Terahertz wave generation through the optical rectification of 780 nm femtosecond laser pulses in ZnGeP2 crystals has been studied. All of the possible interactions of types I and II were analyzed by modeling and experimentally. We demonstrate the possibility of broadband “low-frequency” terahertz generation by an ee–e interaction (with two pumping waves and a generated terahertz wave; all of these had extraordinary polarization in the crystal) and “high-frequency” terahertz generation by an oe–e interaction. The arising possibility of achieving the narrowing of the terahertz generation bandwidth at the oe–e interaction using thicker ZnGeP2 crystals is experimentally confirmed. It has been found that the thermal annealing of as-grown ZnGeP2 crystals and their doping with a 0.01 mass % of Sc reduces the absorption in the “anomalous absorption” region (λ = 0.62–3 μm). The terahertz generation by the oo–e interaction in (110) ZnGeP2:Sc and the as-grown ZnGeP2 crystals of equal thicknesses was compared. It has been found that ZnGeP2:Sc is more efficient for 780 nm femtosecond laser pulses optical rectification.

Terahertz photoconductivity and charge carrier recombination dynamics at two-photon (ZnGeP2) and three-photon (4H-SiC) excitation were studied. Thermally annealed, high-energy electron-irradiated and Sc-doped ZnGeP2 crystals were tested. The terahertz charge carrier mobilities were extracted from both the differential terahertz transmission at a specified photoexcitation condition and the Drude–Smith fitting of the photoconductivity spectra. The determined terahertz charge carrier mobility values are ~453 cm2/V·s for 4H-SiC and ~37 cm2/V·s for ZnGeP2 crystals. The charge carrier lifetimes and the contributions from various recombination mechanisms were determined at different injection levels using the model, which takes into account the influence of bulk and surface Shockley–Read–Hall (SRH) recombination, interband radiative transitions and interband and trap-assisted Auger recombination. It was found that ZnGeP2 possesses short charge carrier lifetimes (a~0.01 ps−1, b~6 × 10−19 cm3·ps−1 and c~7 × 10−40 cm6·ps−1) compared with 4H-SiC (a~0.001 ps−1, b~3 × 10−18 cm3·ps−1 and c~2 × 10−36 cm6·ps−1), i.e., τ~100 ps and τ~1 ns at the limit of relatively low injection, when the contribution from Auger and interband radiative recombination is small. The thermal annealing of as-grown ZnGeP2 crystals and the electron irradiation reduced the charge carrier lifetime, while their doping with 0.01 mass % of Sc increased the charger carrier lifetime and reduced mobility. It was found that the dark terahertz complex conductivity of the measured crystals is not fitted by the Drude–Smith model with reasonable parameters, while their terahertz photoconductivity can be fitted with acceptable accuracy.

The time dynamics of nonequilibrium charge carrier relaxation processes in SI GaAs:EL2 (semi-insulating gallium arsenide compensated with EL2 centers) and HR GaAs:Cr (high-resistive gallium arsenide compensated with chromium) were studied by the optical pump–terahertz probe technique. Charge carrier lifetimes and contributions from various recombination mechanisms were determined at different injection levels using the model, which takes into account the influence of surface and volume Shockley–Read–Hall (SRH) recombination, interband radiative transitions and interband and trap-assisted Auger recombination. It was found that, in most cases for HR GaAs:Cr and SI GaAs:EL2, Auger recombination mechanisms make the largest contribution to the recombination rate of nonequilibrium charge carriers at injection levels above ~(0.5–3)·1018 cm−3, typical of pump–probe experiments. At a lower photogenerated charge carrier concentration, the SRH recombination prevails. The derived charge carrier lifetimes, due to the SRH recombination, are approximately 1.5 and 25 ns in HR GaAs:Cr and SI GaAs:EL2, respectively. These values are closer to but still lower than the values determined by photoluminescence decay or charge collection efficiency measurements at low injection levels. The obtained results indicate the importance of a proper experimental data analysis when applying terahertz time-resolved spectroscopy to the determination of charge carrier lifetimes in semiconductor crystals intended for the fabrication of devices working at lower injection levels than those at measurements by the optical pump–terahertz probe technique. It was found that the charge carrier lifetime in HR GaAs:Cr is lower than that in SI GaAs:EL2 at injection levels > 1016 cm−3.

О некоторых закономерностях распределения химических элементов в живых организмах Огромное количество закономерностей, объединяемых периодическим законом, позволяет предсказывать поведение веществ в различных процессах. Внутренняя структура Периодической системы отражает особенности распределения химических элементов по мере возрастания заряда ядра атомов. Характер изменения фундаментальных характеристик атомов, таких как потенциалы ионизации, энергия сродства к электрону, электроотрицательность, радиусы атомов и ионов и др., в группах сверху вниз и в периодах слева направо обнаруживает глубокую взаимосвязь свойств атомов по отношению друг к другу и тем самым позволяет рассматривать их как единое целое. Целостность-это свойства системы изменяться при изменении свойств ее отдельных составляющих. Периодическая система химических элементов полностью отражает системный подход к их изучению. Установление закономерностей изменения фундаментальных характеристик атомов в периодах и группах позволяет глубже понять явление периодичности, характер перехода количественных отношений в качественные. Ключевые слова: периодический закон, ионизационный потенциал, сродство к электрону, электроотрицательность, заряд ядра, атомные радиусы, макроэлементы, микроэлементы, энергодисперсионный микроанализ, атомно-эмиссионная спектроскопия, масс-спектрометрия с индуктивно связанной плазмой.

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