Absorption at large reverse bias in monolithic GaN-based short-pulse-multi-section laser diodes

We demonstrate pulse periods from 0.13 to 10 ns of GaN-based ridge waveguide laser diodes with monolithically integrated absorbers in the regimes of relaxation oscillations and self-Q-switching as function of gain current and absorber voltage. We introduce a simple model for the self-Q-switching regime, describing the pulse period in terms of current injection and spontaneous emission (including Auger recombination), only. At reverse voltages larger than 35 V the modal absorption exceeds 500 cm(-1), which cannot be explained solely by transitions of bound states in the quantum wells. Calculations based on wavefunction overlap and quantum confined Stark effect (QCSE) predict a decrease of absorption at such large bias. In contrast, we show experimental findings, proving that the absorption further increases. Due to the strong tilt of the band profile in this regime, we take into account the Franz-Keldysh effect in the barriers and the waveguide and discuss its possible influence on the absorption, leading to an increased absorption at large reverse bias.