Chih-Hung Kuo

Influence of Si-doping on the characteristics of InGaN-GaN multiple quantum-well blue light emitting diodes

A detailed study on the effects of Si-doping in the GaN barrier layers of InGaN-GaN multiquantum well (MQW) light-emitting diodes (LEDs) has been performed. Compared with unintentionally doped samples, X-ray diffraction results indicate that Si-doping in barrier layers can improve the crystal and interfacial qualities of the InGaN-GaN MQW LEDs. It was also found that the forward voltage is 3.5 and 4.52 V, the 20-mA luminous intensity is 36.1 and 25.1 mcd for LEDs with a Si-doped barrier and an unintentionally doped barrier, respectively. These results suggests that one can significantly improve the performance of InGaN-GaN MQW LEDs by introducing Si doping in the GaN barrier layers.

Nitride-Based High-Power Flip-Chip LED With Double-Side Patterned Sapphire Substrate

A nitride-based high-power flip-chip (FC) light-emitting diode (LED) with a double-side patterned sapphire substrate (PSS) was proposed and realized. Under 350-mA current injection, it was found that forward voltages were 3.24, 3.26, and 3.25 V for the conventional FC LED, FC LED prepared on PSS, and FC LED with double-side PSS, respectively. It was found that the 350-mA LED output powers were 79.3, 98.1, and 121.5 mW for the conventional FC LED, FC LED prepared on PSS, and FC LED with double-side PSS, respectively. In other words, we can enhance the electroluminescence intensity by 53% without increasing operation voltage of the fabricated LED

In0.23Ga0.77N/GaN MQW LEDs with a low temperature GaN cap layer

Abstract Mg-doped p-GaN epitaxial layers prepared at different temperatures were prepared and characterized. It was found that we could achieve a higher hole concentration and a rough surface by reducing the growth temperature down to 800 °C. In 0.23 Ga 0.77 N/GaN multiquantum well (MQW) light emitting diodes (LEDs) with such a low 800 °C-grown p-GaN cap layer were also fabricated. It was found that we could enhance the LED output intensity by more than 90% with the low 800 °C-grown p-GaN cap layer, as compared to the conventional high 1000 °C-grown p-GaN cap layer.

InGaN/GaN light emitting diodes activated in O/sub 2/ ambient

Mg-doped GaN epitaxial layers were annealed in pure O/sub 2/ and pure N/sub 2/. It was found that we could achieve a low-resistive p-type GaN by pure O/sub 2/ annealing at a temperature as low as 400/spl deg/C. With a 500/spl deg/C annealing temperature, it was found that the forward voltage and dynamic resistance of the InGaN/GaN light emitting diode (LED) annealed in pure O/sub 2/ were both smaller than those values observed from InGaN/GaN LED annealed in pure N/sub 2/. It was also found that an incomplete activation of Mg will result in a shorter LED lifetime.

Enhanced output power in GaN-based LEDs with naturally textured surface grown by MOCVD

GaN-based light-emitting diodes (LEDs) with naturally textured surfaces grown by MOCVD were demonstrated. In this study, a growth-interruption step and a surface treatment using biscyclopentadienyl magnesium (CP/sub 2/Mg) were simultaneously performed to form a plurality of nuclei sites on the surface of a p-type cladding layer, and then a p-type contact layer was grown on the p-type cladding layer, so as to create a p-type contact layer with a rough surface having truncated pyramids. Experimental results indicated that GaN-based LED with the truncated pyramids on the surface exhibited an enhancement in output power of 66% at 20 mA. It is worth noting that the typical 20-mA-driven forward voltage is only slightly higher than those of conventional LEDs (without the Mg-treatment process).

InGaN/GaN tunnel-injection blue light-emitting diodes

A charge asymmetric resonance tunneling (CART) structure was applied to nitride-based blue light emitting diodes (LEDs) to enhance their output efficiency. It was found that with a 20-nm-thick In/sub 0.18/Ga/sub 0.82/N electron emitter layer, we could increase the LED output intensity from 28.3 minicandela (mcd) to 43.2 mcd (i.e., a 53% increase). However, a further increase in electron emitter layer thickness will reduce the intensity due to relaxation. It was also found that we could decrease the 20 mA forward voltage from 4.16 V to 3.58 V with a proper electron emitter layer.

Nitride-based LEDs with an insulating SiO2 layer underneath p-pad electrodes

We proposed a simple method to reduce the current crowding effect of nitride-based light emitting diodes (LEDs) without extra dry etching and refill. It was found that we can achieve much better current spreading by inserting an insulating SiO 2 layer between the epitaxial layer and the p-pad electrode. It was also found that we can enhance light output intensity by 22%. Furthermore, it was found that 20 mA forward voltage only increased slightly from 3.32 to 3.37 V with the insertion of the SiO 2 layer. The reliability of the proposed LED is also good.

InGaN-GaN MQW LEDs with Si treatment

Surface morphologies of the metal-organic chemical vapor deposition-grown p-GaN layers with and without Si treatment were investigated by atomic force microscope and scanning electron microscope. It was found that Si treatment resulted in a much rougher sample surface due to the formation of a thin Si/sub x/N/sub y/ layer. It was also found that forward voltage of the Si-treated InGaN-GaN light-emitting diode (LED) was slightly higher than that of conventional LED without Si treatment. However, it was also found that such Si treatment could also result in a much larger LED output intensity.

Nitride-based light-emitting diodes with p-AlInGaN surface layers

We have prepared bulk p-AlInGaN layers and light-emitting diodes (LEDs) with p-AlInGaN surface layers by metal-organic chemical vapor deposition. By properly control the TMAl and TMIn flow rates, we could match the lattice constant of p-AlInGaN to that of GaN. It was found that surface of the LED with p-AlInGaN layer was rough with a high density of hexagonal pits. Although the forward voltage of the LED with p-AlInGaN layer was slightly larger, it was found that we can enhance the output power by 54% by using p-AlInGaN surface layer.

Nitride-based blue LEDs with GaN/SiN double buffer layers

GaN epitaxial layers and nitride-based multiquantum well light emitting diode (LED) structures with conventional single GaN buffer and GaN/SiN double buffers were prepared by metalorganic chemical vapor deposition. It was found that we could reduce defect density and thus improve crystal quality of the GaN epitaxial layers by using GaN/SiN double buffers. It was also found that we could use such a GaN/SiN double buffer to achieve more reliable nitride-based LEDs.