Terahertz-radiation generation in low-temperature InGaAs epitaxial films on (100) and (411) InP substrates

The spectrum and waveforms of broadband terahertz-radiation pulses generated by low-temperature In$_{0.53}$Ga$_{0.47}$As epitaxial films under femtosecond laser pumping are investigated by terahertz time-resolved spectroscopy. The In$_{0.53}$Ga$_{0.47}$As films are fabricated by molecular-beam epitaxy at a temperature of 200$^\circ$C under different arsenic pressures on (100)-oriented InP substrates and, for the first time, on (411)A InP substrates. The surface morphology of the samples is studied by atomic-force microscopy and the structural quality is established by high-resolution X-ray diffraction analysis. It is found that the amplitude of terahertz radiation from the LT-InGaAs layers on the (411)A InP substrates exceeds that from similar layers formed on the (100) InP substrates by a factor of 3–5.