• Korean Journal of Metals and Materials
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• v.48 no.5
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• pp.456-461
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• 2010

We investigated the In-based ohmic contacts on Nitrogen-face (N-face) n-type GaN, as well as Ga-face n-type GaN, for InGaN-based vertical Light Emitting Diodes (LEDs). For this purpose, we fabricated Circular Transfer Length Method (CTLM) patterns on the N-face n-GaN that were prepared by using a laser-lift off method, as well as on the Ga-face n-GaN that were prepared by using a dry etching method. Then, In/transparent conducting oxide (TCO) and In/TiW schemes were deposited on the CTLM in order for low resistance ohmic contacts to form. The In/TCO scheme on the Ga-face n-GaN showed high specific contact resistance, while the minimum specific contact resistance was only 3${\times}$10$^{-2}$ $\Omega$-cm$^{2}$ after annealing at 300${^{\circ}C}$, which can be attributed to the high sheet resistance of the TCO layer. In contrast, the In/TiW scheme on the Ga-face n-GaN produced low specific contact resistance of 2.1${\times}$10$^{5}$ $\Omega$-cm$^{2}$ after annealing at 500${^{\circ}C}$ for 1 min. In addition, the In/TiW scheme on the N-face n-GaN also resulted in a low specific contact resistance of 2.2${\times}$10$^{-4}$ $\Omega$-cm$^{2}$ after annealing at 300${^{\circ}C}$. These results suggest that both the Ga-face n-GaN and N-face n-GaN.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.16 no.2
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• pp.89-96
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• 2003

Photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopy have been performed at 6 K on the 1540 nm $^4$I$\_$(13/2)/\longrightarrow$^4$I$\_$(15/2)/ emission of Er$\^$+3/ in in situ Er-doped GaN The PL and PLE spectra of in situ Er-doped GaN are compared with those of Er-implanted GaN in this study. The lineshapes of the broad PLE absorption bands and the broad PL bands in the spectra of the in situ Er-doped GaN are similar to those in Er-doped glass rather than in the Er-implanted GaN. The PL spectra of this in situ Er-doped GaN are independent of excitation wavelength and their features are significantly different from the site-selective PL spectra of the Er-implanted GaN. These PL and PLE studies reveal that a single type of Er$\^$3+/ sites is present in the in situ Er-doped GaN and these Er sites are different from those observed in the Er-implanted GaN. In addition, the comparison of the PL single strength illustrates that the excitation of Er$\^$3+/ sites through the energy absorption of defects in Er-implanted GaN.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.132-132
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• 2011

The sheet resistance (Rs) of undoped GaN films on AlN/c-plane sapphire substrate was investigated in which the AlN films were grown by R. F. magetron sputtering method. The Rs was strongly dependent on the AlN layer thickness and semi-insulating behavior was observed. To clarify the effect of crystalline property on Rs, the crystal structure of the GaN films has been studied using x-ray scattering and transmission electron microscopy. A compressive strain was introduced by the presence of AlN nucleation layer (NL) and was gradually relaxed as increasing AlN NL thickness. This relaxation produced more threading dislocations (TD) of edge-type. Moreover, the surface morphology of the GaN film was changed at thicker AlN layer condition, which was originated by the crossover from planar to island grains of AlN. Thus, rough surface might produce more dislocations. The edge and mixed dislocations propagating from the interface between the GaN film and the AlN buffer layer affected the electric resistance of GaN film.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.32 no.3
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• pp.83-88
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• 2022

To improve the crystallinity of GaN, there are researches on surface treatment to control the difference in physical properties between GaN and heterogeneous substrate. 'Low-temperature GaN (LT-GaN)' is one of the ways to solve the problem and we investigated the relationship between growth temperature and properties of LT-GaN in our homemade vertical type HVPE. The LT-GaN nuclei were formed on the sapphire surface at low growth temperatures and they presented differences in the density and crystallinity depending on the growth temperature. Significantly, the stress relaxation effect on the epitaxial GaN (epi-GaN) was affected by the crystallinity of LT-GaN. However, the high crystallinity of LT-GaN exacerbated the crystal quality of epi-GaN because they worked as a catalyst and seed of polycrystalline.

• Korean Journal of Materials Research
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• v.18 no.8
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• pp.450-453
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• 2008

Mg-doped and In-Mg co-doped p-type GaN epilayers were grown in a low-pressure metal organic chemical vapor deposition technique. The effect of In doping on the p-GaN layer was studied through photoluminescence (PL), persistent photoconductivity (PPC), and transmission electron microscopy (TEM) at room temperature. For the In-doped p-GaN layer, the PL intensity increases significantly and the peak position shifts to 3.2 eV from 2.95 eV of conventional p-GaN. Additionally, In doping greatly reduces the PPC, which was very strong in conventional p-GaN. A reduction in the dislocation density is also evidenced upon In doping in p-GaN according to TEM images. The improved optical properties of the In-doped p-GaN layer are attributed to the high crystalline quality and to the active participation of incorporated Mg atoms.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.11a
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• pp.315-316
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• 2006

We fabricated GaN nanopores m the etching process of anodic oxidation of aluminum. The aluminum was deposited by using E-beam evaporator on p-type GaN. After the aluminum was anodized GaN structure was exposed to the electric field with the oxidat species. The fabricated nanopore structure provides the enhanced intensity of light emission at the wavelengths 470 nm. We investigated the structure of the GaN nanopores from FE-SEM and EDS measurements.

