Enhancement of light extraction efficiency of AlGaInP-based light emitting diodes by silicon oxide hemisphere array

Abstract

Surface texturing has been demonstrated to be very effective in improving the extraction efficiency of light emitting diodes (LEDs). In this paper, high-brightness AlGaInP-based vertical LEDs (VLEDs) with nanoscale silicon oxide (SiO2) hemisphere array were successfully fabricated by photoresist thermal reflux technique and laser interference exposure. It is the first time to combine interferential lithography and thermal reflux technique to make a regular nanoscale hemisphere array to enhance LEE for LEDs Compared to LEDs with microscale SiO2 hemisphere array, with planar SiO2 and without SiO2, electroluminescent measurements show that four LEDs have a similar threshold voltage. Simultaneously, the light output power (LOP) of LEDs with nanoscale and microscale SiO2 hemisphere array has been improved up to 40% and 20% at 200 mA, respectively, in comparison to LEDs without SiO2. It fits the simulated results well, which were obtained by the finite-difference time-domain (FDTD) method. Furthermore, it is demonstrated that more light emits out in the direction perpendicular to the epitaxial wafer by angle-resolved EL spectra for LEDs with nanoscale SiO2 hemisphere array, which accords to the simulated optical field distribution images. This kind of high-brightness LEDs with nanoscale SiO2 hemisphere array will have promising applications in meeting different requirements in special situations, such as headlights, flashlights. The new method is capable of fabricating large-scale nanostructured materials with good controllability and low cost, which will be widely used in improving properties of all kinds of LEDs, especially Mini LEDs and Micro LEDs.