Yong-Tae Moon - Academia.edu (original) (raw)
Papers by Yong-Tae Moon
Journal of the Korean Physical Society, 2016
The results of our analysis, which was done by using the finite-difference, time-domain (FDTD) me... more The results of our analysis, which was done by using the finite-difference, time-domain (FDTD) methods suggest that surface-structured light-emitting diodes (LEDs) with a subwavelength aluminum-nitride coating will have an enhanced light extraction efficiency. The use of such a LED structure will reduce both the internal reflection and the impedance mismatch, leading to a 3.2-fold enhancement in the light extraction efficiency compared to that for bare planar LEDs. We also present an improved method of modeling the light emission from the LED’s active layers to numerically calculate the light extraction efficiency of LEDs.
IEEE Electron Device Letters, 2006
Scanning Kelvin probe microscopy was used to detect reverse-bias-induced surface potential change... more Scanning Kelvin probe microscopy was used to detect reverse-bias-induced surface potential changes near the Schottky contact of a GaN Schottky diode. After application of a reverse bias, the surface potential near the Schottky contact gradually decreased with time, indicating an increase of band bending. Surface potential traces recorded after turning off the reverse bias indeed revealed increased band bending near the Schottky contact. A higher reverse bias caused a larger increase of band bending. The authors suggest that a reverse bias facilitates electron tunneling at the edge of the Schottky contact by decreasing the potential barrier width. Capture of these tunneled electrons by surface states causes the observed increase of band bending.
Optics express, Jan 5, 2018
We demonstrated the growth of crack-free high-quality GaN-based UV vertical LEDs (VLEDs) (λ = 365... more We demonstrated the growth of crack-free high-quality GaN-based UV vertical LEDs (VLEDs) (λ = 365 nm) on 6-inch sapphire substrates by using an ex-situ sputtered AlN nucleation layer (NL) and compared their performance with that of UV VLEDs with an in situ low temperature (LT) AlGaN NL. The X-ray diffraction (XRD) results showed that the ex-situ AlN sample contained lower densities of screw-type and edge-type threading dislocations than the in situ AlGaN NL sample. The micro-Raman results revealed that the ex-situ AlN sample was under more compressive stress than the in situ AlGaN sample. As the current was increased, the electroluminescence peaks of both of the samples blue-shifted, reached a minimum wavelength at 1000 mA, and then slightly red-shifted. Packaged VLEDs with the ex-situ AlN NL yielded 6.5% higher light output power at 500 mA than that with the in situ AlGaN NL. The maximum EQEs of the VLED with the in situ AlGaN and ex-situ AlN NLs were 43.7% and 48.2%, respectively....
Optics express, Jan 30, 2018
We investigated the optical and electrical properties of red AlGaInP light-emitting diodes (LEDs)... more We investigated the optical and electrical properties of red AlGaInP light-emitting diodes (LEDs) as functions of chip size, p-cladding layer thickness, and the number of multi-quantum wells (MQWs). External quantum efficiency (EQE) decreased with decreasing chip size. The ideality factor gradually increased from 1.47 to 1.95 as the chip size decreased from 350 μm to 15 μm. This indicates that the smaller LEDs experienced larger carrier loss due to Shockley-Read-Hall nonradiative recombination at sidewall defects. S parameter, defined as ∂lnL/∂lnI, increased with decreasing chip size. Simulations and experimental results showed that smaller LEDs with 5 pairs of MQWs had over 30% higher IQE at 5 A/cm than the LED with 20 pairs of MQWs. These results show that the optimization of the number of QWs is needed to obtain maximum EQE of micro-LEDs.
