Optimization of Trapezoid Coupling Grating for Long-Wave Quantum Well Infrared Photodetector

The relative coupling efficiency of trapezoid coupling grating for long-wave quantum well infrared photodetector is calculated by finite difference time domain algorthms. By considering the lateral etching effects in grating fabrication, the relative coupling efficiency with respect to the grating parameters, such as, grating period, grating depth, grating top width and grating bottom width etc, is computed. The calculated results show that the relative coupling efficiency will reach the largest value for the 8.266µm incident infrared light when taking grating period asp=2.55 µm, grating depth as h=0.622 µm , grating top width as d1=1.253µm , grating bottom width as d2=0.626µm , duty ratio as q=0.5 and the ratio of bottom width and top width as α=0.5.