@article{eldred_abdelhamid_reynolds_el-masry_lebeau_bedair_2020, title={Observing relaxation in device quality InGaN templates by TEM techniques}, volume={116}, ISSN={["1077-3118"]}, DOI={10.1063/1.5139269}, abstractNote={Device quality InGaN templates are synthesized using the semibulk (SB) approach. The approach maintains the film's 2D growth and avoids the formation of indium-metal inclusions. The strain relaxation processes of the grown InxGa1−xN templates are accompanied by variations in the indium content (x) and lattice parameters (a and c) across the InGaN template's thickness as the residual strain is continuously decreasing. This strain and lattice parameters' variation creates difficulties in applying standard x-ray Diffraction (XRD) and Reciprocal Space mapping (RSM) techniques to estimate the residual strain and the degree of the elastic strain relaxation. We used high-resolution High-angle annular dark-field scanning transmission electron microscopy and Energy-dispersive x-ray spectroscopy (EDS) to monitor the variations of the indium content, lattice parameters, and strain relaxation across the growing InxGa1−xN templates. We show that strain relaxation takes place by V-pit defect formation. Some of these V-pits are refilled by the GaN interlayers in the InxGa1−xN SB templates, while others propagate to the template surface. We present an alternative approach combining photoluminescence (PL) and EDS for estimating the degree of strain relaxation in these InxGa1−xN templates. The values obtained for the degree of relaxation estimated from TEM studies and PL measurements are within reasonable agreement in this study. Device quality InxGa1−xN templates with x ∼ 0.08, with a degree of relaxation higher than 70%, are achieved.}, number={10}, journal={APPLIED PHYSICS LETTERS}, author={Eldred, Tim B. and Abdelhamid, Mostafa and Reynolds, J. G. and El-Masry, N. A. and LeBeau, James M. and Bedair, S. M.}, year={2020}, month={Mar} }
 @article{abdelhamid_reynolds_el-masry_bedair_2019, title={Growth and characterization of InxGa1-xN (0 < x < 0.16) templates for controlled emissions from MQW}, volume={520}, ISSN={["1873-5002"]}, DOI={10.1016/j.jcrysgro.2019.05.019}, abstractNote={InxGa1−xN (0 < x < 0.16) templates were grown by Metal Organic Chemical Vapor Deposition (MOCVD) using the semibulk (SB) growth approach. We have studied the impact of different SB design parameters such as the number of (InGaN/GaN) periods, InGaN layer thickness (T), and the GaN substrate quality on the SB-template properties, and its degree of relaxation. SIMS characterization measured the variation of indium content (x) in the template, while photoluminescence reflected the indium content at the topmost layers of the SB template. X-ray diffraction techniques measured the average lattice parameters and degree of strain relaxation through the entire InxGa1−xN SB-templates. The SB approach results in superior material quality relative to the bulk grown InGaN, mainly due to its ability to avoid the inclusion of indium-rich clusters and V-pits in the SB templates. The SB approach slows down the relaxation processes and templates as thick as 750 nm are not fully relaxed. We are reporting on methods to enhance the relaxation processes in InxGa1−xN SB-templates. Finally, when InxGa1−xN templates with 0 ≤ x ≤ 0.16 are used as substrates for InGaN/GaN multiple quantum wells, the emission wavelength is shifted from blue to green by changing the indium content in the InxGa1−xN SB-templates. To the best of our knowledge, the current results present the highest indium content reported in InxGa1−xN SB-templates.}, journal={JOURNAL OF CRYSTAL GROWTH}, author={Abdelhamid, Mostafa and Reynolds, J. G. and El-Masry, N. A. and Bedair, S. M.}, year={2019}, month={Aug}, pages={18–26} }
 @article{akouala_kumar_punugupati_reynolds_reynolds_mily_maria_narayan_hunte_2019, title={Planar Hall effect and anisotropic magnetoresistance in semiconducting and conducting oxide thin films}, volume={125}, ISSN={0947-8396 1432-0630}, url={http://dx.doi.org/10.1007/S00339-019-2592-Y}, DOI={10.1007/s00339-019-2592-y}, number={5}, journal={Applied Physics A}, publisher={Springer Science and Business Media LLC}, author={Akouala, Christer R. and Kumar, Raj and Punugupati, Sandhyarani and Reynolds, C. Lewis and Reynolds, Judith G. and Mily, Edward J. and Maria, Jon-Paul and Narayan, Jagdish and Hunte, Frank}, year={2019}, month={Apr} }
