Obvious improvement of light extraction obtained by anodic aluminum oxide coverage on GaN surface

Anodic aluminum oxide (AAO) films with different porosities were fabricated on the surfaces of InGaN/GaN multiple quantum wells (MQWs). We measured the photoluminescence spectra of these samples and then calculated the light extraction enhancement factors (E). It was found that the light extraction of the MQWs with the AAO films has been greatly enhanced compared to the area without AAO coverage. The maximum value of E reaches 3.5 at a certain wavelength and 2.29 in the integral intensity. The increase of E with the decrease of the porosities demonstrates that the nano-hole structure in the AAO films plays an important role in enhancing the light extraction efficiency.