Gain saturation and carrier distribution effects in molecular beam epitaxy grown GaAsSb/GaAs quantum well lasers

GaAsSbGaAs quantum well (QW) lasers grown by solid source molecular beam epitaxy are fabricated into ridge lasers and tested. These devices have a lasing wavelength around 1.2 μm that is substantially blueshifted relative to the electroluminescence peak. The magnitude of the blueshift increases as the cavity length is shortened, indicating that the blueshift increases with injection level. This blueshift is attributed to material gain saturation and band filling effects. The internal quantum efficiency is ∼75%, the transparency current density is ∼120 A cm2, and the threshold characteristic temperature is ∼60 K, all typical for GaAsSbGaAs based edge emitting lasers. The extracted gain constant is ∼800 cm-1 for single QW active regions and approximately half that amount for double QWs. This discrepancy is attributed to nonuniform carrier distribution in double QW structures.