Band Gap Tuning of Macro-Porous Si Photonic Crystals by Thermally Grown SiO2 Interfacial Layer

By plane wave expansion method (PWM) we modeled the effects of thermal oxidation and oxide etching on Si photonic crystals (PCs) of triangular lattice and proposed that these two processes can be extremely advantageous methods for tuning the photonic band gap and defect frequency. Two dimensional photonic crystals consisting of air cylinders in silicon background are studied before and after oxidation and partial oxide etching. Before oxidation the absolute band gap can be tuned only in a small range of radii (0.404a-0.48a); a is the lattice constant. Within this range, the band gap changes rapidly with the air cylinder radius due to the high dielectric constant of silicon. When thermal oxide interfacial layers are incorporated, the band gap can be tuned by varying the oxide thickness in the range of (0.26a-0.48a). By supercell method, formation of a defect level inside the band gap by means of the interfacial oxide layer and tuning of the defect frequency by varying the oxide thickness are also studied. A monopole defect mode is observed by oxidizing the center cylinder in a 5x5 suppercell of silicon cylinders with radius 0.28a in air background. The defect frequency is tuned by varying the oxide thickness from 0.15a to 0.3a.