Photonic crystal light-emitting structures

Abstract

Design, fabrication, and optical characterization have been performed to study the light-emitting properties of photonic crystal slab structures, two-dimensional photonic crystals patterned in optically-thin slab waveguides with air or low-index claddings. InGaAsP/InP quantum wells emitting at 1.55 ㎛ are mainly employed as active material, and InGaAs/GaAs quantum dots are also used in some experiments. In this photonic crystal slab light-emitting structure, optically-pumped operation of high-efficiency light-emitting diodes and low-threshold lasers are demonstrated. The dispersion relations of photonic crystal slabs are calculated based on the plane-wave method, and the condition for a single guided mode operation is investigated. The calculation results are applied to the design of photonic crystal slabs. Two-types of photonic crystal slab structures are fabricated, a free-standing slab in air and an oxide-supported slab. In the fabrication of two-dimensional photonic crystal patterns, electron-beam lithography and chemically-assisted ion-beam etching technique are employed. Light extraction properties of uniform photonic crystal slabs are investigated varying cladding structures, lattice geometries, and active materials. Over 5 times light-extraction enhancement relative to an as-grown wafer is observed in InGaAsP quantum-well-based photonic crystal slab structures at room temperature. Under high pumping conditions, the contribution of surface recombination can be less than 20% in spite of large surface-to-volume ratio of photonic crystal patterns. By using InGaAs quantum dot active medium, very high extraction enhancement of ~30 is obtained at 78 K. This high extraction efficiency originates from the low carrier diffusion in quantum dots at low temperature and strong extraction capability of the photonic crystal slab. The photonic crystal slab single defect cavity formed in a square array of air holes is studied both experimentally and theoretically. Pul...