Surface-charge controlled AlGaN/GaN-power HFET without current collapse and gm dispersion

Kikkawa, T.; Nagahara, Miyuki; Okamoto, Naoya; Tateno, Yasunori; Yamaguchi, Yasuhiro; Hara, Naoki; Joshin, K.; Asbeck, P.M.

doi:10.1109/iedm.2001.979574

Cited by 79 publications

(72 citation statements)

References 4 publications

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“…Indeed, the Al 2 O 3 IG structure led to more than three orders reduction of leakage currents as As one of the methods of investigating manifestation of current collapse or rf dispersion under gate stress, we compared pulsed mode I -V characteristics between conventional Ni SG and Al 2 O 3 IG HFETs. 2,4,5 The result is shown in Fig. 6.…”

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confidence: 85%

“…In particular, so-called current collapse effects not only degrade microwave output performance but also impede reliable operation of the GaN-based power devices. The current collapse phenomena have often been observed in Schottky-gate AlGaN/GaN heterostructure field-effect transistors ͑SG HFETs͒ under both gate stress [1][2][3][4][5][6] and drain stress. 2,5,7 Some models based on the electron trapping by surface states have been proposed.…”

mentioning

confidence: 99%

“…The current collapse phenomena have often been observed in Schottky-gate AlGaN/GaN heterostructure field-effect transistors ͑SG HFETs͒ under both gate stress 1-6 and drain stress. 2,5,7 Some models based on the electron trapping by surface states have been proposed. 6,7 However, the mechanism for the current collapse is not clarified as yet.…”

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Suppression of current collapse in insulated gate AlGaN/GaN heterostructure field-effect transistors using ultrathin Al2O3 dielectric

Hashizume¹,

Ootomo²,

Hasegawa³

2003

Applied Physics Letters

250

147

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We investigated effects of electronic states at free surfaces of AlGaN/GaN heterostructure field-effect transistors ͑HFETs͒ on the inner current transport at the heterointerfaces. The analysis on transient currents for the air-exposed and H 2 -plasma-treated devices showed that N-vacancy-related near-surface traps play an important role in current collapse in AlGaN/GaN HFETs. An Al 2 O 3 -based surface passivation scheme including an N 2 -plasma surface treatment was proposed and applied to an insulated-gate HFET. A large conduction-band offset of 2. Although significant progress has been achieved in the GaN-based high-power/high-frequency electronic devices, surface-related problems still need an immediate solution. In particular, so-called current collapse effects not only degrade microwave output performance but also impede reliable operation of the GaN-based power devices. The current collapse phenomena have often been observed in Schottky-gate AlGaN/GaN heterostructure field-effect transistors ͑SG HFETs͒ under both gate stress 1-6 and drain stress. 2,5,7 Some models based on the electron trapping by surface states have been proposed. 6,7 However, the mechanism for the current collapse is not clarified as yet.In this letter, we report on passivation effects of the Al 2 O 3 -based insulated-gate ͑IG͒ structure on current collapse in AlGaN/GaN HFETs. Although SiN x films have been used to mitigate the surface problems on the GaN-based devices, 4 -9 it can be argued that its band gap (E G ϳ5 eV) and dielectric constant ͑⑀ϳ7͒ are not suitable for utilization as a gate barrier to Al x Ga 1Ϫx N ͑e.g., E G ϳ4.1 eV and ⑀ϳ9 for xϭ0.3͒. In this aspect, Al 2 O 3 has an advantage over SiN x for the application to IG-type AlGaN/GaN HFETs, due to its larger band gap and higher dielectric constant. For understanding the collapse mechanism and optimizing passivation process, the dynamic response of surface states was investigated in terms of transient currents in gateless HFETs.The AlGaN/GaN heterostructures used in the present study are schematically shown in Fig. 1. The structure consists of undoped GaN, undoped Al x Ga 1Ϫx N, Si-doped Al x Ga 1Ϫx N, and undoped Al x Ga 1Ϫx N layers, all grown by metalorganic vapor phase epitaxy on c-plane sapphire or 6H-SiC substrate. The Al content x ranged from 0.28 to 0.30. Typical values of the electron concentration and mobility of the samples at room temperature were 1.1ϫ10 13 cm Ϫ2 and 900 cm 2 /V s, respectively. As an ohmic contact, a Ti/Al/ Ti/Au layered structure was formed on the surface of GaN/ AlGaN, followed by annealing in N 2 ambient at 800°C for 2 min.A gateless HFET structure with a drain-source spacing of 4 m, shown in Fig. 1͑a͒, was prepared to investigate the correlation between the surface electronic states and inner current transport. The surface of the gateless device was subjected to H 2 plasma and N 2 plasma excited using an electron cyclotron resonance ͑ECR͒ source with a microwave power of 50 W. The process temperature and time were 280°C and 1 min, respectiv...

