Facet roughness analysis for InGaN/GaN lasers with cleaved facets

Abstract

Atomic force microscope images reveal a root-mean-square roughness Δd=16 nm for InGaN/GaN double-heterostructure laser structures with cleaved a-plane facets. The c-plane sapphire substrate cleaves cleanly along both the a and m planes. A theoretical model is developed which shows that the power reflectivity of the facets decreases with roughness by a factor of e−16π2(nΔd/λ0)2, where n is the refractive index of the semiconductor and λ0 is the emission wavelength. Laser emission from the optically pumped cavities shows a TE/TM ratio of 100, an increase in differential quantum efficiency by a factor of 34 above threshold, and an emission line narrowing to 13.5 meV.