Mechanism of current leakage through metal/n-GaN interfaces

Oyama, Susumu; Hashizume, Tamotsu; Hasegawa, Hideki

doi:10.1016/s0169-4332(01)00902-3

Cited by 75 publications

(61 citation statements)

References 11 publications

(14 reference statements)

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“…Many workers believe that the AlGaN/GaN HFET will become the key device in the next-generation high frequency power electronics. Unfortunately, however, these devices still suffer from problems such as I -V dispersion, drain current collapse, [6][7][8][9][10][11] gate-and drain-lag, 12 and large gate leakage currents 13,14 whose mechanisms are not well understood. There is experimental evidence which empirically indicates that they are related to ways of surface preparation and surface passivation, and therefore to the presence of surface states.…”

Section: Introductionmentioning

confidence: 99%

Mechanisms of current collapse and gate leakage currents in AlGaN/GaN heterostructure field effect transistors

Hasegawa

Inagaki

Ootomo

et al. 2003

Journal of Vacuum Science &Amp; Technology B: Microelectronics and Nanometer Structures Processing, Measurement, and Phenomena

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212

153

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In order to clarify the mechanisms of drain current collapse and gate leakage currents in the AlGaN/GaN heterostructure field effect transistor ͑HFET͒, detailed electrical properties of the ungated portion and Schottky-gated portion of the device were investigated separately, using a gateless HFET structure and an AlGaN Schottky diode structure. The gateless device was subjected to plasma treatments and surface passivation processes including our novel Al 2 O 3 -based surface passivation. dc I -V curves of gateless HFETs were highly nonlinear due to virtual gating by surface states. After drain stress, air-exposed, H 2 plasma-treated and SiO 2 -deposited gateless HFETs showed an initial large-amplitude exponential current transient followed by a subsequent smaller, slow, and highly nonexponential response. The former was explained by emission from deep donors at E c Ϫ0.37 eV, and the latter by emission from surface states. Capture transients with stress-dependent capture barriers were also observed. An x-ray photoelectron spectroscopy ͑XPS͒ study indicated that 0.37 eV-deep donors are N-vacancy related. On the other hand, no current transients took place in N 2 plasma treated and Al 2 O 3 -passivated samples. Temperature dependences of I -V curves of Schottky diodes were extremely small and reverse currents were anomalously large. They were explained by the ''thin surface barrier'' ͑TSB͒ model where thermionic field emission and field emission through the TSB region formed by deep donors produce leakage current paths. By combining the results on gateless HFETs and Schottky diodes, a new unified model of near-surface electronic states for the free surface and Schottky interface of AlGaN is proposed. It consists of a U-shaped surface state continuum and N-vacancy related near-surface discrete deep donors. The model can explain the observed large gate leakage and drain current collapse in AlGaN/GaN HFETs in a unified way. It is also shown that our novel Al 2 O 3 passivation, when also used as a gate insulator, can completely suppress current collapse and gate leakage.

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Section: Introductionmentioning

confidence: 99%

Mechanisms of current collapse and gate leakage currents in AlGaN/GaN heterostructure field effect transistors

Hasegawa

Inagaki

Ootomo

et al. 2003

Journal of Vacuum Science &Amp; Technology B: Microelectronics and Nanometer Structures Processing, Measurement, and Phenomena

Self Cite

212

153

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“…In particular, leakage currents through Schottky contacts not only impede device reliability but also degrade power efficiency and noise performance in such devices. In spite of the fact that Schottky diodes formed on GaN and AlGaN are suffering from excess reverse leakage currents that are many orders of magnitude larger than the prediction of the thermionic emission ͑TE͒ model, [1][2][3][4][5][6] only a few studies have focused on the reverse-current characteristics quantitatively.…”

