Review of Pendeo-Epitaxial Growth and Characterization of Thin Films of GaN and AlGaN Alloys on 6H-SiC(0001) and Si(111) Substrates

Discrete and coalesced monocrystalline GaN and AlxGa1−xN layers grown via pendeo-epitaxy (PE) originated from side walls of GaN seed stripes with and without SiNx top masks have been grown via organometallic vapor phase deposition on GaN/AlN/6H-SiC(0001) and GaN(0001)/AlN(0001)/3C-SiC(111)/Si(111) substrates. Scanning and transmission electron microscopies were used to evaluate the external microstructures and the distribution of dislocations, respectively. The dislocation density in the laterally grown sidewall regions and in the regions grown over the SiNx masks was reduced by at least five orders of magnitude relative to the initial GaN seed layers. Tilting of 0.2° in the coalesced GaN epilayers grown over the SiNx masks was determined via X-ray and selected area diffraction; however, tilting was not observed in the material suspended above the SiC substrate and that grown on unmasked stripes. A strong, low-temperature photoluminescence band-edge peak at ~3.45 eV with a FWHM of &lt;300 µeV was determined on the overgrowth material grown on the silicon carbide substrates. The band-edge in the GaN grown on silicon substrates was shifted to a lower energy by 10 meV, indicative of a greater tensile stress.</jats:p

ε-Tubulin Is an Essential Component of the Centriole

Centrioles and basal bodies are cylinders composed of nine triplet microtubule blades that play essential roles in the centrosome and in flagellar assembly. Chlamydomonas cells with the bld2-1 mutation fail to assemble doublet and triplet microtubules and have defects in cleavage furrow placement and meiosis. Using positional cloning, we have walked 720 kb and identified a 13.2-kb fragment that contains ε-tubulin and rescues the Bld2 defects. The bld2-1 allele has a premature stop codon and intragenic revertants replace the stop codon with glutamine, glutamate, or lysine. Polyclonal antibodies to ε-tubulin show peripheral labeling of full-length basal bodies and centrioles. Thus, ε-tubulin is encoded by the BLD2 allele and ε-tubulin plays a role in basal body/centriole morphogenesis