AlN/air distributed Bragg reflector by GaN sublimation from microcracks of AlN

We report the fabrication of a four-period AlN/air distributed Bragg reflector (DBR) by in-situ GaN sublimation from microcracks of AlN. The GaN/AlN multilayer structure was grown on a stripe-patterned and dot-patterned Si substrate, and subsequently annealed at 1200 degrees C in H-2 and NH3 atmosphere. Microcracks were observed on the surface and side face of the AlN/air DBRs. We achieved an AlN/air structure by the decomposition of GaN from the microcracks of AlN. Partially crack-free AlN layers were observed over a 5 x 5 um area in the c-plane of AIN/air DBRs. The root mean square (RMS) values of the surface and back surface of stripe-patterned AlN/air DBRs were 0.94 and 3.3 nm, respectively. The relative reflectivity was measured using a He-Cd laser (442 nm). In some areas, stripe-patterned and dot-patterned AlN/air DBRs showed a high reflectivity of 83.7% and 90.7%, respectively, at the wavelength of 442 nm. (c) 2012 Elsevier By. All rights reserved.