Scientific Reports, 2015
This study examined systematically the mechanism of light interaction in the sapphire/MgF 2 /Al t... more This study examined systematically the mechanism of light interaction in the sapphire/MgF 2 /Al triple-layer omnidirectional reflectors (ODR) and its effects on the light output power in near ultraviolet light emitting diodes (NUV-LEDs) with the ODR. The light output power of NUV-LEDs with the triple-layer ODR structure increased with decreasing surface roughness of the sapphire backside in the ODR. Theoretical modeling of the roughened surface suggests that the dependence of the reflectance of the triple-layer ODR structure on the surface roughness can be attributed mainly to light absorption by the Al nano-structures and the trapping of scattered light in the MgF 2 layer. Furthermore, the ray tracing simulation based upon the theoretical modeling showed good agreement with the measured reflectance of the ODR structure in diffuse mode. A lGaN-based LEDs in the near-ultraviolet (NUV) range are attractive for photo-catalytic deodorizing in air conditioners and refrigerators as well as in identifying counterfeit banknotes 1. In particular, color-rendering due to the high conversion efficiencies of typical phosphors in the UV spectrum has attracted considerable great interest for fabricating white LEDs with AlGaN-based NUV-LED chips for white lighting 2-5. On the other hand, AlGaN-based UV-LEDs normally suffer from very low external quantum efficiency (EQE) due to the poor light extraction efficiency caused by the epitaxial absorption of UV light. In addition, reduced indium compositional fluctuations in InGaN quantum wells with a small indium content weakens the carrier localization in localized energy states, which in turn increases the possibility of carrier trapping at the nonradiative recombination centers by the increase in in-plane carrier diffusion. To overcome these obstacles in AlGaN-based UV-LEDs, noble device structures, such as chip-shaped LED design 6 , photonic crystal 7 , distributed Bragg reflector (DBR) 8 , omnidirectional reflector (ODR) 9 , surface texturing reducing internal light reflection, and surface plasmon 10,11 , have been proposed. In particular, ODR, such as Ag-and Al-based triple-layer schemes at the backside of LED chip, has been used to increase light extraction. On the other hand, the reflectance of an Ag-based reflector decreases rapidly in the UV region. Therefore, Al-based reflectors are preferred because of the relatively high reflectivity, wide stop band, and omnidirectional reflection characteristics in the UV wavelength range. The refractive index of a dielectric layer in the ODR structure should be as low as possible. MgF 2 films, which have a low refractive index in the range, 1.34-1.39, have been used as a dielectric layer because their high optical transparency over a wide wavelength range from 120 nm UV rays in a vacuum to 900 nm infrared rays, as well as good adhesion and high durability. Recently, it was reported that the light extraction efficiency of GaN-based LEDs could be improved significantly using Al-based ODRs 12,13. On the other hand, such studies did not deal with the influence of the optical properties of LEDs according to the roughness of the dielectric-metal interface in the backside ODR system. Understanding the detailed mechanism of light interaction in the ODR scheme is important for controlling and maximizing the enhancement of light extraction in LEDs. This study examined systematically the mechanism of light interaction in the sapphire/MgF 2 /Al triple-layer ODR scheme in terms of the interface roughness with the surface roughness of the sapphire backside. The surface roughness of the sapphire backside critically affected the light extraction efficiency of the ODR scheme and should be minimized to enhance light extraction effectively.
ECS Journal of Solid State Science and Technology
IEEE Photonics Technology Letters
We investigated how the performance and reliability of AlGaInP-based red (620 nm) micro-light-emi... more We investigated how the performance and reliability of AlGaInP-based red (620 nm) micro-light-emitting diodes (micro-LEDs) (<inline-formula> <tex-math notation="LaTeX">$25\times 17\,\,\mu \text{m}^{2}$ </tex-math></inline-formula>) were influenced by the use of <inline-formula> <tex-math notation="LaTeX">$n$ </tex-math></inline-formula>-AlInP ohmic layer and distributed Bragg reflector (DBR). The AlGaAs-based DBR showed reflectivity of 94.9% at 622 nm with a 14 nm-stopband width. The micro-LEDs with <inline-formula> <tex-math notation="LaTeX">$n$ </tex-math></inline-formula>-GaAs gave slightly lower forward voltages by 0.013 – 0.021 V than those with <inline-formula> <tex-math notation="LaTeX">$n$ </tex-math></inline-formula>-Al<sub>0.5</sub>In<sub>0.5</sub>P/<inline-formula> <tex-math notation="LaTeX">$n$ </tex-math></inline-formula>-Al<sub>0.6</sub>Ga<sub>0.4</sub>As and <inline-formula> <tex-math notation="LaTeX">$n$ </tex-math></inline-formula>-Al<sub>0.5</sub>In<sub>0.5</sub>P/DBR. However, the micro-LEDs with <inline-formula> <tex-math notation="LaTeX">$n$ </tex-math></inline-formula>-Al<sub>0.5</sub>In<sub>0.5</sub>P/<inline-formula> <tex-math notation="LaTeX">$n$ </tex-math></inline-formula>-Al<sub>0.6</sub>Ga<sub>0.4</sub>As and <inline-formula> <tex-math notation="LaTeX">$n$ </tex-math></inline-formula>-Al<sub>0.5</sub>In<sub>0.5</sub>P/DBR gave 61% and 125% higher light output power at <inline-formula> <tex-math notation="LaTeX">$20~\mu \text{A}$ </tex-math></inline-formula> compared with that with <inline-formula> <tex-math notation="LaTeX">$n$ </tex-math></inline-formula>-GaAs. It was shown that after annealing at 120 °C for 2,000 h, the forward voltage and the light output power at 4.7 A/cm<sup>2</sup> of the micro-LEDs with <inline-formula> <tex-math notation="LaTeX">$n$ </tex-math></inline-formula>-Al<sub>0.5</sub>In<sub>0.5</sub>P/DBR were degraded by 0.09% and 6.33%, respectively, with reference to those before annealing.
