Seung Wan Chae

Improvement of the luminous intensity of light-emitting diodes by using highly transparent Ag-indium tin oxide p-type ohmic contacts

We have investigated Ag-indium tin oxide (ITO) scheme for obtaining high-quality p-type ohmic contacts for GaN-based light-emitting diodes (LEDs). The Ag(1 nm)-ITO(200 nm) contacts exhibit greatly improved electrical characteristics when annealed at temperatures in the range 400/spl deg/C-600/spl deg/C for 1 min in air, yielding specific contact resistances of /spl sim/10/sup -4/ /spl Omega//spl middot/cm/sup 2/. In addition, the contacts give transmittance of about 96% at 460 nm, which is far better than that of the conventionally used oxidized Ni-Au contacts. It is shown that the luminous intensity of blue LEDs fabricated with the Ag-ITO contacts is about three times higher than that of LEDs with oxidized Ni-Au contacts. This result strongly indicates that the Ag-ITO scheme can serve as a highly promising p-type ohmic contact for the realization of high brightness near ultraviolet LEDs.

Highly transparent and low-resistant ZnNi/indium tin oxide Ohmic contact on p-type GaN

The authors report the improvement of GaN light-emitting diodes (LEDs) by applying a ZnNi/indium tin oxide (ITO) (5nm∕380nm) electrode with high transparency and low resistance to p-GaN. The Pt/ITO (5nm∕380nm), Ni∕Au∕ITO (2.5nm∕5nm∕380nm), and Ni∕Au (2.5nm∕5nm) electrodes were prepared and annealed at 400, 500, and 600°C for 1min in air. The ZnNi/ITO contacts showed the lowest specific contact resistance of ∼1.27×10−4Ωcm2 and the highest transmittance of ∼90% at 460nm. LEDs fabricated with ZnNi/ITO p electrodes showed the best performance with a forward voltage of 3.28V and a typical brightness of 11. 7mcd at 20mA.

High-temperature electro-optical degradation of DC-Aged InGaN based high power GaN LEDs

Failure mechanisms in high brightness III-nitride-based light-emitting diodes (LEDs) and lasers, emitting in the visible and ultraviolet wavelength range, are extensively studied for their influence on device lifetime and reliability. The conventional chip structures have very good optical parameter and excellent long-term stability. However, many companies have released their chips for operation below 200˚C only [1, 2].

Low-resistance and high-reflectivity Al based reflectors for p-GaN flip process

We report a high-power light-emitting diode (LED) scheme based on aluminum (Al) reflector, commonly used as an n-GaN ohmic contact. The Cu doped In2O3 (5nm)/ITO (380nm) interlayer was deposited by electron beam evaporator and subsequently annealed at 500°C After annealing, we sputtered Al (400nm thick)/Ti-W (30nm) on the ITO interlayer to reflect the visible light. From the systematic experiment and the following analyses with InGaN/GaN multiple- quantum-well (MQW) LEDs, the reflectance of electrode based Al was measured to be ~ 90% at a wavelength of 450nm, which is higher than that of the common used Ni/Ag/Pt scheme. The forward- bias voltages of CIO/ITO/Al/Ti-W pelectrodes were as low as 3.2-3.3V. Furthermore, Al reflector showed higher thermal stability and lower leakage currents than those of typical Ag reflector, in which the mean leakage current of Ni/Ag and CIO/ITO/Al/Ti-W contacts were estimated to be 0.54, 0.12uA at an injection current of -5V, respectively.