Shih-Yung Huang

GaN-based light-emitting diodes with indium tin oxide texturing window layers using natural lithography

There is a significant gap between the internal and external efficiencies of conventional GaN light-emitting diodes (LEDs). The reason for this shortfall is the narrow escape cone for light in high refractive index semiconductors. In this letter, the p-side-up GaN∕sapphire LEDs with surface textured indium tin oxide (ITO) widow layers were investigated using natural lithography with polystyrene spheres as the etching mask. Under optimum etching conditions, the surface roughness of the ITO film can reach 140 nm while the polystyrene sphere on the textured ITO surface is maintained at about 250–300 nm in diameter. The output power of the ITO∕GaN LED with and without surface texturing is 10.9, and 8.5 mW at 20 mA, respectively. The LEDs fabricated using the surface-textured ITO produced an output power that exceeded that of the planar-surface LED by about 28% at 20 mA.

High-power GaN-mirror-Cu light-emitting diodes for vertical current injection using laser liftoff and electroplating techniques

A large-area (1 /spl times/ 1 mm) vertical conductive GaN-mirror-Cu light-emitting diode (LED) fabricated using the laser liftoff and electroplating techniques is demonstrated. Selective p-GaN top area was first electroplated by the thick copper film, and then an excimer laser was employed to separate the GaN thin film from the sapphire substrate. The luminance intensity of the vertical conductive p-side-down GaN-mirror-Cu LED presented about 2.7 times in magnitude as compared with that of the original GaN-sapphire LED (at 20 mA). The light output power for the GaN-mirror-Cu LED was about twofold stronger (at 500 mA). A more stable peak wavelength shift under high current injection was also observed.

Fabrication and efficiency improvement of micropillar InGaN∕Cu light-emitting diodes with vertical electrodes

We present a micropillar surface structure based on the enhancement of the light extraction efficiency of the near-ultraviolet (409nm) vertical-conducting InGaN light-emitting diode (LED) with an electroplated Cu substrate. The micropillar InGaN∕Cu LED (chip size: 1×1mm2) was fabricated using a combination of patterned sapphire substrate (PSS), laser lift-off, and copper electroplating processes. The PSS and Cu substrate can offer the advantages of dislocation reduction and thermal heat sink, respectively. It was found that the light output power (at 350mA) of the micropillar InGaN∕Cu LED sample can be improved by 39% as compared with that of the conventional InGaN∕Cu LED one. This significant enhancement in output power could be attributed to the increase of the extraction efficiency which is a result of the increase in photon escaping probability caused by scattering the emission light at the micropillar surface. The light extraction efficiency can be further optimized by tuning the micropillar spacing,...

An 83% enhancement in the external quantum efficiency of ultraviolet flip-chip light-emitting diodes with the incorporation of a self-textured oxide mask

We demonstrate here a 380-nm ultraviolet InGaN flip-chip (FC) light-emitting diode (LED) with self-textured oxide mask (STOM-FCLED) structures fabricated in a large-area (1125 × 1125 μm2) FC configuration. An 83% enhancement in the external quantum efficiency was achieved for the STOMFCLEDs when compared with FCLEDs without the STOM structure operating at an injection current of 350 mA. For STOM-FCLEDs operating at an injection current of 1000 mA, a light output of approximately 400 mW was obtained. These results could be attributed to the introduction of the STOM structure, which not only reduces the density of threading dislocation but also intensifies the LED light extraction.

Characteristics of Flip-Chip InGaN-Based Light-Emitting Diodes on Patterned Sapphire Substrates

We report on the characteristics of high-power near-ultraviolet (425 nm) flip-chip InGaN light-emitting diodes (LEDs) fabricated onto a patterned sapphire substrate (PSS). When the PSS flip-chip LED (chip size: 1 mm2) operated at a 20 mA forward current at room temperature, the forward voltage and the light output power were 3.15 V and 6.8 mW, respectively. It was found that the PSS flip-chip LED has similar current–voltage characteristics to those of a conventional flip-chip LED. The luminance intensity of the PSS flip-chip LED was approximately 43% lager than that of the conventional flip-chip LED (at 100 mA). Moreover, the light output power was greatly increased by 59% for the PSS sample at a forward injection current of 350 mA compared with that of the conventional flip-chip LED. This result was attributed to the increase in the probability of photons escaping from the LED samples, resulting in the enhancement of light extraction efficiency. The effect of the PSS on the flip-chip LED structure has been simulated and shows a good correlation with the measured results.

