Negative photoresist micro-lens for enhancing fiber-coupled InGaAs/AlGaAs MQW LED performance

The feasibility of using DNR-L300 negative photoresist to fabricate the micro-lens on InGaAs/AlGaAs MQW LED for enhancing the fiber-coupled LED performance was studied in this report. The measurement results indicate that the transmittance of DNR-L300 photoresist can reach nearly 90 percent and remains unchanged as long as the wavelength is longer than 800 nm. Thus, the infrared light-emitting diode with an emission wavelength peak at 917 nm is adopted for this study. By controlling developing time and melting process, the lens diameter and height were characterized via Dektak profilometer and optical microscope so as to obtain the optimum condition for forming micro lenses. The experiment results show that the micro-lens thickness as high as ~25μm could be achieved by performing the melting temperature at 200 °C for 10 minutes after the photolithographic process. In addition, by using such a thick micro-lens fabricated from negative photoresist, more than 30% increase of fiber - coupled LED output intensity could be obtained as compared with those without having micro-lens. More details of the experimental results will be revealed and discussed in this report.