Generation of terahertz radiation in antennas based on epitaxial films of semiconductors and topological insulators

The terahertz (THz) wave generation by photoconductive antennas fabricated on the low-temperature and high- temperature grown In0.5Ga0.5As semiconductor and Bi2-xSbxTe3-ySey (BSTS) topological insulator films is studied by the terahertz time-domain spectroscopy method. THz generation property of In0.5Ga0.5As layers grown by molecular beam epitaxy on GaAs substrates with (100) and (111)A crystallographic orientations is compared with THz generation capability of the BSTS films grown by the MOCVD method on a sapphire substrate. Antennas of the both types were excited by radiation of Er3+ -fiber laser at 1.56 um wavelength. THz generation by InGaAs-based antennas on (111)A GaAs substrates was 3–4 times more effective than the same antennas fabricated on the (100) wafers. It was found that the generation of THz waves was more efficient in an island film of BSTS having a total thickness of about tens nanometers with that chemical composition where the volume contribution to conductivity was suppressed. Strong amplification of the THz radiation power has been demonstrated after applying an external electric field to the topological insulator film.