Reduced dislocation densities in selectively-grown GaN layers enable novel optical waveguide structures for transverse-mode stabilization

Current research on nitride-based materials is rapidly improving the performance of electronic and photonic devices. A very recent development makes it possible to operate nitride-based laser diodes under CW current injection at room temperature. However, the operating current density and device lifetime are still not good enough to satisfy the requirements of optical systems, so further advances in layered crystals and device structures are needed to overcome the problems associated with nitride devices. One of the biggest problems is the high density of the dislocations which can reach 10⁸ to 10¹⁰ cm^-2 that occur even with a carefully designed crystal-growth technique. Reducing high density of crystal defects will lower the light scattering loss in optical waveguides, thus further improving their lasing characteristics. This work describes how the crystal-defect density of nitride layers can be reduced by using a selective-growth technique. We found that the dislocation density in a GaN layer formed by the lateral growth mode was drastically decreased and measured by TEM observation