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Yongin, South Korea

Ryu S.R.,Dongguk University | Ram S.D.G.,Dongguk University | Lee S.J.,Dongguk University | Cho H.-D.,Dongguk University | And 7 more authors.
Applied Surface Science | Year: 2015

Mg doped GaN nanorods were grown on undoped n-type GaN nanorods uniaxial on monolayer graphene by hydride vapor phase epitaxy (HVPE) method. The monolayer graphene used as the bottom electrode and a substrate as well provides good electrical contact, acts as a current spreading layer, well suitable for the growth of hexagonal GaN nanorod. In addition it has a work function suitable to that of n-GaN. The formed p-n nanorods show a Schottky behavior with a turn on voltage of 3V. Using graphene as the substrate, the resistance of the nanorod is reduced by 700 times when compared with the case without using graphene as the current spreading layer. The low resistance of graphene acts in parallel with the resistance of the GaN buffer layer, and reduces the resistance drastically. The formed p-n junction in a single GaN nanorod is visualized by Kelvin Force Probe Microscopy (KPFM) to have distinctively contrast p and n regions. The measured contact potential difference of p-and n-region has a difference of 103mV which well confirms the formed regions are electronically different. Low temperature photoluminescence (PL) spectra give evidence of dopant related acceptor bound emission at 3.2eV different from 3.4eV of undoped GaN. The crystalline structure, compositional purity is confirmed by X-ray diffraction (XRD), Transmission and Scanning electron microcopies (SEM), (TEM), Energy dispersive analysis by X-ray (EDAX) and X-ray photoelectron spectroscopy (XPS) as well. © 2015 Elsevier B.V. All rights reserved. Source

Ryu S.R.,Dongguk University | Gopal Ram S.D.,Dongguk University | Kwon Y.H.,Dongguk University | Yang W.C.,Dongguk University | And 5 more authors.
Journal of Materials Science | Year: 2015

Herein, we report the self-aligned growth of GaN nanorods on different orientations of sapphire like c-, a-, r- and m-plane substrates by hydride vapor phase epitaxy. Vertical c-axis orientation of GaN NRs is obtained on c-plane [0001] and a-plane $$\left[ { 1 1\bar{2}0} \right]$$112¯0 sapphire and a skew or inclined NRs on r-plane, and inclined intertwined but self-aligned NR array was formed on m-plane sapphire. GaN (002) and (004) peaks were obtained on c- and a-plane sapphire, whereas (110), (103), and (103) only were observed on r- and m-planes, respectively. In the case of r- and m-plane-grown GaN, A1 transverse optical mode is dominant, and the A1 longitudinal optical mode is suppressed. Conversely, in the case of c- and a-plane, it is reversed. The probable reason is the optical mode vibrations difference along the differently inclined NRs surfaces. In addition, the specimen exhibits surface optical modes too. The optical behavior of GaN NR on m-sapphire shows an intensity variation when measured in different angular rotations of the specimen by photoluminescence which is because of the higher area of excitation in the case of axial surfaces and lower area of excitation in radial surface. Their epitaxial crystallographic relationship with the substrates and the reasons for the self-aligned orientations are discussed. The anomalies found in the optical behavior are attributed to Raman antenna effect and so on. The self-aligned intertwined GaN NRs find suitable applications in polarizer. © 2015, Springer Science+Business Media New York. Source

Seo Y.G.,Korea Electronics Technology Institute | Kim J.,QSI Co. | Hwang S.-M.,Soft Epi Inc. | Kim J.,Korea University | And 3 more authors.
Journal of the Korean Physical Society | Year: 2015

This work examines the anisotropic microstructure and the lattice distortions of nonpolar a-plane (Formula Presented.) GaN (a-GaN) films by using the grazing-incidence X-ray diffraction technique. Faulted a-GaN films typically exhibit an in-plane anisotropy of the structural properties along the X-ray in-beam directions. For this reason, the anisotropic peak broadenings of the X-ray rocking curves (XRCs) were observed for various angle (phi) rotations for a-GaN films with and without SiNx interlayers. Analysis revealed the peak widths of the XRCs displayed an isotropic behavior for a nonpolar a-GaN bulk crystal. Thus, the in-plane anisotropy of the XRC peak widths for nonpolar a-GaN films apparently originates from the heteroepitaxial growth of the a-GaN layer on a foreign substrate. The lattice distortion analysis identified the presence of compressive strains in both the two in-plane directions (the c- and the m-axis), as well as a tensile strain along the normal growth direction. In addition, the observed frequency shifts in the Raman E2 (high) mode for the a-GaN films showed the existence of considerable in-plane compressive strain on both a-GaN films, as confirmed by the lattice distortion analysis performed using the grazing-incidence XRD method. © 2015, The Korean Physical Society. Source

Patent
Soft Epi Inc. | Date: 2013-11-29

The disclosure relates to an m-plane substrate, a growth inhibitor region located on the m-plane substrate, the growth inhibitor region having a plurality of windows for growing a III-nitride semiconductor, a seed layer formed at least at regions corresponding to the plurality of windows on the m-plane substrate, and a III-nitride semiconductor layer grown from the seed layer and coalesced after propagated along a-axis and c-axis directions.

Jang S.,Dankook University | Kim H.,Dankook University | Soo Kim D.,Soft Epi Inc. | Hwang S.-M.,Soft Epi Inc. | And 2 more authors.
Applied Physics Letters | Year: 2013

We report on the anisotropic carrier transport properties of semipolar (11 2 ̄ 2) GaN films with low defect density. We utilized the asymmetric lateral epitaxy to obtain various semipolar (11 2 ̄ 2) GaN films having significantly reduced partial dislocations and basal-plane stacking faults (BPSFs). The directionally dependent carrier transport was observed with the lower sheet resistances (Rsh) along the [1 1 ̄ 00] direction. The Rsh ratios of semipolar (11 2 ̄ 2) GaN films were found to be relatively smaller than those of nonpolar a-plane GaN films, possibly due to low BPSF density and the reduced in-plane electric field induced by BPSF along the [11 2 ̄ 3] direction at wurtzite domain boundaries. © 2013 AIP Publishing LLC. Source

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