Using photonic crystals (PCs), the extraction efficiency of the light-emitting diodes (LEDs) can be greatly enhanced by the effects of photonic band gap (PBG) and grating diffraction. The two theoretical methods are also discussed. Meanwhile, we demonstrate that LEDs can achieve high extraction efficiency by employing photonic crystal as diffraction grating. PCs with square lattice of cylindrical unit cells are fabricated in GaN layer of GaN-based blue LED. We present a theoretical discussion on the extraction efficiency of PC-LED, which relies on the effective medium theory and transmission matrix method to investigate the effect of lattice constant. The results show that the extraction efficiency of the high performance LEDs can achieve 61.8% when the lattice constant is 270 nm.
Numerical calculations based on the transfer matrix method are carried out,and the results of band gap with resonance peaks are obtained.The electron beam lithography technology(EBL) and induction coupling plasma(ICP) etching are used to make the photonic crystal(PC) structures,and from several scanning electron microscope images,the PC structures are observed with features closing to the design. In order to create the tiny PC structures in the right places of the waveguide by the EBL technology at different time,some alignment markers are deposited on the chip,which are made of gold that deposited on titanium for its good adhesion to the underlying Si.An optical testing bed is designed for measurement of the optical characterization of PC structures.Through the analysis of the measured data,a AA value of 0.8 nm is obtained and for the centre frequency of 1547 nm,a very high quality factor value of 1933 can be obtained.The 3-nm difference represents only a 0.2%error from the theoretical centre.
The tunable micro-cavity based on one-dimensional(1D) photonic crystal doped by KTP is designed.The optical transmission properties in the doped one-dimensional defect photonic crystals are analyzed using transfer matrix method(TMM).According to the electro-optic effect,the refractive index ellipsoid equation is established with the applied alternating current at both coordinate axes,and the characteristics of temperature-optics and modulation are studied.Numerical calculations and experimental results show that the tuning range is ～40 nm.
