Polarized THz radiation is increasingly being investigated and applied in the new interdisciplinary field “TeraNano.” We report the generation of terahertz (THz) radiation by a linearly polarized femtosecond optical pulse in black phosphorus (BP) crystallites grown by chemical vapor deposition. Characterization of THz radiation is performed by time-resolved THz spectroscopy. It was found that BP emits elliptically polarized THz radiation with an ellipticity of ε = 0.77 ± 0.03. A saturation was found in the dependence of the THz intensity on the intensity of the incident optical pump for the latter higher than 6 mJ / cm2. The results of our work can provide new fundamental knowledge needed to create detectors and generators based on BP in the THz range.
We report on a novel-designed superlattice (SL) InGaAs/InAlAs with artificially introduced epitaxial stresses into functional layers. The optimized and fabricated strained SL demonstrates a sub-picosecond photocarrier lifetime of 1.7 ps nevertheless featuring a rather moderate mobility. By means of numerical simulation we observe a decrease in the energy band gap of strained photoconductive layer InGaAs. In addition, the timedomain spectroscopic measurements reveal an increase in the spectrum amplitude of surface THz emission in the strained SL compared to lattice-matched one. We associate the decrease in photocarrier lifetime as well as the increase in the spectrum amplitude with residual strain in the SL caused by epitaxial stresses. The obtained results are of specific interest to THz science community since they open a way toward fabrication of cost-effective THz photoconductive devices for biomedical applications.
We present the results of numerical and experimental study of the photoconductive antennas (PCAs) based on GaAs and its ternary compounds. We produced three photoconductive materials with different indium content, which then were applied for fabrication of the THz PCAs. These PCAs were used as emitters of the THz pulsed spectrometer. We evaluated the stationary transient current generated by the PCAs, simulated their I-V characteristics, and compared them with the experimental ones. Using the finite integration method, we studied the thermal properties of the PCAs and demonstrated significant influence of the heat-sink on the leakage currents of the InGaAs-based PCA. We showed that the heat-sink reduces the operation temperature of the InGaAs-based PCAs by 40-64 % depending on the indium content. The observed results might be interesting for applications of the PCAs in THz pulsed spectroscopy and imaging.
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