Conditions required for the streaming effect and the optical-phonon transit-time resonance to take place in a compensated bulk GaN are analyzed in detail. Monte Carlo calculations of the high-frequency differential electron mobility are carried out. It is shown that the negative dynamic differential mobility can be realized in the terahertz frequency range, at low lattice temperatures of 30-77 K, and applied electric fields of 3-10 kV/cm. New manifestations of the streaming effect are revealed, namely, the anisotropy of the dynamic differential mobility and a specific behavior of the diffusion coefficient in the direction perpendicular to the applied electric field. The theory of terahertz radiation transmission through the structure with an epitaxial GaN layer is developed. Conditions for the amplification of electromagnetic waves in the frequency range of 0.5-2 THz are obtained. The polarization dependence of the radiation transmission coefficient through the structure in electric fields above 1 kV/cm is found.
Abstract. We have studied the high-frequency properties of the non-equilibrium electron gas in GaN samples subjected to electric and magnetic fields. Spectra of the complex tensor of the dynamical mobility have been calculated for THz frequency range. For the compensated GaN and low temperatures, in the intervals of electric fields of the few kV /cm and magnetic fields of the few T the existence of the cyclotron and optical phonon transit-time resonances has been identified. We have shown that interplay of two resonances gives rise to specific spectra of THz transmission and absorption (or gain). We suggest that experimental investigation of these effects will facilitate elaboration of field controlled devices for THz optoelectronics.
Low-temperature high-field electron transport is studied for compensated bulk GaN subjected to crossed electric and magnetic fields. The electron kinetics, distribution function, and field dependencies of the magneto transport characteristics are analyzed by using the Monte-Carlo method. At zero magnetic field, for an ionized impurity concentration of 1016 cm−3 and an electron concentration of 1015 cm−3, it is shown that dissipative streaming transport with a strong anisotropic electron distribution in the momentum space is realized at electric fields in the range 3−10 kV/cm and for a lattice temperature of 30 K. The magnetic field destroys the dissipative streaming transport. Indeed, for a magnetic field greater than 4 T, the electrons are predominantly confined in a region of the momentum space where their energy is smaller than the optical phonon energy and the strong inelastic scattering by optical phonons is practically eliminated. A quasi-ballistic electron transport occurs in the form of a vortex-like motion in the momentum space. The axis of rotation of this vortex coincides with the average electron momentum. A general analysis of the distribution function suitable for any configuration of the Hall circuit is presented. The main magneto transport characteristics (dissipative current, Hall current, and Hall electric field) are studied for the short and open Hall circuits. We show that the magneto transport measurements can provide valuable information on the main features of the electron distribution function and electron dynamics in GaN. Finally, we suggest that the strong dependency of the dissipative current on the parameters of the Hall circuit can be used for current modulation and current switching.
Abstract. High-field electron transport has been studied in crossed electric and magnetic fields in bulk GaN with doping of 10 16 cm -3 and compensation around 90% at the low lattice temperature (30 K). The electron distribution function, the field dependences of the ohmic and Hall components of the drift velocity have been calculated using the Monte Carlo method in the wide range of applied electric (3…15 kV/cm) and magnetic (1…10 T) fields. Two external electrical circuits with short-and open-circuited Hall contacts have been analyzed. For a sample with short-circuited Hall contacts, there are the ranges of magnetic and electric fields where the non-equilibrium electron distribution function has a complicated topological structure in the momentum space with a tendency to formation of the inversion population. For these samples, field dependences of the ohmic and Hall components of the drift velocity have specific character. The ohmic component has the inflection point that corresponds to the maximum point of the Hall component. For the sample with open-circuited Hall contacts, field dependences of the drift velocity demonstrate a sub-linear growth without any critical points. It has been shown that there are ranges of the applied electric and magnetic fields for which the drift velocity exceeds zero magnetic field values.
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