Al-rich AlGaN and AlN Growth on Bulk AlN Single Crystal Substrate

Al-rich AlGaN and AlN epitaxial thin films were grown by metalorganic chemical vapor deposition (MOCVD) on both vicinal (0001)-oriented native single crystal AlN substrates and AlN templates grown on vicinal (0001)-oriented sapphire to develop the first all-inclusive surface kinetic framework for the control of surface morphology in the IIInitrides. The role of dislocation density on the surface morphology of these thin films is discussed. A Burton, Cabrera, and Frank (BCF) theory-based model was formulated and utilized to understand the dependence of the surface kinetics on the vapor supersaturation, sigma, and substrate misorientation angle, alpha. Transitioning from a surface with 2D nuclei to one with bilayer steps required a decrease in sigma or an increase in alpha, whereas the suppression of step-bunching required an increase in sigma or a decrease in alpha. Furthermore, there are many surface defects that exist on these layers which have not yet been properly classified. These defects, namely cracks, pits, and hillocks, will be studied and methods for preventing the formation of them will be presented. Ultimately, having the ability to achieve defect free and atomically smooth surfaces will be made possible through these results and allow for much better device performance due to an enhancement in interface smoothness and a reduction in scattering events both optically and electrically.;The first high quality non-polar Al-rich AlGaN and AlN epitaxial thin films were realized by MOCVD growth on (1-100)-oriented single crystalline AlN substrates. The dependence of the surface morphology, structural quality, and unintentional impurity concentrations on the growth temperature was studied in order to determine the most appropriate growth conditions for high quality epitaxial layers. Optically smooth surfaces (RMS roughness of 0.4 nm) and high crystalline quality, as demonstrated by the presence of FWHM values for (10-10) rocking curves along [0001] of less than 18 arcsec, were achieved for films grown above 1350 °C. Furthermore, sharp (FWHM values less than 550 microeV) and intense near band edge luminescence was observed in homoepitaxial (1-100) AlN films. A reduction in unintentional oxygen impurity levels was seen with an increase in growth temperature. These high crystalline quality films are suitable for device applications and hold great potential for providing an ideal platform for deep UV emitters without polarization related effects.;The electrical and optical properties of Si- and Mg-doped AlGaN epitaxial thin films spanning the entire composition range from GaN to AlN were studied. A clear onset of over compensation was observed in the free carrier concentration and photoluminescence for high doping concentrations above 1 to 3 x 1019 cm-3 for both Si and Mg doping. The role of dislocations on the compensation levels was investigated by growing films on both native (single crystalline AlN and GaN) and foreign (sapphire) substrates. Hybrid density functional theory calculations were implemented to provide further insight on the identification of point defects which incorporated during growth. Point defect identification made it possible to reduce the concentration of compensating defects in Si-doped AlGaN providing a means of improving the conductivity. These results further the current understanding of the role of extended and point defects on the material properties of AlGaN and offer guidance for improving the performance of future devices.