 @article{el-masry_zavada_reynolds_reynolds_liu_bedair_2017, title={Electric field control of ferromagnetism at room temperature in GaCrN (p-i-n) device structures}, volume={111}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.4986431}, DOI={10.1063/1.4986431}, abstractNote={We have demonstrated a room temperature dilute magnetic semiconductor based on GaCrN epitaxial layers grown by metalorganic chemical vapor deposition. Saturation magnetization Ms increased when the GaCrN film is incorporated into a (p-GaN/i-GaCrN/n-GaN) device structure, due to the proximity of mediated holes present in the p-GaN layer. Zero field cooling and field cooling were measured to ascertain the absence of superparamagnetic behavior in the films. A (p-GaN/i-GaCrN/n-GaN) device structure with room temperature ferromagnetic (FM) properties that can be controlled by an external applied voltage has been fabricated. In this work, we show that the applied voltage controls the ferromagnetic properties, by biasing the (p-i-n) structure. With forward bias, ferromagnetism in the GaCrN layer was increased nearly 4 fold of the original value. Such an enhancement is due to carrier injection of holes into the Cr deep level present in the i-GaCrN layer. A “memory effect” for the FM behavior of the (p-i-n) GaCrN device structure persisted for 42 h after the voltage bias was turned off. These measurements also support that the observed ferromagnetism in the GaCrN film is not due to superparamagnetic clusters but instead is a hole-mediated phenomenon.}, number={8}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={El-Masry, N. A. and Zavada, J. M. and Reynolds, J. G. and Reynolds, C. L., Jr. and Liu, Z. and Bedair, S. M.}, year={2017}, month={Aug}, pages={082402} }
 @misc{reynolds_reynolds_2014, title={Progress in ZnO Acceptor Doping: What Is the Best Strategy?}, volume={2014}, ISSN={["1687-8124"]}, DOI={10.1155/2014/457058}, abstractNote={This paper reviews the recent progress in acceptor doping of ZnO that has been achieved with a focus toward the optimum strategy. There are three main approaches for generating p-type ZnO: substitutional group IA elements on a zinc site, codoping of donors and acceptors, and substitution of group VA elements on an oxygen site. The relevant issues are whether there is sufficient incorporation of the appropriate dopant impurity species, does it reside on the appropriate lattice site, and lastly whether the acceptor ionization energy is sufficiently small to enable significant p-type conduction at room temperature. The potential of nitrogen doping and formation of the appropriate acceptor complexes is highlighted although theoretical calculations predict that nitrogen on an oxygen site is a deep acceptor. We show that an understanding of the growth and annealing steps to achieve the relevant acceptor defect complexes is crucial to meet requirements.}, journal={ADVANCES IN CONDENSED MATTER PHYSICS}, author={Reynolds, Judith G. and Reynolds, C. Lewis}, year={2014} }
 @article{reynolds_reynolds_crespo_gillespie_chabak_davis_2013, title={Dislocations as quantum wires: Buffer leakage in AlGaN/GaN heterostructures}, volume={28}, ISSN={["0884-2914"]}, DOI={10.1557/jmr.2013.76}, abstractNote={Abstract}, number={13}, journal={JOURNAL OF MATERIALS RESEARCH}, author={Reynolds, C. Lewis, Jr. and Reynolds, Judith G. and Crespo, Antonio and Gillespie, James K. and Chabak, Kelson D. and Davis, Robert F.}, year={2013}, month={Jul}, pages={1687–1691} }
 @article{reynolds_reynolds_mohanta_muth_rowe_everitt_aspnes_2013, title={Shallow acceptor complexes in p-type ZnO}, volume={102}, ISSN={["1077-3118"]}, DOI={10.1063/1.4802753}, abstractNote={We show that N-doped ZnO films grown on sapphire can exhibit significant (∼1018 cm−3) room-temperature p-type behavior when sufficient nitrogen (N) is incorporated and the material is annealed appropriately. Substitutional N on the oxygen (O) sublattice is a deep acceptor; however, shallow acceptor complexes involve N, H, and zinc vacancies (VZn). Combining secondary ion mass spectrometry, Raman-scattering, photoluminescence, and Hall-effect data, we establish the evolution of N from its initial incorporation on a Zn site to a final shallow acceptor complex VZn_NO_H+ with an ionization energy of ca. 130 meV. This complex is responsible for the observed p-type behavior.}, number={15}, journal={APPLIED PHYSICS LETTERS}, author={Reynolds, J. G. and Reynolds, C. L., Jr. and Mohanta, A. and Muth, J. F. and Rowe, J. E. and Everitt, H. O. and Aspnes, D. E.}, year={2013}, month={Apr} }
