Enhanced light extraction from free-standing InGaN/GaN light emitters using bio-inspired backside surface structuring

Light extraction from InGaN/GaN-based multiple-quantum-well (MQW) light emitters is enhanced using a simple, scalable, and reproducible method to create hexagonally close-packed conical nano- and micro-scale features on the backside outcoupling surface. Colloidal lithography via Langmuir-Blodgett dip-coating using silica masks (d = 170-2530 nm) and Cl2/N2-based plasma etching produced features with aspect ratios of 3:1 on devices grown on semipolar GaN substrates. InGaN/GaN MQW structures were optically pumped at 266 nm and light extraction enhancement was quantified using angle-resolved photoluminescence. A 4.8-fold overall enhancement in light extraction (9-fold at normal incidence) relative to a flat outcoupling surface was achieved using a feature pitch of 2530 nm. This performance is on par with current photoelectrochemical (PEC) nitrogen-face roughening methods, which positions the technique as a strong alternative for backside structuring of c-plane devices. Also, because colloidal lithography functions independently of GaN crystal orientation, it is applicable to semipolar and nonpolar GaN devices, for which PEC roughening is ineffective.

Pynn, C.D., Chan, L., Lora Gonzalez, F., Berry, A., Hwang, D., Wu, H., Margalith, T., Morse, D.E., Denbaars, S.P. and Gordon, M.J.
Optics Express
Volume: 25
Number: 14
Pages: 15778-15785
Date: July, 2017
ICB Affiliated Authors: Michael J Gordon