Polarization-dependent terahertz emission from ART-assisted InP nanostructures monolithically grown on Si (001) substrates

We report polarization-dependent terahertz (THz) emission from aspect-ratio-trapping (ART)-assisted InP nanostructures monolithically grown on Si (001) using metal-organic chemical vapor deposition (MOCVD). Periodic SiO₂ slabs laterally confine InP nanostructures over centimeter-scale areas. Transmission electron microscopy (TEM) and high-resolution X-ray diffraction (HRXRD) confirm high crystallinity and a fully relaxed lattice. Fs-laser-pumped THz time-domain spectroscopy reveals pronounced anisotropy. Excitation with the pump polarization perpendicular to the nanostructure axis yields more than twice the emission amplitude of the parallel geometry, with the integrated-field ratio saturating at 2.4. In the frequency domain, the perpendicular configuration also exhibits a higher peak frequency, indicating a shorter effective carrier lifetime. We attribute the enhanced emission to abrupt, repeated velocity modulations of photo-carriers that encounter nanoscale SiO₂ boundaries transverse to transport, which amplifies the temporal derivative of the photocurrent via a lateral photo-Dember-type mechanism. These results establish ART-InP nanostructures on Si as a Si-compatible platform for compact, polarization-controllable THz emitters and provide clear geometric handles to engineer anisotropic THz responses.