Strained-layer InGaAs/GaAs/AlGaAs single quantum well lasers with high internal quantum efficiency

Low threshold current density strained-layer In0.2Ga0.8As/GaAs/AlGaAs single quantum well lasers, emitting at 980 nm, have been grown by molecular beam epitaxy. Contrary to what has been reported for broad-area lasers with pseudomorphic InGaAs active layers grown by metalorganic chemical vapor deposition, these layers exhibit a high internal quantum efficiency (∼90%). The maximum external differential quantum efficiency is 70%, limited by an anomalously high internal loss possibly caused by a large lateral spreading of the optical mode. In addition, experimental results supporting the theoretically predicted strain-induced reduction of the valence-band nonparabolicity and density of states are presented.