Bandgap calculation of a 2-D photonic crystal and its application towards a thin film solar cell

Two-dimensional (2-D) photonic crystals (PhCs) of a square lattice have been investigated to find the complete photonic band gap. Band diagram calculations have been performed using the simulator "PWE band solver" of the software package optiFDTDTM, based on a plane wave expansion method. Air holes in the dielectric background with four different shapes have been considered. Parameters like filling fraction, rod/air hole orientation angle and material dielectric constant have been varied. It has been found that PhCs with square air holes have the largest gap; the gap-midgap ratio is 13.66% for GaAs (when filling fraction, f=0.680 and orientation angle,theta=30 degrees). Finally, a proposal is made to improve the efficiency of a thin film solar cell using this photonic crystal as a back reflector.