Lateral carrier confinement for ultralow threshold quantum dot VCSELs

Semiconductor laser diodes have continually shrunk in size, a trend driven by the desire for low threshold current, high modulation speed, and lateral mode control. Oxide-defined apertures have demonstrated improved performance by reducing optical losses and current spreading in VCSELs, but carrier losses due to lateral diffusion in the active layer remain uncontrolled. This leakage of carriers due to lateral diffusion is of a great problem for small lasers due to the large surface-to-volume ratio. Furthermore, carriers can diffuse in two dimensions in VCSELs, adding to the severity of the problem. Modeling of the carrier dynamics show that about half of injected carriers are lost through lateral diffusion for InGaAs/GaAs QW VCSELs 5 /spl mu/m in diameter; and at 2 /spl mu/m, more than 80% of the carriers laterally diffuse out of the active region. Thus, further miniaturization of lasers requires that we address the problem of lateral carrier leakage. We report that ground and second state lasing devices do exhibit threshold currents reduced by an amount predicted by numerical modeling.