Regrowth and annealing of In0.22Ga0.78As and GaAs quantum well graded-index separate confinement heterostructure lasers

We investigate the impact of two-step molecular beam epitaxy on the performance of GRINSCH lasers with In0.22Ga0.78As and GaAs quantum wells (QWs) in the active region. The buried regrown interface lies in the Al-containing optical waveguide section. The interface has been cleaned in situ prior to regrowth by hydrogen-assisted oxide desorption and re-evaporation of a sacrificial GaAs cap layer. Two-step epitaxy leaves the internal quantum efficiencies of the laser devices unchanged but increases the internal losses. The threshold current density increases for the lasers with GaAs QWs. whereas for those with In0.22Ga0.78As QWs it decreases by up to 35%. We attribute this to a thermal annealing during re-evaporation and find a similar behaviour for structures that have been treated with post-growth rapid thermal annealing.