Comparison of chip size effects of thin film GaN-based μLEDs fabricated by plasma etching and ion implantation processing

Abstract

We investigated the effects of chip size and N-polar n-GaN surface roughening on the performance of conventional thin-film blue-light micro-light-emitting diodes (TFFC μLEDs) and As⁺ ion isolated TFFC blue μLEDs. For this, TFFC μLEDs with two different sizes of 10 × 10 μm² and 25 × 25 μm² pixel array were fabricated. In all samples, N-face n-GaN surfaces were etched using a 4 M KOH solution after laser lift-off (LLO) process. A 2 min-etching resulted in the formation of pyramids (size: ∼90 – ∼270 nm), while the 4 min-etching produces pyramids (∼370 – ∼780 nm). Regardless of treatments, all samples exhibit similar forward bias characteristics. For all samples, the light output power increased after n-GaN surface roughening. Before the LLO process, the 10 μm-μLEDs showed higher EQE than the other samples with the implanted μLEDs showing the lowest EQE. All samples exhibited their highest EQE after optimal 4-min etching. Unlike before LLO, after 4 min-etching, the 10 μm- and 25 μm-μLEDs show almost similar EQEs, while the implanted μLEDs reveal a slightly lower EQE than the mesa μLEDs, but produce up to 74 % EQE improvement. Furthermore, the 10 μm-μLEDs showed the shortest photoluminescence (PL) decay, while the 25 μm-μLEDs gave the longest PL decay. The 10 μm μLEDs showed the highest ideality factor and the As⁺ ion-implanted μLEDs gave the lowest value. Based on time resolved PL and ideality factor, the size and etching time dependence of the EQE characteristics of all samples are described and discussed.