 @article{lai_paskova_wheeler_chung_grenko_johnson_udwary_preble_evans_2012, title={Indium incorporation in InGaN/GaN quantum wells grown on m-plane GaN substrate and c-plane sapphire}, volume={209}, ISSN={["1862-6319"]}, DOI={10.1002/pssa.201127345}, abstractNote={Abstract}, number={3}, journal={PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE}, author={Lai, K. Y. and Paskova, T. and Wheeler, V. D. and Chung, T. Y. and Grenko, J. A. and Johnson, M. A. L. and Udwary, K. and Preble, E. A. and Evans, K. R.}, year={2012}, month={Mar}, pages={559–564} }
 @article{dumcenco_levcenco_huang_reynolds_reynolds_tiong_paskova_evans_2011, title={Characterization of freestanding semi-insulating Fe-doped GaN by photoluminescence and electromodulation spectroscopy}, volume={109}, ISSN={["1089-7550"]}, DOI={10.1063/1.3592343}, abstractNote={A detailed optical characterization of a freestanding wurtzite semi-insulating Fe-doped GaN (SI-GaN:Fe) grown by hydride-vapor-phase-epitaxy was carried out by photoluminescence (PL) and contactless electroreflectance (CER) at 10 and 300 K, respectively, and photoreflectance at 300 K. Low-temperature PL spectrum of the Ga-face consisted of the Fe3+ impurity characteristic series of IR peaks with a sharp zero-phonon line (ZPL) at 1.299 eV, yellow and blue broad emission bands, and near-band-edge (NBE) emission in the ultraviolet region. The narrow linewidth of 135 μeV of the ZPL and the measured energy difference of ∼70 meV between the ZPL and E2 (high) phonon replica, which is sensitive to the lattice strain, shows good crystal quality and a strain-free incorporation of iron. The obtained transition energies of A, B, and C excitonic features in the CER spectra and the n = 2 excited states (2s) of the A and B excitons enable the estimation of the exciton binding energies. In addition to the free excitonic recombination, the PL spectrum of the Ga-face exhibited clear donor and acceptor related features in the NBE region, while the N-face exhibited a broad emission band related to the free-to-bound recombination only. The differences were explained by the presence of impurity-induced band-tail states in the N-face SI-GaN:Fe due to an increased impurity density and the incorporation of large volume vacancy-type defects.}, number={12}, journal={JOURNAL OF APPLIED PHYSICS}, author={Dumcenco, D. O. and Levcenco, S. and Huang, Y. S. and Reynolds, C. L., Jr. and Reynolds, J. G. and Tiong, K. K. and Paskova, T. and Evans, K. R.}, year={2011}, month={Jun} }
 @article{lai_paskova_wheeler_grenko_johnson_udwary_preble_evans_2010, title={Effect of m-plane GaN substrate miscut on InGaN/GaN quantum well growth}, volume={312}, ISSN={["1873-5002"]}, DOI={10.1016/j.jcrysgro.2010.01.020}, abstractNote={The effect of m-plane GaN substrate miscut on the growth of InGaN/GaN quantum wells (QWs) was investigated. It was found that the miscut toward [0 0 0 1] c+-axis resulted in an increase of In incorporation efficiency and in a green-shift of the QW emission, while the miscut toward [1 1 2 0] a-axis resulted in even higher In compositions but it also led to an increased epitaxial surface roughness and deterioration of the QW structures. The results indicated that miscut toward a-axis is undesirable while miscut toward c+-axis is beneficial for achieving longer wavelength emission in QWs grown on m-plane GaN substrates.}, number={7}, journal={JOURNAL OF CRYSTAL GROWTH}, author={Lai, K. Y. and Paskova, T. and Wheeler, V. D. and Grenko, J. A. and Johnson, M. A. L. and Udwary, K. and Preble, E. A. and Evans, K. R.}, year={2010}, month={Mar}, pages={902–905} }
 @article{grenko_ebert_reynolds_duscher_barlage_johnson_preble_paskova_evans_2010, title={Optimization of homoepitaxially grown AlGaN/GaN heterostructures}, volume={207}, ISSN={["1862-6300"]}, DOI={10.1002/pssa.200925508}, abstractNote={Abstract}, number={10}, journal={PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE}, author={Grenko, J. A. and Ebert, C. W. and Reynolds, C. L., Jr. and Duscher, G. J. and Barlage, D. W. and Johnson, M. A. L. and Preble, E. A. and Paskova, T. and Evans, K. R.}, year={2010}, month={Oct}, pages={2292–2299} }
 @article{grenko_reynolds_barlage_johnson_lappi_ebert_preble_paskova_evans_2010, title={Physical Properties of AlGaN/GaN Heterostructures Grown on Vicinal Substrates}, volume={39}, ISSN={0361-5235 1543-186X}, url={http://dx.doi.org/10.1007/S11664-010-1153-0}, DOI={10.1007/s11664-010-1153-0}, number={5}, journal={Journal of Electronic Materials}, publisher={Springer Science and Business Media LLC}, author={Grenko, J. A. and Reynolds, C. L., Jr. and Barlage, D. W. and Johnson, M. A. L. and Lappi, S. E. and Ebert, C. W. and Preble, E. A. and Paskova, T. and Evans, K. R.}, year={2010}, month={Mar}, pages={504–516} }
