Soft Epi Inc.

Yongin, South Korea

Soft Epi Inc.

Yongin, South Korea
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Lee I.-H.,Korea University | Polyakov A.Y.,National University of Science and Technology "MISIS" | Hwang S.-M.,Soft Epi Inc. | Shmidt N.M.,RAS Ioffe Physical - Technical Institute | And 7 more authors.
Applied Physics Letters | Year: 2017

Electrical stressing of near-UV (peak wavelength 390-395 nm) multi-quantum-well GaN/InGaN light emitting diodes at a high drive current of 650 mA and elevated temperature of 110 °C causes a significant degradation in external quantum efficiency (EQE), correlated with the formation of nitrogen interstitial-related electron traps at Ec - 0.8 eV. The dependence of the spectral density of current noise SI on forward current If showed two regions prior to accelerated aging, with SI ∼ If due to the current flow via localized leakage channels (presumably dislocations) and SI ∼ If2 related to the generation-recombination noise caused by the Ec - 0.8 eV states and Ev + 0.75 eV hole traps in the space charge region. Electrical stress for <922 h did not change the EQE but gradually increased both reverse and forward leakage current. This was accompanied by a gradual increase in the density of the hole traps, but not the electron traps. The mechanism appears to be the displacement of Ga and In atoms, with the interstitials decorating dislocations and forming local leakage channels. For stress times >922 h, the peak EQE decreased from 26% to 15% and was accompanied by a further increase in the leakage current and density of both types of traps. One of the 20 studied diodes showed an anomalously high forward leakage current, and the noise spectrum in it was dominated by the SI ∼ If4 region typical for the presence of local overheated areas (presumably local In composition fluctuations). The EQE of this sample began to degrade after a much shorter stress time of 258 h. © 2017 Author(s).

Lee I.-H.,Korea University | Polyakov A.Y.,National University of Science and Technology "MISIS" | Smirnov N.B.,National University of Science and Technology "MISIS" | Zinovyev R.A.,National University of Science and Technology "MISIS" | And 5 more authors.
Applied Physics Letters | Year: 2017

Deep electron and hole traps were studied by admittance spectroscopy (AS) and deep level transient spectroscopy (DLTS) with electrical and optical (ODLTS) injection for GaN-based multi-quantum-well (MQW) light emitting diodes (LEDs) operating in the near-UV (385-390 nm), blue (445 nm), and green (515 nm) spectral regions. AS spectra were dominated by freezing out of Mg acceptors at temperatures around 150 K, by shallow centers in the MQW region, and, for green LEDs, by deeper electron traps with a level near Ec − 0.27 eV located in the MQW region. DLTS spectra showed electron traps with levels Ec − 0.8 eV (NUV), Ec − 0.5 eV (blue), Ec − 0.6 eV (blue and NUV), and Ec − 0.27(green LEDs). In ODLTS, hole traps near Ev + 0.75 eV (NUV), Ev + 0.65 eV (blue), and Ev + 0.45 eV (green LEDs) originating in the quantum well (QW) region were detected (the QW character was confirmed by using excitation light that generated electron-hole pairs only within the QWs). The levels of the electron and hole traps in LED structures differing in the In composition in the QWs were well aligned with respect to the vacuum level. © 2017 Author(s).

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.

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.

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.

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.

Seo Y.G.,Korea Electronics Technology Institute | Shin S.H.,Soft Epi Inc. | Kim D.S.,Soft Epi Inc. | Yoon H.-D.,Korea Electronics Technology Institute | And 3 more authors.
Journal of Nanoscience and Nanotechnology | Year: 2015

In-plane structural anisotropy is characteristic of nonpolar (1120) a-plane GaN (a-GaN) films grown on r-plane sapphire substrates. The anisotropic peak broadenings of X-ray rocking curves (XRCs) are clearly observed with M- or W-shaped dependence on the azimuth angles. We investigated the optical properties of both M- and W-shaped a-GaN samples with room and low-temperature photoluminescence (PL) measurements. The W-shaped a-GaN film showed higher PL intensity and more compressive strain compared to the M-shaped a-GaN film, whereas the XRC peak widths of the M-shaped a-GaN film on the azimuth angles are lower than those of W-shaped specimens, indicating that better crystalline quality was obtained. We speculate that the PL intensity and strain state of a-GaN layers may be more influenced by the crystallinity of a specific crystal orientation or direction, especially along the m-axis as opposed to the c-axis. This occurrence is most likely due to anisotropic defect distributions, resulting from differences in dangling bond densities of (0001) and {1-100} facets. Copyright © 2015 American Scientific Publishers All rights reserved.

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.