D. M. Kuo

Enhanced Performance of GaN-Based Vertical Light-Emitting Diodes with Circular Protrusions Surmounted by Hexagonal Cones and Indium–Zinc Oxide Current Spreading Layer

The performance of vertically structured GaN-based light-emitting diodes (VLEDs) with an efficient surface roughening scheme that uses KrF laser irradiation, chemical wet etching, and an indium–zinc oxide (IZO) transparent conductive layer atop the n-GaN surface is investigated. The GaN surface, with circular protrusions and hexagonal cones, gives photons multiple opportunities to find escape cones, and the IZO film acts as a current spreading layer. The fabricated VLEDs with the proposed surface roughening scheme exhibited 79.3 and 65.1% increases in light output power at 350 and 750 mA, respectively, and showed a relatively low forward voltage compared to that of regular VLEDs.

Enhanced Light Output of Vertical-Structured GaN-Based Light-Emitting Diodes with TiO2/SiO2 Reflector and Roughened GaOx Surface Film

GaN-based thin-film vertical-structured light-emitting diodes (VLEDs) with a GaOx film atop an n-GaN layer roughened via KrF laser irradiation and a TiO2/SiO2 distributed Bragg reflector (DBR) are proposed and investigated. As compared with regular VLEDs with an Al reflector and without a roughened GaOx film, the proposed VLEDs with a chip size of 1 mm2 show a typical increase in light output power by 68% at 350 mA and by 51% at 750 mA, which is attributed to the enhanced reflectivity and current blocking capability of the DBR layer, the surface roughening with circular GaN protrusions, and the formation of a surface GaOx film by KrF laser irradiation.

Enhanced Light Output of AlGaInP Light Emitting Diodes Using an Indium--Zinc Oxide Transparent Conduction Layer and Electroplated Metal Substrate

The use of indium–zinc oxide (IZO) as a transparent conduction layer (TCL) for electroplated nickel metal substrate AlGaInP light-emitting diodes with a 300×300 µm2 chip size was investigated with regard to both fabrication and effectiveness in improving light extraction efficiency. A metal system consisting of AuGe/Au was deposited to form ohmic contact dots for the n+-GaAs layer, and then an IZO film was deposited to serve as a TCL. Compared with conventional light emitting diodes (LEDs) with GaAs substrates, the proposed LEDs show an increase in light output power (i.e., ΔLop/Lop) by 116.7% at 20 mA and 168.9% at 100 mA.

Enhanced Light Output of Vertical GaN-Based LEDs with Surface Roughening Using Sizu-Controllable SiO 2 Nanotube Arrays

Surface Roughening Using Size-Controllable SiO2 Nanotube Arrays Der-Ming Kuo, Shui-Jinn Wang, Kai-Ming Uang, Tron-Min Chen, Wei-Chi Lee, and Pei-Ren Wang Institute of Microelectronics, Dept. of Electrical Eng., National Cheng Kung Univ., Tainan, Taiwan Department of Electrical Engineering, WuFeng Institute of Technology, Chia-yi, Taiwan *Phone: +886-6-2757575-62351, Fax: +886-6-2763882, E-mail: sjwang@mail.ncku.edu.tw

The Preparation of SiO 2 Nanotubes with Controllable inner/outer Diameter and Length using Hydrothermally Grown ZnO Nanowires

Diameter and Length using Hydrothermally Grown ZnO Nanowires Der-Ming Kuo, Shui-Jinn Wang, Kai-Ming Uang, Wei-Chih Tsai, Wen-I Hsu, Wei-Chi Lee, Pei-Ren Wang, Chih-Ren Tseng Institute of Microelectronics, Dept. of Electrical Eng., National Cheng Kung Univ., Tainan, Taiwan Department of Electrical Engineering, WuFeng Institute of Technology, Chia-yi, Taiwan *Phone: +886-6-2757575-62351, Fax: +886-6-2763882, E-mail: sjwang@mail.ncku.edu.tw

A Screen Printed Sn-based Dicing-Free Metal Substrate Technology for the Fabrication of Vertical-Structured GaN-based Light-Emitting Diodes

A Screen Printed Sn-Based Dicing-Free Metal Substrate Technology for the Fabrication of Vertical-Structured GaN-Based Light-Emitting Diodes Pei-Ren Wang , Po-Hung Wang, Hon-Yi Kuo, Kai-Ming Uang, Tron-Min Chen, Der-Ming Kuo, and Shui-Jinn Wang Institute of Microelectronics, Dept. of Electrical Eng., National Cheng Kung Univ., Tainan, Taiwan Dept. of Electrical Eng., Wu Feng Institute of Technology, Chia-yi, Taiwan *Phone: +886-6-2757575-62351, Fax: +886-6-2763882, E-mail: sjwang@mail.ncku.edu.tw

Use of Current-Blocking Layer to Enhance Performance of Vertical GaN-Based Light-Emitting Diodes with a Ni-Plating Substrate

A great progress in display technology and solid-state lighting sources has been made by the use of GaN-based light-emitting diodes (LEDs) [1-2]. Above all, the improvement in efficiency and light power is important features for LEDs to promote the new era applications in photonics. Nevertheless, current spreading is still an imperative challenge for GaN-based LEDs due to p-GaN layer of relatively lower doping concentration and lateral-conducting structure using insulated sapphire. To alleviate the current crowding effect (CCE) and/or enhance the external quantum efficiency of conventionally lateral GaN-LEDs, efforts have been made by means of flip-chip technique [1], vertical conducting structure [3], or surface texturing [4], etc. Recently, the authors’ group has developed Vertical-structure Metallic-substrate GaN-based Light-Emitting Diodes named as VM-LEDs [5-6], as shown in Fig. 1(a). Such an n-side-up vertical structure shows a significant alleviation for thermal and CCE of lateral LEDs. However, a substantial increase in efficiency must be achieved for competing with conventional lighting sources. Furthermore, a portion of injected carriers will be confined under the contact pad owing to its shortest current path. Accordingly, a considerable amount of generated light will be absorbed or reflected by the opaque metal pad. To solve this problem, a selective activation of p-GaN layer [7] or an insulating SiO2 current blocking layer (CBL) [8] under the p-pad electrode was adopted for the lateral-conducting GaN-based LEDs. To further enhance the light output of regular VM-LEDs, we developed a CBL scheme for vertical GaN-based LEDs. In this work, the VM-LEDs with SiO2 film as a CBL were fabricated by patterned LLO and Ni-plating technologies. The effectiveness of the CBL for vertical-structured GaN LEDs was also simulated and examined.