Effect of Waveguide Structure for Suppression of Ripples in the Far-Field Pattern of a 405-nm InGaN-GaN Laser Diode

Abstract

This paper investigates the impact of the waveguide structure on ripples in the far-field pattern of a laser diode, 405-nm In$_{0.08}$Ga$_{0.92}$N/In$_{0.015}$Ga$_{0.085}$N grown on a sapphire substrate. The leakage of the transverse mode to an n-GaN buffer layer is found to induce ripples in the far field patterns perpendicular to the junction plane. We numerically computed the far-field patterns and the optical confinement factor of n-GaN waveguide layers of various thicknesses. An optimal thickness of the layer was derived from the numerical simulation, with a minor modification through measurements. Experiments showed remarkably smooth far-field patterns with a minimum ripple ratio of 4.2 \% are attainable using the proposed thicknesses of the n-Al$_{0.08}$Ga$_{0.92}$N/GaN cladding and the n-GaN waveguide layers