@article{lu_collazo_dalmau_durkaya_dietz_raghothamachar_dudley_sitar_2009, title={Seeded growth of AlN bulk crystals in m- and c-orientation}, volume={312}, ISSN={["1873-5002"]}, DOI={10.1016/j.jcrysgro.2009.10.008}, abstractNote={Seeded growth of AlN boules was achieved on m-(1 0 1¯ 0) and c-(0 0 0 1¯) orientations by physical vapor transport (PVT). The single crystalline m- and c-plane seeds were cut from freestanding AlN single crystals. AlN boules 12 mm in diameter and 7 mm in height were grown at source temperatures around 2280 °C in N2 atmosphere at 500 Torr of total pressure. Under identical process conditions, the m- and c-plane boules exhibited the same growth rates, 150–170 μm/h, and similar expansion angles, 22–27°, which indicated that the growth was controlled by the thermal profile inside the crucible rather than by crystallographic differences. X-ray rocking curve analysis and Raman spectroscopy confirmed that both m- and c-plane grown crystals possessed high crystalline quality. The dislocation density in both crystals was non-uniform and in the range 102–105 cm−2, as characterized by X-ray topography.}, number={1}, journal={JOURNAL OF CRYSTAL GROWTH}, author={Lu, P. and Collazo, R. and Dalmau, R. F. and Durkaya, G. and Dietz, N. and Raghothamachar, B. and Dudley, M. and Sitar, Z.}, year={2009}, month={Dec}, pages={58–63} }
 @article{lu_collazo_dalmau_durkaya_dietz_sitar_2008, title={Different optical absorption edges in AlN bulk crystals grown in m- and c-orientations}, volume={93}, ISSN={["1077-3118"]}, DOI={10.1063/1.2996413}, abstractNote={AlN single crystals were grown on m-plane (101¯0) and c-plane (0001¯) AlN seeds under identical growth conditions. The m-plane AlN crystals exhibited substantially lower oxygen incorporation, ∼1018cm−3, than the c-plane crystals, ∼1019cm−3. By investigating optical transmission spectra, m-plane AlN had absorption bands at 4.05 and 4.35eV, while c-plane AlN had an absorption band edge at 4.85eV. These below bandgap absorption bands strongly correlate with the reported transitions related to Al vacancy-impurity complexes, such as the complex of an Al vacancy and two oxygen atoms, (VAl–2ON)1− and the complex of an Al vacancy and one oxygen atom, (VAl–ON)2−, becoming the major cause for the poor, below bandgap optical transparency (α>200cm−1) of these crystals.}, number={13}, journal={APPLIED PHYSICS LETTERS}, author={Lu, P. and Collazo, R. and Dalmau, R. F. and Durkaya, G. and Dietz, N. and Sitar, Z.}, year={2008}, month={Sep} }
 @article{lu_edgar_cao_hohn_dalmau_schlesser_sitar_2008, title={Seeded growth of AlN on SiC substrates and defect characterization}, volume={310}, ISSN={["1873-5002"]}, DOI={10.1016/j.jcrysgro.2008.01.010}, abstractNote={In this study, seeded sublimation growth of aluminum nitride (AlN) on SiC substrates was investigated. Large diameter (15–20 mm) and thick (1–2 mm) AlN layers were demonstrated on Si-face, 3.5° off-axis 6H-SiC (0 0 0 1). A c-axis growth rate of 15–20 μm/h was achieved at 1830 °C, and the surface morphology was highly textured: step features were formed with a single facet on the top of the layer. High-resolution X-ray diffraction (HRXRD), X-ray photoelectron spectroscopy (XPS), and molten KOH/NaOH etching were employed to characterize the AlN layers. The AlN crystals grew highly orientated along the c-axis, however, the impurities of Si (3–6 at%) and C (5.9–8 at%) from the SiC changed the lattice constants of AlN and shifted the AlN (0 0 .2) 2θ value from pure AlN toward SiC. All the growth surfaces had Al-polarity and the dislocation density decreased from 108 to 106 cm−2 as the film thickness increased from 30 μm to 2 mm.}, number={10}, journal={JOURNAL OF CRYSTAL GROWTH}, author={Lu, P. and Edgar, J. H. and Cao, C. and Hohn, K. and Dalmau, R. and Schlesser, R. and Sitar, Z.}, year={2008}, month={May}, pages={2464–2470} }