 @article{reynolds_grenko_2009, title={Crystallographic plane dependent Fe and Si dopant incorporation and activation in InP}, volume={206}, ISSN={["1862-6300"]}, DOI={10.1002/pssa.200824271}, abstractNote={Abstract}, number={4}, journal={PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE}, author={Reynolds, C. Lewis, Jr. and Grenko, Judith A.}, year={2009}, month={Apr}, pages={691–696} }
 @article{lai_paskova_wheeler_grenko_johnson_barlage_udwary_preble_evans_2009, title={Excitation current dependent cathodoluminescence study of InGaN/GaN quantum wells grown on m-plane and c-plane GaN substrates}, volume={106}, ISSN={["1089-7550"]}, DOI={10.1063/1.3264729}, abstractNote={InGaN/GaN quantum wells (QWs) grown with identical conditions on m-plane and c-plane GaN substrates were studied by cathodoluminescence spectroscopy. At a low current of 10 nA, the emission intensity and wavelength of the m-plane aligned QWs were found to be about two times stronger and 19.5 nm blueshifted with respect to that of the c-plane aligned QWs. An increase in the current over three orders of magnitude was found to result in an increase in the emission intensities, with faster saturation in the m-plane aligned QWs. This was explained by the screening of quantum-confined Stark effect in the emission efficiency of the c-plane aligned QWs.}, number={11}, journal={JOURNAL OF APPLIED PHYSICS}, author={Lai, K. Y. and Paskova, T. and Wheeler, V. D. and Grenko, J. A. and Johnson, M. A. L. and Barlage, D. W. and Udwary, K. and Preble, E. A. and Evans, K. R.}, year={2009}, month={Dec} }
 @article{grenko_reynolds_schlesser_hren_bachmann_sitar_kotula_2004, title={Nanoscale GaN whiskers fabricated by photoelectrochemical etching}, volume={96}, ISSN={["0021-8979"]}, DOI={10.1063/1.1788841}, abstractNote={GaN whiskers with nanoscale dimensions have been fabricated by photoelectrochemical (PEC) etching in dilute H3PO4 electrolyte. Etching in lower concentration H3PO4 electrolyte for 1 h or for a short time of 5 min at a higher concentration results in individual whiskers with a density of ∼2×109cm−2 and diameters to 15nm. It is observed that ∼10% of them have formed nearly perfect hexagonal plates on the top of the whiskers, which appear to evolve into flowerlike features upon extended etching to 12 min. Such hexagonal plates have not been reported previously in the PEC etching of GaN. The presence of a dislocation along the central axis of the needles is clearly demonstrated, and the etch pattern is suggested to be related to the growth mechanism for GaN on sapphire. When etched for times >30min, these whiskers are typically arranged in clusters with a density of 2–5×107cm−2 and have ten or more whiskers contributing to the central top of the cluster.}, number={9}, journal={JOURNAL OF APPLIED PHYSICS}, author={Grenko, JA and Reynolds, CL and Schlesser, R and Hren, JJ and Bachmann, K and Sitar, Z and Kotula, PG}, year={2004}, month={Nov}, pages={5185–5188} }
 @article{grenko_reynolds_schlesser_bachmann_rietmeier_davis_sitar_2004, title={Selective etching of GaN from AlGaN/GaN and AlN/GaN structures}, volume={9}, DOI={10.1557/s1092578300000405}, abstractNote={Thick GaN layers as well as AlGaN/GaN and AlN/GaN heterostructures grown by metalorganic vapor phase epitaxy have been photoelectrochemically (PEC) etched in various dilute electrolytes, and bandgap-selective etching has been demonstrated in heterostructures. This result is a significant step forward in the fabrication of group III-nitride devices and one-dimensional photonic bandgap (PBG) structures in the deep UV. Based on initial results from thick GaN layers, a method was developed to achieve self-stopping selective etching of thin GaN layers in AlGaN/GaN and AlN/GaN heterostructures. Selective PEC etching requires the use of a suitable light source with photon energies larger than the bandgap of GaN, but smaller than that of AlGaN or AlN, thus enabling selective hole generation in the GaN layers to be etched. Additionally, it is imperative to use an electrolyte that supports PEC etching of GaN without chemically etching AlGaN or AlN.}, number={5}, journal={MRS Internet Journal of Nitride Semiconductor Research}, author={Grenko, J. A. and Reynolds, C. L. and Schlesser, R. and Bachmann, K. and Rietmeier, Z. and Davis, R. F. and Sitar, Z.}, year={2004} }