Hot-electron transport in AlGaN∕GaN two-dimensional conducting channels

Abstract

We report on experimental studies of high-field electron transport in AlGaN / GaN two-dimensional electron gas. The velocity-electric field characteristics are extracted from 10 to 30 ns pulsed current-voltage measurements for 4.2 and 300 K. An electron drift velocity as high as 1.7 ϫ 10 7 cm/ s was obtained in the fields 150 kV/ cm. Estimates of thermal budget of the system show that overheating of the electrons exceeds 1700 K at highest electric fields achieved in the experiment. Group III-nitride materials possess unique physical properties, which allow one to suggest that the materials have excellent potential for applications in high-power, highfrequency, and high-temperature electronics. 1 These suggestions are based mainly on theoretical results on high-field transport [see, for example, Refs. 2-4]. To date, there is a lack of experimental data on specific characteristics of both bulklike and heterostructure nitrides under high fields.For the nitride materials, large electron concentrations are rather typical. This provides a dominance of electronelectron collisions over other scattering mechanisms, and implies that the distribution function of the electrons under nonequilibrium occurs in the form close to the shifted Maxwellian function. Such a distribution is characterized by two parameters: an effective electron temperature T e and a drift velocity V dr . The achieved drift velocity is of fundamental importance, since it determines the current, high-speed capability, and high-frequency operation. For nitrides, the theory predicts V dr as high as 2 ϫ 10 7 to 3 ϫ 10 7 cm/ s in dc fields about 130-150 kV/ cm. Time-resolved measurements 5 of electroabsorption in GaN confirm achieving very high velocities for ultrashort ͑ϳ200 fs͒ time intervals. However, for steady-state or quasi-steady-state conditions, direct measurements of the drift velocity meet considerable difficulties. Particularly, high electric fields and currents in the nitrides give rise to high dissipative power and a large Joule heating. The latter, in turn, induces additional electron scattering and limits V dr , masking truly nonequilibrium hot-electron effects. 6 Thus, correct measurements of this characteristic have to be done in pulse regimes. 7-9 Another parameter, the electron temperature, determines stochastic characteristics of the electrons, their fluctuations, and current noise. In this letter, we present experimental results on the velocity-field characteristics in AlGaN / GaN heterostructures obtained by using 10-30 ns pulse current-voltage measurements in the range of electric fields up to 150 kV/ cm. We also estimate and discuss the electron temperature of nonequilibrium electrons.The investigated devices were fabricated from Since the contacts contribute to the voltage drop along the sample, for correct determination of the average electric field in the device, the contact resistance was carefully measured in the low-field regime.To determine the electron drift velocity, we used the relationshipwhere I is the current, e is the ...

Electron transport in a coupled GaN/AlN/GaN channel of nitride HFET

“…The cut-off frequency is related to the average carrier velocity in a two-dimensional electron gas (2DEG) channel. The experimental reports show that the room temperature electron velocity values in GaN-based 2DEG channels lie between (1-3)×10 7 cm/s [3][4][5][6][7][8][9]. While the low-field electron mobility tends to decrease as the density of 2DEG increases, the high-field drift velocity is not a monotonous function of the density [10].…”

Enhancement by electric field of high-speed photoconductivity in AlGaN∕GaN heterostructures

“…The obtained value of the activation energy practically coincides with the energy of the LO phonons in GaN, 92 meV, which was deduced from hot carrier transport experiments. 7,9 About the same phonon energy of 91 meV was obtained from optical measurements. 10 The coincidence of the activation energy extracted from photoconductivity measurements and the LO-phonon energy seems to be unexpected.…”

“…Using the mobility comparison method, 7,8 we deduced the field dependence of the electron temperature in the conducting channel T e ͑E͒, which is shown in the inset to Fig. 3.…”

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

“…The strong electron-opticalphonon coupling, large optical phonon energy, sufficiently high electron mobility are inherent for these materials [1][2][3]. In the literature, nitride materials are widely discussed as candidates for development of the electrical pumping THz sources, particularly, based on the Gunn effect (under ultra-strong applied electric fields ≈100 kV/cm) [4][5][6][7] as well as streaming transport regime and the optical-phonon transit-time resonance (OPTTR) (under moderate applied electric fields ≈2…10 kV/cm) [8][9][10][11][12]. The streaming transport regime is associated with formation of the strongly-anisotropic distribution function under the sufficiently strong applied electric field.…”