IEEE Photonics Technology Letters
This letter examined the use of a patterned ion-damaged current blocking layer (patterned-IDCBL).... more This letter examined the use of a patterned ion-damaged current blocking layer (patterned-IDCBL). A 50-Å-InGaN layer grown as the top epitaxial layer was transformed into an insulator fabricated by oxygen plasma treatment, in which the dot patterns are regularly arranged over the active areas of the light-emitting diode (LED) and inserted beneath the p-electrode. The results showed that the light output power increased by 16.8% at 60 mA compared with the conventional LEDs, and that the electrostatic discharge resistance is effectively improved by the patterned-IDCBL.
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures
The effect of the growth rate of the nucleation layer on the growth of a high temperature GaN lay... more The effect of the growth rate of the nucleation layer on the growth of a high temperature GaN layer has been studied by observing the in situ normal incidence reflectance during the growth of GaN by metalorganic chemical vapor deposition. This study revealed that the lateral ...
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 2004
We report that ambient thermal annealing is a promising method for recovering the dry-etch-induce... more We report that ambient thermal annealing is a promising method for recovering the dry-etch-induced damage on Mg-doped GaN surfaces. The surface electrical properties of dry-etched Mg-doped GaN can be fully recovered by thermal annealing using as an ambient gas at ...
Applied Physics Letters, 2001
The temperature dependence of the photoluminescence (PL) of InGaN films, grown by metalorganic ch... more The temperature dependence of the photoluminescence (PL) of InGaN films, grown by metalorganic chemical vapor deposition, has been investigated. A strained InGaN thin film which contains composition-fluctuated regions shows the so-called S-shaped temperature dependence of the dominant PL peak energy. However, an InGaN thick film which contains quantum dot-like In-rich regions shows a sigmoidal temperature dependence of the dominant PL
physica status solidi (a), 2010
1 Department of Electronics Engineering, Catholic University of Daegu, Hayang, Kyeongsan, Kyeongb... more 1 Department of Electronics Engineering, Catholic University of Daegu, Hayang, Kyeongsan, Kyeongbuk 712-702, Republic of Korea 2 LED R&amp;amp;amp;D Center, LG Innotek, 16 Woomyeon-dong, Seocho-gu, Seoul 137-140, Republic of Korea 3 Department of ...
III-nitride semiconductor materials have been largely developed for use in optoelectronic devices... more III-nitride semiconductor materials have been largely developed for use in optoelectronic devices such as light emitting diodes (LED) and laser diodes (LD)[1]. The AlGaN/GaN heterostructure has recently been the subject of considerable interest in the fabrication of ...
Optics express, Jan 10, 2015
We study light-extraction efficiency (LEE) of AlGaN-based deep-ultraviolet light-emitting diodes ... more We study light-extraction efficiency (LEE) of AlGaN-based deep-ultraviolet light-emitting diodes (DUV-LEDs) using flip-chip (FC) devices with varied thickness in remaining sapphire substrate by experimental output power measurement and computational methods using 3-dimensional finite-difference time-domain (3D-FDTD) and Monte Carlo ray-tracing simulations. Light-output power of DUV-FCLEDs compared at a current of 20 mA increases with thicker sapphire, showing higher LEE for an LED with 250-μm-thick sapphire by ~39% than that with 100-μm-thick sapphire. In contrast, LEEs of visible FCLEDs show only marginal improvement with increasing sapphire thickness, that is, ~6% improvement for an LED with 250-μm-thick sapphire. 3D-FDTD simulation reveals a mechanism of enhanced light extraction with various sidewall roughness and thickness in sapphire substrates. Ray tracing simulation examines the light propagation behavior of DUV-FCLED structures. The enhanced output power and higher LEE stro...
