ENHANCEMENT OF OPTICAL GAIN OF SEMICONDUCTORS EMBEDDED IN 3-DIMENSIONAL PHOTONIC CRYSTALS

The three-dimensional photonic crystals used in this study were synthe tic opals, composed of submicron silica spheres, close-packed in a fac e-centered cubic structure with a period of 200 nm, that exhibit photo nic stopbands around 600 nm. We present measurements of the optical ga in of CdS quantum dots (QDs) embedded inside the interstitials between the silica spheres, Unlike the usual gain spectra of CdS QDs in glass matrices, which display maximum gain at energies of the first quantum -confined transitions, for QDs embedded in photonic crystals the gain maximum is shifted toward the high-frequency edge of the photonic stop band (2.2 eV) far below the absorption edge of the semiconductor (2.5 eV). Studies of temperature, intensity, and orientation dependencies o f the gain spectra allow one to ascribe the observed effect to gain en hancement caused by multiple coherent Bragg scattering of light in the periodic photonic crystal. (C) 1997 American Institute of Physics.