Ohmic contacts to Al‐rich AlGaN heterostructures

Douglas, Erica Ann; Reza, Shahed; Sanchez, Carlos Anthony; Koleske, D. D.; Allerman, Andrew A.; Klein, Brianna; Armstrong, Andrew M.; Kaplar, Robert; Baca, Albert G.

doi:10.1002/pssa.201600842

Cited by 50 publications

(25 citation statements)

References 31 publications

(47 reference statements)

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“…32 However, no implementation of a selective area ohmic contact using regrowth 7,33 together with graded composition 32 in an AlGaN-channel HEMT has yet been reported.…”

Section: Resultsmentioning

confidence: 99%

Al_0.85Ga_0.15N/Al_0.70Ga_0.30N High Electron Mobility Transistors with Schottky Gates and Large On/Off Current Ratio over Temperature

Baca

Klein

Allerman

et al. 2017

ECS J. Solid State Sci. Technol.

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AlGaN-channel high electron mobility transistors (HEMTs) are among a class of ultra wide-bandgap transistors that are promising candidates for RF and power applications. Long-channel Al x Ga 1-x N HEMTs with x = 0.7 in the channel have been built and evaluated across the −50 • C to +200 • C temperature range. These devices achieved room temperature drain current as high as 46 mA/mm and were absent of gate leakage until the gate diode forward bias turn-on at ∼2.8 V, with a modest −2.2 V threshold voltage. A very large I on /I off current ratio, of 8 × 10 9 was demonstrated. A near ideal subthreshold slope that is just 35% higher than the theoretical limit across the temperature range was characterized. The ohmic contact characteristics were rectifying from −50 • C to +50 • C and became nearly linear at temperatures above 100 • C. An activation energy of 0.55 eV dictates the temperature dependence of off-state leakage. AlGaN-channel high electron mobility transistors (HEMTs) are among a class of ultra wide-bandgap transistors (UWBG) that are promising candidates for power and RF applications.1-9 Their promise derives from the large critical electric field, which scales as a power law with the bandgap of the material, 10 e.g. E C ∼ E G 2.5 (the exact dependence is a topic of active research) and provides favorable power and RF figures of merit. Enhancement-mode HEMTs are required for power applications, while depletion-mode HEMTs are suitable for RF applications. Power electronics applications utilize GaN/AlGaN HEMTs with dielectric insulators as a means of achieving a large gate voltage swing for high current density and low on-resistance. The dielectric insulators also suppress gate leakage, but at the expense of substantial interface charge density and the potential for hot electrons inducing unwanted trapped charges in the dielectric. These latter effects make gates employing dielectric insulators unsuitable for RF applications with GaN/AlGaN HEMTs.Al y Ga 1-y N/Al x Ga 1-x N HEMTs with high Al in the channel, x = 0.7 and larger, have promising figures of merit and are candidates for next generation power and RF applications. 1,7,11,12 With a bandgap of >5.8 eV, the Al 0.85 Ga 0.15 N barrier is practically an insulator, but since it is combined with a modest conduction band offset to the Al x Ga 1-x N channel it has both insulator and Schottky-like properties. As a crystallographic insulator-like material, it has potential for a very good interface with nearly lattice matched Al x Ga 1-x N channel adjacent to the 2-dimensional electron gas (2DEG). Even as a Schottky barrier it can have a large turn-on voltage to enhance the voltage swing and current drive capability. Although promising, Al x Ga 1-x N channel HEMTs lack maturity and do not yet match the high current density of AlGaN/GaN HEMTs due both to the difficulty of achieving good ohmic contacts and the lack of aggressive dimensional scaling to compensate for limitations of the low-field electron mobility, which is limited by alloy scattering.In this work ...

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“…32 However, no implementation of a selective area ohmic contact using regrowth 7,33 together with graded composition 32 in an AlGaN-channel HEMT has yet been reported.…”

Section: Resultsmentioning

confidence: 99%

Al_0.85Ga_0.15N/Al_0.70Ga_0.30N High Electron Mobility Transistors with Schottky Gates and Large On/Off Current Ratio over Temperature

Baca

Klein

Allerman

et al. 2017

ECS J. Solid State Sci. Technol.

