Phase Formation and Morphology in Nickel and Nickel/Gold Contacts to Gallium Nitride

Venugopalan, H. S.; Mohney, Suzanne E.; Luther, B. P.; DeLucca, J. M.; Wolter, Scott D.; Redwing, Joan M.; Bulman, G. E.

doi:10.1557/proc-468-431

Cited by 22 publications

(10 citation statements)

References 10 publications

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“…Wet etching was used to remove the metal film and expose the p-GaN surface. Figure 3 shows that deep pits ͑some more than 150 nm deep͒ were formed in the p-GaN after the Ni/Au contacts were annealed at 800°C for 1 min; a result consistent with 11 In contrast, the substrate surface corresponding to the NiIn contacts annealed at 800°C for 1 min ͑Fig. 4͒ does not show these deep pits but rather a roughness consisting of perturbations on the order of about 20 nm.…”

supporting

confidence: 63%

“…7,8 Despite being successfully used in these devices, the contacts typically exhibit a specific contact resistance ( c ) in the 10 Ϫ3 -10 Ϫ2 ⍀ cm 2 range 9,10 and show poor thermal stability. 11 The standard approach used to form ohmic contacts to p-GaN has been to select metals with large work functions such as Pd, Pt, Ni, and Au and depositing them in multilayer combinations. 10,12 However, none of these schemes has yielded a contact with the desired less than 10 Ϫ5 ⍀ cm 2 resistance typically considered device quality.…”

mentioning

confidence: 99%

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The electrical behavior of Pt3In7 and NiIn contacts to p-GaN

Ingerly

Chang

Chen

1999

Applied Physics Letters

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Based on the criteria for the solid-state exchange reaction with p-GaN, we have investigated the intermetallic compounds, Pt 3 In 7 and NiIn, as possible ohmic contacts. The as-deposited contacts were found to be rectifying and using current-voltage characterization rapid thermal annealing of the contacts was shown to significantly decrease their resistance, with contacts annealed at 800°C for 1 min yielding the lowest resistance. Pt 3 In 7 contacts to p-GaN when annealed at 800°C for 1 min exhibited a specific contact resistance ( c ) of 9.5ϫ10 Ϫ2 ⍀ cm 2 while NiIn was more than an order of magnitude lower at 8.0ϫ10Ϫ3 ⍀ cm 2 . The NiIn contacts also show a lower specific contact resistance than the more traditionally used Ni/Au contacts ( c ϭ1.3ϫ10 Ϫ2 ⍀ cm 2 ) processed under the same conditions. Atomic force microscopy was used to examine the morphology of the reacted contacts. While the Ni/Au contacts showed the formation of deep spikes ͑Ͻ200 nm͒ after annealing the NiIn contact showed a much smoother reaction region with no evidence of spiking. © 1999 American Institute of Physics. ͓S0003-6951͑99͒04517-9͔GaN is a wide band gap semiconductor with tremendous promise for optical applications. When alloyed with InN and AlN it can be used to fabricate high efficiency optical devices such as light emitting diodes ͑LEDs͒ and lasers that operate in the visible ͑yellow to blue͒ and ultraviolet ͑uv͒ ranges.1,2 The addition of blue and green LEDs to the already available reds, oranges, and yellows completes the visible spectrum, allowing LEDs to be used for applications such as traffic lights and large flat full-panel displays.3,4 Additionally, blue and uv lasers will have a significant impact on high-density information storage using magnetic and optical media. 4 Aside from its applications in optoelectronics, GaN's wide band gap, good thermal conductivity, and chemical stability make it an ideal candidate for use in high temperature and high power electronic devices. 5,6 Despite the availability of commercial GaN based products, technical challenges still limit these devices. One major concern is the metal contacts to GaN semiconductors, because contacts with a high resistance can substantially reduce the performance of GaN based optical and electrical devices. In fact, the high resistance of the metal contact to p-type GaN is one of the most significant problems limiting laser diode performance. 4Currently Ni/Au is employed as an ohmic contact to p-GaN in most LED and laser applications. 7,8 Despite being successfully used in these devices, the contacts typically exhibit a specific contact resistance ( c ) in the 10 Ϫ3 -10 Ϫ2 ⍀ cm 2 range 9,10 and show poor thermal stability.11 The standard approach used to form ohmic contacts to p-GaN has been to select metals with large work functions such as Pd, Pt, Ni, and Au and depositing them in multilayer combinations. 10,12 However, none of these schemes has yielded a contact with the desired less than 10 Ϫ5 ⍀ cm 2 resistance typically considered device quality.In an atte...

