Design and fabrication of nanoscale antireflection structures with linearly graded refractive index

We demonstrate nanoscale antireflection structures on GaAs substrate with linearly graded effective refractive index using a lenslike shape transfer for broadband light-absorbing device application. From reflectance calculation of cone- and parabola-shaped subwavelength grating (SWG) structures, it is found that the parabola shaped structures has lower mean reflectance compared to that of the cone shaped structures over a wide wavelength range. The fabricated SWG structures with parabola shape show the reflectance of below 5 % in a 300-1200 nm wavelength range.