Materials Science Forum, 2006
Improved structural quality and radiative efficiency were observed in GaN thin films grown by met... more Improved structural quality and radiative efficiency were observed in GaN thin films grown by metalorganic chemical vapor deposition on in situ-formed SiN and TiN porous network templates. The room temperature carrier decay time of 1.86 ns measured for a TiN network sample is slightly longer than that for a 200 μm-thick high quality freestanding GaN (1.73 ns). The linewidth of the asymmetric X-Ray diffraction (XRD) (1012) peak decreases considerably with the use of SiN and TiN layers, indicating the reduction in threading dislocation density. However, no direct correlation is yet found between the decay times and the XRD linewidths, suggesting that point defect and impurity related nonradiative centers are the main parameters affecting the lifetime.
physica status solidi (c), 2005
We have grown GaN layers by MOCVD on a set of nanoporous SiC templates with different porosity an... more We have grown GaN layers by MOCVD on a set of nanoporous SiC templates with different porosity and morphology, produced by etching the anodized porous SiC starting material in a H 2 environment at temperatures ~1500 °C, in an effort to attain improved films. The hydrogen etching serves to remove surface damage caused during mechanical polishing prior to anodization, remove the skin layer associated with anodization, tune the pore size, and consolidate pore geometry. Growth conditions favoring lateral overgrowth of GaN were employed on this set of samples to obtian GaN to a thickness of 2 µm. Atomically smooth surfaces were obtained for the epitaxial GaN layers. The GaN quality is highly dependent on the specifics of the porous templates used. An intensity increase of up to a factor of 30 was observed in the GaN excitonic peak compared to GaN grown on standard SiC substrate. The I-V data indicated significant reduction in the leakage current (in reverse bias) compared to GaN grown on standard SiC. The dependence of optical properties, crystalline quality, and surface morphology on the particulars of porous SiC templates is discussed.
Journal of the Korean Physical Society, 2016
The results of our analysis, which was done by using the finite-difference, time-domain (FDTD) me... more The results of our analysis, which was done by using the finite-difference, time-domain (FDTD) methods suggest that surface-structured light-emitting diodes (LEDs) with a subwavelength aluminum-nitride coating will have an enhanced light extraction efficiency. The use of such a LED structure will reduce both the internal reflection and the impedance mismatch, leading to a 3.2-fold enhancement in the light extraction efficiency compared to that for bare planar LEDs. We also present an improved method of modeling the light emission from the LED’s active layers to numerically calculate the light extraction efficiency of LEDs.
IEEE Electron Device Letters, 2006
Scanning Kelvin probe microscopy was used to detect reverse-bias-induced surface potential change... more Scanning Kelvin probe microscopy was used to detect reverse-bias-induced surface potential changes near the Schottky contact of a GaN Schottky diode. After application of a reverse bias, the surface potential near the Schottky contact gradually decreased with time, indicating an increase of band bending. Surface potential traces recorded after turning off the reverse bias indeed revealed increased band bending near the Schottky contact. A higher reverse bias caused a larger increase of band bending. The authors suggest that a reverse bias facilitates electron tunneling at the edge of the Schottky contact by decreasing the potential barrier width. Capture of these tunneled electrons by surface states causes the observed increase of band bending.
Optics express, Jan 5, 2018
We demonstrated the growth of crack-free high-quality GaN-based UV vertical LEDs (VLEDs) (λ = 365... more We demonstrated the growth of crack-free high-quality GaN-based UV vertical LEDs (VLEDs) (λ = 365 nm) on 6-inch sapphire substrates by using an ex-situ sputtered AlN nucleation layer (NL) and compared their performance with that of UV VLEDs with an in situ low temperature (LT) AlGaN NL. The X-ray diffraction (XRD) results showed that the ex-situ AlN sample contained lower densities of screw-type and edge-type threading dislocations than the in situ AlGaN NL sample. The micro-Raman results revealed that the ex-situ AlN sample was under more compressive stress than the in situ AlGaN sample. As the current was increased, the electroluminescence peaks of both of the samples blue-shifted, reached a minimum wavelength at 1000 mA, and then slightly red-shifted. Packaged VLEDs with the ex-situ AlN NL yielded 6.5% higher light output power at 500 mA than that with the in situ AlGaN NL. The maximum EQEs of the VLED with the in situ AlGaN and ex-situ AlN NLs were 43.7% and 48.2%, respectively....
