@article{frajtag_nepal_paskova_bedair_el-masry_2013, title={Multifacet semipolar formation by controlling the groove depth via lateral sidewall epitaxy}, volume={367}, ISSN={["1873-5002"]}, DOI={10.1016/j.jcrysgro.2012.12.039}, abstractNote={We demonstrate InxGa1−xN/GaN light emitting diode structures with different sets of multifacet semipolar formation grown laterally on m-plane sidewalls formed by stripe patterning on preliminary grown c-plane GaN template. It was found that regrowth on shallow side walls within the GaN template resulted in a single semipolar (11¯01) facet, while deeper side walls led to multifacet semipolar formation. Very deep etching through the entire GaN template reaching the underlying sapphire substrates resulted in a combination of semipolar (11¯01) and nonpolar (11¯00) facets. The results indicate that the depth of the groove patterning can be used as a tool for controlling the set of semipolar facet formation. In addition, the growth rate in different crystallographic directions was studied and possible factors affecting the growth rates are discussed.}, journal={JOURNAL OF CRYSTAL GROWTH}, author={Frajtag, P. and Nepal, N. and Paskova, T. and Bedair, S. M. and El-Masry, N. A.}, year={2013}, month={Mar}, pages={88–93} }
 @article{frajtag_hosalli_samberg_colter_paskova_el-masry_bedair_2012, title={Overgrowth of GaN on GaN nanowires produced by mask-less etching}, volume={352}, ISSN={["0022-0248"]}, DOI={10.1016/j.jcrysgro.2011.12.055}, abstractNote={We report on the generation of GaN nanowires (NWs) using mask-less reactive ion etching (RIE). The NWs are believed to be the result of a high etching rate in regions where a high dislocation density is present in the GaN films grown on sapphire substrates. We have studied the effect of defect densities in the original GaN films and its relation to the generation of these NWs. We show that defect reduction in the overgrown GaN is related to the presence of a network of embedded voids generated between these nanowires during the regrowth on the etched nanowires. We show that further reduction in dislocation density can be achieved by repeating the process of nanowire generation and overgrowth. Also we report on the residual strain and curvature in GaN after the first and second embedded voids approach (EVA).}, number={1}, journal={JOURNAL OF CRYSTAL GROWTH}, author={Frajtag, P. and Hosalli, A. M. and Samberg, J. P. and Colter, P. C. and Paskova, T. and El-Masry, N. A. and Bedair, S. M.}, year={2012}, month={Aug}, pages={203–208} }
 @article{frajtag_el-masry_nepal_bedair_2011, title={Embedded voids approach for low defect density in epitaxial GaN films}, volume={98}, ISSN={["1077-3118"]}, DOI={10.1063/1.3540680}, abstractNote={We have developed a technique for defect reduction in GaN epitaxial films grown on sapphire substrates. This technique relies on the generation of high densities of embedded microvoids (∼108/cm2), a few microns long and less than a micron in diameter. These voids are located near the sapphire substrate, where high densities of dislocations are present. Network of embedded voids offer free surfaces that act as dislocation sinks or termination sites for the dislocations generated at the GaN/sapphire interface. Both transmission electron and atomic force microscopy results confirm the uniform reduction of the dislocation density by two orders of magnitude.}, number={2}, journal={APPLIED PHYSICS LETTERS}, author={Frajtag, P. and El-Masry, N. A. and Nepal, N. and Bedair, S. M.}, year={2011}, month={Jan} }
