MOCVD of GaN on silicon substrate is a very complicated process with the coupling of heteroepitaxy, fluid dynamics, and chemical mechanisms. This dissertation presents the effect of fluid dynamics and reactor design, specifically the susceptor geometry, susceptor rotation, growth pressure, inlet configuration, and flow distribution, on the epitaxial growth of GaN on Si (111) in a new commercial MOCVD reactor. The properties of the GaN/Si films were characterized using XRD, PL, FT-IR, SEM, AFM, and Hall effect. The fluid dynamics within the reactor was simulated using CFD codes. High quality GaN/Si films were achieved through this work.
The geometry of the susceptor greatly affects the structural quality of GaN/Si films. For the manufacturer-supplied susceptor geometry, though single crystal GaN films could be obtained with an AlN buffer layer, the films were dark/gray in appearance with a rough morphology and a broad x-ray rocking curve (FWHM>2°). After modifying the susceptor geometry, smooth, mirror-like, single crystal GaN films were obtained with the best x-ray rocking curve FWHM of 0.2°. Simulation results showed that the geometry of the susceptor had significant effect on the vertical velocity distribution. A higher vertical velocity gradient over the modified susceptor was probably the main reason for the film quality improvement.
The inlet configuration and flow distribution have a significant effect on the growth rate, uniformity, morphology, and structural quality of GaN/Si films. The availability of TMG determines the film growth rate and uniformity, but the relationship between TMG mass flux and growth rate is complicated. Adduct formation has very little effect on the film growth rate and reaction efficiency.
GaN growth rate decreases with increasing pressure. Moderate pressure changes have little effect on the flow pattern but have a significant effect on the temperature distribution. The temperature gradient over the susceptor increases with the increase of pressure. No direct relationship between the susceptor spin rate and the quality of GaN/Si films was found, but the quality of films grown without rotation was poor.