Effect of waveguide structure for suppression of ripples in the far-field pattern of a 405-nm InGaN-GaN Laser Diode

This paper investigates the impact of the waveguide structure on ripples in the far-field pattern of a laser diode, 405-nm In0.08Ga0.92N/In0.015Ga0.085N 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-Al0.08Ga0.92N/GaN cladding and the n-GaN waveguide layers