Two-dimensional Hot Electrons Research Articles

Quantum coupling and self-heating impacts on threshold voltages of GaN metal–insulator-semiconductor high-electron-mobility transistors

A transient heat conduction equation has been proposed to describe the cooling process of a hot two-dimensional electron gas layer in a GaN-based transistor. This equation serves as the basis for a physical analytical model that explains the impacts of hot electrons in the hot two-dimensional electron gas layer via quantum coupling on the threshold voltage of GaN-based transistors. The temperature of the two-dimensional electron gas layer decreases to ambient temperature as time increases, and the threshold voltage shifts caused by such a temperature will recover with time. The proposed model accurately reflects the observed recovery of threshold voltage over time in experiments. At the same time, it offers insight into how the gate voltage, the source-drain voltage, and the ambient temperature can shift the threshold voltage in these transistors. The simplicity and analytic nature of this proposed model not only provide a physical origin of the threshold voltage instability in GaN-based devices but also offer the possibility for improving device reliability by selecting appropriate device physical parameters.

Electron heating in GaN/AlGaN quantum well in a longitudinal electric field

The heating of electrons under longitudinal optical phonon scattering in a triangular GaN/AlGaN quantum well was studied theoretically. The energy loss rate of electrons was calculated in consideration of the dynamical screening and the hot phonon effect. The dependence of the electron temperature on the longitudinal electric field was calculated. The integral terahertz emission of hot two-dimensional electrons was simulated. The role of coupled plasmon-phonon mode scattering in the GaN/AlGaN quantum well was discussed.

Emission of terahertz radiation from selectively doped AlGaN/GaN heterostructures under the heating of two-dimensional electrons by an electric field

The emission of terahertz radiation from a AlGaN/GaN heterostructure under the heating of two-dimensional electrons in a lateral electric field is studied. The field dependence of the temperature of hot electrons is determined from an analysis of experimental volt-ampere characteristics. A theoretical model of the thermal radiation of hot two-dimensional electrons is considered, and the calculation results are compared with an experiment on terahertz radiation emission.

Particle swarm approach for parameter optimization of quantum well nano structure

Analytical optimization techniques suffer from slow convergence in complex solution space. Heuristics-based swarm intelligence is an efficient alternative to analytical optimization techniques. In this paper, particle swarm optimization approach is utilized for better and efficient nano-device modeling. Mobility of two-dimensional hot electrons in modulation doped square quantum well of AlGaAs/GaAs which is determined using heated drifted Fermi–Dirac distribution function and relevant scattering mechanisms is taken as the fitness/objective function. The 2D carrier concentration, quantum well width and lattice temperature of the quantum well are taken as the input variables. The algorithm with three input variables is then utilized to get optimized values of input parameters to get desired ac and dc mobility values.

Blackbody-like emission of terahertz radiation from AlGaN/GaN heterostructure under electron heating in lateral electric field

The authors report on the observation and study of terahertz radiation emission from modulation-doped AlGaN/GaN heterostructure under conditions of heating of a two-dimensional electron gas in the lateral electric field. The experimental results are compared with the theoretical model of blackbody-like emission from hot two-dimensional electrons. Complementary transport measurements and a theoretical simulation were carried out to determine the dependence of effective electron temperature on electric field. The role of nonequilibrium optical phonon accumulation is discussed.

High Frequency Transport of Two-Dimensional Hot Electrons in CdS Quantum Well with Inserted Barrier Layer

High frequency transport of two-dimensional hot electrons in a CdS quantum well with an inserted barrier layer is studied in the framework of a heated drifted Fermi-Dirac distribution function for the carrier characterised by an electron temperature and a drifted crystal momentum. Carrier scattering by acoustic deformation potential, polar optic phonons and background ionized impurities are incorporated in the present calculations. The insertion of the thin barrier layer leads to a decrease in carrier scattering and to an increase in carrier mobility. The variation of ac and dc mobility with quantum well width and 2D electron concentration in the presence of field are also calculated. It was found that mobility increases with increase in both the channel width and the 2D carrier concentration. The 3 dB cut-off frequency is found to be enhanced reflecting better high frequency response upon introduction of thin barrier layer into the CdS quantum well.

