Nanofabrication techniques for lasers with two-dimensional photonic crystal mirrors

The fabrication of photonic crystals (PC) involves a periodic modulation of the refractive index on nanometer scales thus requiring state-of-the-art patterning and dry etch technologies. In this article, we compare three different mask techniques for the fabrication of ridge waveguide lasers with two-dimensional triangular PC mirrors. After defining the hole pattern in 500 nm polymethylmetacrylate by 100 kV e-beam lithography the structure is transferred to the mask layer. The first mask layer is a metal mask consisting of Ti/Cr/Ti. The second one is formed by wet chemical oxidation of a buried 60 nm AlAs layer and the third one uses a single ${\mathrm{SiO}}_{\mathrm{2}}$ layer in order to transfer the hole pattern into the semiconductor. The periods of the PC, with an average air filling factor of 45%, were chosen in the range of 160–400 nm in order to probe the region where high reflectivity of the PC is expected. The observed laser performance is used to deduce information about the quality of the fabricated PCs. The advantages of each technique are discussed, leading to conclusions for future techniques for the fabrication process of photonic crystals.