Subwavelength antireflection gratings for GaSb in visible and near-infrared wavelengths

We fabricated a two-dimensional subwavelength grating (SWG) on a GaSb substrate. The SWG was patterned by electron-beam lithography and etched by a fast atom beam with SF6 and Cl-2 gases. The SWG consisted of tapered gratings with a 350-nm-period and a 1280-nm-deep groove. The reflectivity at wavelengths from 500 nm to 2300 nm was measured and compared with the results calculated on the basis of rigorous coupled-wave analysis (RCWA). At wavelengths from 500 run to 2000 nm, the SWG decreased the reflection,as much as 5 to 10% from the original value of approximately 40% of the GaSb substrate. The thermal stability of the SWG was also studied by measuring the reflection spectra of heated samples.