Yong Chun Kim

Effect of electron blocking layer on efficiency droop in InGaN/GaN multiple quantum well light-emitting diodes

The effect of an electron blocking layer (EBL) on the efficiency droop in InGaN/GaN multiple quantum well light-emitting diodes (LEDs) is investigated. At low current density, the LEDs with a p-AlGaN EBL show a higher external quantum efficiency (EQE) than LEDs without an EBL. However, the EQE of LEDs without an EBL is higher than LEDs with an EBL as injection current density is increased. The improved EQE of LEDs without an EBL at high current density is attributed to the increased hole injection efficiency.

Enhanced emission efficiency of GaN∕InGaN multiple quantum well light-emitting diode with an embedded photonic crystal

A photonic crystal (PC) structure of periodic SiO2 pillar cubic array is embedded in n-GaN layer of InGaN∕GaN multiple quantum well (MQW) blue (480nm) light-emitting diode (LED). The diameter, period, and depth of SiO2 pillar are 124±6, 230±10, and 130±10nm, respectively. The increments of 70% for external quantum efficiency, 17% for internal quantum efficiency, and 45% for light extraction efficiency from photoluminescence measurement, and 33% for optical output power at 20mA are observed for LEDs with an embedded PC layer. This improvement can be attributed to the increased extraction efficiency by PC effect as well as increased internal quantum efficiency due to the decrease of dislocation density in n-GaN layer because of an epitaxial lateral over-growth process.

Enhanced optical power and low forward voltage of GaN-based light- emitting diodes with Ga-doped ZnO transparent conducting layer

Ga-doped ZnO (ZnO:Ga) films were grown by metalorganic chemical vapor deposition as transparent conducting layers for GaN light-emitting diodes (LEDs). The forward voltage of LEDs with ZnO:Ga was 3.3 V at 20 mA. The low forward voltage was attributed to the removal of a resistive ZnGa2O4 phase, decreased resistivity of ZnO:Ga films, and increased hole concentration in p-GaN by thermal annealing process. The light output power of LEDs with ZnO:Ga was increased by 25% at 20 mA compared to that of LEDs with Sn-doped indium oxide due to the enhanced transmittance and the increased hole concentration in p-GaN.

Effect of Mg doping in the barrier of InGaN/GaN multiple quantum well on optical power of light-emitting diodes

We report on Mg doping in the barrier layers of InGaN/GaN multiple quantum wells (MQWs) and its effect on the properties of light-emitting diodes (LEDs). Mg doping in the barriers of MQWs enhances photoluminescence intensity, thermal stability, and internal quantum efficiency of LEDs. The light output power of LEDs with Mg-doped MQW barriers is higher by 19% and 27% at 20 and 200 mA, respectively, than that of LEDs with undoped MQW barriers. The improvement in output power is attributed to the enhanced hole injection to well layers in MQWs with Mg-doped barriers.

Improvement of GaN-based light-emitting diodes using p-type AlGaN/GaN superlattices with a graded Al composition

We investigated the effect of graded Al composition in the p-type AlGaN/GaN superlattices (SLs) of InGaN/GaN multiple quantum well light-emitting diodes (LEDs) to improve their performance. The light output power and external quantum efficiency (EQE) of LEDs with Al composition grading was increased compared with those of LEDs without Al grading, indicating that the efficiency droop was reduced. The improved output power and EQE of LEDs with a graded Al composition was attributed to the increased hole injection by the reduced AlGaN barrier height and the suppression of potential spikes between the graded AlGaN and GaN layers in SLs.

Improvement of light output power of InGaN/GaN light-emitting diode by lateral epitaxial overgrowth using pyramidal-shaped SiO 2

We report on the improvement of light output power of InGaN/GaN blue light-emitting diodes (LEDs) by lateral epitaxial overgrowth (LEO) of GaN using a pyramidal-shaped SiO(2) mask. The light output power was increased by 80% at 20 mA of injection current compared with that of conventional LEDs without LEO structures. This improvement is attributed to an increased internal quantum efficiency by a significant reduction in threading dislocation and by an enhancement of light extraction efficiency by pyramidal-shaped SiO(2) LEO mask.

Enhanced light extraction efficiency in flip-chip GaN light-emitting diodes with diffuse Ag reflector on nanotextured indium-tin oxide

We investigated a flip-chip light emitting diode (FCLED) with a diffuse reflector fabricated by depositing a Ag film on a nanotextured indium-tin oxide (ITO) layer. The FCLED with a diffuse Ag reflector showed remarkably good adhesion and high reflectance than that with a specular Ag reflector deposited on the planar ITO layer. The optical output power of FCLED with the diffuse Ag reflector was enhanced by 161.3% at 300mA compared to that with the specular Ag reflector.

Improving the Performance of Green LEDs by Low-Temperature Annealing of p-GaN with PdZn

This article reports the electrical properties of p-GaN annealed at low activation temperature by using a PdZn film in green InGaN/GaN multiquantum well (MQW) light-emitting diodes (LEDs). Electroluminescence (EL) intensity of green MQW LED annealed at 600°C using PdZn was improved by 33% at 20 mA compared to that annealed at 800°C without PdZn. These results are attributed to an increase of the hole concentration of p-GaN due to removal of hydrogen in p-GaN by PdZn and a decrease in thermal damage of MQW at low activation temperature.

Effect of PdZn film on the performance of green light-emitting diodes

PdZn was used to improve the electrical properties of p-GaN annealed at low activation temperature for high efficiency green light-emitting diodes (LEDs). A hole concentration of p-GaN annealed at 600 °C with PdZn was almost 28 times higher than that of p-GaN annealed at 800 °C without PdZn. SIMS analysis showed that hydrogen concentration in p-GaN annealed with PdZn is decreased compared to that without using PdZn because the PdZn enhances hydrogen desorption from the Mg-doped p-GaN film at low temperature. The green MQW LED annealed at 600 °C using PdZn showed improved electrical characteristic and optical output power compared to that annealed at 800 °C without using PdZn. These results are attributed to the increase of hole concentration of p-GaN due to removal of hydrogen in p-GaN by PdZn and the decrease in thermal damage of MQW at low activation temperature.