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supporting

confidence: 63%

mentioning

confidence: 99%

The electrical behavior of Pt3In7 and NiIn contacts to p-GaN

Ingerly

Chang

Chen

1999

Applied Physics Letters

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“…Y. Koide et al, using x-ray diffraction (XRD), reported an NiO layer and no evidence of interaction between the metals and GaN for Ni/Au contacts annealed in an O 2 /N 2 ambient [6]. On the other hand, H. S. Venugopalan et al [13] found an NiGa phase for the annealed Ni/n-GaN scheme and J. T. Trexler et The ESCA depth profiles of Pd/Au contacts are shown in Fig. 8.…”

Section: Electrical Propertiesmentioning

confidence: 99%

Microstructure and Electrical Properties of Low Temperature Processed Ohmic Contacts to p-Type GaN

Park¹,

Song²,

Anderson³

2002

ETRI J

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With Ni/Au and Pd/Au metal schemes and low temperature processing, we formed low resistance stable Ohmic contacts to p‐type GaN. Our investigation was preceded by conventional cleaning, followed by treatment in boiling HNO3:HCl (1:3). Metallization was by thermally evaporating 30 nm Ni/15 nm Au or 25 nm Pd/15 nm Au. After heat treatment in O2 + N2 at various temperatures, the contacts were subsequently cooled in liquid nitrogen. Cryogenic cooling following heat treatment at 600 ·C decreased the specific contact resistance from 9.84·10−4 Ωcm2 to 2.65·10−4 Ωcm2 for the Ni/Au contacts, while this increased it from 1.80·10−4 Ωcm2 to 3.34·10−4 Ωcm2 for the Pd/Au contacts. The Ni/Au contacts showed slightly higher specific contact resistance than the Pd/Au contacts, although they were more stable than the Pd contacts. X‐ray photoelectron spectroscopy depth profiling showed the Ni contacts to be NiO followed by Au at the interface for the Ni/Au contacts, whereas the Pd/Au contacts exhibited a Pd:Au solid solution. The contacts quenched in liquid nitrogen following sintering were much more uniform under atomic force microscopy examination and gave a 3 times lower contact resistance with the Ni/Au design. Current‐voltage‐temperature analysis revealed that conduction was predominantly by thermionic field emission.

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“…For the latter metallization, islanding is quite severe after 700 "C annealing due to reaction of the Ni with the GaN. (23)(24)(25) From the earlier discussion, we would expect the contact properties to improve at elevated temperatures because of the increased hole density and more efficient thermionic hole emission across the metal -GaN interface. Figure 4 shows the I-V characteristics for the 700 "C (Ni/Au and W) or 800 "C(WSi) annealed samples, as a function of the measurement temperature(25 -300 "C).…”

Section: A P-ganmentioning

confidence: 99%

W and WSix Ohmic contacts on p- and n-type GaN

Cao¹,

Ren²,

Pearton³

et al. 1999

Journal of Vacuum Science &Amp; Technology A: Vacuum, Surfaces, and Films

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W and WSi ohmic contacts on both p-and n-type GaN have been annealed at temperatures fiom 300 -1000 "C. There is minimal reaction ( S 100 A broadening of the metal/GaN interface) even at 1000 "C. Specific contact resistances in the SZ-cm2 range are obtained for WSi, on Si-implanted GaN with a peak doping concentration of -5 x lo2' ~m -~, after annealing at 950 "C. On p-GaN, leaky Schottky diode behavior is observed for W, WSi, and Ni/Au contacts at room temperature, but true ohmic characteristics are obtained at 250 -300 "C, where the specific contact resistances are typically in the Gcm2 range. The best contacts for W and WSi, are obtained after 700 "C annealing for periods of 30 -120 secs. The formation of P-W2N interfacial phases appear to be important in determining the contact quality.

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Phase Formation and Morphology in Nickel and Nickel/Gold Contacts to Gallium Nitride

Cited by 22 publications

References 10 publications

The electrical behavior of Pt3In7 and NiIn contacts to p-GaN

The electrical behavior of Pt3In7 and NiIn contacts to p-GaN

Microstructure and Electrical Properties of Low Temperature Processed Ohmic Contacts to p-Type GaN

W and WSix Ohmic contacts on p- and n-type GaN

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