Bragg diffraction from indium phosphide infilled fcc silica colloidal crystals

Abstract

Here we present results on Bragg diffraction in the optical range from indium phosphide infilled solid face-centered-cubic silica colloidal crystals. Scanning electron microscopy and optical properties indicate that the semiconductor is homogeneously grown within the three-dimensional lattice of voids in the colloidal crystal. The photonic-crystal behavior of the periodic dielectric is enhanced as a result of the high contrast of dielectric constants when InP is introduced. ͓S0163-1829͑98͒02848-3͔Photonic crystals have attracted much attention since they were first proposed a decade ago. 1,2 These materials exhibit a periodic spatial modulation of the dielectric constant, which is responsible for the appearance of diffraction effects in a region of frequencies determined by the distances in which the modulation occurs. 3 Important technological applications have been proposed for such materials when designed to operate in the visible region of the spectrum. 4 In that direction, a great attention has been paid recently to the photonic crystal behavior of colloidal crystals. [5][6][7][8][9][10][11] These are made of submicrometric particles arranged in three-dimensional ͑3D͒ periodic structures in a medium of different dielectric constant, thus presenting Bragg diffraction effects in the optical region. However, in order to develop a technology based thereupon, some of their physical features have to be improved. A main point is that a dielectric constant contrast of 1 / 2 Ϸ16 is needed, 12 rather than 1 / 2 Ϸ2 that has been reached so far. Furthermore, a material with applications in photonics should be easy to handle, which will pose restrictions on its mechanical stability.We have studied the photonic crystal properties of InP infilled mechanically stabilized face-centered-cubic ͑fcc͒ colloidal crystals made of silica spheres ͑opals͒. Using metalorganic chemical-vapor deposition ͑MOCVD͒, we have grown InP ( Ϸ12) within the void lattice of the silica matrix. The homogeneous distribution of the high guest material in the low host achieved by this method gives rise to enhanced photonic crystal properties as has been proved by optical reflectance measurements. Bragg reflections in the visible and near infrared ͑NIR͒ region caused by the crystalline planes in the SiO 2 -InP composites are between 1.5 and 2 times more intense than those presented by the bare silica matrix. Different sphere-size colloidal crystals have been infilled, hence a systematic study of the variation of the optical properties vs the sphere size was possible. It showed that the optical region in which the photonic behavior is observed can be accurately tuned by controlling the sphere size of the matrix.Mechanically stabilized fcc silica colloidal crystals with the sphere diameter ranging from 200 to 550 nm were prepared following a recipe that has been previously described in detail. 9,13 As a result of the preparation process, the spheres are in contact and, therefore, the lattice constant of the samples is determined by the radius of the part...

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