We describe a terahertz time-domain-spectroscopy system that is based on photoconductive components fabricated from low-temperature-grown GaBiAs epitaxial layers and activated by femtosecond $1.03\mu \text{m}$ pulses emitted by an Yb:fiber laser. Experiments performed with the laser pulses of different durations have evidenced that the spectral range of the system is limited by the photoexcited carrier lifetime. The optical to terahertz conversion efficiency of the system exceeds ${10}^{-4}$ with the usable spectral range of about 3 THz in the case of 170 fs excitation pulses.

Polarized terahertz radiation generated from (112)-oriented InSb surfaces is investigated as a function of the sample azimuthal orientation under excitation from femtosecond Yb:KGW laser pulses. The expressions describing the optical rectification and the surface electric-field-induced optical rectification in reflection from zinc-blende crystals, such as InSb, are calculated. It is shown the contributions of both these effects should be taken into account when describing terahertz emission from InSb surfaces.

(GaIn)(AsBi) layers were grown on a GaAs substrate. Their alloy composition, structural characteristics as well as the optical and electrical parameters were determined. It was found that by incorporating Bi and In into the lattice of GaAs, the energy bandgaps can be as narrow as 0.6 eV. These epitaxial layers of quaternary bismide alloys have shorter than a one picosecond carrier lifetime and a relatively large dark resistivity, demonstrating that this material is a good candidate for ultrafast optoelectronics applications. Thick quaternary bismide layers were used for the fabrication of photoconductive antenna type THz radiation detectors activated by femtosecond laser pulses. The performance of THz detectors manufactured from (GaIn)(AsBi) layers was comparable to that of previously reported Ga(AsBi) devices, but the range of optical wavelengths at which the detectors can be activated was considerably wider, covering the technologically important 1.55 μm wavelength range.

Graphene has shown great potential for ultra-high frequency electronics. However, using graphene in electronic devices creates a requirement for electrodes with low contact resistance. Thermal annealing is sometimes used to improve the performance of contact electrodes. However, high-temperature annealing may introduce additional doping or defects to graphene. Moreover, an extensive increase in temperature may damage electrodes by destroying the metal–graphene contact. In this work, we studied the effect of high-temperature annealing on graphene and nickel–graphene contacts. Annealing was done in the temperature range of 200–800 °C and the effect of the annealing temperature was observed by two and four-point probe resistance measurements and by Raman spectroscopy. We observed that the annealing of a graphene sample above 300 °C increased the level of doping, but did not always improve electrical contacts. Above 600 °C, the nickel–graphene contact started to degrade, while graphene survived even higher process temperatures.

Quaternary GaInAsBi alloy epitaxial layers were grown on InP substrates with 6% Bi. It was found that the thick layers remain fully strained. The measured carrier lifetimes were of the order of a few picoseconds. The terahertz (THz) emission was investigated using a GaInAsBi layer as an unbiased surface emitter and as a substrate for photoconductive antenna. It was observed that fabricated THz emitters were sensitive to the optical pulses with wavelengths longer than 2 μm. The demonstrated spectral characteristics of THz pulses obtained when using an Er-doped fiber laser for photoexcitation were comparable with those observed in other emitters used for THz-time-domain spectroscopy systems.