Nonlinear Dynamics In Semiconductor Superlattices Under Terahertz And Magnetic Fields

Interaction between terahertz (THz) radiation and semiconductor nanostructures has been the subject of growing interest both theoretically and experimentally. When a magnetic field is applied to the system, the electronic and optical properties will be strongly modified and many interesting phenomena will show up. In this thesis, we study the nonlinear dynamics of electrons in superlattices (SLs) under THz electric field and magnetic field. The contents and main conclusions are listed as follows:1. Electron transport in resonant tunnelling SLs driven by crossed electric and magnetic fields has been studied using discrete drift diffusion model. By considering the effect of magnetic field on electron transport, we calculated the velocity-field characteristic under different magnetic fields. Spatiotemporal evolution of electric field domain and time-dependent current oscillation have been obtained by solving the drift diffusion equations. It is found that dynamic electric field domain can be converted to the stationary one by increasing the magnetic field.2. Chaotic dynamics in resonant tunnelling SLs driven by electric and magnetic fields has been studied. When a small ac signal is superimposed on the self-oscillating system, a typical nonlinear dynamic system is constructed and different current oscillation modes show up, which is attributed to the nonlinear interaction between the internally generated periodic motion of the accumulated charge wave and the external ac signal. Several kinds of chaos-detecting methods, including Poincare bifurcation diagram, phase plot, first return map, and Fourier spectra, were used to distinguish periodic, quasiperiodic, and chaotic states.3. We have numerically calculated the current characteristic of miniband SLs under THz electric field. It is found that harmonic current exhibits resonant peaks whenω_b = mω, whereω_B andωare frequencies of Bloch oscillation and external THz field, respectively. In addition, we have studied the dc-to-rf conversion efficiency and relation between maximum efficiency and dc electric field of the SL system. 4. Chaotic dynamics in miniband SLs under crossed electric and magnetic fields has been investigated. It is shown that the coupling of electrons in the miniband to the self-consistent field produces a cooperative nonlinear oscillatory mode which, when interacting with the oscillatory external field, the intrinsic Bloch-type oscillatory mode, and cyclotron oscillatory mode, leads to the appearance of complicated dynamics, including chaos.