Photonics Crystal Design Of Overlay Of Light-Emitting Diode

Light-emitting diode (LED) is a widely used solid state light source. LED has the advantage of long-life, high reliability, environment protection, small volume and so on, and it was called new generation light source. However, the extraction efficiency of traditional LED was low, many traditional methods were used to improve its efficiency, but the result has been not good so far.Photonics crystals are special optical materials. The most remarkable and widely used effect is photonics crystal band gap, and the transmission of optics is controlled by this effect. Photonics crystals have been used in LED to improve extraction efficiency greatly since 1990s.The structure of overlay of LED is designed as photonics crystal based on other study in this thesis. Firstly, the theory and application of photonics crystal and LED are introduced in detail. Secondly, the calculations methods of plane-wave expansion (PWE) method and finite difference time domain (FDTD) method are introduced. Thirdly, the plane-wave expansion method is used to calculate band gaps for one-dimensional photonic crystal with GaN medium, and the widest crystal band gap is found by the change of filling ratio. The photonic crystal structure is applied in GaN based LED, and the extraction efficiency of LED is simulated by FDTD method. The Variation of extraction efficiency of LED and the height of photonic crystal column is obtained by FDTD. The difference and connection of photonic crystal band gap effect and grating diffraction effect for one-dimensional photonic crystal LED are studied. Finally, the application of band gap effect of two-dimensional photonics crystal is studied by PWE in LED. A novel structure which is adding a half sphere to the top of column is designed and this structure is better than single photonics crystal LED.