Characterization and Extended Defect Control in III-Nitrides

The origin of inversion domains (IDs) in N-polar AlN grown on sapphire by metalorganic chemical vapor deposition (MOCVD) was studied by a combination of potassium hydroxide (KOH) and Transmission Electron Microscopy (TEM) techniques. It was found that the decomposition of sapphire at the AlN/sapphire interface is encouraged during AlN growth and that AlN grown above decomposed sapphire regions exhibited Alpolarity. Decomposition was found to occur in both Al-polar and N-polar AlN layers grown on sapphire, however, as the decomposition process encouraged Al-polar growth, IDs were only present in N-polar AlN material. The origin of the decomposition process during AlN growth on sapphire is discussed.;Dislocation density reduction in N-polar GaN grown on sapphire by MOCVD was achieved for the first time by implementation of the lateral epitaxial overgrowth (LEO). For N-polar GaN LEO, a patterned dielectric mask was deposited on a smooth N-polar GaN template and the template was placed back into the reactor for N-polar GaN regrowth. Dislocations were observed by TEM to be reduced from ∼1010 cm-2 in standard N-polar GaN grown on sapphire to ∼107 cm-2 with the LEO technique. Lateral-to-vertical growth ratios were also determined for a single N-polar GaN LEO growth condition along two crystallographic directions.;High Al-content AlGaN layers grown on single crystal AlN were observed by scanning TEM (STEM) to exhibit highly inhomogeneous properties dependent on the surface morphology of the underlying AlN homoepitaxial layer. Ga-rich streaks following the growth front of the AlGaN layer were observed in AlGaN layers grown on step-bunched AlN homoepitaxial layers. Additionally, a thin (∼ 50 nm), Al-rich AlGaN layer between the AlN homoepitaxial layer and the AlGaN film were observed in AlGaN grow on both step-bunched and step meandering AlN homoepitaxial layers. Atomic Force Microscopy (AFM) investigations of thin (< 10 nm) AlGaN on AlN homoepitaxial layers of varying surface morphology indicate relaxation of AlGaN by surface pitting in AlGaN grown on step-bunched and step meandering AlN. AlGaN grown on AlN homoepitaxy exhibiting bi-layer step morphology showed no signs of relaxation by pitting during initial AlGaN growth. These results suggest an influence of AlN homoepitaxial layer surface morphology on the initial strain state, and ultimately the compositional uniformity, of a subsequently deposited AlGaN layer.