Current relaxation analysis in AlGaN/GaN high electron mobility transistors

Polyakov, A. Y.; Smirnov, N. B.; Shchemerov, Ivan; Lee, In Hwan; Jang, T.; Dorofeev, A. A.; Gladysheva, N. B.; Kondratyev, E. S.; Turusova, Yulia A.; Zinovyev, R. A.; Turutin, Andrei V.; Ren, F.; Pearton, S. J.

doi:10.1116/1.4973973

Cited by 14 publications

(46 citation statements)

References 38 publications

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“…9,[15][16][17] In this paper, we suggest both phenomena (i.e. temperature activated capture with no temperature activated current and the appearance of hole traps signals) can be attributed to multistage process involving deep traps in the AlGaN barrier emitting and subsequently capturing electrons, forming a step in the space charge moving toward the AlGaN/GaN interface.…”

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confidence: 99%

“…Good fits can be achieved when using 2-3 extended exponents describing capture and emission in the presence of broadened barriers for capture, or by Gaussian broadening of the logarithm of relaxation time describing broadening of the discrete level into Gaussian energy bands. 9 The advantage of this approach is the much faster convergence while providing physically meaningful parameters of the broadening process.One of the things that still requires better understanding is the frequent observation of the capture process being thermally activated, with the activation energy of 0.4-0.9 eV. 6,[9][10][11] In the basic model * Electrochemical Society Fellow.…”

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confidence: 99%

“…9 The advantage of this approach is the much faster convergence while providing physically meaningful parameters of the broadening process.…”

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confidence: 99%

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Gate-Lag in AlGaN/GaN High Electron Mobility Transistors: A Model of Charge Capture

Polyakov

Smirnov

Shchemerov

et al. 2017

ECS J. Solid State Sci. Technol.

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Gate and drain current transients following the application of a step/pulse reverse bias to the gate of AlGaN/GaN HEMTs can be described by a superposition of 2-3 extended exponents with characteristic times of the main process having activation energy of 0.7-0.8 eV. The drain current relaxation is a consequence of charge trapping and movement in the AlGaN barrier. A qualitative model explains this process by movement of a step of charge trapped on deep states in the barrier and movement of the step toward the interface by multiple emission/capture hops. The process is assumed to be confined to channels in AlGaN (presumably dislocations) surrounded by potential barriers, preventing effective injection of the carriers into the channels with forward bias pulses. The model qualitatively explains the often reported appearance of hole-trap-like signals in deep level studies of AlGaN/GaN HEMT structures and the persistent changes in capacitance and current of these structures occurring upon pulsing and illumination. One of the most serious problems with III-Nitrides-based high electron mobility transistors (HEMTs) is the phase delay of the drain current upon pulsed change of the gate bias, so called "gate-lag". [1][2][3] This phenomenon causes increase of the switching time and long-term drift of the threshold voltage and the drain current. The generally accepted view is the gate-lag is caused by trapping of electrons flowing from the gate at high reverse voltage and subsequent capture of electrons by deep centers under the gate. Both the capture and emission process from these traps can be studied by analysis of gate and drain transients as a function of pulsing conditions and temperature by using current or capacitance deep level transient spectroscopy (CDLTS or DLTS) 2-5 or by direct measurements of individual transients.1,6-9These measurements provide the concentration and position of the traps involved and their capture cross sections. This is complicated by the presence of multiple traps, strong non-uniform electrical and strain fields, and the contribution of the band-like states related to extended defects and to surface or interface states. As a result, the drain and gate current relaxation curves are non-exponential. A common approach is the deconvolution of the actual relaxations into a sum of independent exponential relaxations and fitting the pre-exponential coefficients to experiment.6 Various methods to improve the convergence and reproducibility of the procedure exist. 7,8 Another popular approach is to build the derivative of the relaxation curve on the logarithm of time, find the peaks in such plots, and trace the peak position variation with temperature to extract the activation energy and capture cross section of the traps.2,3,9 The number of peaks in either approach is quite limited (typically, 2-3) in either method, 9 but the peaks are generally broad which requires invoking a large number of exponents to attain good fit in the basic method, 6 while providing no knowledge on the physical nature o...

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Gate-Lag in AlGaN/GaN High Electron Mobility Transistors: A Model of Charge Capture

Polyakov

Smirnov

Shchemerov

et al. 2017

ECS J. Solid State Sci. Technol.

