<title>Stimulated emission in quantum wires fabricated by cleaved edge overgrowth</title>

We have used the molecular beam growth technique we call cleaved edge overgrowth to fabricate highly efficient lasers, which operate in the 1D quantum limit. The active region of our laser consists of quantum wires that form at the T-shaped intersections of 7 nm wide GaAs quantum wells grown along the (001) and after an in situ cleave along the (110) crystal axis. These intersections are, in turn, embedded in a T-shaped dielectric waveguide, which confines the optical mode to the vicinity of the quantum wires. The precise control of the quantum wire dimensions achievable in this way allows the observation of stimulated optical emission from the lowest exciton state in optically pumped devices. The implied absence of band-gap renormalization effects suggests an enhanced stability of the exciton gas phase in 1D. This is consistent with the observed red-shift of the quantum wire photoluminescence signal with respect to the quantum well signal of about 17 meV which strongly exceeds the shift predicted by theory for free carrier transitions and indicates an enhancement of the 1D exciton binding energy by more than 50%.