Electrically Tunable, CMOS-Compatible Metamaterial Based on Semiconductor Nanopillars

With the advent of autonomous vehicles imminent, a solid-state approach to beam steering is necessary for more affordable lidar tracking systems. Capable of dynamic control of light with subwavelength components, electrically tunable metamaterials show potential in this field as well as other applications. Here, we demonstrate a nanopillar-based metamaterial composed of Ge and Al-doped ZnO (AZO), whose optical properties can be modulated by the field effect and whose fabrication process is compatible with complementary metal-oxide-semiconductor (CMOS) technology. From reflectance spectra, wavelength shifts up to 240 nm of the optical resonances are measured in our fabricated device with gate biases from −4 to 4 V. A high differential reflectance of more than 40% in this voltage range is experimentally shown. Then, through an effective medium approximation, we can describe the nanopillar array as a macroscopic metamaterial and calculate the phase shift of this device. With optimization of the nanopillar parameters, a large phase modulation approaching 270° is possible according to simulations, which is promising for beam steering applications.