Youn-joon Sung

Refractive sapphire microlenses fabricated by chlorine-based inductively coupled plasma etching.

We have fabricated refractive sapphire microlenses and characterized their properties for what we believe to be the first time. We use thermally reflown photoresist lenslet patterns as a mask for chlorine-based dry etch of sapphire. Pattern transfer to the mechanically hard and chemically inert sapphire substrate is made possible by an inductively coupled plasma etch system that supplies a high-density plasma gas. Processed sapphire microlenses exhibit properties close to the ideal and operate nearly in the diffraction limit.

Effect of GaN Microlens Array on Efficiency of GaN-Based Blue-Light-Emitting Diodes

In this study, GaN-based vertical light-emitting diodes (VLEDs) were fabricated by a laser lift-off (LLO) process and the effects of microlens formation by plasma etching on the optical properties of the LLO GaN-based VLED devices were investigated. By forming a 5–10 µm microlens array on the LLO GaN-based VLEDs, the measured light emission intensities at 460 nm and in the direction normal to the surface of the device increased by approximately 40% and 100% compared with those of the LLO GaN-based VLED without the microlens array for 10 µm and 5 µm microlens arrays, respectively.

Increase of output power and lifetime by improving the heat dissipation of GaN-based laser diodes

The enhanced output power with improved lifetime is required for the GaN-based blue-violet laser diode (LD) as a light source for Blu-ray Disc or HD-DVD. In this paper, the output power levels and aging behaviors in GaN-based LDs grown on sapphire substrates were compared in epi-up and epi-down bonding. At low current level, the two bondings show little differences in L-I characteristics. At high current level, however, the epi-up bonding shows a rapidly decreased slope efficiency in L-I characteristics with increasing current injection. On the contrary, the slope efficiency in epi-down bonding is not so much deteriorating as that in epi-up bonding. The differences in junction temperature between epi-up and epi-down bonding are large at higher current levels. The junction temperature of epi-up bonding is about two times higher than that of epi-down bonding, implying efficient heat dissipation in epi-down bonding. At aging test, the epi-down bonding LD shows lower degradation rate at the aging slope than that of epi-up bonding LD. The degradation rate is accelerated by poor heat dissipation in epi-up bonding. Thus, for the higher power and longer lifetime, it is necessary to employ efficient heat dissipation structures such as epi-down bonding for the GaN-based LD on sapphire substrate.