Single-Mode Stimulated Emission in a Quantum-Wire Laser Fabricated by Cleaved-Edge Overgrowth

Abstract

We have used the molecular beam growth technique, we call Cleaved Edge Overgrowth to fabricate highly efficient lasers, which operate in the ID 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 interpretation that the observed quantum wire response is due to exciton recombination is based on the near spectral constancy of the emission over almost 3 orders of magnitude in excitation power from low power luminescence to a single mode lasing line. 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%.