Impact of the mesa etching profiles on the spectral hole burning effects in quantum dot lasers

We investigated the impact of mesa etching profiles on the emission spectra of In(Ga)As quantum dot ridge waveguide lasers grown by metal-organic chemical vapour deposition. The mesa etching was terminated: (i) well before the waveguide, (ii) directly at the waveguide, (iii) after the waveguide forming tilted sidewalls and (iv) after the waveguide forming vertical sidewalls. We found a dramatic impact of the etching profiles on the spectral intensity modulation of the longitudinal modes. The spectral hole burning effect due to the Fabry-Perot cavity resonances causes strong modulation of the lasing spectrum, if the etching profile is terminated at the waveguide, or when the mesa sidewalls are tilted. In addition, deep-etched-through mesas with vertical sidewalls demonstrate extra spectral features induced by the high Q-factor modes originating due to the total internal reflection at the vertical sidewalls. In contrast, no intensity modulation is found in the shallow mesa devices, due to the weak effective refractive index step. The present results indicate extended opportunities for the emission spectrum control characteristic of quantum dot lasers.