Optics express, Jan 30, 2018
We investigated the optical and electrical properties of red AlGaInP light-emitting diodes (LEDs)... more We investigated the optical and electrical properties of red AlGaInP light-emitting diodes (LEDs) as functions of chip size, p-cladding layer thickness, and the number of multi-quantum wells (MQWs). External quantum efficiency (EQE) decreased with decreasing chip size. The ideality factor gradually increased from 1.47 to 1.95 as the chip size decreased from 350 μm to 15 μm. This indicates that the smaller LEDs experienced larger carrier loss due to Shockley-Read-Hall nonradiative recombination at sidewall defects. S parameter, defined as ∂lnL/∂lnI, increased with decreasing chip size. Simulations and experimental results showed that smaller LEDs with 5 pairs of MQWs had over 30% higher IQE at 5 A/cm than the LED with 20 pairs of MQWs. These results show that the optimization of the number of QWs is needed to obtain maximum EQE of micro-LEDs.
Scientific Reports, 2015
This study examined systematically the mechanism of light interaction in the sapphire/MgF 2 /Al t... more This study examined systematically the mechanism of light interaction in the sapphire/MgF 2 /Al triple-layer omnidirectional reflectors (ODR) and its effects on the light output power in near ultraviolet light emitting diodes (NUV-LEDs) with the ODR. The light output power of NUV-LEDs with the triple-layer ODR structure increased with decreasing surface roughness of the sapphire backside in the ODR. Theoretical modeling of the roughened surface suggests that the dependence of the reflectance of the triple-layer ODR structure on the surface roughness can be attributed mainly to light absorption by the Al nano-structures and the trapping of scattered light in the MgF 2 layer. Furthermore, the ray tracing simulation based upon the theoretical modeling showed good agreement with the measured reflectance of the ODR structure in diffuse mode. A lGaN-based LEDs in the near-ultraviolet (NUV) range are attractive for photo-catalytic deodorizing in air conditioners and refrigerators as well as in identifying counterfeit banknotes 1. In particular, color-rendering due to the high conversion efficiencies of typical phosphors in the UV spectrum has attracted considerable great interest for fabricating white LEDs with AlGaN-based NUV-LED chips for white lighting 2-5. On the other hand, AlGaN-based UV-LEDs normally suffer from very low external quantum efficiency (EQE) due to the poor light extraction efficiency caused by the epitaxial absorption of UV light. In addition, reduced indium compositional fluctuations in InGaN quantum wells with a small indium content weakens the carrier localization in localized energy states, which in turn increases the possibility of carrier trapping at the nonradiative recombination centers by the increase in in-plane carrier diffusion. To overcome these obstacles in AlGaN-based UV-LEDs, noble device structures, such as chip-shaped LED design 6 , photonic crystal 7 , distributed Bragg reflector (DBR) 8 , omnidirectional reflector (ODR) 9 , surface texturing reducing internal light reflection, and surface plasmon 10,11 , have been proposed. In particular, ODR, such as Ag-and Al-based triple-layer schemes at the backside of LED chip, has been used to increase light extraction. On the other hand, the reflectance of an Ag-based reflector decreases rapidly in the UV region. Therefore, Al-based reflectors are preferred because of the relatively high reflectivity, wide stop band, and omnidirectional reflection characteristics in the UV wavelength range. The refractive index of a dielectric layer in the ODR structure should be as low as possible. MgF 2 films, which have a low refractive index in the range, 1.34-1.39, have been used as a dielectric layer because their high optical transparency over a wide wavelength range from 120 nm UV rays in a vacuum to 900 nm infrared rays, as well as good adhesion and high durability. Recently, it was reported that the light extraction efficiency of GaN-based LEDs could be improved significantly using Al-based ODRs 12,13. On the other hand, such studies did not deal with the influence of the optical properties of LEDs according to the roughness of the dielectric-metal interface in the backside ODR system. Understanding the detailed mechanism of light interaction in the ODR scheme is important for controlling and maximizing the enhancement of light extraction in LEDs. This study examined systematically the mechanism of light interaction in the sapphire/MgF 2 /Al triple-layer ODR scheme in terms of the interface roughness with the surface roughness of the sapphire backside. The surface roughness of the sapphire backside critically affected the light extraction efficiency of the ODR scheme and should be minimized to enhance light extraction effectively.
