Photonic technology, using light instead of electrons as the information carrier, is increasingly replacing electronics in communication and information management systems. Microscopic light manipulation, for this purpose, is achievable through photonic bandgap materials, a special class of photonic crystals in which three-dimensional, periodic dielectric constant variations controllably prohibit electromagnetic propagation throughout a specified frequency band. This can result in the localization of photons, thus providing a mechanism for controlling and inhibiting spontaneous light emission that can be exploited for photonic device fabrication. In fact, carefully engineered line defects could act as waveguides connecting photonic devices in all-optical microchips, and infiltration of the photonic material with suitable liquid crystals might produce photonic bandgap structures (and hence light-flow patterns) fully tunable by an externally applied voltage. However, the realization of this technology requires a strategy for the efficient synthesis of high-quality, large-scale photonic crystals with photonic bandgaps at micrometre and sub-micrometre wavelengths, and with rationally designed line and point defects for optical circuitry. Here we describe single crystals of silicon inverse opal with a complete three-dimensional photonic bandgap centred on 1.46 microm, produced by growing silicon inside the voids of an opal template of dose-packed silica spheres that are connected by small 'necks' formed during sintering, followed by removal of the silica template. The synthesis method is simple and inexpensive, yielding photonic crystals of pure silicon that are easily integrated with existing silicon-based microelectronics.

Germanium inverse opals with a full photonic bandgap in the NIR region are accessible by CVD. Deposition of digermane on sintered opals made of silica microspheres, followed by removal of the silica by etching, yields inverted Ge opals (see Figure for an SEM image of a cleaved edge, revealing the Ge layer) whose lattice parameters, network topology, and Ge coating thickness determine the optical properties of the inverse Ge opal.

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contaminants, and were obtained by combining AES with sequential ionbombardment until comparable compositions were obtained for consecutive data points.Layer thicknesses (used to calculate growth rate) were determined by llipsometry and from a calibrated scanning electron micrograph of cleaned amples. Double crystal X-ray diffraction was carried out using a Bede system iith a first crystal of silicon.The Me,AINH, adduct was synthesized by a modification of published lrocedure 1231. NH, was bubbled slowly through a solution of Me,Al (29.6 g, d.41 mol) in pentane (I00 cm3) which led to the precipitation of a white crystalline solid. Volatiles were removed by distillation in vacuo. The Me,AlNH, adduct (35.5 g, 0.40 mol) was subsequently, characterized by 'H NMR and ICP-ES.'H NMR(C6D6)b(ppm; -0.53 (singlet, 9H, AI(CH,),), -0.03 (singlet, 3H, NH3). ICP-ES; A l % expected 30.3; % found 30.6. The AIN films were deposited in a conventional horizontal MOVPE reactor using RF substrate heating. The Me,AINH, adduct source (estimated vapor pressure 0.5 Torr at room temperature) was maintained at 45°C and the reactor inlet lines were trace heated at > 60 "C to prevent adduct condensation. To compensate for the relatively low volatility of the adduct, both source and reactor were operated at low pressure. AIN deposition took place at 65 Torr while the bubbler containing the adduct was pressure controlled at 250 Torr. Palladium silver liffused hydrogen was used in precursor pick up (300 SCCM) and as a carrier Aas (8 llmin).Si(100) and sapphire(u-AI2O,) single crystal wafers were used as substrates. The Si(100) substrates were degreased whilst the sapphire substrates (Escete BV Holland) were supplied with epi-ready surfaces which were annealed for 10 min at 1000°C under hydrogen prior to film growth. Additional pre-treatment with a sulfuric acid/phosphorous acid mixture had little influence on the final epitaxial morphology.

Silicon is the “veteran” semiconductor in the management of electrons. The recent quest for optoelectronic and photonic materials suggests that new architectures of silicon structured over multiple length scales may still be the optimum material for the transition from electron‐based to photon‐basped computers and communication systems. This Research News article is focussed on recent research accomplishments in fabrication and self‐assembly methods of shaping elemental silicon over nanometer to micrometer length scales for applications in electronics, optoelectronics, and photonics.

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