Interaction of terahertz electromagnetic field with metallic grating: Near-field zone

We have developed theory for the interaction of THz radiation with a sub-wavelength metallic grating. The structure of electric fields of the electromagnetic wave under the metallic grating has been studied in the near-field zone. Spatial distributions of the electric field components and the electric energy density have been obtained for the transmitted wave through the grating. An effect of strong local enhancement of the electric field has been detected. Spatial dependences of the polarization of the transmitted wave has been analyzed for the near-field zone.Comment: 11 pages, 5 figure

Wave excitations of drifting two-dimensional electron gas under strong inelastic scattering

We have analyzed low-temperature behavior of two-dimensional electron gas in polar heterostructures subjected to a high electric field. When the optical phonon emission is the fastest relaxation process, we have found existence of collective wave-like excitations of the electrons. These wave-like excitations are periodic in time oscillations of the electrons in both real and momentum spaces. The excitation spectra are of multi-branch character with considerable spatial dispersion. There are one acoustic-type and a number of optical-type branches of the spectra. Their small damping is caused by quasi-elastic scattering of the electrons and formation of relevant space charge. Also there exist waves with zero frequency and finite spatial periods - the standing waves. The found excitations of the electron gas can be interpreted as synchronous in time and real space manifestation of well-known optical-phonon-transient-time-resonance. Estimates of parameters of the excitations for two polar heterostructures, GaN/AlGaN and ZnO/MgZnO, have shown that excitation frequencies are in THz-frequency range, while standing wave periods are in sub-micrometer region.Comment: 26 pages and 6 figure

Electric Current and Noise in Long GaN Nanowires in the Space-Charge Limited Transport Regime

We studied electric current and noise in planar GaN nanowires (NWs). The results obtained at low voltages provide us with estimates of the depletion effects in the NWs. For larger voltages, we observed the space-charge limited current (SCLC) effect. The onset of the effect clearly correlates with the NW width. For narrow NWs the mature SCLC regime was achieved. This effect has great impact on fluctuation characteristics of studied NWs. At low voltages, we found that the normalized noise level increases with decreasing NW width. In the SCLC regime, a further increase in the normalized noise intensity (up to 1E4 times) was observed, as well as a change in the shape of the spectra with a tendency towards slope -3/2. We suggest that the features of the electric current and noise found in the NWs are of a general character and will have an impact on the development of NW-based devices.Comment: 12 pages, 4 figures in Fluctuation and Noise Letters (2017

Spatial dispersion of the high-frequency conductivity of two-dimensional electron gas subjected to a high electric field : Collisionless case

We present the analysis of high-frequency (dynamic) conductivity with the spatial dispersion, $\sigma (\omega, {\bf q})$, of two-dimensional electron gas subjected to a high electric field. We found that at finite wavevector, ${\bf q}$, and at high fields, the high-frequency conductivity shows following peculiarities: strong non-reciprocal dispersion; oscillatory behavior; a set of frequency regions with negative $\sigma'$; non-exponential decay of $\sigma'$ and $\sigma''$ with frequency (opposite to the Landau damping mechanism). We illustrate the general results by calculations of spectral characteristics of particular plasmonic heterostructures on the basis of III-V semiconductor compounds. We conclude that the detailed analysis of the spatial dispersion of the dynamic conductivity of 2DEG subjected to high electric fields is critically important for different THz applications

THz frequency- and wavevector-dependent conductivity of low-density drifting electron gas in GaN: Monte Carlo calculations

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