Impact of porosity on the structural and optoelectronic properties of nanoporous GaN double layer fabricated via combined electrochemical and photoelectrochemical etching

Nanoporous GaN double layer structures with porosity ranging from 10% to 60% are fabricated via a combined electrochemical etching and photoelectrochemical etching process. The porosity as well as the variation in the size and shape of the nanopores are controlled by regulating the applied voltage in the etching process. With the increase in the porosity, the biaxial stress and reflectance index of the nanoporous GaN double layer decrease from 0.74 GPa and 2.4 to 0.42 GPa and 2.0, respectively. Furthermore, the photoluminescence intensity of the InGaN/GaN multi-quantum wells grown on the nanoporous GaN is approximately three times higher than that on the as-grown reference GaN. The enhanced photoluminescence intensity can be attributed to the porosity controlled through the incorporated nanopores, which increase the light extraction efficiency. The light generated in the active layer is further extracted due to scattering by the nanopores.