Electron drift velocity in AlGaN/GaN channel at high electric fields

Ardaravičius, L.; Matulionis, A.; Liberis, J.; Kiprijanovič, O.; Ramonas, M.; Eastman, L.F.; Shealy, J. R.; Vertiatchikh, A.

doi:10.1063/1.1626258

Cited by 109 publications

(59 citation statements)

References 18 publications

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“…In the case of the heterostructures, models were created to study the role of non-equilibrium optical phonons and how they can lower the average drift velocity. The velocity observed in the experiments of this study is incompatible with the onset of non-equilibrium phonons that has been suggested earlier to explain low observed velocities [17]. Hence, the reduction observed earlier is unlikely to be due to the onset of non-equilibrium phonons, and more likely to inhomogeneity effects, as well as poor contacts.…”

Section: Bothcontrasting

confidence: 51%

“…In contrast to this, however, there are both experiments and Monte Carlo simulations which suggest that a much lower value of the velocity occurs, of the order of 1×10 7 cm/s at fields above 10 kV/cm [14,15,16]. This same group has, however, obtained a drift velocity above 2×10 7 cm/s at around 140 kV/cm [17], with essentially linear behavior at lower fields, by using short pulses. They attribute the lower values observed earlier to carrier heating.…”

Section: Introductionmentioning

confidence: 86%

“…Nevertheless, neither of these reports have the velocity predicted for this heterostructure, and the importance of non-equilibrium phonons was suggested as being important in lowering the velocity [17].…”

Section: Introductionmentioning

confidence: 99%

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High field effects of GaN HEMTs.

Barker

Shul

2004

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This report represents the completion of a Laboratory-Directed Research and Development (LDRD) program to develop and fabricate geometric test structures for the measurement of transport properties in bulk GaN and AlGaN/GaN heterostructures. A large part of this study was spent examining fabrication issues related to the test structures used in these measurements, due to the fact that GaN processing is still in its infancy. One such issue had to do with surface passivation. Test samples without a surface passivation, often failed at electric fields below 50 kV/cm, due to surface breakdown. A silicon nitride passivation layer of approximately 200 nm was used to reduce the effects of surface states and premature surface breakdown. Another issue was finding quality contacts for the material, especially in the case of the AlGaN/GaN heterostructure samples. Poor contact performance in the heterostructures plagued the test structures with lower than expected velocities due to carrier injection from the contacts themselves. Using a titanium-rich ohmic contact reduced the contact resistance and stopped the carrier injection. The final test structures had an etch constriction with 3 varying lengths and widths (8×2, 10×3, 12x3, 12×4, 15×5, and 16×4 m) and massive contacts. A pulsed voltage input and a four-point measurement in a 50 Ω environment was used to determine the current through and the voltage dropped across the constriction. From these measurements, the drift velocity as a function of the applied electric field was calculated and thus, the velocity-field characteristics in n-type bulk GaN and AlGaN/GaN test structures were determined. These measurements show an apparent saturation velocity near to 2.5×10 7 cm/s at 180 kV/cm and 3.1×10 7 cm/s, at a field of 140 kV/cm, for the bulk GaN and AlGaN heterostructure samples, respectively.These experimental drift velocities mark the highest velocities measured in these materials to date and confirm the predictions of previous theoretical models using ensemble Monte Carlo simulations.

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Section: Bothcontrasting

confidence: 51%

Section: Introductionmentioning

confidence: 86%

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High field effects of GaN HEMTs.

Barker

Shul

2004

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“…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.…”

Section: ͑2͒mentioning

confidence: 99%

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

Danilchenko

Zelensky

Drok

et al. 2007

Applied Physics Letters

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The authors report a large response in the conductivity of AlGaN∕GaN heterostructures to a 10ns UV laser pulses. The dynamics of the conductivity response follows the time evolution of the laser pulse. This fast photoconductivity component shows a remarkable enhancement in high electric fields. For the field ≈15kV∕cm, it increases by at least one order of magnitude at temperatures of 4.2 and 300K. This photoconductivity enhancement is found to be related to the hot electron effect. The authors propose an explanation for the observed phenomena. The mechanism of the photoconductivity enhancement involves nonequilibrium LO phonons generated by hot carriers.

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“…6 Thus, correct measurements of this characteristic have to be done in pulse regimes. [7][8][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.…”

mentioning

confidence: 99%

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

Danilchenko

Zelensky

Drok

et al. 2004

Applied Physics Letters

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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 ...

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Electron drift velocity in AlGaN/GaN channel at high electric fields

Cited by 109 publications

References 18 publications

High field effects of GaN HEMTs.

High field effects of GaN HEMTs.

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

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

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