Reflectivity characteristics of high refractive index contrast sub-wavelength grating mirror without low index spacer layer

High refractive index contrast sub-wavelength grating (HCG) without a low-index spacer layer between a grating layer and semiconductor was investigated. By the 2D-FDTD analysis of reflection spectrum of the proposed HCG, an interesting characteristic was found out that was input direction dependence of the reflectivity. When a plane wave input from air and semiconductor, the reflectivity spectra were different at specific wavelength range. To investigate the cause of such characteristics, low-index spacer layer thickness dependence of the reflectivity characteristics and light intensity distribution were analysed. The evanescent wave was suggested as the cause of the reflectivity characteristics.