Two-dimensional photonic crystal laser mirrors
Ridge waveguide lasers with an integrated 2D photonic crystal (PC) mirror have been successfully fabricated on an InGaAs/AlGaAs laser structure emitting around 995 nm. The investigated 2D PCs consist of air holes in a semiconductor arranged in a triangular lattice with periods from a = 180 to 400 nm with different lattice orientations. This is fabricated using high-resolution 100 kV electron beam lithography in connection with a triple-metal-layer mask and electron cyclotron resonance dry etching, yielding etch depths around 550 nm. The capability of this fabrication technology for semiconductor feature sizes down to 30 nm is demonstrated. The performance of the lasers with a PC mirror with respect to both laser threshold and differential efficiency clearly depends on the period and orientation of the PC lattice. This behaviour can be understood using simulations of the PC reflectivity based on 2D transfer matrix methods and finite-element analysis of the waveguide properties. The feedback from the PC mirror is confirmed using Fourier transform reflectometry analysis of a sub-threshold laser spectrum.