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“…Gaussian-Broadening.-Polyakov et al 22 have proposed the possibility of band-like distribution of defect states in the band-gap, as opposed to a discrete energy level, that can contribute to widening of the peak observed in the current transients. Such a band of defect states are expected to be distributed around a peak energy level E o .…”

Section: Resultsmentioning

confidence: 99%

“…More recently, non-exponential nature of transients has been attributed to the presence of band-like distribution of trap states in the GaN band-gap. 22 This work presents and discusses in detail, using FLOODS TCAD, how factors associated with defect distribution in the band-gap can individually affect the nature of the drain-current transient response. To the author's knowledge, very few works have discussed multiple trap levels in a TCAD framework 23 and none have considered establishing a comprehensive understanding of how different trap parameters can influence the nature of transients.…”

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confidence: 99%

Simulation of Deep-Level Trap Distributions in AlGaN/GaN HEMTs and Its Influence on Transient Analysis of Drain Current

Mukherjee

Patrick

Law

2017

ECS J. Solid State Sci. Technol.

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AlGaN/GaN high electron mobility transistors for high efficiency power switching applications are susceptible to charge trapping by deep-levels in the GaN buffer resulting in current collapse during gate and drain voltage swings. Although drain-current transient based methodologies have been used consistently to extract trap parameters, the factors affecting the non-exponential nature of the transient are still not well understood. No effort at accurately replicating multiple deep-levels in the GaN buffer to simulate transient response of GaN based power devices has been reported previously. In this work, we present numerical simulation results of HEMTs having multiple discrete trap states as well as band-like distribution of traps in the GaN band-gap. GaN based High Electron Mobility Transistors (HEMT)s, which leverage wide-band-gap related properties, are established as ideal candidates for high-power, high-efficiency and high-frequency applications ranging from RF communication to power conversion. 1,2However, the most unremitting technological challenge limiting the wide-spread adoption of GaN process technology is understanding and predicting their reliability and degradation modes therein. Many concur that most of the reliability-limiting mechanisms and issues are related to the presence of defect states in the forbidden band-gap of GaN, and the subsequent performance degradation associated with such defects. [3][4][5][6][7][8] Drain-current transient analysis experiments have helped shed light on the degradation observed in switching performance, often manifesting in AlGaN/GaN HEMTs as gate lag, drain lag and current collapse.9,10 The collapse is attributed to electron trapping comprised of lateral and vertical components. The lateral component due to tunneling of electrons from the gate to surface states at the AlGaN/insulator interface is facilitated by large bias difference between the gate and drain (under off-state and high drain bias).11-13 However, this phenomenon has been observed to be suppressed by improved passivation techniques.13 Under similar bias conditions, a vertical trapping component, which deteriorates dynamic performance, dominates in devices with improves passivation. The mechanism is expected to involve injection of 2DEG electrons deeper into the buffer and consequent trapping for several buffer designs. [8][9][10][11][12][13] If the traps directly underneath the gate dominate, a shift in dynamic threshold is observed. However, if the traps in the drain access region dominate, they end up depleting the 2DEG in this region thereby increasing the dynamic on-resistance.Much of experimental work identifying GaN buffer traps responsible for deterioration of dynamic performance utilize thermal dependence of the relaxation time constants to extract trap activation energy.11,14 Current relaxation time constants are obtained by taking the derivative of such transients and typically indicate the presence of multiple trapping centers. The extracted derivatives assume an asymmetric shape, with ...

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An Improved Performance of High Power Application of Al0.25Ga0.75N/AlN/GaN/Al0.25Ga0.75N Pseudo-morphic High Electron Mobility Transistor (PHEMT): Numerical Simulation Study

Khaouani

Hamdoune

Bouazza

et al. 2021

Artificial Intelligence and Heuristics for Smart Energy Efficiency in Smart Cities

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Current relaxation analysis in AlGaN/GaN high electron mobility transistors

Cited by 14 publications

References 38 publications

Gate-Lag in AlGaN/GaN High Electron Mobility Transistors: A Model of Charge Capture

Gate-Lag in AlGaN/GaN High Electron Mobility Transistors: A Model of Charge Capture

Simulation of Deep-Level Trap Distributions in AlGaN/GaN HEMTs and Its Influence on Transient Analysis of Drain Current

An Improved Performance of High Power Application of Al0.25Ga0.75N/AlN/GaN/Al0.25Ga0.75N Pseudo-morphic High Electron Mobility Transistor (PHEMT): Numerical Simulation Study

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