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Terahertz emission from InAs excited by the femtosecond optical pulse is investigated. The hydrodynamic model is developed for the simplified analysis of the terahertz emission induced by the photo-Dember effect. The hydrodynamic model predicts that the amplitude of the transient photocurrent is proportional to the difference between the squared velocities of photoexcited electrons and holes. The predictions of the hydrodynamic model are compared to the results of the rigorous ensemble Monte Carlo simulations. The dependences of the intensity of terahertz emission on the optical fluence, on the photon energy, and on the optical pulse duration are studied. At low intensities of the optical pulse, the emitted terahertz energy is proportional to the power ranging between 3/2 and 2 of the optical pulse intensity. The emitted terahertz energy saturates at high intensities of the optical pulse. The spectral dependence of the terahertz emission from InAs is investigated. It is found that the intensity of terahertz emission profoundly depends on the optical pulse duration.

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By Monte Carlo simulations we calculate static and dynamic charge transport properties of bulk wurtzite GaN in the presence of high electric fields. The microscopic model is validated by comparison with available experiments. On this basis a double-drift impact avalanche transit time diode made of wurtzite GaN is investigated and optimized by performing ensemble Monte Carlo simulations of the diode self-consistently coupled with a load circuit. The large-signal ac characteristics show that avalanche diodes based on GaN can operate as microwave generators in a wide frequency range up to 0.7 THz. A maximum efficiency of about 18% is found at 0.45 THz.

Electron relaxtion after an instantaneous application of a dc electric field ranging from 10 V/cm to 1 kV/cm is studied numerically by a many‐particle Monte Carlo method. The model takes into account polar optical, acoustic, and impurity scattering in the nonparabolic central valley. In the limited range of doping, electric field, and temperature the electron mean energy and drift velocity oscillate. The oscillation frequency is nearly proportional to the applied electric field (approximately 35 GHz at 60 V/cm). The oscillations are associated with a shuttle‐type electron motion in the Debye sphere of k‐space they are not heavely damped if the electron runaway is favoured inside and restrained outside the Debye sphere.