Experimental and theoretical study of substrate modes in (Al,In)GaN laser diodes

Abstract

In semiconductor laser diodes, high refractive index epitaxial layers can act as parasitic waveguides and cause severe losses to the mode propagating in the laser waveguide. For (Al,In)GaN laser diodes the parasitic modes are typically caused by the SiC or GaN substrate or buffer layers. Substrate modes have an impact on near-field and far-field of the waveguide mode, on laser threshold, and on gain spectra. We present scanning near-field measurements of the substrate mode and demonstrate that the period of the standing wave in the GaN substrate varies over a wide range and critically depends on the effective refractive index of the waveguide mode.