Design And Simulation Of Ferromagnetic Semiconductor Heterostructures With High Curie Temperature And High Polarization

In this work, we have investigated the magnetic characteristics of III-V based ferromagnetic heterostructures. According to the theory of RKKY interaction and Zener model, the ferromagnetic characteristics of different low dimensional ferromagnetic semiconductor structures have been studied by solving the coupled Schrodinger and Poisson equations self-consistently. We mainly studied effects of different acceptor types, doping modes and concentration on the Curie temperature (T_C) and deeply discussed the modulating behavior of electric field to the Curie temperature in Mn delta doped GaAs/AlGaAs quantum well. We also analyzed the spin polarized current and tunneling behavior. The results are very useful to obtain high Curie temperature and polarization in low dimensional ferromagnetic semiconductor materials. The paper mainly contains the following works:1. Within the mean-field approximations, we calculated the dual acceptors behavior in Mn delta doped GaAs/p-AlGaAs heterostructures self-consistently, and studied the influences of both acceptor doping concentrations and modes on ferromagnetic properties. T_C step-up as the Be concentration increases, while T_C increases continuously as the effective Mn concentration. We analyzed physics mechanism of different dopants and the contribution to pd exchange interaction. On this basis, we built the dual delta modulated doping heterostructures. The results indicated that the ferromagnetic transition temperature can be increased by about 70K.2. The model of Mn selectively delta-doped GaAs/AlGaAs wide quantum wells is established. The electric field controlled Curie temperature for different delta-doping positions and well width has been investigated in detail. The results show that T_C in the wide quantum wells (>20 nm) can be increased rapidly by applying low electric field. For quantum wells with 40nm well width, an applied electric field of 0.3meV/nm enhances T_C up to five times than ones without the applied field. The established models make it possible for spintronic devices operating at room temperature.3. Using WinGreen simulation software, we explored the spin tunneling behavior of InGaN/GaMnN ferromagnetic resonant tunneling diode, and mainly analyzed the effects of In concentration and temperature on the current density and polarization of electric filed modulating devices. We can observe the remarkable spin splitting current for In concentration is 15 %( more than that in reservoirs) even when the splitting energy is 10 meV. The almost 100% polarization can be obtained at low temperature. Even if at room temperature, the 8% polarization also can be obtained. The spin orientation of tunneling current can be selected by different applied electric fields. It provides an effective method to modulate the spin orientation and polarization of output current in spintronic devices.