Metallo-dielectric diamond and zinc-blende photonic crystals

Diamond and zinc-blende photonic crystals are studied both in the purely dielectric case and in the presence of small inclusions of a low absorbing metal. It is shown that small metal inclusions can have a dramatic effect on the photonic band structure. Several complete photonic band gaps (CPBG’s) can open in the spectrum, between the 2nd-3rd, 5th-6th, and 8th-9th bands. Unlike in the purely dielectric case, in the presence of small inclusions of a low absorbing metal the largest CPBG for a moderate dielectric constant (ε ≤ 10) turns out to be the 2nd-3rd CPBG. The 2nd-3rd CPBG is the most important CPBG, because it is the most stable against disorder. For a diamond and zinc-blende structure of nonoverlapping dielectric and metallodielectric spheres, a CPBG begins to decrease with an increasing dielectric contrast roughly at the point where another CPBG starts to open–a kind of gap competition. A CPBG can even shrink to zero when the dielectric contrast increases further. Metal inclusions have the biggest effect for the dielectric constant ε ∈ [2, 12], which is a typical dielectric constant at near infrared and in the visible for many materials, including semiconductors and polymers. It is shown that one can create a sizeable and robust 2nd-3rd CPBG at near infrared and visible wavelengths even for a photonic crystal which is composed of more than 97% low refractive index materials (n ≤ 1.45, i.e., that of silica glass or a polymer). In the case of silica spheres with a silver core, the 2nd-3rd CPBG opens for a metal-volume fraction fm ≈ 1.1% and has a gap width to midgap frequency ratio of 5% for fm ≈ 2.5%. Within the 2nd-3rd CPBG of 5%, absorption remains very small (≤ 2.6% once the CPBG is centered at a wavelength λ ≥ 750 nm), which should be tolerable in most practical applications. The metallo-dielectric structures display a scalinglike behavior, which makes it possible to scale the CPBG from microwaves down to the ultraviolet wavelengths. Aluminum, copper, and gold cores yield almost identical results, provided that sphere radius rs ≥ 250 nm. Present address: ESTEC/ESA, Electromagnetics Division, P.O. Box 299, NL-2200 AG Noordwijk, The Netherlands www.amolf.nl/research/photonic materials theory/moroz/moroz.html