OBSERVATION OF BISTABILITY IN GAAS QUANTUM-WELL VERTICAL-CAVITY SURFACE-EMITTING LASERS

Two different types of bistability in proton-implanted GaAs quantum-we ll (QW) vertical-cavity surface-emitting lasers (VCSEL's) have been ob served. The first type of bistability has a small hysteresis width (si milar to 50 mu A) in the light versus current and voltage versus curre nt characteristics. Light-induced large negative differential resistan ce, random fluctuations, and self-pulsations are observed at the switc hing point. The emission patterns show that the bistability occurs at a spatially localized area under the output facet that covers only a s mall fraction of the similar to 15-mu m-diameter aperture. The bistabi lity stems from spatially localized saturable absorption. The second t ype of bistability has a large hysteresis width (similar to 1 mu A) in the L-I characteristics and is observed well above the threshold curr ent. In this case, no observable bistable loop exists in the voltage v ersus current characteristics, and the bistability is associated with transverse mode-hopping.