Index-Antiguiding in Narrow-Ridge GaN-Based Laser Diodes Investigated by Measurements of the Current-Dependent Gain and Index Spectra and by Self-Consistent Simulation

The threshold current density of narrow (1.5 μm) ridge-waveguide InGaN multi-quantum-well laser diodes and the shape of their lateral far-field patterns strongly depend on the etch depth of the ridge waveguide. Both effects can be attributed to strong index-antiguiding. The value of the antiguiding factor R = 10 is experimentally determined near threshold by measurements of the current-dependent gain and refractive index spectra. The device performances are simulated self-consistently, solving the Schrödinger-Poisson equations and the equations for charge transport and waveguiding. Assuming a carrier-induced index change that matches the experimentally determined antiguiding factor, both the measured high-threshold current and the shape of the far-field pattern of lasers with shallow ridges can be reproduced theoretically.