 @article{frajtag_samberg_el-masry_nepal_bedair_2011, title={Embedded voids formation by overgrowth on GaN nanowires for high-quality GaN films}, volume={322}, ISSN={["0022-0248"]}, DOI={10.1016/j.jcrysgro.2011.02.032}, abstractNote={We report on the epitaxial growth of GaN films on GaN nanowires. GaN nanowires were prepared by the mask-less dry etching technique. The etched, then annealed nanowires form semi-polar and non-polar plane facets with hexagonal symmetry. The different growth rates on the different plane facets result in the formation of void networks. These networks of embedded voids are located near the sapphire substrate, where a high density of dislocations is present. The voids, a few microns in length and a fraction of a micron in diameter, offer free surfaces for dislocation termination, enabling the embedded void approach (EVA) to reduce dislocations. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) studies show uniform reduction of the dislocation density over large area substrates by about three orders of magnitude and lower surface roughness than the GaN starting material.}, number={1}, journal={JOURNAL OF CRYSTAL GROWTH}, author={Frajtag, P. and Samberg, J. P. and El-Masry, N. A. and Nepal, N. and Bedair, S. M.}, year={2011}, month={May}, pages={27–32} }
 @article{nepal_frajtag_zavada_el-masry_bedair_wetzel_khan_2011, title={Light emitting diodes based on sidewall m-plane epitaxy of etched GaN/sapphire templates}, volume={8}, ISSN={["1862-6351"]}, DOI={10.1002/pssc.201000983}, abstractNote={Light emitting diodes (LEDs) were grown on the etched m-plane of c-plane GaN/sapphire templates by metal organic chemical vapor deposition (MOCVD). The LEDs, with InxGa1-xN/GaN quantum wells (QWs), were studied and current-voltage measurements show p-n diode behavior. TEM image analysis established that the QWs are on the {101} sidewall semi-polar plane. Electroluminescence measurements on the fabricated LEDs display an emission peak at 487 nm, with a blue shift of only 4 nm on increasing injected current density from 0.3 to 100 A/cm2. The demonstrated sidewall approach significantly reduces the quantum confined Stark Effect found in QWs grown on c-plane substrates (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)}, number={7-8}, journal={PHYSICA STATUS SOLIDI C: CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 8, NO 7-8}, author={Nepal, N. and Frajtag, P. and Zavada, J. M. and El-Masry, N. A. and Bedair, S. M. and Wetzel, C and Khan, A}, year={2011} }
 @inproceedings{luen_nepal_frajtag_zavada_brown_hommerich_bedair_el masry_2010, title={Ferromagnetism and near infrared luminescence in neodymium and erbium doped gallium nitride via diffusion}, volume={1183}, DOI={10.1557/proc-1183-ff06-01}, booktitle={Novel materials and devices for spintronics}, author={Luen, M. O. and Nepal, N. and Frajtag, P. and Zavada, J. M. and Brown, E. and Hommerich, U. and Bedair, S. M. and El Masry, N. A.}, year={2010}, pages={45–50} }
 @article{nepal_luen_zavada_bedair_frajtag_el-masry_2009, title={Electric field control of room temperature ferromagnetism in III-N dilute magnetic semiconductor films}, volume={94}, ISSN={["1077-3118"]}, DOI={10.1063/1.3110963}, abstractNote={We report on the electrical field control of ferromagnetism (FM) at room temperature in III-N dilute magnetic semiconductor (DMS) films. A GaMnN layer was grown on top of an n-GaN substrate and found to be almost always paramagnetic. However, when grown on a p-type GaN layer, a strong saturation magnetization (Ms) was observed. This FM in GaMnN can be controlled by depletion of the holes in the GaMnN/p-GaN/n-GaN multilayer structures. We have demonstrated the dependence of the FM on the thickness of the p-GaN in this heterostructure and on the applied bias to the GaN p-n junction. The Ms was measured by an alternating gradient magnetometer (AGM) and a strong correlation between the hole concentration near the GaMnN/p-GaN interface and the magnetic properties of the DMS was observed. At room temperature an anomalous Hall effect was measured for zero bias and an ordinary Hall effect for reverse bias in a fully depleted p-GaN layer. This is in close agreement with the AGM measurement results.}, number={13}, journal={APPLIED PHYSICS LETTERS}, author={Nepal, N. and Luen, M. Oliver and Zavada, J. M. and Bedair, S. M. and Frajtag, P. and El-Masry, N. A.}, year={2009}, month={Mar} }