Photoconductive antennas based on epitaxial films In0.5Ga0.5As on GaAs (111)A and (100)A substrates with a metamorphic buffer

The terahertz (THz) wave generation by the spiral photoconductive antennas fabricated on the low-temperature and high-temperature grown undoped and Si-doped In0.5Ga0.5As films is studied by the terahertz time-domain spectroscopy method. The In0.5Ga0.5As layers were grown by molecular beam epitaxy on GaAs substrates with (100) and (111) A crystallographic orientations utilizing step-graded InxGa1-xAs metamorphic buffer. The antennas are excited by radiation of Er3+-fiber laser at 1.56 mu m wavelength in two regimes: with pulse durations of 2.5 ps or 100 fs. It is found that the THz wave generation is 3-4 times more effective in the case of InGaAs-based antennas on (111)A GaAs substrates as compared to the (100) substrates. Power-voltage characteristic of the LT-InGaAs antenna up to and beyond threshold breakdown voltage are reported.