• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 1995.11a
• /
• pp.71-73
• /
• 1995

In this work, we synthsized GaN powders by the direct reactions of Ga with NH$_3$at the temperature range of 950∼1150$^{\circ}C$ and we growth the GaN thin films on Si and sapphire substrates using the synthesized GaN powders by the vapor phase epitaxy method. The synthesized powder had hexagonal crystal structures with lattice constants of a$\sub$0/=3.1895${\AA}$, c$\sub$0/=5.18394${\AA}$. The reaction rates of GaN were increased with both reaction time and temperature, however it did not depends on the flow rates of NH$_3$. The island type GaN crystals were grown on (0001) sapphire substrates and fast lateral growth of GaN on (111) Si substrate than sapphire was observed in our experiments.

• Korean Journal of Materials Research
• /
• v.17 no.1
• /
• pp.1-5
• /
• 2007

GaN thin fan were grown by spin coated colloidal GaOOH precursor. Polycrystalline GaNs with crystalline size of $10{\sim}100nm$ were grown on $SiO_2$ substrate. The shape of crystallite above $900^{\circ}C$ had the hexagonal plate and column type. X-ray diffraction patterns for them correspond to those of the hexagonal wurtzite GaN. With increasing droplets. i.e, thickness of deposited layers, XRD intensity increased. PL (photoluminescence) spectrum consisted with an weak near band-edge emission at 3.45 eV and a broad donor-acceptor emission band at 3.32 eV. From the low temperature PL measurement on GaN grown at $800^{\circ}C$ that the shallow donor-acceptor recombination induced emission was more intense than the near band-edge excitonic emission.

• Proceedings of the IEEK Conference
• /
• 2006.06a
• /
• pp.575-576
• /
• 2006

It was analyzed qualitatively the light extraction in GaN-on-sapphire LEDs based on a simple model. The light extraction efficiency in the LEDs is simulated numerically by using ray tracing method. In the present study, the extraction efficiency was simulated on three different types of LEDs, which a have a different pattered sapphire substrate. And, the role of the patterned sapphire substrate are analyzed and discussed. Based on the analysis, the improvements of extraction efficiency in the LED structures were discussed and these analyses are helpful in the design of high brightness GaN LEDs.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.31 no.6
• /
• pp.386-391
• /
• 2018

An epitaxial GaN layer was grown on a cone-shape-patterned sapphire substrate (PSS) (Sample A) and an AlN-buffered PSS (Sample B) with two growth steps under the same process conditions by employing the hydride vapor phase epitaxy (HVPE) method. We have investigated the characteristics of the GaN layer grown on two kinds of substrates at each growth step. The cross-sectional SEM image of the GaN layer grown on the two types of substrates showed growth states of GaN layers formed during the 1st and 2nd growth steps with different growth durations. Dislocation density was obtained by calculation using the FWHM value of the rocking curve for (002) and (102). Sample A showed 2.62+08E and 6.66+08E and sample B exhibited 5.74+07E and 1.65+08E for two different planes. The red shift was observed is photoluminescence (PL) analysis and Raman spectroscopy results. GaN layers grown on AlN-buffered PSS exhibited better optical and crystallographic properties than GaN layers grown on PSS.

• Transactions on Electrical and Electronic Materials
• /
• v.10 no.2
• /
• pp.40-43
• /
• 2009

The authors fabricated a nanopatterned surface on a GaN thin film deposited on a sapphire substrate and used that as an epitaxial wafer on which to grow an InGaN/GaN multi-quantum well structure with metal-organic chemical vapor deposition. The deposited GaN epitaxial surface has a two-dimensional photonic crystal structure with a hexagonal lattice of 230 nm. The grown structure on the nano-surface shows a Raman shift of the transverse optical phonon mode to $569.5\;cm^{-1}$, which implies a compressive stress of 0.5 GPa. However, the regrown thin film without the nano-surface shows a free standing mode of $567.6\;cm^{-1}$, implying no stress. The nanohole surface better preserves the strain energy for pseudo-morphic crystal growth than does a flat plane.

• Proceedings of the Korean Vacuum Society Conference
• /
• 1999.07a
• /
• pp.121-121
• /
• 1999

Gallium nitride (GaN) semiconductor is intensively under investigation for commercialization of short wavelength light emitting devices and laser diodes. One of serious obstacles to overcome is to reduce the defect density in GaN film grown by various techniques such as MOCVD, HVPE, etc. Many research groups including SAIT are trying to improve the defect density to 106-107/cm2 from the level of 108-1010/cm2. We have investigated epitaxial growth behaviour of GaN thin and thick films under hidride vapour phase epitaxy (HVPE) condition. In this report, we present the microstructural and crystallographical characteristics of the GaN films grown on sapphire (0001) substrate which were studied by both conventional and high-resolution transmission electron microscopy (TEM). Also we present some microscopic analysis results obtained from GaN films grown by ELO(dpitzsial lateral overgrowth)-HVPE and from GaN quantum well structures grown by MOCVD. Another serious problem in growing GaN thick film by HVPE is internal micro-cracks. We also comment the origin of the micro-crack.

• Proceedings of the Materials Research Society of Korea Conference
• /
• 2003.03a
• /
• pp.92-92
• /
• 2003

• Proceedings of the Materials Research Society of Korea Conference
• /
• 2001.05a
• /
• pp.107-107
• /
• 2001

• Journal of the Institute of Electronics Engineers of Korea SD
• /
• v.44 no.4
• /
• pp.91-96
• /
• 2007

The light extraction efficiency in GaN-on-sapphire LEDs based on a simple model was analyzed qualitatively. The light extraction efficiency in the LEDs is simulated numerically by using ray tracing method. In the present study, the extraction efficiency was simulated on flat LED and PSS(patterned sapphire substrate) LED. The role of the patterned sapphire substrate in PSS LED are analyzed and discussed. And, the effects of reflectance on flat LED and PSS LED were investigated. This analysis of simulation results provide a numeric figure for the extraction efficiency of LEDs and are helpful in the design of high brightness GaN LEDs.

• Journal of the Korean Vacuum Society
• /
• v.14 no.4
• /
• pp.222-228
• /
• 2005

Undoped GaN epitaxial layer was grown on c-plane sapphire substrate by a two-step growth with metalorganic chemical vapor deposition(MOCVD). We have investigated the effects of the variation of final growth temperature on surface morphology, roughness, crystal quality, optical property, and electrical property In a horizontal MOCVD reactor, the film was grown at 300 Tow low-pressure with a fixed nucleation temperature of $500^{\circ}C$, varing the final growth temperature from $850\~1050^{\circ}C$ . The undoped GaN epilayers were characterized by atomic force microscopy, high-resolution x-ray diffractometer, photoluminescence, and Hall effect measurement.