Wonseok Lee - Academia.edu (original) (raw)
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Papers by Wonseok Lee
Journal of Crystal Growth, 2003
ABSTRACT
Journal of Electronic Materials, 2006
The design and growth of GaN/InGaN heterojunction bipolar transistors (HBTs) by metalorganic chem... more The design and growth of GaN/InGaN heterojunction bipolar transistors (HBTs) by metalorganic chemical vapor deposition (MOCVD) are studied. Atomic-force microscopy (AFM) images of p+InGaN base layers (∼100 nm) deposited under various growth conditions indicate that the optimal growth temperature is limited to the range between 810 and 830°C due to a trade-off between surface roughness and indium incorporation. At these temperatures, the growth pressure must be kept above 300 Torr in order to keep surface pit density under control. An InGaN graded-composition emitter is adopted in order to reduce the number of V-shaped defects, which appear at the interface between GaN emitter and InGaN base and render an abrupt emitter-base heterojunction nearly impossible. However, the device performance is severely limited by the high p-type base contact resistance due to surface etching damage, which resulted from the emitter mesa etch.
Journal of Crystal Growth, 2006
We investigated the electrical and structural qualities of Mg-doped p-type In 0.01 Ga 0.99 N and ... more We investigated the electrical and structural qualities of Mg-doped p-type In 0.01 Ga 0.99 N and GaN layers grown under different growth conditions by metalorganic chemical vapor deposition. It was found that we obtained a lower hole concentration and rough surface by reducing the growth temperature down to 930 1C in the case of p-GaN. A slight improvement of the hole concentration was obtained for Mg-doped In 0.01 Ga 0.99 N grown at 840 1C, but this was accompanied by pit formation on the surface. In 0.19 Ga 0.81 N/GaN and In 0.25 Ga 0.75 N/GaN multiple-quantum-well (MQW) light-emitting diodes (LED) with such different p-layers were also grown. It was found from photoluminescence studies that the optical and structural properties of the MQW in the LED structure were improved by reducing the growth temperature of the p-layer due to reduced thermal annealing effect of the active region during p-layer growth. However, it was also found the electroluminescence intensity was lower for the LEDs with p-In 0.01 Ga 0.99 N layers grown at 840 1C. r
Journal of Electronic Materials, 2006
We investigated the electrical and structural qualities of Mg-doped p-type GaN layers grown under... more We investigated the electrical and structural qualities of Mg-doped p-type GaN layers grown under different growth conditions by metalorganic chemical vapor deposition (MOCVD). Lower 300 K free-hole concentrations and rough surfaces were observed by reducing the growth temperature from 1,040°C to 930°C. The hole concentration, mobility, and electrical resistivity were improved slightly for Mg-doped GaN layers grown at 930°C with a lower growth rate, and also an improved surface morphology was observed. In0.25Ga0.75N/GaN multiple-quantum-well light emitting diodes (LEDs) with p-GaN layers grown under different conditions were also studied. It was found from photoluminescence studies that the optical and structural properties of the multiple quantum wells in the LED structure were improved by reducing the growth temperature of the p-layer due to a reduced detrimental thermal annealing effect of the active region during the GaN:Mg p-layer growth. No significant difference in the photoluminescence intensity depending on the growth time of the p-GaN layer was observed. However, it was also found that the electroluminescence (EL) intensity was higher for LEDs having p-GaN layers with a lower growth rate. Further improvement of the p-GaN layer crystalline and structural quality may be required for the optimization of the EL properties of long-wavelength (∼540 nm) green LEDs.
IEEE/OSA Journal of Display Technology, 2007
High-quality InGaN-GaN multiquantum well (MQW) light-emitting diode (LED) structures were prepare... more High-quality InGaN-GaN multiquantum well (MQW) light-emitting diode (LED) structures were prepared by temperature ramping method during metalorganic chemical vapor deposition (MOCVD) growth. It was found that we could reduce the 20-mA forward voltage and increase the output intensity of the nitride-based green LEDs by increasing the growth temperature of GaN barrier layers from 700 C to 950 C. The 20-mA output power and maximum output power of the nitride-based green LEDs with high temperature GaN barrier layers was found to be 2.2 and 8.9 mW, respectively, which were more than 65% larger than those observed from conventional InGaN-GaN green LEDs. Such an observation could be attributed to the improved crystal quality of GaN barrier layers. The reliability of these LEDs was also found to be reasonably good.
