A Thermodynamic Approach to Ohmic Contact Formation to p-GaN

Liu, Bo; Ahonen, M.; Holloway, Paul H.

doi:10.1557/s1092578300005251

Cited by 3 publications

(5 citation statements)

References 19 publications

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“…Thus, the prevention of N outdiffusion by the NiO layer could lead the contact interfacial region to be in a N-rich condition. 15 This resulted in the production of a number of Ga vacancies below the interfacial region. However, a number of N atoms were outdiffused in the Ru and Ir contacts.…”

Section: Discussionmentioning

confidence: 99%

Transparent Ohmic contacts of oxidized Ru and Ir on p-type GaN

Jang

Lee

2003

Journal of Applied Physics

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Disorder induced semiconductor to metal transition and modifications of grain boundaries in nanocrystalline zinc oxide thin film J. Appl. Phys. 112, 073101 (2012) Control of normal and abnormal bipolar resistive switching by interface junction on In/Nb:SrTiO3 interface Appl. Phys. Lett. 101, 133506 (2012) Cross-plane electronic and thermal transport properties of p-type La0.67Sr0.33MnO3/LaMnO3 perovskite oxide metal/semiconductor superlattices J. Appl. Phys. 112, 063714 (2012) Polarization Coulomb field scattering in In0.18Al0.82N/AlN/GaN heterostructure field-effect transistors Low-resistance, high-transparency, and thermally stable Ohmic contacts on p-type GaN were achieved using Ru and Ir. Oxidation annealing under O 2 atmosphere led to the reduction of contact resistivity by greater than one order of magnitude, compared to annealing under N 2 . The bilayer contacts of Ru ͑50 Å͒/Ni ͑50 Å͒ and Ir ͑50 Å͒/Ni ͑50 Å͒ exhibited a low contact resistivity of ϳ4ϫ10 Ϫ5 ⍀ cm 2 and high light transmittance of ϳ85% after annealing at 500°C for 1 min under O 2 . The barrier height for hole injection could decrease via contact formation of RuO 2 ͑or IrO 2 ) on p-type GaN. The Au-free contact structure of NiO/RuO 2 (IrO 2 )/GaN led to high light transmittance and good thermal stability.

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Section: Discussionmentioning

confidence: 99%

Transparent Ohmic contacts of oxidized Ru and Ir on p-type GaN

Jang

Lee

2003

Journal of Applied Physics

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“…The specific resistance of this contact, measured by the C-TLM method [17], was in the range 2-5 × 10 −5 cm 2 after rapid thermal annealing at 650 • C in vacuum. For our Schottky contacts (Ni/Ti/Pt/Au), the nitride over gallide (NOG) metalization approach proposed by Liu et al [18] was used. The NOG concept assumes that a gallide forming metal (Ni) creates a stable interface with GaN while the nitride forming metal (Ti) limits N outdiffusion.…”

Section: Experimental Approachmentioning

confidence: 99%

“…The NOG concept assumes that a gallide forming metal (Ni) creates a stable interface with GaN while the nitride forming metal (Ti) limits N outdiffusion. While the formation of a gallide has yet to be clearly demonstrated, it has been shown to reduce the Schottky barrier (φ p ) to p-GaN [18] and so should be suitable for a Schottky barrier on n-GaN (φ n ), assuming that the Schottky-Mott limit applies: φ p = E g + χ s − ϕ m = E g − φ n (here E g and X s are the bandgap and electron affinity of GaN respectively and ϕ m is the contact metal work function). A 200 nm SiO 2 layer was deposited by PECVD at 300 • C before 100 μm diameter circular Ni/Ti/Pt/Au (50/10/50/200 nm) Schottky contacts were defined by lift-off lithography and deposited on the Ga (epi-) face of the wafer material, again by e-beam evaporation.…”

Section: Experimental Approachmentioning

confidence: 99%

“…In this study, the nitride-overgallide approach was employed, which has potential benefits in terms of maximizing the Schottky barrier height on n-GaN. However, it has been suggested [18] that excessive reaction of Ti with out-diffused N from GaN can lead to N vacancies and possible stability issues and this may be the reason for the degradation of the J--V characteristic observed in the 400 • C non-biased storage test after 120 h. Refractory metals such as Mo, Ir [26] or alloys such as Ni-Ga [10] may need to be considered as alternative diffusion barriers.…”

Section: Long-term Diode Reliabilitymentioning

confidence: 99%

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Free-standing gallium nitride Schottky diode characteristics and stability in a high-temperature environment

O’Mahony¹,

Zimmerman

Steffen

et al. 2009

Semicond. Sci. Technol.

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Schottky diodes have been fabricated using low-resistivity n-type free-standing GaN substrates with a reduced defect density lowly doped n-type epi-layer and an Ni/Ti/Pt/Au Schottky contact metalization. A thermionic field emission current transport mechanism was identified with a Schottky barrier height of about 0.75 eV and a diode ideality of 1.1 measured at 25 • C, both of which increase with measurement temperature up to 200 • C. The diodes were subjected to long-term testing under forward current (1.3 A cm −2 ) or reverse voltage (−3.5 V) biased storage at 300 • C in N 2 for 466 h and were also monitored under non-biased storage conditions for up to 1000 h at 350 • C and 400 • C in N 2 or at 300 • C for 1500 h in air. Except for the non-biased storage test at 400 • C, the diodes show <10% drift in ideality and barrier height during the long-term storage tests. For the 400 • C test, there is a significant increase in both barrier height and ideality over a relatively short storage period (48 h). This to be the first reported study on the long-term stability of Schottky diodes on free-standing GaN and while no catastrophic (e.g. thermal runaway) degradation of any of the diodes was observed, it is proposed that optimized thermal annealing of the Ni-based Schottky contact metalization in the temperature range 350-400 • C is necessary for stable long-term operation at high temperature.

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“…In the absence of similar outdiffusion of N atoms, this results in the creation of Ga vacancies at the metal/p-GaN interface. 20 In this study, we investigated the mechanism for Ohmic contact formation of the oxidized Ni/Au contacts on p-type GaN. We employed three-dimensional ͑3D͒ secondary ion mass spectroscopy ͑SIMS͒ mapping to observe elemental interdiffusions between the contact metals and the substrate directly.…”

Section: Introductionmentioning

confidence: 99%

Mechanism for Ohmic contact formation of oxidized Ni/Au on p-type GaN

Jang

Kim

Lee

2003

Journal of Applied Physics

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The mechanism for Ohmic contact formation of oxidized Ni/Au on p-type GaN was investigated using three-dimensional secondary ion mass mapping and synchrotron photoemission spectroscopy. Annealing under O2 ambient caused the preferential outdiffusion of Ni to the contact surface to form NiO, leading to the final contact structure of NiO/Au/p-GaN. Ga atoms were dissolved in the Au contact layer and the oxygen atoms incorporated during annealing promoted the outdiffusion of Ga atoms from the GaN layer, leaving Ga vacancies below the contact. The drastic reduction of contact resistivity by the oxidation annealing could be attributed to the formation of Ga vacancies, which plays a role in increasing the net hole concentration and lowering the Fermi level position.

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A Thermodynamic Approach to Ohmic Contact Formation to p-GaN

Cited by 3 publications

References 19 publications

Transparent Ohmic contacts of oxidized Ru and Ir on p-type GaN

Transparent Ohmic contacts of oxidized Ru and Ir on p-type GaN

Free-standing gallium nitride Schottky diode characteristics and stability in a high-temperature environment

Mechanism for Ohmic contact formation of oxidized Ni/Au on p-type GaN

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