• Applied Science and Convergence Technology
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• v.26 no.4
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• pp.79-85
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• 2017

The crack-free AlGaN template has been successfully grown by using selective area growth with triangular GaN facet. The triangular GaN stripe structure was obtained by vertical growth rate enhanced mode with low growth temperature of $950^{\circ}C$ and high growth pressure of 500 torr. The lateral growth rate enhanced mode of AlGaN for crack-free and flat surface was also investigated. Low pressure of 30 torr and high V/III ratio of 4400 were favorable for lateral growth of AlGaN. It was confirmed that the $4{\mu}m$ -thick $Al_{0.2}Ga_{0.8}N$ was crack-free over entire 2-inch wafer. The dislocation density of $Al_{0.2}Ga_{0.8}N$ was as low as ${\sim}7.6{\times}10^8/cm^2$ measured by cathodoluminescence. Based on the high quality AlGaN with low dislocation density, the ultraviolet laser diode epitaxy with cladding, waveguide and GaN/AlGaN multiple quantum well (MQW) was grown by metalorganic chemical vapor deposition. The stimulated emission at 349 nm with full width at half maximum of 1.8 nm from the MQW was observed through optical pumping experiment with 193 nm KrF laser. We also have fabricated the deep ridge type ultraviolet laser diode (UV-LD) with $5{\mu}m-wide$ and $700{\mu}m-long$ cavity for electrical properties. The turn on voltage was below 5 V and the resistance was ${\sim}55{\Omega}$ at applied voltage of 10 V. The amplified spontaneous emission spectrum of UV-LD was also observed from pulsed current injection.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.11 no.2
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• pp.43-48
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• 2001

GaN micro-crystals were synthesized through the direct reaction of $NH_3$with a Ga-melt. The bubbling technique in the atmospheric $NH_3$ ambient was employed and dark-gray-colored GaN micro-crystals with various sizes ranging from 0.5~30$\mu \textrm{m}$ were obtained. It was confirmed that product yield increased with increasing reaction temperature. The synthesized GaN micro-crystals were characterized by using a particle size analyzer, SEM, XRD and PL. The variation of reaction temperature from $850^{\circ}C$ to $1150^{\circ}C$ result in morphological change and in optical characteristics of GaN micro-crystals. Especially; GaN micro-crystals synthesized at 10sec showed the highest crystallinity and low yellow band luminescence.

• Journal of the Korean Society for Heat Treatment
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• v.29 no.3
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• pp.124-131
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• 2016

GaN and InN epilayers with nucleation layer (LT-buffer) were grown on (0001) sapphire substrates by radio-frequency plasma-assisted molecular beam epitaxy (RF-MBE). As-grown and annealed GaN and InN nucleation layers grown at various growth condition were observed by reflection high-energy electron diffraction (RHEED). When temperature of effusion cell for III source was very low, diffraction pattern with cubic symmetry was observed and zincblende nucleation layer was flattened easily by annealing. As cell temperature increased, LT-GaN and LT-InN showed typical diffraction pattern from wurtzite structure, and FWHM of (10-12) plane decreased remarkably which means much improved crystalline quality. Diffraction pattern was changed to be from streaky to spotty when plasma power was raised from 160 to 220 W because higher plasma power makes more nitrogen adatoms on the surface and suppressed surface mobility of III species. Therefore, though wurtzite nucleation layer was a little hard to be flattened compared to zincblende, higher cell temperature led to easier movement of III surface adatoms and resulted in better crystalline quality of GaN and InN epilayers.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.66-69
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• 2001

Effect of $N_2$ flow rate on properties of GaN thin films grown by plasma-enhanced molecular beam epitaxy(PEMBE) was discussed to optimize the quality of thin films. It was found that at low $N_2$ flow rate indicating high III/V flux ratio, the growth rate of GaN thin films was controlled by $N_2$ flux, and at high $N_2$ flow rate the growth rate was not controlled by $N_2$ flux any longer. It was also found that III/V flux ratio affected film quality. The film grown at higher $N_2$ flow rate showed low background carrier concentration, higher carrier mobility, and narrow FWHM in band-edge emission of low temperature PL. It is thought that the film in more Ga flux region was grown by 2-dimensional layer-by-layer growth mode, and the film in more nitrogen region was grown by 3-D island growth mode. All samples exhibited a good crystallinity.

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

• Proceedings of the Korean Vacuum Society Conference
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• 1996.06a
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• pp.32-33
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• 1996

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.292-292
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• 2014

Wide band gap semiconductors, such as III-nitrides (GaN, AlN, InN, and their alloys), SiC, and diamond are expected to play an important role in the next-generation electronic devices. Specifically, GaN-based high electron mobility transistors (HEMTs) have been targeted for high power, high frequency, and high temperature operation electronic devices for mobile communication systems, radars, and power electronics because of their high critical breakdown fields, high saturation velocities, and high thermal conductivities. For the stable operation, high power, high frequency and high breakdown voltage and high current density, the fabrication methods have to be optimized with considerable attention. In this study, low ohmic contact resistance and smooth surface morphology to AlGaN/GaN on 2 inch c-plane sapphire substrate has been obtained with stepwise annealing at three different temperatures. The metallization was performed under deposition of a composite metal layer of Ti/Al/Ni/Au with thickness. After multi-layer metal stacking, rapid thermal annealing (RTA) process was applied with stepwise annealing temperature program profile. As results, we obtained a minimum specific contact resistance of $1.6{\times}10^{-7}{\Omega}cm2$.

• Journal of Adhesion and Interface
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• v.24 no.2
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• pp.60-63
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• 2023

The AlGaN/GaN heterostructure has high electron mobility due to the two-dimensional electron gas (2-DEG) layer, and has the characteristic of high breakdown voltage at high temperature due to its wide bandgap, making it a promising candidate for high-power and high-frequency electronic devices. Despite these advantages, there are factors that affect the reliability of various device properties such as current collapse. To address this issue, this paper used metal-organic chemical vapor deposition to continuously deposit AlGaN/GaN heterostructure and SiN passivation layer. Material and electrical properties of GaN HEMTs with/without SiN cap layer were analyzed, and based on the results, low-frequency noise characteristics of GaN HEMTs were measured to analyze the conduction mechanism model and the cause of defects within the channel.

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

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.15 no.5
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• pp.441-448
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• 2002

The electrical properties of the GaN-based green light emitting diodes(LEDs) with the Mg-doped p-GaN layer activated in $N_2$ or $O_2$ ambient have been compared. For the $N_2$ -ambient activation the current-voltage behavior of LEDs has been found to be improved when the Mg dopants activation was performed in the higher temperature. However, for the $O_2$-ambient activation the current-voltage characteristic has been observed to be enhanced when the Mg dopants activation was carried out in the lower temperature. The minimum forward voltage at 20mA was obtained to be 4.8 V for LEDs with the p-GaN layer activated at $900^{\circ}C$ in the $N_2$ ambient and 4.5V for LEDs with the p-GaN layer treated at $700^{\circ}C$ in the $O_2$ambient, repectively. The forward voltage reduction of the LEDs treated in the $O_2$-ambient may be related to the oxygen co-doping of the p-GaN layer during the activation process. The $O_2$ -ambient activation process is useful for the enhancement of the LED performance as well as the fabrication process since this process can activate the Mg dopants in the low temperature.