ECS Journal of Solid State Science and Technology
IEEE Photonics Technology Letters
We investigated how the performance and reliability of AlGaInP-based red (620 nm) micro-light-emi... more We investigated how the performance and reliability of AlGaInP-based red (620 nm) micro-light-emitting diodes (micro-LEDs) (<inline-formula> <tex-math notation="LaTeX">$25\times 17\,\,\mu \text{m}^{2}$ </tex-math></inline-formula>) were influenced by the use of <inline-formula> <tex-math notation="LaTeX">$n$ </tex-math></inline-formula>-AlInP ohmic layer and distributed Bragg reflector (DBR). The AlGaAs-based DBR showed reflectivity of 94.9% at 622 nm with a 14 nm-stopband width. The micro-LEDs with <inline-formula> <tex-math notation="LaTeX">$n$ </tex-math></inline-formula>-GaAs gave slightly lower forward voltages by 0.013 – 0.021 V than those with <inline-formula> <tex-math notation="LaTeX">$n$ </tex-math></inline-formula>-Al<sub>0.5</sub>In<sub>0.5</sub>P/<inline-formula> <tex-math notation="LaTeX">$n$ </tex-math></inline-formula>-Al<sub>0.6</sub>Ga<sub>0.4</sub>As and <inline-formula> <tex-math notation="LaTeX">$n$ </tex-math></inline-formula>-Al<sub>0.5</sub>In<sub>0.5</sub>P/DBR. However, the micro-LEDs with <inline-formula> <tex-math notation="LaTeX">$n$ </tex-math></inline-formula>-Al<sub>0.5</sub>In<sub>0.5</sub>P/<inline-formula> <tex-math notation="LaTeX">$n$ </tex-math></inline-formula>-Al<sub>0.6</sub>Ga<sub>0.4</sub>As and <inline-formula> <tex-math notation="LaTeX">$n$ </tex-math></inline-formula>-Al<sub>0.5</sub>In<sub>0.5</sub>P/DBR gave 61% and 125% higher light output power at <inline-formula> <tex-math notation="LaTeX">$20~\mu \text{A}$ </tex-math></inline-formula> compared with that with <inline-formula> <tex-math notation="LaTeX">$n$ </tex-math></inline-formula>-GaAs. It was shown that after annealing at 120 °C for 2,000 h, the forward voltage and the light output power at 4.7 A/cm<sup>2</sup> of the micro-LEDs with <inline-formula> <tex-math notation="LaTeX">$n$ </tex-math></inline-formula>-Al<sub>0.5</sub>In<sub>0.5</sub>P/DBR were degraded by 0.09% and 6.33%, respectively, with reference to those before annealing.
IEEE Photonics Technology Letters
This letter examined the use of a patterned ion-damaged current blocking layer (patterned-IDCBL).... more This letter examined the use of a patterned ion-damaged current blocking layer (patterned-IDCBL). A 50-Å-InGaN layer grown as the top epitaxial layer was transformed into an insulator fabricated by oxygen plasma treatment, in which the dot patterns are regularly arranged over the active areas of the light-emitting diode (LED) and inserted beneath the p-electrode. The results showed that the light output power increased by 16.8% at 60 mA compared with the conventional LEDs, and that the electrostatic discharge resistance is effectively improved by the patterned-IDCBL.
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures
The effect of the growth rate of the nucleation layer on the growth of a high temperature GaN lay... more The effect of the growth rate of the nucleation layer on the growth of a high temperature GaN layer has been studied by observing the in situ normal incidence reflectance during the growth of GaN by metalorganic chemical vapor deposition. This study revealed that the lateral ...
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 2004
We report that ambient thermal annealing is a promising method for recovering the dry-etch-induce... more We report that ambient thermal annealing is a promising method for recovering the dry-etch-induced damage on Mg-doped GaN surfaces. The surface electrical properties of dry-etched Mg-doped GaN can be fully recovered by thermal annealing using as an ambient gas at ...