Journal of Crystal Growth, 2003
ABSTRACT
Journal of Electronic Materials, 2006
The design and growth of GaN/InGaN heterojunction bipolar transistors (HBTs) by metalorganic chem... more The design and growth of GaN/InGaN heterojunction bipolar transistors (HBTs) by metalorganic chemical vapor deposition (MOCVD) are studied. Atomic-force microscopy (AFM) images of p+InGaN base layers (∼100 nm) deposited under various growth conditions indicate that the optimal growth temperature is limited to the range between 810 and 830°C due to a trade-off between surface roughness and indium incorporation. At these temperatures, the growth pressure must be kept above 300 Torr in order to keep surface pit density under control. An InGaN graded-composition emitter is adopted in order to reduce the number of V-shaped defects, which appear at the interface between GaN emitter and InGaN base and render an abrupt emitter-base heterojunction nearly impossible. However, the device performance is severely limited by the high p-type base contact resistance due to surface etching damage, which resulted from the emitter mesa etch.
Journal of Crystal Growth, 2006
We investigated the electrical and structural qualities of Mg-doped p-type In 0.01 Ga 0.99 N and ... more We investigated the electrical and structural qualities of Mg-doped p-type In 0.01 Ga 0.99 N and GaN layers grown under different growth conditions by metalorganic chemical vapor deposition. It was found that we obtained a lower hole concentration and rough surface by reducing the growth temperature down to 930 1C in the case of p-GaN. A slight improvement of the hole concentration was obtained for Mg-doped In 0.01 Ga 0.99 N grown at 840 1C, but this was accompanied by pit formation on the surface. In 0.19 Ga 0.81 N/GaN and In 0.25 Ga 0.75 N/GaN multiple-quantum-well (MQW) light-emitting diodes (LED) with such different p-layers were also grown. It was found from photoluminescence studies that the optical and structural properties of the MQW in the LED structure were improved by reducing the growth temperature of the p-layer due to reduced thermal annealing effect of the active region during p-layer growth. However, it was also found the electroluminescence intensity was lower for the LEDs with p-In 0.01 Ga 0.99 N layers grown at 840 1C. r
Journal of Electronic Materials, 2006
We investigated the electrical and structural qualities of Mg-doped p-type GaN layers grown under... more We investigated the electrical and structural qualities of Mg-doped p-type GaN layers grown under different growth conditions by metalorganic chemical vapor deposition (MOCVD). Lower 300 K free-hole concentrations and rough surfaces were observed by reducing the growth temperature from 1,040°C to 930°C. The hole concentration, mobility, and electrical resistivity were improved slightly for Mg-doped GaN layers grown at 930°C with a lower growth rate, and also an improved surface morphology was observed. In0.25Ga0.75N/GaN multiple-quantum-well light emitting diodes (LEDs) with p-GaN layers grown under different conditions were also studied. It was found from photoluminescence studies that the optical and structural properties of the multiple quantum wells in the LED structure were improved by reducing the growth temperature of the p-layer due to a reduced detrimental thermal annealing effect of the active region during the GaN:Mg p-layer growth. No significant difference in the photoluminescence intensity depending on the growth time of the p-GaN layer was observed. However, it was also found that the electroluminescence (EL) intensity was higher for LEDs having p-GaN layers with a lower growth rate. Further improvement of the p-GaN layer crystalline and structural quality may be required for the optimization of the EL properties of long-wavelength (∼540 nm) green LEDs.
IEEE/OSA Journal of Display Technology, 2007
High-quality InGaN-GaN multiquantum well (MQW) light-emitting diode (LED) structures were prepare... more High-quality InGaN-GaN multiquantum well (MQW) light-emitting diode (LED) structures were prepared by temperature ramping method during metalorganic chemical vapor deposition (MOCVD) growth. It was found that we could reduce the 20-mA forward voltage and increase the output intensity of the nitride-based green LEDs by increasing the growth temperature of GaN barrier layers from 700 C to 950 C. The 20-mA output power and maximum output power of the nitride-based green LEDs with high temperature GaN barrier layers was found to be 2.2 and 8.9 mW, respectively, which were more than 65% larger than those observed from conventional InGaN-GaN green LEDs. Such an observation could be attributed to the improved crystal quality of GaN barrier layers. The reliability of these LEDs was also found to be reasonably good.