Three-dimensional macroporous silicon photonic crystal with large photonic band gap

Abstract

Three-dimensional (3D) photonic crystals with 3D complete photonic band gaps exhibit interesting optical properties. First they promise to allow the inhibition of spontaneous emission 1-4 for light frequencies within the gap. Moreover, the 3D confinement of light at defects eliminates scattering losses and can therefore lead to high Q microresonators and efficient photonic crystal waveguides. Indeed 3D photonic crystals have been fabricated and are known as Yablonovites, 5,6 Lincoln log structures, 7,8 or self-ordered inverse opals.9 However, the fabrication of structures with band gaps in the near infrared or visible spectral region is difficult (Yablonovite), tedious (Lincoln log), or the structures suffer from disorder (self-ordered opals). This limits the sizes of perfect structures to a few lattice constants. To achieve a more extended Yablonovite-like 3D photonic crystal Lourtioz et al.10,11 used a combination of photoelectrochemical macropore etching in silicon and subsequent drilling of two pore sets with a focused ion beam (FIB). The FIB drilling of the etched macroporous silicon is faster than of bulk material and the problem of redeposition of milled material is minimized at the same time. We apply this technique to fabricate an alternative 3D photonic crystal structure recently proposed by Hillebrand et al., 12 which consists only of two orthogonal interpenetrating pore sets in a high index material (Fig. 1). Each pore set of our structure consists of a pattern of two-dimensional (2D) hexagonally arranged pores forming a 3D structure of orthorhombic symmetry with the primitive lattice vectors a = ͑1 0 0͒, b = ͑1/2 ͱ 3/2 1/2͒, andThe resulting first Brillouin zone resembles the slightly distorted Brillouin zone of a fcc lattice (Fig. 2(a)). We performed band-structure calculations using silicon with a refractive index of 3.5 as the matrix material applying the MPB program developed by Johnson. 13 When the ratio of the pore radius r to lattice constant a of both pore sets is r / a = 0.38, a maximum complete 3D photonic band gap of ⌬ / center = 25.1% is obtained (Fig. 2(b)). The gap appears at low normalized frequencies in the band structure between the second and third bands and should therefore be insensitive to modest disorder.We realized the described structure by first creating a 2D hexagonal pattern of etch pits applying a KOH solution on the (100) surface of an n-type silicon wafer. The position of the etch pits and the lattice constant of a = 500 nm were lithographically defined. Afterwards the structured side of the wafer was immersed in hydrofluoric acid and a photoelectrochemical etch process 14 was used to create 50-m-deep macropores in the silicon wafer starting at the etch pits. The radius of the photoelectrochemically etched pores r etch = 190 nm was determined by the etch current. This pore pattern already forms a 2D photonic crystal 15-17 and the characteristic 2D band gaps were observed in reflection measurements confirming the given structure parameters a and r etch . The structure ...

Ultrafast optical switching of photonic crystals

“…Much better control over both the structure and the filling fraction can be obtained in samples that are made by etching of single crystalline materials, whose nonlinear optical properties are known from z-scan measurements (see Appendix C). Three-dimensional photonic crystals can then be fabricated by etching away material from a single crystalline wafer by combining electro-chemical etching with focussed ion beam milling [52], or by a two-step focused ion beam milling experiment [53]. An example of a GaP photonic crystal made by focussed ion beam milling is shown in Fig.…”

“…Direct laser writing in photoresist [48,49] or in high refractive index chalcogenide glasses [50] allows for the fabrication of defects inside three dimensional photonic crystals. Furthermore, three dimensional photonic crystals were fabricated by a two-step etching process [51,52] or by focused ion beam milling [53], which allows the fabrication of crystals with a diamond symmetry single crystalline wafers, see Fig. 1.3D.…”

Introducing Defects in 3D Photonic Crystals: State of the Art

“…First, the introduction of arbitrarily shaped defects presents an unresolved problem. Second, structures created this way show at best a very narrow cPBG [40] unless the process is combined with focused-ion-beam milling of channels, [41] which significantly reduces the simplicity of this method. …”

Field Emission Scanning Electron Microscopy (FESEM) characterisation of the porous silica nanoparticulate structure of marine diatoms

“…Biological nanomaterials have been mainly used in manufacturing products due to their movable synthetic ratio, green and renewable situation, complex arrangements, and natural enhanced functions [1,2]. Diatoms are unicellular photosynthetic algae with exoskeletons, called as frustules which consist of amorphous hydrated silica valves, self-assembled with highly organised pore arrangements [3].…”