Applied Physics Letters, 2001
The temperature dependence of the photoluminescence (PL) of InGaN films, grown by metalorganic ch... more The temperature dependence of the photoluminescence (PL) of InGaN films, grown by metalorganic chemical vapor deposition, has been investigated. A strained InGaN thin film which contains composition-fluctuated regions shows the so-called S-shaped temperature dependence of the dominant PL peak energy. However, an InGaN thick film which contains quantum dot-like In-rich regions shows a sigmoidal temperature dependence of the dominant PL
physica status solidi (a), 2010
1 Department of Electronics Engineering, Catholic University of Daegu, Hayang, Kyeongsan, Kyeongb... more 1 Department of Electronics Engineering, Catholic University of Daegu, Hayang, Kyeongsan, Kyeongbuk 712-702, Republic of Korea 2 LED R&amp;amp;amp;D Center, LG Innotek, 16 Woomyeon-dong, Seocho-gu, Seoul 137-140, Republic of Korea 3 Department of ...
III-nitride semiconductor materials have been largely developed for use in optoelectronic devices... more III-nitride semiconductor materials have been largely developed for use in optoelectronic devices such as light emitting diodes (LED) and laser diodes (LD)[1]. The AlGaN/GaN heterostructure has recently been the subject of considerable interest in the fabrication of ...
Optics express, Jan 10, 2015
We study light-extraction efficiency (LEE) of AlGaN-based deep-ultraviolet light-emitting diodes ... more We study light-extraction efficiency (LEE) of AlGaN-based deep-ultraviolet light-emitting diodes (DUV-LEDs) using flip-chip (FC) devices with varied thickness in remaining sapphire substrate by experimental output power measurement and computational methods using 3-dimensional finite-difference time-domain (3D-FDTD) and Monte Carlo ray-tracing simulations. Light-output power of DUV-FCLEDs compared at a current of 20 mA increases with thicker sapphire, showing higher LEE for an LED with 250-μm-thick sapphire by ~39% than that with 100-μm-thick sapphire. In contrast, LEEs of visible FCLEDs show only marginal improvement with increasing sapphire thickness, that is, ~6% improvement for an LED with 250-μm-thick sapphire. 3D-FDTD simulation reveals a mechanism of enhanced light extraction with various sidewall roughness and thickness in sapphire substrates. Ray tracing simulation examines the light propagation behavior of DUV-FCLED structures. The enhanced output power and higher LEE stro...
Materials Science Forum, 2006
Improved structural quality and radiative efficiency were observed in GaN thin films grown by met... more Improved structural quality and radiative efficiency were observed in GaN thin films grown by metalorganic chemical vapor deposition on in situ-formed SiN and TiN porous network templates. The room temperature carrier decay time of 1.86 ns measured for a TiN network sample is slightly longer than that for a 200 μm-thick high quality freestanding GaN (1.73 ns). The linewidth of the asymmetric X-Ray diffraction (XRD) (1012) peak decreases considerably with the use of SiN and TiN layers, indicating the reduction in threading dislocation density. However, no direct correlation is yet found between the decay times and the XRD linewidths, suggesting that point defect and impurity related nonradiative centers are the main parameters affecting the lifetime.
physica status solidi (c), 2005
We have grown GaN layers by MOCVD on a set of nanoporous SiC templates with different porosity an... more We have grown GaN layers by MOCVD on a set of nanoporous SiC templates with different porosity and morphology, produced by etching the anodized porous SiC starting material in a H 2 environment at temperatures ~1500 °C, in an effort to attain improved films. The hydrogen etching serves to remove surface damage caused during mechanical polishing prior to anodization, remove the skin layer associated with anodization, tune the pore size, and consolidate pore geometry. Growth conditions favoring lateral overgrowth of GaN were employed on this set of samples to obtian GaN to a thickness of 2 µm. Atomically smooth surfaces were obtained for the epitaxial GaN layers. The GaN quality is highly dependent on the specifics of the porous templates used. An intensity increase of up to a factor of 30 was observed in the GaN excitonic peak compared to GaN grown on standard SiC substrate. The I-V data indicated significant reduction in the leakage current (in reverse bias) compared to GaN grown on standard SiC. The dependence of optical properties, crystalline quality, and surface morphology on the particulars of porous SiC templates is discussed.