Improvement In Light Output Power Research Articles

Light Output Improvement of Oxide-Textured InGaN-Based Light-Emitting Diodes by Bias-Assisted Photoelectrochemical Oxidation With Imprint Technique

The improvement of light output power in InGaN-GaN multiple quantum-well (MQW) light-emitting diodes (LEDs) with oxide textural films are observed. The oxide textural films are grown by alternating current bias-assisted photoelectrochemical oxidation with an imprint technique. At an injection current of 20 mA, the light output power of the oxide-textured InGaN-GaN MQW LEDs is 22% higher than that of the conventional LEDs. Relatively low values in leakage current for the oxide-textured are also observed, as compared to the conventional LEDs. This enhancement in the oxide-textured LEDs performance is attributed to the increase in external quantum efficiency by the nanoscale roughness of the convex oxide films and to the passivation in possible leakage paths of the devices.

Improved Light Output Power of GaN-based LEDs by Enhancing Current Injection and Spreading - Invited

not Available.

Laser Liftoff GaN Thin-Film Photonic Crystal GaN-Based Light-Emitting Diodes

We fabricated a thin-film vertical-injection light-emitting diode (LED), which uses a highly efficient coherent external scattering of trapped light by photonic crystal (PhC). The PhC patterns (a = 1200 nm) were formed on top of the n-GaN surface after laser liftoff of the sapphire substrate. This light extraction structure just above micron scale was prepared by a conventional photolithography (lambdac = 405 nm). The Si-gel-encapsulated thin-film LED with PhC patterns (a = 1 200 nm), which had a depth of 500 nm, demonstrated up to 76% improvement in light output power at a forward current of 60 mA, compared with the nonpatterned thin film LED.

Power-enhanced ITO omni-directional reflective AlGaInP LEDs by two-dimensional wavelike surface texturing

An n-side up-type AlGaInP multiple-quantum-well light-emitting diode (LED) has been developed by texturing the current spreading layer utilizing photolithography followed by an anisotropic etching process over n-AlGaInP grown by metalorganic chemical vapor deposition. The GaP-ITO-Ag omni-directional reflective LEDs with the wavelike textured surfaces provide a reasonable improvement in light output power and efficiency over the corresponding conventional structures. The luminous intensity of the surface-textured LED is 1.46 times greater than that of the conventional LED in the normal direction. The output power (at 350 mA) of the surface-textured LED is increased approximately 40% as compared with that of the conventional LED. Additionally, the optical simulation also presents a tendency towards the ray extraction ratio as the size of the wavelike hole changes, confirming a proper formation of pattern size associated with the fabrication process.

High-Performance AlGaInP/GaAs Light-Emitting Diodes with a Carbon-Doped GaP/Indium–Tin Oxide Contact Layer

An alternative heavily carbon-doped GaP (GaP:C) contact layer is demonstrated to form a good ohmic contact to electron-beam-evaporation indium–tin oxide (ITO) spreading layer on the AlGaInP light-emitting diode (LED) with a GaAs absorbing substrate. The LEDs with GaP:C/ITO contact layer provide a substantial improvement in light output power over conventional structures (without GaP:C/ITO). The AlGaInP LEDs with GaP:C/ITO structures exhibited a higher external quantum efficiency (3.24%) and larger light output power (5.9 mW) under a dc operation of 160 mA than those of 2.01% and 1.93 mW at 120 mA for the conventional structures, showing an earlier saturation behavior of current-power characteristics. These positive results are tentatively attributed to the introduction of the GaP:C/ITO current-spreading structures in the LEDs.

Use of anisotropic laser etching to the top n-GaN layer to alleviate current-crowding effect in vertical-structured GaN-based light-emitting diodes

To equalize the resistance of all possible current paths in regular vertical-conducting metal-substrate GaN-based light-emitting diodes (VM-LEDs), an anisotropic laser etching to the surface layer (n-GaN) of 40mil VM-LEDs for improving light emission uniformity and light output power is proposed and demonstrated. The feasibility of the proposed scheme was verified by current and light emission distribution as well as light extraction rate simulations. In conjunction with a nonuniform excimer laser beam irradiation through a mask and rotation of the epitaxy wafer, VM-LEDs with a concave-surface n-GaN layer were also fabricated. Typical improvement in light output power by 38%–26% at an injection current of 350mA as compared to the one without anisotropic etching has been obtained.

The use of transparent indium–zinc oxide/(oxidized-Ni/Au) ohmic contact to GaN-based light-emitting diodes for light output improvement

In this study, a low-resistant and high-transparent ohmic contact to p-GaN layer using an indium–zinc oxide (IZO)/(oxidized-Ni/Au) contact system was investigated to enhance light extraction of GaN-based light-emitting diodes (LEDs). Improvement in the light output of GaN-based blue LEDs as a function of the IZO film thickness was examined and an optimum thickness of around 300 nm has been found. Under an injection current in the 10−50 mA range, as compared to the case without IZO film, about 35−28% improvement in light output power (Lop) has been obtained. Comparisons of Lop and its reliability for LEDs with an IZO or indium–tin oxide transparent conduction layer were also made. In addition, compared to IZO/GaN samples without the patterned surface, the LEDs fabricated using a patterned IZO surface show a 23.1% improvement in Lop at 20 mA.

Improvement in Light-Output Power of InGaN∕GaN LED by Formation of Nanosize Cavities on p-GaN Surface

To improve the extraction efficiency of InGaN/GaN multiple quantum well light-emitting diodes LEDs , nanosize cavities werefabricated on a top p-GaN surface by inductively coupled plasma etching utilizing self-assembled platinum clusters as an etchmask. The relative output power was increased up to 88% compared to that of the LED without nanosize cavities. This result couldbe attributed to an enhancement in the escape of light due to the angular randomization by the nanosize cavities and to the reducedcontact resistance due to the increased contact area between the transparent metal layers and the p-GaN.© 2005 The Electrochemical Society. DOI: 10.1149/1.2076987 All rights reserved.Manuscript submitted April 25, 2005; revised manuscript received July 19, 2005. Available electronically October 7, 2005.

Performance enhancement of InGaN light-emitting diodes by laser lift-off and transfer from sapphire to copper substrate

Laser lift-off technique was employed to carry out transfer of prefabricated InGaN multiple-quantum-well light-emitting diodes (LEDs) from sapphire onto Cu substrate. Silver epoxy was used as the bonding material. Characterization results showed tremendous device improvements in terms of maximum allowable current, light output power, and reliability from the use of conductive Cu substrate. LEDs on Cu could withstand a maximum current of 530 mA before breakdown while those on sapphire could only withstand 350 mA. At 40 mA, light output power of LEDs on sapphire and Cu was 0.74 and 0.95 mW, respectively. In addition, reliability test at constant current of 300 mA showed improvement in light output power for LEDs on Cu whereas LEDs on sapphire suffered deterioration with time.

Novel High-Radiance Surface-Emitting Light Emitting Diode Structure with Circular 45° Corner Reflector and Microlens

A new type of light-emitting diode(LED) with a circular 45° corner reflector and microlens is proposed and fabricated. The improvement of light output power of the proposed LED structure is calculated and compared with that of the conventional surface-emitting LED type. A microlens is fabricated on LED using the UV curing method. The HBr–H3PO4–K2Cr2O7 chemical etchant is developed for fabricating the circular 45° corner reflector. The measured light-current curve of the proposed LED shows that, compared to conventional LEDs, the output power increases considerably at high current level and the linearity is significantly improved by the circular 45° corner reflector. From the spectra measurement, we can confirm that the proposed LED structure shows combined characteristics of both conventional surface- and edge-emitting LEDs.