Vertical-cavity surface-emitting lasers with lateral carrier confinement

Introduction: Optics is a viable solution to address the limitations of copper-based electronics in short-distance interconnects [1]. In these compact systems, devices must meet the stringent requirements imposed by the power budget and the thermal restriction. Recently, VCSELs have received considerable interest for board and chip level interconnects owing to their small footprints, ease of fabrication in arrays, and high-speed operation at low power dissipation. Smaller VCSELs are even more favourable in terms of speed and power consumption. However, as the dimension of VCSELs scales down, threshold currents do not scale accordingly owing to optical diffraction loss [2], current spreading [3], and carrier diffusion [4]. Optical diffraction loss can be reduced using tapered oxide aperture [2], and current spreading can be eliminated by placing the aperture close to the active region. Once carriers enter the quantum wells (QWs), the large lateral concentration gradient drives carriers to diffuse outwards and, consequently, a significant portion of the current does not provide useful gain to the optical modes and is dissipated as heat. To alleviate the problem, carriers must be confined laterally inside the QWs. In this Letter, we report a new VCSEL-compatible quantum well intermixing (QWI) process to achieve lateral carrier confinement. Using a sacrificial silicon-doped InGaP layer, we were able to selectively intermix InGaAs QWs for 980 nm VCSELs and our smallest 1 mm diameter device shows 40% reduction of threshold with the implementation of lateral carrier confinement.