T-shaped GaAs quantum-wire lasers and the exciton Mott transition

Abstract

T-shaped GaAs quantum-wire (T-wire) lasers fabricated by the cleaved-edgeovergrowth method with molecular beam epitaxy on the interface improved by agrowth-interrupt high-temperature anneal are measured to study the laser device physicsand fundamental many-body physics in clean one-dimensional (1D) systems. Acurrent-injection T-wire laser that has 20 periods of T-wires in the active regionand a 0.5 mm long cavity with high-reflection coatings shows a low thresholdcurrent of 0.27 mA at 30 K. The origin of the laser gain above the lasing threshold isstudied with the high-quality T-wire lasers by means of optical pumping. The lasingenergy is about 5 meV below the photoluminescence (PL) peak of free excitons,and is on the electron–hole (e–h) plasma PL band at a high e–h carrier density.The observed energy shift excludes the laser gain due to free excitons, and itsuggests a contribution from the e–h plasma instead. A systematic micro-PL studyreveals that the PL evolves with the e–h density from a sharp exciton peak, via abiexciton peak, to an e–h-plasma PL band. The data demonstrate an importantrole of biexcitons in the exciton Mott transition. Comparison with microscopictheories points out some problems in the picture of the exciton Mott transition.