Hon-Yi Kuo

Current Spreading and Blocking Designs for Improving Light Output Power from the Vertical-Structured GaN-Based Light-Emitting Diodes

In this work, use of localized Ti deposition associated with a transparent indium-zinc-oxide (IZO) layer is proposed to serve as Schottky current blocking and current spreading layer, respectively. In addition, an inductively coupled plasma (ICP) mesa etching on the surface layer (n-GaN) of regular vertical-conducting metal-substrate GaN-based light-emitting diodes (VM-LEDs) is also proposed to further enhance current spreading of the device. Through a two-dimensional device simulator, the calculated results indicate that significant avoidance of the current-crowding effect under cathode contact pad could be obtained once the n-GaN layer etching depth and width, IZO thickness, and Schottky current blocking width have been optimized. In experiments, 1000 m 1000 m GaN-based blue LEDs with an ICP mesa etching of 250 m in width and 2 m in depth on the surface n-GaN layer, 200 m in Schottky current blocking width, and a 300-nm-thick IZO layer have the been successfully fabricated. As compared to the regular VM-LEDs without the use of the present technology, typical improvement in light emission uniformity and light output power by about 6% and 38% at an injection current of 350 mA have been obtained.

A Sn-based metal substrate technology for the fabrication of vertical-structured GaN-based light-emitting diodes

Through the use of tin (Sn) based solder balls and patterned laser lift-off technique, a metal substrate technology was proposed for the fabrication of vertical-structured metal substrate GaN-based light-emitting diodes (VM-LEDs). Advantages including reserving the merits of metallic substrate and simplifying the fabrication processes of vertical-structured GaN-based LEDs were demonstrated. As compared to conventional sapphire substrate GaN-based LEDs, the fabricated VM-LEDs with an emission area of 620×620μm2 show an increase in light output power about 145.36% at 350mA with a significant decrease in forward voltage from 4.51to3.46V.

Use of Elastic Conductive Adhesive as the Bonding Agent for the Fabrication of Vertical Structure GaN-Based LEDs on Flexible Metal Substrate

Through the use of elastic conductive adhesive (ECA) as the bonding agent and patterned laser lift-off technology, a flexible metal substrate technology for the fabrication of vertical structured GaN-based light-emitting diodes (flex-LEDs) was proposed and demonstrated. It showed that the flex-LEDs have negligible changes in dominant wavelength-current and light output intensity-current-voltage characteristics when subjected to an external bending stress, indicating that the ECA used in the present technology performed well as a buffer to external stresses. As compared with conventional sapphire substrate GaN-based LEDs, Flex-LEDs with a chip size of 600 x 600 mum2 showed an increase in light output intensity (power) about 216% (80%) at 120 mA with an essential decrease in forward voltage from 3.51 to 3.3 V.

Enhanced Performance of Vertical GaN-Based LEDs With Highly Reflective

Through the use of polystyrene nano-spheres as a 2-D mask for the patterned-deposition of indium-zinc-oxide (IZO) and annealed Pt-Al-Pt as a high reflectivity p -ohmic/mirror layer, vertical GaN-LEDs with atop periodic IZO nano-wells (NW-VLEDs) were fabricated. At 350 mA, NW-VLEDs exhibited a crucial VF reduction of 0.1 V with an enhancement of 87% in light output and 92% in power conversion efficiency as compared to regular vertical GaN-LEDs, which should be attributed to the combination of the effectiveness of high-reflectivity ohmic contact, IZO current spreading layer, and the enhanced light extraction efficiency from the periodic nano-wells.

P

In this work, a vertical-structured Ni/u-GaN (2 µm)/n-GaN (1.5 µm) Schottky barrier diodes (SBDs) employing an electroplating nickel substrate and laser lift-off processes is proposed and experimental results are reported. A metal system comprising a Ti/Al/Ti/Au mutilayer structure was used to form ohmic contact to n-GaN. A specific contact resistance as low as 6.64×10-5 Ωcm2 has been obtained after sample thermal annealing in Ar ambient at 800 °C for 30 s. A KOH etching to the u-GaN epilayer after the removal of sapphire was conducted and effect of KOH etching time on the device performance of the fabricated Schottky diodes was also investigated. Vertical-structured GaN SBDs with die size of 400×400 µm2 and Schottky contact area of 200 µm in diameter have been successfully fabricated. The extracted values of Schottky barrier height (ΦB), series resistance (Rs), and ideality factor (η) of the 60-s-KOH etched SBDs were 0.78 eV, 1.9 mΩ, and 1.06, respectively.

-ohmic Contact and Periodic Indium–Zinc–Oxide Nano-Wells

A dicing-free substrate technology was proposed and demonstrated to simplify the fabrication of vertical-structured metal substrate GaN-based light-emitting diodes (VM-LEDs) using a Sn-based solder screen printing technique with patterned laser lift-off technology. As compared with conventional sapphire substrate GaN-based LEDs, VM-LEDs with an effective emission area of 1000×1000 µm2 were found to have a 0.38 (0.87) V reduction in forward voltage at 350 (700) mA. In addition, their enhancement in light output power in the current range of 350–700 mA was found to successively increase from 55 to 76%. By considering these results, the power conversion efficiency of VM-LEDs was found to be 2.14 times that of regular LEDs at 700 mA.

A vertical-structured Ni/GaN schottky barrier diode using electroplating nickel substrate

A highly reflective ohmic contact and surface roughening by KrF excimer laser technique to improve the optoelectronic properties of high-power vertical metallic-substrate GaN-based light-emitting diodes (VM-LEDs) were proposed and investigated. A metal system comprising of Ni/Ag/Ni was employed to serve as a reflector and ohmic contact to p-GaN, which exhibits a good ohmic contact (3.05times10-4 Omega cm2) and high reflectivity (89% at the wavelength of 465 nm) after thermal annealing at 500degC in N2 ambient for 10 min. After the removal of sapphire using laser lift-off process (LLO), KrF excimer laser irradiation was adopted to etch the u-GaN layer and then roughen the surface of the exposed n-GaN layer. As compared to regular lateral-structure GaN-based LEDs with ITO transparent conduction layer (TCL), the fabricated VM-LEDs with a chip size of 1000 mumtimes1000 mum demonstrated a typical increase in light output power (Lop) (i. e., DeltaLop/Lop) by 325.5% at 350 mA with a decrease in forward voltage (Vf) from 3.67 V down to 3.41 V. As compared to the VM-LEDs with u-GaN etching employing inductively coupled plasma, about 125% enhancement in Lop has been obtained at 350 mA from the proposed samples.

A Screen-Printed Sn-Based Substrate Technology for the Fabrication of Vertical-Structured GaN-Based Light-Emitting Diodes

In the above titled paper (ibid., vol. 20, no. 7, pp. 523-525, 1 Apr 08), there were errors in Table I. The correct table is presented here.

Use of Highly Reflective Ohmic Contact and Surface KrF Laser Roughening to Improve Light Output of Vertical 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

Corrections to “Use of Elastic Conductive Adhesive as the Bonding Agent for the Fabrication of Vertical Structure GaN-Based LEDs on Flexible Metal Substrate” [1 Apr 08 523-525]

Jui-Chiang Chou, Chun-Wei Yao, Hong-Kuei Hsu, and Hon Kuan 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 Optoelectronics Semiconductor Center of Southern Taiwan Univ. of Technology, Tainan, Taiwan *Phone: +886-6-2757575-62351, Fax: +886-6-2763882, E-mail: sjwang@mail.ncku.edu.tw