GENERATION OF SEQUENCES OF STRONG ELECTRIC MONOPULSES IN NITRIDE FILMS

This paper presents theoretical investigation of the excitation of the sequences of strong nonlinear monopulses of space charge waves from input small envelope pulses with microwave carrier frequencies due to the negative differential conductivity in n-GaN and n-InN films. The stable numerical algorithms have been used for nonlinear 3D simulations. The sequences of the monopulses of the strong electric field of 3 – 10 ps durations each can be excited. The bias electric field should be chosen slightly higher than the threshold values for observing the negative differential conductivity. The doping levels should be moderate 1016 –1017 cm-3in the films of £ 2 mm thicknesses. The input microwave carrier frequencies of the exciting pulses of small amplitudes are up to 30 GHz in n-GaN films, whereas in n-InN films they are lower, up to 20 GHz. The sequences of the electric monopulses of high peak values are excited both in the uniform nitride films and in films with non-uniform conductivity. These nonlinear monopulses in the films differ from the domains of strong electric fields in the bulk semiconductors. In the films with non-uniform doping the nonlinear pulses are excited due to the inhomogeneity of the electric field near the input end of the film and the output nonlinear pulses are rather domains.

THOMAS-FERMI METHOD FOR COMPUTING THE ELECTRON SPECTRUM AND WAVE FUNCTIONS OF HIGHLY DOPED QUANTUM WIRES IN N-SI

The application of Thomas - Fermi method to calculate the electron spectrum in highly doped n-Si quantum wires is presented under finite temperatures, where the many-body effects, like exchange, are taken into account. The electron potential energy is calculated from a single equation. Then the electron energy sub-levels and wave functions within the potential well are simulated from the Schrödinger equation. For axially symmetric wave functions the shooting method has been used. Two methods have been applied to solve the Schrödinger equation in the case of the anisotropic effective mass, the variation method and the iteration procedure for the eigenvectors of the Hamiltonian matrix

A Novel Displacement-amplifying Compliant Mechanism Implemented on a Modified Capacitive Accelerometer

The micro-accelerometers are devices used to measure acceleration. They are implemented in applications such as tilt-control in spacecraft, inertial navigation, oil exploration, etc. These applications require high operating frequency and displacement sensitivity. But getting both high parameter values at the same time is difficult, because there are physical relationships, for each one, where the mass is involved. When the mass is reduced, the operating frequency is high, but the displacement sensitivity decreases and vice versa. The implementation of Displacement-amplifying Compliant Mechanism (DaCM) supports to this dependence decreases. In this paper the displacement sensitivity and operation frequency of a Conventional Capacitive Accelerometer are shown (CCA). A Capacitive Accelerometer with Extended Beams (CAEB) is also presented, which improves displacement sensitivity compared with CCA, and finally the implementation of DACM´s in the aforementioned devices was also carried out. All analyzed cases were developed considering the in-plane mode. The Matlab code used to calculate displacement sensitivity and operating frequency relationship is given in Appendix A

Multifrequency microwave sounding of nonlinear objects

Numerical modelling process of nonlinear dispersion of powerful microwave pulses on the objects containing semi-conductor components is realized. The attention is given to an irradiation by ultrashort pulses on various carrier frequencies. Numerical modelling is based on the integrated equations for the induced current. Possibility of multifrequency nonlinear dispersion use with allocation both summed, and difference frequencies is shown

Superheterodyne amplification of electromagnetic waves of optical and terahertz bands in gallium nitride films

Superheterodyne amplification of electromagnetic waves of optical and terahertz bands in the case of three-wave interaction in n–GaN films with the space change wave of millimeter band amplified due to negative differential resistance is studied. It is shown that amplification of the space change wave in n–GaN films may be achieved on higher frequencies f ≤ 500 GHz than when using GaAs. The case of three-wave resonant interaction of two counter-propagating waves with the space charge wave is considered for the waveguide on based on GaN film on dielectric substrate. It is shown that gain of electromagnetic waves of optical band may reach 20–40 dB on the waveguide lengths of up to 100 μm

Propagation of centimeter and millimeter spin-dipolar waves in nonuniform magnetic fields

Propagation of exchangeless spin-dipolar waves (SDW) of centimeter (f ~ 3–20 GHz) and millimeter (f ~ 30–60 GHz) wavelength ranges in ferrite films into nonuniform magnetic fields was researched analytically and numerically. Applied magnetic field is directed along film plane and it is slightly nonuniform in this plane. Proposed SDW propagation in magnetic fields was researched with complex geometric optics. We have shown a possibility of SDW type transformation from superficial SDW into backward volume SDW along propagation trajectory in both centimeter and millimeter wavelength range. An influence of electromagnetic delay on SDW propagation in nonuniform magnetic fields is essential in millimeter wavelength range and it can modify wave trajectories

Integrated silicon p–i–n structures with highly doped p++, n++ regions for modulation in terahertz frequency band

Modulators of terahertz range on the base of silicon integrated p–i–n-structures are investigated theoretically. The generalization of the Fletcher boundary conditions at the injecting contacts has been put forward for the case of highly doped p++, n++ regions, where both forbidden gap narrowing and dependence of coefficients of diffusion on doping concentration are taken into account. The problem of double injection into i-region has been simulated in a two-dimensional case. The investigations of modulation properties of integrated p–i–n-structures in the terahertz range have demonstrated a possibility to use these structures up to the frequencies 8 THz

Collapse of the surface dusty plasma waves under the plasma–beam instability

The nonlinear dynamics of the dusty plasma–dusty beam instability is investigated in the dusty plasma waveguides bounded by dielectrics. The dusty plasma includes the positive ions as the light component and the negative dust as the heavy component. A beam of dust particles moves along the waveguide. The set of hydrodynamic equations for the dust and beam particles, namely, the continuity equations and the equations for the momentum jointly with the Poisson one are used. The Boltzmann distribution is used for the ions. The electric and hydrodynamic boundary conditions are applied at the interfaces. The simulations have demonstrated that the dusty sound waves of small amplitudes are the subject to amplification with a high increment due to the convective instability, even when the concentration of the beam particles is ≤0.1 of the uniform dust concentration. The amplification very rapidly transits to the regime of strong surface nonlinearity, and near the interfaces the variations of the dust concentration reach extremely high values, where the collapse of the beam dust component occurs