Tae-Kyung Yoo

Scribing blue LED wafer using laser-induced plasma-assisted ablation with a Q-switched Nd:YAG laser

Transparent materials, such as sapphire, are found to be scribed and cut freely by sparks form metal surface on which q-switched Nd:YAG laser beam is focused through the transparent materials. This method is successfully applied to split each device for a blue LED wafer including about ten thousands of blue LEDs grown on a sapphire wafer.

Scribing and cutting of sapphire wafer with Q-switched Nd:YAG laser

Transparent and hard materials such as sapphire are used for many industrial applications such as optical windows, hard materials on mechanical contact against abrasion, and buffer materials for semiconductor emitting device etc. Even the harder materials such as diamond are usually used to scribe and cut the materials to be used for various applications, while it has a problem of abrasion of the harder material itself and a problem of limit in shape of cut. The material is also known to be cut by the laser with very high peak power or with a wavelength possible to be easily absorbed in the material. But the lasers are usually accompanied with an economical problem of their high cost. We demonstrated, for the first time in my knowledge, that transparent materials can be scribed and cut freely by sparks induced by a Q-switched Nd:YAG laser beam focused on the metal surface.

Al free active region high power laser diode array on misoriented wafers

Nowadays, high power laser diodes are widely used in many applications due to their high wall plug efficiency, improved long-term reliability, and small size in addition to reductions in their cost. One of the main concerns in growth of InGaP/InGaAsP material systems using MOCVD is an indium carry over. It occurs when a relatively indium poor InGaAsP layer is grown on an InGaP layer. It is well known that the use of an intermediate layer such as GaP reduces the indium carry over. Also there has been a report that the use of an intermediate layer alone is not sufficient to suppress the indium carry over when a MOCVD system with large volume reactor is used. In this paper we present properties of 808 nm laser diodes grown on GaAs wafers having different misorientation angles. It is found that a reduction of indium carry over can be achieved by using misoriented GaAs wafers. This also leads to significantly improved L-I characteristics of lasers. The results are shown of room temperature photoluminescence measurements in InGaP/InGaAsP/InGaP single quantum well structures.

Development of high power laser diode

We have recently observed that laser diodes operate firmly with high power and long lifetime at room temperature. This high power laser diodes can be properly used for micro-heating, micro-welding, soldering, material processing, medical applications, and pumping solid state laser. In the study, we report several significant characteristics of Al-free laser diodes through packaging the chips produced at LG CIT. The active layer of the laser diodes consists of InGaAsP and the structure is gain-guided and single quantum well. Al-free laser diodes not having COD (catastrophic optical damage) caused from Al oxidation have longer lifetimes and less opportunities to make initial failure when compared to AlGaAs laser diodes. The width of experimental laser diodes is 1 cm, with cavity length 0.5 mm and thickness 120 /spl mu/m.

Device characteristics of index-guided In/sub x/Ga/sub 1-x/N/In/sub y/Ga/sub 1-y/N MQW laser diodes grown by low-pressure metal organic chemical vapor deposition

Device characteristics of index-guided In/sub x/Ga/sub 1-x/N/In/sub y/Ga/sub 1-y/N MQW laser diodes were investigated in terms of ridge depth and etching conditions. We report room temperature pulsed operation of In/sub x/Ga/sub 1-x/N/In/sub y/Ga/sub 1-y/N multiple quantum well (MQW) laser diodes with optimized ridge depth.

Variation of polarization tilt in GaInP/AlGaInP visible laser diodes

The dependence of polarization angle to the quantum well structural parameters and measurement conditions is investigated for GaInP/AlGaInP index-guided laser diodes. The laser diodes that have been studied are 635, 650 and 670 nm band laser diodes with strained quantum well active regions. It has been found that the polarization of radiation along (0 1 -1) direction varies by several degrees from ordinary TE/TM mode determined by the growth direction. The polarization tilt varies with respect to the strain and misorientation of the substrates. The polarization tilt seems to result from the birefringence in the asymmetric crystal structure induced by the strain of GaInP quantum well and the substrate misorientation toward [0 1 1].