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“…[1][2][3][4][5][6] Therefore, several groups including ours are developing high electron mobility transistors (HEMTs) with EBG Al x Ga 1−x N channel and barrier layers. [7][8][9][10][11] However, for achieving high BFOM, in addition to a large breakdown voltage a simultaneous low device specific ONresistance is also required. This resistance comprises of a sum of the contributions from the channel resistance (R CH ), and the contact resistance (R C ).…”

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confidence: 99%

High figure of merit extreme bandgap Al_0.87Ga_0.13N-Al_0.64Ga_0.36N heterostructures over bulk AlN substrates

Hussain

Mamun

Floyd

et al. 2023

Appl. Phys. Express

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We report on high-quality n-Al0.87Ga0.13N-A0.64Ga0.36N heterostructures over single crystal AlN. For these pseudomorphic heterostructures, high resolution X-ray and X-ray Topographic analysis was used to establish a threading dislocation density of 7x103 cm-2. Using reverse composition graded n+-AlxGa1-xN contact layers, we obtained linear ohmic contacts with 4.3 Ω-mm specific resistance. A critical breakdown field > 11 MV/cm was also measured. In combination with the channel resistance of 2400 Ω/sq , these translate to a Baliga’s Figure of Merit (BFOM) of 2.27 GW/cm2. This, to the best of our knowledge is the highest reported value for extreme bandgap (EBG) AlGaN heterostructures.

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“…15,16) Figure 4(c) shows the R C values reported for the AlGaN HEMTs as a function of the Al composition of the AlGaN channel layer. 6,9,[16][17][18][19][20][21][22] In Fig. 4(c), conventional ohmic technologies such as regrowth contact (solid diamonds) or metal alloy contact (solid circles) show an exponential increase in the R C with Al composition.…”

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confidence: 99%

“…The inset shows the TLM fitting result (e), and the contact resistance R C as a function of the Al composition in AlGaN channel layers. The solid diamonds and circles indicate the reported R C values of the regrowth contacts and metal alloy contacts, respectively 6,9,[16][17][18][19][20][21][22].…”

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confidence: 99%

AlN/Al_0.5Ga_0.5N HEMTs with heavily Si-doped degenerate GaN contacts prepared via pulsed sputtering

Maeda

Ueno

Kobayashi

et al. 2022

Appl. Phys. Express

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This paper reports AlN barrier Al0.5Ga0.5N with heavily Si-doped degenerate GaN contacts prepared by pulsed sputtering. Selectively regrown n-type GaN contacts exhibit typical degenerate properties with the electron concentration and mobility of 2.6 × 1020 cm−3 and 115 cm2V-1s−1, resulting in a record low contact resistance R c of 0.43 Ωmm. The AlN/Al0.5Ga0.5N HEMTs displayed a remarkable DC output characteristic with a maximum drain current density of 250 mA/mm, a transconductance of 32 mS/mm, and an On/Off ratio >106. The present results show potential overcoming challenges in ohmic contact formation for high-power and high-frequency AlGaN electron devices with high Al composition.

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Ohmic contacts to Al‐rich AlGaN heterostructures

Cited by 50 publications

References 31 publications

Al_0.85Ga_0.15N/Al_0.70Ga_0.30N High Electron Mobility Transistors with Schottky Gates and Large On/Off Current Ratio over Temperature

Al_0.85Ga_0.15N/Al_0.70Ga_0.30N High Electron Mobility Transistors with Schottky Gates and Large On/Off Current Ratio over Temperature

High figure of merit extreme bandgap Al_0.87Ga_0.13N-Al_0.64Ga_0.36N heterostructures over bulk AlN substrates

AlN/Al_0.5Ga_0.5N HEMTs with heavily Si-doped degenerate GaN contacts prepared via pulsed sputtering

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Ohmic contacts to Al‐rich AlGaN heterostructures

Cited by 50 publications

References 31 publications

Al0.85Ga0.15N/Al0.70Ga0.30N High Electron Mobility Transistors with Schottky Gates and Large On/Off Current Ratio over Temperature

Al0.85Ga0.15N/Al0.70Ga0.30N High Electron Mobility Transistors with Schottky Gates and Large On/Off Current Ratio over Temperature

High figure of merit extreme bandgap Al0.87Ga0.13N-Al0.64Ga0.36N heterostructures over bulk AlN substrates

AlN/Al0.5Ga0.5N HEMTs with heavily Si-doped degenerate GaN contacts prepared via pulsed sputtering

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Product

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About

Al_0.85Ga_0.15N/Al_0.70Ga_0.30N High Electron Mobility Transistors with Schottky Gates and Large On/Off Current Ratio over Temperature

Al_0.85Ga_0.15N/Al_0.70Ga_0.30N High Electron Mobility Transistors with Schottky Gates and Large On/Off Current Ratio over Temperature

High figure of merit extreme bandgap Al_0.87Ga_0.13N-Al_0.64Ga_0.36N heterostructures over bulk AlN substrates

AlN/Al_0.5Ga_0.5N HEMTs with heavily Si-doped degenerate GaN contacts prepared via pulsed sputtering