Modulation-Doped Multiple Quantum Wells of Aligned Single-Wall Carbon Nanotubes.

Heterojunctions, quantum wells, and superlattices with precise doping profiles are behind today's electronic and photonic devices based on III-V compound semiconductors such as GaAs. Currently, there is considerable interest in constructing similar artificial 3D architectures with tailored electrical and optical properties by using van der Waals junctions of low-dimensional materials. In this study, the authors have fabricated a novel structure consisting of multiple thin (≈20 nm) layers of aligned single-wall carbon nanotubes with dopants inserted between the layers. This 'modulation-doped' multiple-quantum-well structure acts as a terahertz polarizer with an ultra-broadband working frequency range (from ≈0.2 to ≈200 THz), a high extinction ratio (20 dB from ≈0.2 to 1 THz), and a low insertion loss (<2.5 dB from ≈0.2 to 200 THz). The individual carbon nanotube films-highly aligned, densely packed, and large (2 in. in diameter)-were produced using vacuum filtration and then stacked together in the presence of dopants. This simple, robust, and cost-effective method is applicable to the fabrication of a variety of devices relying on macroscopically 1D properties of aligned carbon nanotube assemblies. [ABSTRACT FROM AUTHOR]