Lateral carrier confinement in miniature lasers using quantum dots

Although quantum-dot (QD) lasers are yet to reach their promise of ultralow threshold and high characteristic temperature because of QD size nonuniformity, we have found that they can be used to effectively limit the lateral diffusion of carriers in the active region, enabling the scaling of lasers to small lateral dimensions. Although oxide apertures continue to enable improved performance in vertical-cavity surface-emitting lasers (VCSEL's) by reducing optical losses and current spreading, lateral carrier losses remain uncontrolled. We investigate QD active material in which lateral diffusion is intentionally reduced. Cathodoluminescence (CL) results demonstrate reduced lateral diffusion in the material with which we expect 50% reduction in the threshold current for 1-mu m-wide edge-emitters or 5-mu m-diameter VCSEL's. We have made QD stripe lasers with submicrometer widths that lase from the ground state and have quantified the lateral carrier reduction in the QD laser active region. We show empirically that the degree of lateral carrier confinement is dependent on the quantum state from which lasing occurs and demonstrate 63% reduction in lateral carrier leakage for the ground-state lasers, Finally, the scaling of threshold current in QD VCSEL's is compared with that of quantum-well (QW) VCSEL's by numerical modeling for future design considerations.