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confidence: 85%

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confidence: 99%

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Suppression of current collapse in insulated gate AlGaN/GaN heterostructure field-effect transistors using ultrathin Al2O3 dielectric

Hashizume¹,

Ootomo²,

Hasegawa³

2003

Applied Physics Letters

250

147

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“…Thereafter, SiN x -based surface passivation a͒ Electronic mail: hashi@rciqe.hokudai.ac.jp structures have been applied to the GaN/AlGaN HFETs. 1,[15][16][17][18][19] Green et al 15 and Lee et al 16 reported the improvement of rf-power performance in the GaN/AlGaN HFETs. The reduction of current collapse was reported in the SiN x IG GaN/AlGaN HFET, 17 or the SiN x -passivated GaN/ AlGaN HFETs.…”

Section: Introductionmentioning

confidence: 99%

“…The reduction of current collapse was reported in the SiN x IG GaN/AlGaN HFET, 17 or the SiN x -passivated GaN/ AlGaN HFETs. 1,18,19 Other dielectrics such as SiO 2 , Ga 2 O 3 , MgO and the native oxide of AlGaN have also been applied to the surface passivation of GaN and AlGaN surfaces. Therrien et al 20 reported the passivation process including separate plasma oxidation of GaN and the deposition of thick SiO 2 film using remote plasma.…”

Section: Introductionmentioning

confidence: 99%

Surface passivation of GaN and GaN/AlGaN heterostructures by dielectric films and its application to insulated-gate heterostructure transistors

Hashizume

Ootomo

Inagaki

et al. 2003

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

220

170

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We have systematically investigated effects of plasma processing, formation of Si-based dielectrics, and formation of a thin Al 2 O 3 film on the chemical and electronic properties of GaN and GaN/ AlGaN heterostructure surfaces. The surface treatment in H 2 -plasma excited by electron-cyclotron-resonance ͑ECR͒ source, produced nitrogen-vacancy-related defect levels at GaN and AlGaN surfaces, while the ECR-N 2 -plasma treatment improved electronic properties of the surfaces. The deposition of a SiO 2 film on GaN and AlGaN surfaces was found to induce high-density interface states, due to unexpected and uncontrollable oxidation reactions on the surfaces during the deposition process. In comparison, the SiN x /GaN passivation structure prepared by ECR-plasma assisted chemical vapor deposition showed good interface properties with the minimum D it value of 1ϫ10 11 cm Ϫ2 eV Ϫ1 . However, excess leakage currents governed by FowlerNordheim tunneling were observed in the SiN x /Al 0.3 Ga 0.7 N structure, due to a relatively small conduction band offset of 0.7 eV between SiN x and Al 0.3 Ga 0.7 N. A novel Al 2 O 3 -based passivation structure was proposed and fabricated by molecular beam deposition of Al and subsequent ECR O 2 -plasma oxidation. In situ x-ray photoelectron spectroscopy showed successful formation of the Al 2 O 3 layer with a thickness of 3.5 nm and a large conduction band offset of 2.1 eV between Al 2 O 3 and A 0.3 Ga 0.7 N. The GaN/AlGaN insulated-gate heterostructure field-effect transistors ͑IG HFETs͒ having the Al 2 O 3 -based passivation structure showed a good gate control of drain currents up to V GS ϭϩ3 V and achieved drain saturation current of 0.8 A/mm. The observed maximum g m value is 120 mS/mm. No current collapse was observed in the Al 2 O 3 IG HFETs, indicating a remarkable advantage of the present Al 2 O 3 -based passivation structure.

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Reduction of on‐resistance in ion‐implanted GaN/AlGaN/GaN HEMTs with low gate leakage current

Nomoto

Satoh

Nakamura

2010

Elect Comm in Japan

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SUMMARYSi ion-implanted GaN/AlGaN/GaN HEMTs with extremely low gate leakage current and low source resistance prepared without any recess etching process are demonstrated. The source/drain regions were formed using Si ion implantation into undoped GaN/AlGaN/GaN on a sapphire substrate. After ion implantation into source/drain regions at an energy of 80 keV, the performance was significantly improved. The on-resistance was reduced from 26.2 to 4.3 Ω-mm. The saturation drain current and maximum transconductance increased from 284 to 723 mA/mm and from 48 to 147 mS/mm.

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Surface-charge controlled AlGaN/GaN-power HFET without current collapse and gm dispersion

Cited by 79 publications

References 4 publications

Suppression of current collapse in insulated gate AlGaN/GaN heterostructure field-effect transistors using ultrathin Al2O3 dielectric

Suppression of current collapse in insulated gate AlGaN/GaN heterostructure field-effect transistors using ultrathin Al2O3 dielectric

Surface passivation of GaN and GaN/AlGaN heterostructures by dielectric films and its application to insulated-gate heterostructure transistors

Reduction of on‐resistance in ion‐implanted GaN/AlGaN/GaN HEMTs with low gate leakage current

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