Millimeter and Sub-millimeter wave Response of Two-Dimensional Hot Electrons in delta doped PbTe Quantum Well

Millimeter and sub-millimeter wave response of two-dimensional hot electrons in double delta doped GaAs quantum well is studied here incorporating deformation potential acoustic, polar optic, ionized background and remote impurity scatterings in the framework of heated drifted Fermi-Dirac distribution function. The inclusion of delta doping is found to enhance the two-dimensional electron density which in turn improves the ac mobility in the GaAs quantum wells thereby providing scope of getting higher speed devices in future.

Effects of Double Delta Doping on Millimeter and Sub-millimeter Wave Response of Two-Dimensional Hot Electrons in GaAs Nanostructures

Effects of Double Delta Doping on Millimeter and Sub-millimeter Wave Response of Two-Dimensional Hot Electrons in GaAs Nanostructures

Optical absorption coefficients in two-dimensional semiconductors under strong magnetic field

We calculate the photon absorption coefficient of hot two-dimensional electrons in the presence of a strong magnetic field. The electrons interact strongly with the optical phonons and the acoustic phonons in quantum wells. The dependence of the optical absorption on the magnetic field is obtained by using the quantum mechanical kinetic theory. It is found that the photon absorption spectrum displays a local magnetophonon resonance. The magnetophonon absorption resulting from inelastic scattering between Landau levels is more pronounced at higher temperature. The effect of subband nonparabolicity on the absorption coefficient is also discussed.

Resonant Optical Absorption in Semiconductor Quantum Wells

We have calculated the intraband photon absorption coefficients of hottwo-dimensional electrons interacting with polar-optical phonon modes inquantum wells. The dependence of the photon absorption coefficients on thephoton wavelength λ is obtained both by using the quantummechanical theory and by the balance-equation theory. It is found that thephoton absorption spectrum displays a local resonant maximum, correspondingto LO energy, and the absorption peak vanishes with increasing theelectronic temperature.

Effects of acoustic anisotropy and screening on the energy relaxation of hot electrons in heterojunctions and quantum wells

In this paper we present theoretical calculations of the angle and mode dependence of the phonon emission by hot two-dimensional electrons in gallium arsenide. We compare them with experimental results of heat-pulse studies of the acoustic-phonon emission in ${\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}/\mathrm{A}\mathrm{l}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}$ heterojunctions and GaAs quantum wells. It is shown that the ratio of the strengths of the longitudinal- and transverse-acoustic modes is correctly predicted only by a theoretical model that properly includes the effects of acoustic anisotropy on the electron-phonon matrix elements, screening, and the form of the confining potential. As a result of this work, we are finally able to account for why longitudinal phonon emission from a heterojunction is not seen in heat-pulse experiments despite the fact that earlier theories predicted that it should be the dominant mode.

Thermodynamic Energy of Semi-Infinite Solids with a Two-Dimensional Hot Electron Gas near the Surface

Expressions for the thermodynamic energy of semi-infinite solids with a hot electron layer near the stress-free surface are derived for films and for large samples. Conditions are determined under which this energy is associated with the hot electron excitation energy, with the nonequilibrium Rayleigh waves energy, and with the equilibrium bulk phonon energy. The calculations use the Keldysh diagram technique.

Efficient Silicon Device Simulation with the Local Iterative Monte Carlo Method

The Local Iterative Monte Carlo technique (LIMO) is used for an effective simulation of hot electron distributions in silicon MOSFETs. This new Monte Carlo approach yields an efficient use of the computational resources due to a different iteration scheme. In addition the necessary computation time can be further reduced by a reuse of the computational expensive MC step simulation results in the iteration process. The later possibility is investigated in detail in this work. Results for short channel MOSFETs demonstrates that correct two-dimensional hot electron distributions can be calculated by LIMO within 1 hour on a standard work station.

