Peculiarities of THz-electromagnetic wave transmission through the GaN films under conditions of cyclotron and optical phonon transit-time resonances

The theory of THz radiation transmission through the film of compensated GaN of cubic modification under action of electric and magnetic fields has been developed. In the THz frequency range, spectra of the dynamic mobility tensor have been obtained for applied steady-state electric fields of several kV/cm and magnetic fields of several T. The spectra of transmission, reflection and loss coefficients have been analyzed for the Voigt configuration used for the applied fields. It has been shown that the transmitted wave becomes elliptically polarized, and the spectra of polarization characteristics such as ellipticity and rotation angle of the large axis of polarization ellipse were investigated under conditions of cyclotron resonance and optical phonon transit-time one. It has been found that, in certain frequency bands, polarization characteristics have the features valid for both resonances. The new optical method based on the analysis of ellipticity and rotation angle spectra is offered for determination of the low-field mobility

Theory of high-field electron transport in the heterostructures AlxGa₁₋xAs/GaAs/AlxGa₁₋xAs with delta-doped barriers. Effect of real-space transfer

Steady-state electric characteristics of quantum heterostructures AlxGa₁₋xAs/GaAs/AlxGa₁₋xAs with -doped barriers have been analyzed in this work. It has been shown that at high doping the additional low-conductive channels are formed in the barrier layers. Current-voltage characteristics of the structure were obtained in the wide interval of applied electric fields up to several kV/cm being based on the solution of Boltzmann transport equation. It has been found that in the electric fields higher than 1 kV/cm the effect of exchange of the carriers between the high-conductive channel of the GaAs quantum well and the channels in the AlGaAs barriers becomes essential. This effect gives rise to the appearance of the strongly nonlinear current-voltage characteristics with a portion of negative differential conductivity. The developed model of heterostructure is adequate to those recently fabricated and studied by Prof. Sarbey’s group. The obtained results explain some observation of this paper. It has been found that the effect of electron real-space transfer takes place at both low temperatures and room temperatures, which opens perspectives to design novel type nanostructured current controlled device

Monte Carlo Simulation of hot electron effects in compensated GaN semiconductor at moderate electricfields

The electron distribution function and transport characteristics of hot electrons in GaN semiconductor are calculated by the Monte Carlo method. We studied the electron transport at temperatures of 10, 77, and 300 K under low and moderate electric fields. We found that, at low temperatures and low electric fields (a few hundreds of V/cm), the second “ohmic” region is to be observed on the I-V characteristic. In this case, the mean energy is very slowly dependent on the field. The streaming effect can occur in bulk GaN with low electron concentration (<10¹⁶ cm⁻³) at low temperatures and electric fields of a few kV/cm

Electron transport in crossed electric and magnetic fields under the condition of the electron streaming in GaN

High-field electron transport has been studied in crossed electric and magnetic fields in bulk GaN with doping of 10¹⁶ 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 value

Comparison of electron transport in polar materials for the models of low-density and high-density electron gas. Application to bulk GaN

We analyzed the steady-state electron transport for bulk GaN in frame of two opposite approaches: the electron temperature approach that assumes a high-density electron gas and numerical single-particle Monte-Carlo method that assumes a lowdensity electron gas and does not take into account electron-electron (e-e) scattering. We have also presented an analytical solution of the Boltzmann transport equation based on diffusion approximation. The transport characteristics such as the drift velocity electric field, V d (E), and mean electron energy electric field, ε(E), have been calculated at nitrogen and room temperatures in the wide range of applied electric fields from zero fields up to runaway ones (~100 kV/cm) for both approaches. Our calculations were performed for doped semiconductor with equal impurity and electron concentrations, Ni = n =10¹⁶ cm⁻³. The electron distribution functions in various ranges of applied fields have been also demonstrated. Within the range of heating applied fields 0– 300 V/cm, we found a strong difference between the transport characteristics obtained by means of the balance equations (electron temperature approach) and Monte-Carlo procedure. However, the Monte-Carlo calculations and diffusion approximation show a good agreement at 77 K. Within the range of moderate fields 1–10 kV/cm at 77 K, we established that the streaming effect can occur for low-density electron gas. In spite of significant dissimilarity of a streaming-like and a shifted Maxwellian distribution functions, the calculated values of Vd(E) and ε(E) show similar sub-linear behavior as the functions of the applied field E. In the high-field range 20–80 kV/cm, the streaming effect is broken down, and we observe practically linear behavior of both Vd(E) and ε(E) for both approaches. At higher fields, we point out the initiation of the runaway effect

Diffusion properties of electrons in GaN crystals subjected to electric and magnetic fields

We have studied the diffusion coefficient of hot electrons in GaN crystals under moderate electric (1...10 kV/cm) and magnetic (1...4 T) fields. Two configurations, parallel and crossed fields, have been analyzed. The study was carried out for compensated bulk- like GaN samples for various lattice temperatures (30...300 K) and impurity concentrations (10 16 ...10 17 cm -3 ). We found that at low lattice temperatures and low impurity concentrations, electric-field dependences of the transversal-to-current components of the diffusion tensor are non-monotonic for both configurations, while diffusion processes are mainly controlled by the magnetic field. With increasing the lattice temperature or impurity concentration, behaviour of the diffusion tensor becomes more monotonous and less affected by the magnetic field. We showed that this behaviour of the diffusion processes is caused by the distinct kinetics of hot electrons in polar semiconductors with strong electron-optical phonon coupling. We have suggested that measurements of the diffusion coefficient of electrons subjected to electric and magnetic fields facilitate identification of features of different electron transport regimes and development of more efficient devices and practical applications

Be-ion implanted p-n InSb diode for infrared applications. Modeling, fabrication and characterization

Transport theory for modeling the electric characteristics of high-quality p-n diodes has been developed. This theory takes into account a non-uniform profile of p- doping, finite thickness of the quasi-neutral regions and possible non-uniformity of the bulk recombination coefficient. The theory is based on related solutions of the Poisson equation, drift-diffusion equation and continuity equation with a generation-recombination term taking into account the simple band-to-band generation/recombination model. We have ascertained that the non-uniform profile of p-doping can lead to formation of p-n junctions with a specific two-slope form of the electrostatic barrier and two regions with the high built-in electric fields. We have found that at strong p + -doping the band structure of the InSb p-n junction has the form that can facilitate the emergence of additional mechanisms of current flow due to the tunneling and avalanche effects at the reverse bias. Using the literary data of the electron and hole lifetimes in InSb at cryogenic temperatures, we have found that the coefficient of bulk recombination can have an essential spatial dependence and considerably increases in the space charge region of p-n diode. The theory was applied to our analysis of p-n InSb diodes with p + -doping by using Be-ion implantation performed in ISP NASU. The theory predicts optimal conditions for detection of infrared emission. The technological process of fabrication, processing and testing has been described in details. Theoretically, it has been found that for parameters of the fabricated diodes and at 77 K the dark currents limited by diffusion and generation-recombination mechanisms should be less than 0.1 μA at the inverse bias of the order of 0.1 V. The measured diode’s I-V characteristics were expected to have strong asymmetry, however, dark currents are by one order larger than those predicted by theory. The latter can be associated with additional current mechanisms, namely: tunneling and avalanche effects