Korotyeyev V. Theoretical study of the terahertz oscillations that excited by the electron drift in the quantum wells

The dissertation is devoted to investigations of the high-field and high-frequency electron transport in low-dimensional semiconductor heterostructures for development a new concepts of electrically pumped terahertz generation. The analytical approaches for theoretical description of the streaming effect and phonon transit-time resonance (OPTTR) effect in the nitride based quantum wells has been developed. Using Baraff approximation, the solution Boltzman transport equation for stationary and nonstationary applied electric field under strong anisotropic electron distribution was found. Based on obtained distribution functions the calculations of kinetic characteristics of two-dimensional electron gas (2DEG) were performed. Under stationary electron streaming the dependence of drift velocity on applied electric field show quasisaturation behavior whereas transverse diffusion coefficient appreciably decreases. It turned out that parameters of group III nitride heterostructures and features of 2DEG facilitate observation of streaming regime of electron transport. In frame of linear analysis of nonstationary task, it was demonstrated that 2DEG shows negative dynamical mobility (NDM) under proper electric field in the frequency region 0.2-2 THz. The obtained values of NDM were sufficient for excitation of oscillations in modern microresonators. Nonlinear analysis of electromagnetic oscillations with TE1,0 polarization in the metal microresonator excited by active heterostructure element (a diode) was carried out. At the realistic parameters of the diode and resonator, it was shown that generation of coherent terahertz electromagnetic waves takes place with power up to hundreds mW and efficiency 2-5%. Second part of dissertation is devoted to elaboration of the theoretical basis of the nonlinear regime of the optical phonons generation by drift of dense 2DEG. It was shown that practically single-mode generation of confinement optical phonon is achieved at the electron drift velocity 2-2.2*107 cm/c that correspond applied electric field a few kV/cm for GaAs quantum wells. Keywords: Boltzman transport equation, electron transport, nitrides, THz generation and optical phonons.