High electric field transport inIn0.53Ga0.47Asquantum wells under nonquantizing magnetic fields at low temperatures

Hall mobility, magnetoresistance coefficient, and Hall-to-drift mobility ratio of two-dimensional hot electrons in ${\mathrm{In}}_{0.53}{\mathrm{Ga}}_{0.47}\mathrm{As}$ square quantum wells are calculated for classical magnetic fields for lattice temperatures in the range 4\char21{}15 K considering the degeneracy of the distribution function and incorporating screened deformation-potential acoustic, ionized impurity, and alloy disorder scattering. The variations of the galvanomagnetic coefficients with the channel width, the lattice temperature, and the electric and magnetic fields are studied. The magnetoresistance is found to change more remarkably than the Hall mobility or the Hall ratio with changes in the lattice temperature, the channel width, and the electric and magnetic fields.

Two-dimensional hot-electron transport in GaAs-AlGaAs heterojunctions

The mobility of a two-dimensional electron gas in GaAs-AlGaAs heterojunction is recomputed through solving numerically the balance equation. The peculiarity of the present study lies in that a new expression for the distribution function and the renormalized phonon frequency are used in the computation. Compared with those reported by previous authors, our result shows better agreement with the experimental data.

Observation of energy loss by a hot two-dimensional electron gas into coupled plasmon–phonon modes

We observed the phonons emitted by a two-dimensional electron gas in GaAs/AlGaAs heterojunctions for various carrier concentrations, by a nanosecond pulse technique. We found that the feature which has usually been regarded as the crossover from acoustic to optic phonon emission then occurred at different power levels. We propose that a process of energy loss via excitation of coupled plasmon–optic phonon modes can explain this and other results, notably the weakness of the longitudinal mode observed, and the high value of the measured energy loss.

Angular and mode distribution of acoustic phonon emission by hot 2D electrons in GaAs: the effect of acoustic anisotropy and screening

We report a detailed theoretical study of the angular and polarization dependence of the acoustic phonon emission by a hot two-dimensional electron gas (2DEG) in GaAs/AlGaAs heterojunctions and quantum wells (QW) and compare the results with some recent heat pulse measurements. We use a model which not only includes the dynamical screening of electron–phonon interaction but also takes proper account of the finite “thickness” of the 2D gas and above all, considers the strong acoustic anisotropy of the electron–phonon matrix elements and the propagation process. For QW with different widths we demonstrate the strong dependence of the angular distribution on the well width. For heterostructures in the (0 0 1)-plane, we can explain, in contrast to earlier theoretical studies, the phenomena of missing longitudinal modes for phonon emission close to the two-dimenional electron gas (2DEG) normal.

Low-temperature galvanomagnetic transport coefficients of the two-dimensional hot electrons in GaAs quantum wells

Galvanomagnetic transport coefficients of the two-dimensional hot electrons in a square quantum well of GaAs were calculated for lattice temperatures of 4, 10 and 15 K using a heated Fermi–Dirac distribution function. Electron energy loss via screened deformation potential acoustic phonon scattering was considered. In electron momentum loss, background ionized impurity scattering was additionally incorporated. The magnetoresistance coefficient was found to be more sensitive than the Hall mobility to the changes in the channel width, magnetic field, and electric field.

Effects of nonequilibrium longitudinal optic phonons on the high-frequency response of the two-dimensional hot electrons in polar semiconductor quantum wells

The high-frequency response of degenerate hot electrons itinerant two-dimensionally in GaAs and square quantum wells are studied, incorporating the relevant scattering mechanisms and the effects of the nonequilibrium longitudinal optic phonons. The 3 dB cut-off frequency where small-signal AC mobility falls to 0.707 of its low-frequency value is found to be significantly enhanced when the nonequilibrium phonons are included.

Phonon emission by hot 2D electrons and holes in a Gallium Arsenide heterojunction: The influence of screening and acoustic anisotropy

The process of energy relaxation by phonon emission of hot two-dimensional electrons and holes in GaAs/AlGaAs heterojunctions has been studied using the heat-pulse technique for carrier temperatures below 40 K. To explain the experimental findings and to understand fully the process of electron– (or hole–) phonon coupling, theoretical calculations of the angular and polarization dependence of the emitted acoustic phonons were made. Phonon emission studies give detailed information concerning the phonon wave vector and polarization dependence of the emission process. This allows, in connection with the corresponding numerical simulations, interesting conclusions regarding the properties of the 2D carrier system itself (e.g. strength of carrier–phonon coupling constants, confinement of the 2D carriers perpendicular to the 2D system) to be reached.