Large reduction of leakage currents in AlGaN Schottky diodes by a surface control process and its mechanism

Kotani, Junji; Kaneko, Motozo; Hasegawa, Hideki; Hashizume, Tamotsu

doi:10.1116/1.2216722

Cited by 50 publications

(43 citation statements)

References 31 publications

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“…Before applying the surface control process, leakage currents in the Pd Schottky diode were very large, about 10 −3 -10 −4 A/cm 2 at a reverse bias of −1.5 V. Current changes caused by hydrogen exposure in such diodes were very small, 2 one order of magnitude at most at exposure to 10 Torr hydrogen. On the other hand, by applying the surface control process, reverse current densities of the diode were reduced by three to four orders of magnitude down to about 10 −7 A/cm 2 at a reverse bias of −1.5 V. Thus, the surface control process is not only effective for Au/ Ni Schottky diodes as reported previously, 10 but also for Pd Schottky diodes. This effect not only increased the hydrogen sensitivity of the diode, but also made a detailed analysis of the I-V and C-V characteristics as presented here possible.…”

Section: A Effect Of Surface Control Process On I-v Characteristics mentioning

confidence: 50%

“…In order to remove oxygen from the AlGaN layer, a surface control process, which we recently proposed, 10 was applied before Pd deposition. As shown in Fig.…”

Section: Methodsmentioning

confidence: 99%

“…[3][4][5][6][7] Recently, we explained the leakage currents in nitride-based Schottky barriers by the thin surface barrier ͑TSB͒ model 8,9 and, based on this, we have successfully reduced leakage currents in Ni/ Au/ AlGaN Schottky diodes by applying a novel surface control process for oxygen gettering. 10 The purpose of this article is to investigate hydrogen sensing characteristics and mechanism of a Pd/ AlGaN / GaN Schottky diode subjected to the oxygen gettering process. After oxygen gettering, the diode showed high hydrogen detection sensitivities and fast turn-on and turn-off characteristics in air.…”

Section: Introductionmentioning

confidence: 99%

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Hydrogen sensing characteristics and mechanism of Pd∕AlGaN∕GaN Schottky diodes subjected to oxygen gettering

Hasegawa

Akazawa

2007

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

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Hydrogen sensing characteristics in vacuum and in air were investigated on Pd Schottky diodes that were formed on AlGaN / GaN two-dimensional electron gas wafer and subjected to a surface control process for oxygen gettering. By applying the surface control process, leakage currents in Pd/ AlGaN / GaN Schottky diode were greatly reduced. Such diodes showed high hydrogen detection sensitivities and fast turn-on and -off characteristics in air, although they showed very slow turn-off behavior in vacuum. From detailed measurements of current-voltage ͑I-V͒, capacitance-voltage ͑C-V͒, and current transient characteristics, the sensing mechanism was explained in terms of Schottky barrier height reduction caused by formation of interface dipole by atomic hydrogen. It was shown that dipole formation is controlled in air by the Langmuir isotherm type adsorption behavior, including the reaction between atomic hydrogen and oxygen. Discrepancies in Schottky barrier height values deduced from I-V and C-V measurements have indicated that current transport is not by the standard thermionic emission process, but by the thermionic field emission process through the thin surface barrier ͑TSB͒ in accordance with the TSB model.

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Section: A Effect Of Surface Control Process On I-v Characteristics mentioning

confidence: 50%

“…In order to remove oxygen from the AlGaN layer, a surface control process, which we recently proposed, 10 was applied before Pd deposition. As shown in Fig.…”

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Hydrogen sensing characteristics and mechanism of Pd∕AlGaN∕GaN Schottky diodes subjected to oxygen gettering

Hasegawa

Akazawa

2007

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

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“…A good agreement between these SBH values indicated that the Ni/AlGaN structure had good interface quality without an additional interfacial layer such as an oxide layer. Although relatively high leakage currents flow at the reverse bias region, 12,13 as shown in Fig. 1͑a͒, an excellent linearity of 1 / C 2 -V plots is obtained in the given reverse bias range.…”

mentioning

confidence: 88%

Near-midgap deep levels in Al0.26Ga0.74N grown by metal-organic chemical vapor deposition