• Journal of Sensor Science and Technology
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• v.17 no.5
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• pp.346-349
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• 2008

A metal-semiconductor-metal (MSM) ultraviolet (UV) photodetector (PD) is proposed as an effective UV sensing device for integration with a GaN n-channel MISFET on auto-doped p-type GaN grown on a silicon substrate. Due to the high hole barrier of the metal-p-GaN contact, the dark current density of the fabricated MSM PD was less than $3\;nA/cm^2$ at a bias of up to 5 V. Meanwhile, the UV/visible rejection ratio was 400 and the cutoff wavelength of the spectral responsivity was 365 nm. However, the UV/visible ratio was limited by the sub-bandgap response, which was attributed to defectrelated deep traps in the p-GaN layer of the MSM PD. In conclusion, an MSM PD has a high process compatibility with the n-channel GaN Schottky barrier MISFET fabrication process and epitaxy on a silicon substrate.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1997.04a
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• pp.66-69
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• 1997

The p-GaN fins doped with the impurity of Zn were grown on n-GaN films to prevent the defects from the lattice mismatch with sapphire substrates by HVPE. For growth of the high quality n-GaN, the optimized conditions were at first deduced from the results of various HCI gas flow rates and growth temperatures. On the basis of these conditions, p-GaN films were grown and investigated of the characteristics. The FWHM of the double crystal rocking curve of n-GaN was decreased and the hexagonal phases on the surface of GaN films were tend to be vivid with the inoement of HCI gas flow rates. Finally the n-type GaN films with FWHM of 648arcsec were obtained at 10cc/min of HCI gas. As the GaN films were grown with the above conditions, Zn was introduced in the form of vapor as a dopant for p-GaN films. But when Zn vaporized at 77$0^{\circ}C$ was doped to the films, the crystallites of Zn were distributed uniformly on the surface of the GaN film due to the over-doped.

• Journal of Sensor Science and Technology
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• v.10 no.4
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• pp.207-213
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• 2001

A Schottky type GaN ultraviolet photodetector with a mesa structure was fabricated by depositing an Al ohmic contact on an $n^+$-GaN layer and a Pt Schottky contact on a GaN layer. The undoped GaN(0.5um)/$n^-$-GaN(0.1 um)/$n^+$-GaN(1.5 um) multi-layer structure was grown on a sapphire substrate using MOCVD. The Schottky contact properties were characterized for different passivation conditions. The leakage current of the fabricated Schottky diode was 2 nA at a reverse voltage of 5V. Plus the photocurrent was 120uA using a hydrargyrum lamp with an optical power of 1mW at a wavelength of 365 nm. The diode exhibited an ultraviolet-visible rejection ratio of $10^2$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.50-50
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• 2008

ZnO has been extensively studied for optoelectronic applications such as blue and ultraviolet (UV) light emitters and detectors, because it has a wide band gap (3.37 eV) anda large exciton binding energy of ~60 meV over GaN (~26 meV). However, the fabrication of the light emitting devices using ZnO homojunctions is suffered from the lack of reproducibility of the p-type ZnO with high hall concentration and mobility. Thus, the ZnO-based p-n heterojunction light emitting diode (LED) using p-Si and p-GaN would be expected to exhibit stable device performance compared to the homojunction LED. The n-ZnO/p-GaN heterostructure is a good candidate for ZnO-based heterojunction LEDs because of their similar physical properties and the reproducibleavailability of p-type GaN. Especially, the reduced lattice mismatch (~1.8 %) and similar crystal structure result in the advantage of acquiring high performance LED devices with low defect density. However, the electroluminescence (EL) of the device using n-ZnO/p-GaN heterojunctions shows the blue and greenish emissions, which are attributed to the emission from the p-GaN and deep-level defects. In this work, the n-ZnO:Ga/p-GaN:Mg heterojunction light emitting diodes (LEDs) were fabricated at different growth temperatures and carrier concentrations in the n-type region. The effects of the growth temperature and carrier concentration on the electrical and emission properties were investigated. The I-V and the EL results showed that the device performance of the heterostructure LEDs, such as turn-on voltage and true ultraviolet emission, developed through the insertion of a thin intrinsic layer between n-ZnO:Ga and p-GaN:Mg. This observation was attributed to a lowering of the energy barriers for the supply of electrons and holes into intrinsic ZnO, and recombination in the intrinsic ZnO with the absence of deep level emission.