Lattice constant effects of photonic crystals on the extraction of guided mode of GaN based light emitting diodes
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- Fu, X., Zhang, B., Kang, X. et al. Sci. China Technol. Sci. (2011) 54: 1. doi:10.1007/s11431-010-4196-9
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We have fabricated a series of square-lattice hole photonic crystal (2PhC) arrays simultaneously at the un-current injection region on a special sample of GaN based light emitting diode (LED) by using focus ion beam milling (FIBM). The lattice constants of the 2PhC arrays vary from 230 to 1500 nm, while the 2PhC arrays have a constant area of about 9 μm × 18 μm and a fixed depth of 150±10 nm which approaches but does not penetrate the active layer. Microscopic electroluminescence images and spectral measurements consistently confirm that the top emitting intensities from different 2PhCs are all enhanced compared with the unpatterned region. It is demonstrated that the output coupling of propagating guided modes is realized by the diffracted transmission of the 2PhCs. The enhancement factors of the guided modes compared with the unpatterned region are plotted as function of the lattice constant. It is found that the highest enhancements for the extraction of guided modes were obtained for the lattice constant of 230 and 460 nm of 2PhCs. The results are discussed by the two-dimensional rigorous coupled wave analysis (RCWA).