UC Santa Barbara

The first section of this thesis presents an experimental investigation for validating Vegard’s Law for InxAl1-xN on GaN. Vegard’s law is useful for correlating materials composition and band gap to the a-lattice parameter, however it is primarily utilized for materials synthesized from powders and deviations for InAlN have been reported in the literature. Coherent InxAl1-xN (x = 0.15 to x = 0.28) films were grown by metalorganic chemical vapor deposition on GaN templates to investigate if the films obey Vegard’s Law by comparing the film stress-thickness product from wafer curvature before and after InxAl1-xN deposition. The In composition and film thickness were verified using atom probe tomography and high resolution x-ray diffraction, respectively. Ex-situ curvature measurements were performed to analyze the curvature before and after the InxAl1-xN deposition. At ~In0.18Al0.82N, no change in curvature was observed following InAlN deposition; confirming that the films obey Vegard’s law and that ~In0.18Al0.82N is lattice matched to GaN. The relaxed a0- and c0- lattice parameters of InxAl1-xN were experimentally determined and are in agreement with lattice parameters predicted by Vegard’s law.

The second section of this thesis will present the growth and characterization of AlGaN/AlN for deep UV LEDs. Growth studies on AlN buffer and n-AlGaN will be discussed. First, we explore the dependence of the interlayer growth temperature on the AlN crystal quality, defect density, and surface morphology. The crystal quality was characterized using omega rocking curve scans and the threading dislocation density was determined by plan view transmission electron microscopy. The growth resulted in a threading dislocation density (TDD) of 7 x 108 cm-2, indicating a significant reduction in the dislocation density of AlN in comparison to direct growth of AlN on SiC (~1010-1011 cm-2). Atomic force microscopy images demonstrate a clear step-terrace morphology that is consistent with step flow growth at high temperature. Reducing the interlayer growth temperature increases the TD inclination and thus enhances TD-TD interactions. The TDD is decreased via fusion and annihilation reactions. Following that, we will discuss the growth studies conducted for growing AlGaN. First we will discuss finding the optimal conditions for growing smooth UID-AlGaN for a variety of alloy compositions as the UV LED will need AlGaN with Al% between 40-65%. Then the growth and electrical characterization of n-AlGaN will be discussed. After processing, the electron mobility, resistivity, and carrier concentration of n-Al0.43Ga0.57N was 96 cm2/Vs, 15 mΩ-cm, and 4 x 1018 cm-3, respectively.