AlGaInP/mirror/Si light-emitting diodes with vertical electrodes by wafer bonding

In a previous study, we reported a highly efficient AlGaInP light-emitting diode (LED) with a Au/AuBe/SiO2/Si mirror substrate (MS) fabricated by wafer bonding, where a planar electrode structure is used. In view of the more efficient epilayer area utilized, AlGaInP/mirror/barrier/Si LEDs with vertical electrodes are proposed in this work. A variety of barrier layers (Pt/Ti, TaN/Ta, and TiN/Ti) have been incorporated into the mirror structure. The mirror quality after bonding is a confirmed key issue in obtaining vertical MS–LEDs with high brightness. It is found that AuBe thickness has a large effect on the final MS–LED performance due to the difference in the interdiffusion of Be atoms in each mirror structure. The diffusion of excess Be atoms diffusing to the mirror side results in a rougher surface and inferior reflectivity. The luminance intensity of an AlGaInP LED chip (626 nm) with an optimum AuBe thickness can reach a maximum of ∼165 mcd at 20 mA with a forward voltage of 2.1 V. After encapsulatio...

High-Performance InGaN-Based Green Resonant-Cavity Light-Emitting Diodes for Plastic Optical Fiber Applications

High-performance InGaN-based green resonant-cavity light-emitting diodes (RCLEDs) with a plating Cu substrate for plastic optical fiber communication applications are reported. Good stability of emission wavelength was obtained at 0.016 nm/mA . The RCLEDs presents low temperature dependence, showing only a 3% drop in light output power as the temperature increasing from 25 to 85degC. The superior performance can be attributed to the decreased dynamic series resistance and the enhanced thermal dissipation of the heat sink substrate.

GaN-based green resonant cavity light-emitting diodes

GaN-based resonant cavity light-emitting diodes (RCLEDs) have been successfully fabricated on Si substrate by laser lift-off and wafer bonding techniques. A five-pair TiO2/SiO2 dielectric distributed Bragg reflector (DBR) (with 85% reflectivity) and an Ag layer (with 99% reflectivity) were employed as top and bottom mirrors, respectively, for front emission RCLEDs. The room temperature light output power of the RCLED was 1.5 times that of similar LED structures without a top DBR mirror under 20 mA injection current. The cavity modes exhibit a linewidth of 5.5 nm at 525 nm wavelength, which corresponds to a quality factor about 100. Moreover, the full width at half maximum of the emission can be reduced to 35 nm, as a result of the effect of the resonant cavity.

High-density plasma-induced etch damage of wafer-bonded AlGaInP/mirror/Si light-emitting diodes

Dry etch of wafer-bonded AlGaInP/mirror/Si light-emitting diodes (LEDs) with planar electrodes was performed by high-density plasma using an inductively coupled plasma (ICP) etcher. The etching characteristics were investigated by varying process parameters such as Cl2/N2 gas combination, chamber pressure, ICP power and substrate-bias power. The corresponding plasma properties (ion flux and dc bias), in situ measured by a Langmuir probe, show a strong relationship to the etch results. With a moderate etch rate of 1.3 μm/min, a near vertical and smooth sidewall profile can be achieved under a Cl2/(Cl2+N2) gas mixture of 0.5, ICP power of 800 W, substrate-bias power of 100 W, and chamber pressure of 0.67 Pa. Quantitative analysis of the plasma-induced damage was attempted to provide a means to study the mechanism of leakage current and brightness with various dc bias voltages (−110 to −328 V) and plasma duration (3–5 min) on the wafer-bonded LEDs. It is found that the reverse leakage current increases and t...

Deep etch of GaP using high-density plasma for light-emitting diode applications

Deep etching of GaP was performed by high-density plasma using an inductively coupled plasma (ICP) etcher. The effects of process parameters such as the gas combination (Cl2/N2), chamber pressure, inductive power and rf chuck power were investigated. The dependences of the etch rates and selectivity on the rf chunk power and chamber pressure were studied using the response surface method. The results obtained can be further interpreted by the plasma properties (ion flux and dc bias) measured in situ by a Langmuir probe. With an increase in the chamber pressure to 4 Pa, a maximum etch rate of ∼7.5 μm/min for GaP can be obtained under a Cl2/(Cl2+N2) gas mixture of 0.8, ICP power of 800 W, and rf power of 100 W. The increase in the etch rate with an increase in chamber pressure indicates that reactive radicals are the main etching species. To clarify the etching mechanism, the surface reaction of GaP under various Cl2/(Cl2+N2) gas mixtures was investigated by x-ray photoelectron spectroscopy and atomic force...