Low thermal-mass LEDs: size effect and limits

In this work, low thermal-mass LEDs (LTM-LEDs) were developed and demonstrated in flip-chip configuration, studying both experimentally and theoretically the enhanced electrical and optical characteristics and the limits. LTM-LED chips in 25 x 25 mu m(2), 50 x 50 mu m(2), 100 x 100 mu m(2) and 200 x 200 mu m(2) mesa sizes were fabricated and comparatively investigated. Here it was revealed that both the electrical and optical properties are improved by the decreasing chip size due to the reduced thermal mass. With a smaller chip size (from 200 mu m to 50 mu m), the device generally presents higher current density against the bias and higher power density against the current density. However, the 25 x 25 mu m(2) device behaves differently, limited by the fabrication margin limit of 10 mu m. The underneath mechanisms of these observations are uncovered, and furthermore, based on the device model, it is proven that for a specific flip-chip fabrication process, the ideal size for LTM-LEDs with optimal power density performance can be identified. (c) 2014 Optical Society of America