The influences of polarization and structure parameters on the intersubband transition frequency within terahertz (THz) range and oscillator strength in GaN/AlGaN step quantum well have been investigated by solving Schrödinger and Poisson equations self-consistently. The results show that the Al mole compositions of step quantum well and space barrier have a significant effect on the THz intersubband transition frequency. A specific phenomenon is found that the minimum energy spacing between the ground state and first excited state can be achieved as the Al mole composition of space barrier is about twice of that of step well. In particular, an intersubband transition with energy of 19.8 meV (4.83 THz) can be obtained with specifically designed parameters. This specific phenomenon still exists in a wide range of step well width and a narrow range of well width with less than 3% fluctuation of the Al mole composition of barrier. In addition, oscillator strength and dipole matrix element versus the widths of well and step well, the influences of doping location and concentration on the absorption coefficient, are also investigated in detail in this study. The results should be of benefit to the design of devices operating in the THz frequency range.
The magnetic anisotropy energy (MAE) of bulk D022-Mn3X (X = Ga, Ge), Mn3X/MgO, and Mn3X/STiO3(STO) heterostructures is calculated from first principles calculations. The main source of the large perpendicular magnetic anisotropy (PMA) of bulk Mn3X is identified as Mn atoms in the Mn-Mn layer. In the four heterostructures, the magnetic moment of interfacial Mn atoms was reversed when Mn3X was epitaxially grown on MgO and STO substrates. More importantly, a large in-plane tensile strain induced by lattice mismatch between Mn3X and MgO significantly changes the MAE, explaining the difficulty in experiments to obtain PMA in epitaxial Mn3X/MgO. Furthermore, interface and surface Mn atoms also help to enhance the PMA of Mn3X/STO (MgO) heterostructures due to dxy and dz2 states changing from occupied states in bulk Mn3X to unoccupied states in the interface (surface) Mn of the heterostructures. These results suggest that the PMA of manganese compound heterostructures can be produced by decreasing the lattice mismatch with substrates and will guide the search for ultrathin manganese compound films with high PMA epitaxially grown on substrates for the application of spintronic devices.
This paper presents a kind of AC electronic load for testing AC power source with energy recycling capability. The proposed structure is based on back to back single-phase PWM rectifiers of the voltage-source type. The operation principle of the model is described in detail to research the power matching problem and dc bus harmonic phenomenon. To achieve power balance and good performance, an independent control strategy for the two PWM rectifiers is proposed. In addition, a novel control technique of compensating second-harmonic voltage of dc bus is put forward. The research is proved to be effective in power recovery by the prototype experiments.
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