Sugawara

Kotani

Hashizume

2009

Applied Physics Letters

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A deep level with an activation energy of 1.0 eV in n-type Al 0.26 Ga 0.74 N grown by metal-organic chemical vapor deposition was detected by deep-level transient spectroscopy ͑DLTS͒ with a sampling time window of several seconds. The deep-level density was 6 ϫ 10 15 cm −3 . At the temperatures around which the DLTS peaks were observed, capacitance transient was measured. Under the dark condition, a capacitance increase was observed, corresponding to the thermal emission of electrons from the level with 1.0 eV activation energy. After that, we observed a large capacitance increase under illumination with 2.3 eV photon energy. On the basis of potential simulation taking account of deep levels, we found that the photoinduced capacitance change arose from electron emission from additional near-midgap levels in energy ranging from E C − 1.5 to E C − 2. Deep levels in AlGaN induce not only serious degradation, such as drain current instability and lack of long-term reliability, in AlGaN/GaN-based transistors 1,2 but also significant reduction in light-emitting efficiency in ultraviolet light-emitting diodes and laser diodes using AlGaN materials. 3 Although photoluminescence ͑PL͒ or cathodoluminescence ͑CL͒ investigation has shown some characteristic luminescence peaks related to deep electronic levels in AlGaN and AlN, 3-7 electrical characterization on deep levels in AlGaN or AlGaN/GaN heterostructure has been reported only a few times. [8][9][10][11] In particular, the deep-level transient spectroscopy ͑DLTS͒ method only detected deep levels with activation energies under 0.9 eV, 10 in spite of the fact that a near-midgap level can act as a dominant recombination center rather than a level near conduction or valence band. To detect near-midgap levels in AlGaN, a temperature range should extend to 800 K in a typical DLTS measurement condition. In such very high temperatures, a Schottky or a p-n junction suffers from serious leakage and thermal junction breakdown. In this letter, we characterize near-midgap deep levels in AlGaN grown by metal-organic chemical vapor deposition ͑MOCVD͒ using a combination of DLTS and photoassisted capacitance transient methods.We used a Si-doped n-Al 0.26 Ga 0.74 N layer with a thickness of 1.0 m grown at 1000°C on a sapphire substrate by MOCVD. Hall measurements determined the typical values of electron concentration and mobility of the AlGaN layer at room temperature ͑RT͒ to be 2 ϫ 10 17 cm −3 and 100 cm 2 / V s, respectively. As a ring-shaped Ohmic contact, a Ti/Al/Ti/Au multilayer structure ͑20/50/20/150 nm͒ was deposited on the AlGaN surface, followed by an annealing at 800°C for 1 min in N 2 ambient. A circular Schottky electrode with a diameter of 200 m was fabricated at the center of the Ohmic ring by an electron-beam deposition of Ni.To try to detect deep levels with large activation energies in a temperature range as low as possible in the DLTS measurement, a time window of up to several seconds was used with an optimized signal sampling system and a temperaturesweeping rate...

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“…A GaN layer after growth naturally contains many defects near the surface. 3,9,44 These defects tend to generate electronic surface levels that capture carriers, resulting in nonradiative recombination and degradation of the light emitting efficiency. Through oxidation, these defects could have been consumed into the oxide layer: namely, defects near the surface could be reduced by oxidation.…”

Section: Surface Passivation Effectsmentioning

confidence: 99%

Improvements of electronic and optical characteristics of n-GaN-based structures by photoelectrochemical oxidation in glycol solution

Shiozaki

Hashizume

2009

Journal of Applied Physics

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Surface control of n-GaN was performed by applying a photoelectrochemical oxidation method in a glycol solution to improve the optical and electronic characteristics. The fundamental properties of the oxidation were investigated. The oxidation, chemical composition, and bonding states were analyzed by x-ray photoelectron spectroscopy and micro-Auger electron spectroscopy, in which confirmed the formation of gallium oxide on the surface. The oxide formation rate was about 8 nm/min under UV illumination of 4 mW/ cm 2 . After establishing the basic properties for control of n-GaN oxidation, the surface control technique was applied to achieve low-damage etching, enhancement of the photoluminescence intensity, and selective passivation of the air-exposed sidewalls in an AlGaN/GaN high electron mobility transistor wire structure. The capacitance-voltage measurement revealed the minimum interface-state density between GaN and anodic oxide to be about 5 ϫ 10 11 cm −2 eV −1 , which is rather low value for compound semiconductors.

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Large reduction of leakage currents in AlGaN Schottky diodes by a surface control process and its mechanism

Cited by 50 publications

References 31 publications

Hydrogen sensing characteristics and mechanism of Pd∕AlGaN∕GaN Schottky diodes subjected to oxygen gettering

Hydrogen sensing characteristics and mechanism of Pd∕AlGaN∕GaN Schottky diodes subjected to oxygen gettering

Near-midgap deep levels in Al0.26Ga0.74N grown by metal-organic chemical vapor deposition

Improvements of electronic and optical characteristics of n-GaN-based structures by photoelectrochemical oxidation in glycol solution

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