Takeshi Kawashima

GaN-based surface-emitting laser with two-dimensional photonic crystal acting as distributed-feedback grating and optical cladding

We demonstrate GaN-based distributed-feedback surface-emitting lasers grown on sapphire substrates with a two-dimensional (2D) square-lattice photonic crystal (PhC) that forms a high-aspect-ratio void array (void diameter: 65 nm and depth: 220 nm). The 2D PhC layer acts as both distributed-feedback grating and p-type optical cladding of a separate confinement heterostructure. To form the 2D PhC in the nitride semiconductor layers, we developed an embedding process that uses mass-transport phenomena. Crystallographic facets appeared on the inner walls of the embedded voids. Room-temperature lasing action was observed at 406.0 nm for a PhC lattice constant of 162.5 nm. The threshold current density was 9.7 kA/cm2 for a 120-μm-square p-contact electrode.

Fine Crystallographic Facets of Photonic Crystal Voids Embedded in GaN-Based Semiconductor by Mass Transport

We developed a technique for fabricating photonic crystal (PhC) voids embedded in GaN by dry etching, mass transport, and annealing. We report the annealing conditions and shape of the embedded PhC voids. After dry etching to pattern PhC air holes, they are fully capped with a flat GaN layer (34 nm thick) by annealing at 1025 °C. Inner void walls exhibit GaN crystallographic facets. Upon annealing at 900 °C, the air holes are not capped and instead become narrower with increasing annealing duration. Hence, both the shape and diameter can be controlled in the fabrication of PhC structures in GaN.

GaN-based distributed-feedback surface-emitting laser with embedded two-dimensional photonic crystal fabricated by mass-transport technique

We report on GaN-based distributed-feedback surface-emitting lasers on a sapphire substrate. Two-dimensional photonic crystal gratings in our device were embedded into GaN-based structures by mass-transport phenomena. We have observed room-temperature pulsed lasing at 406.0 nm.