tunneling microscopy. Screw or mixed dislocations emerging at the GaN surface create straight steps with a density of 1010 cm−2 at film thickness 40 nm. These steps evolve into single arm, interlocking double arm, and closed-loop spirals with a density of 109 cm−2 for 100 nm thick films. These spirals further evolve into spiral mounds with a density of 107 cm−2 for films thicker than 200 nm. A model was proposed to explain the formation and reduction of the spiral density as a function of film thickness.; Spiral formation was suppressed by using SiC vicinal substrates. The competition between spiral growth and step flow growth was responsible for the suppression of spiral growth. The critical terrace width for which the spiral mounds can be suppressed was estimated to be 80 nm under our growth conditions.; A domain wall super structure was observed when one-third monolayer of manganese was deposited on the pseudo (1 x 1) GaN(0001) surface at 500°C. On the atomic scale, the domains have a hexagonal shape with a (10 x 10) periodicity on average. Within the domain, a (√3 x √3) reconstruction is formed. A model was proposed to explain the formation of the domain wall and the (√3 x √3) structure.; Single phase Ga_1−xMn_xN with x as high as 0.12 was grown on 6H-SiC(0001) and Al₂O₃(0001) substrates by plasma assisted MBE using nitrogen-hydrogen. Hydrogen was found to have significant effects on growth kinetics, suppressing phase segregation and the formation of secondary compounds.