We modeled the two dimensional photonic crystal consisting of air cylinders in silicon background by using plane wave expansion method. In this particular structure, the absolute band gap can be tuned only in a small range of normalized radii (0.404-0.48). Within this range, the band gap changes rapidly with the air cylinder radius due to the high dielectric constant of silicon. In addition, we modeled the structures with interfacial layers of Al{sub}2O{sub}3 and SiO{sub}2 deposited by atomic layer deposition (ALD). As the thickness of the deposited layer varies from 0 to 0.05a (a=lattice constant), the band gap changes respectively by 3.7% and 2.5% for Al{sub}2O{sub}3 and SiO{sub}2. For a photonic crystal of lattice constant 400nm, the interfacial layer thickness is equivalent to 20nm, which is well within the scale that can be accurately controlled by ALD. Therefore, fine tuning of photonic band gap can be achieved by ALD.
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