Fabrication of subwavelength, binary, antireflection surface-relief structures in the near infrared

Subwavelength, binary surface-relief structures are artificial materials with an effective index of refraction that can be tailored by varying the duty cycle of the binary pattern. These structures have the significant advantage of requiring only a single lithography and etch step for fabrication. We demonstrate a specifically designed antireflection structure in a material system (GaAs) and at a wavelength (975 nm) directly integrable with GaAs-based vertical cavity surface-emitting lasers and which exhibits strong polarization-dependent properties. Fabrication is performed using electron beam lithography and reactive-ion-beam etching. The observed reflectivity is 2% for TE polarization and 23% for TM polarization, a difference in reflectivity of over a factor of 10 for the two polarizations.