mentioning

confidence: 99%

Leakage mechanism in GaN and AlGaN Schottky interfaces

Hashizume¹,

Kotani²,

Hasegawa³

2004

Applied Physics Letters

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182

112

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Based on detailed temperature-dependent current-voltage (I -V -T) measurements the mechanism of leakage currents through GaN and AlGaN Schottky interfaces is discussed. The experiments were compared to calculations based on thin surface barrier model in which the effects of surface defects were taken into account. Our simulation method reproduced the experimental I -V -T characteristics of the GaN and AlGaN Schottky diodes, and gave excellent fitting results to the reported Schottky I -V curves in GaN for both forward and reverse biases at different temperatures. The present results indicate that the barrier thinning caused by unintentional surface-defect donors enhances the tunneling transport processes, leading to large leakage currents through GaN and AlGaN Schottky interfaces. © 2004 American Institute of Physics. ͓DOI: 10.1063/1.1762980͔ Although significant progress has been achieved in GaNbased high-power/high-frequency electronic devices and ultraviolet photodetectors, surface-related problems still need an immediate solution. In particular, leakage currents through Schottky contacts not only impede device reliability but also degrade power efficiency and noise performance in such devices. In spite of the fact that Schottky diodes formed on GaN and AlGaN are suffering from excess reverse leakage currents that are many orders of magnitude larger than the prediction of the thermionic emission ͑TE͒ model, 1-6 only a few studies have focused on the reverse-current characteristics quantitatively.Yu et al. 7 and Miller et al. 8 discussed the leakage mechanism in GaN and AlGaN Schottky interfaces on the basis of the field-emission ͑FE͒ tunneling transport assuming a triangular Schottky potential. However, unreasonably higher donor densities than the actual doping concentration were required in their calculation for reproduction of the experimental data. Thus, they expected some other processes such as defect-assisted tunneling to enhance leakage currents. Other groups also suggested the trap-assisted tunneling model to explain the leakage mechanism in the reverse bias region. 2,9 However, such model requires an unlikely multistep tunneling process or defect continuum with a wide energy band throughout a depletion region in semiconductor. Sawada et al. 10 proposed a surface patch model to explain forward current characteristics. Miller et al. 11 have recently suggested a leakage mechanism associated with a variablerange-hopping conduction through threading dislocations. However, little is known for the physical mechanism of excess leakage currents in GaN and AlGaN Schottky diodes.This letter discusses the mechanism of leakage currents through GaN Schottky interfaces, investigating transport properties of Schottky diodes using temperature-dependent current-voltage (I -V -T) measurements for both forward and reverse biases. A simulation method for the calculation of currents based on the thin surface barrier ͑TSB͒ model 5 is discussed. The measured currents were compared to the calculated ones for different tempe...

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“…The high electric fields encountered in SiC and other wide band gap materials lead to significant tunneling through the Schottky barrier thus increasing the leakage current by many orders of magnitude over that predicted by simple thermionic emission (TE) calculations [3][4][5][6][7][8][9][10]. However, the tunneling leakage current, which calculated with the extracted SBH from forward I-V data, is discrepancy of the experimental data [3], [4], [9]. In these works, the authors assume that the barrier height does not depend on the applied bias despite the bias voltage is elevated.…”

Section: Introductionmentioning

confidence: 99%

Reverse bias-dependence of schottky barrier height on silicon carbide: influence of the temperature and donor concentration

Latreche¹

2014

International Journal of Physical Research

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The work deals with the dependences of the Schottky barrier height (SBH) on the reverse bias voltage, temperature and on donor concentration of metal/4H-SiC Schottky diodes. Using the tunneling modeling we have shown that the Schottky barrier height on silicon carbide strongly depends on the reverse bias voltage, temperature and doping concentration. At room temperature, the Schottky barrier height increases with increasing the reverse bias voltage at high doping concentration (about 10 16 cm -3 ), while, at low doping concentration (about 10 15 cm -3 ) the Schottky barrier height decreases with increasing the reverse bias voltage. These behaviors are independent of the Schottky barrier lowering effect. That means other effects occur at the barrier and depend on the reverse applied bias. The barrier height increases with increasing temperature and doping concentration under reverse bias conditions. The barrier heights extracted from the Padovani-Stratton formulas are close to the barrier heights extracted from the Tsu-Esaki formula in particular for the thermionic-field emission.

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Mechanism of current leakage through metal/n-GaN interfaces

Cited by 75 publications

References 11 publications

Mechanisms of current collapse and gate leakage currents in AlGaN/GaN heterostructure field effect transistors

Mechanisms of current collapse and gate leakage currents in AlGaN/GaN heterostructure field effect transistors

Leakage mechanism in GaN and AlGaN Schottky interfaces

Reverse bias-dependence of schottky barrier height on silicon carbide: influence of the temperature and donor concentration

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