High-temperature structural behavior of Ni/Au Contact on GaN(0001)

Kim, Chong Cook; Kim, Jong Kyu; Lee, Jong‐Lam; Je, Jung Ho; Yi, Min-Su; Noh, Do Young; Hwu, Y.; Ruterana, P.

doi:10.1557/s1092578300000168

Cited by 13 publications

(8 citation statements)

References 11 publications

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“…The XPS spectra were obtained using Al Kα radiation (hν = 1.486 keV) from the samples annealed at 550 °C for 30 min in vacuum and air, respectively. At the high temperature of 500 °C, we found a Ni 4 N compound in Ni/Au contacts using X-ray diffraction and reported in the previous paper [11]. The interfacial reactions of GaN decomposition and nitride formation release Ga to metal layers, and then the out-diffused metal Ga can be used as a reliable barometer of the GaN decomposition.…”

Section: Methodssupporting

confidence: 74%

Metal/GaN reaction chemistry and their electrical properties

Kim¹,

Seol

Kim

et al. 2004

Physica Status Solidi (b)

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We investigated the reaction chemistry of metal contacts to GaN during annealing using X-ray photoelectron spectroscopy (XPS). GaN decomposition was estimated, using XPS, to occur in N 2 annealed Ni-alloy contacts at 550 °C. The reaction was greatly accelerated by the catalytic effect of Au and Pt. The decomposition was correlated with the rapid degradation of electrical properties during annealing. The results suggest that high-temperature applications may be critically limited by the degradation of metal contacts especially due to activated Ni reactivity in Ni-alloyed contacts. Meanwhile, the thermal stability of Ni/Au contact greatly improves by suppressing the activated Ni reactivity, which is able to be obtained by forming preferential Ni -O bonding through annealing in air.

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Section: Methodssupporting

confidence: 74%

Metal/GaN reaction chemistry and their electrical properties

Kim¹,

Seol

Kim

et al. 2004

Physica Status Solidi (b)

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“…The occurrence of a large leakage current in LEDs made with the single Ag contact was attributed to the indiffusion of Ag into the active region of LEDs. 16 This indicates that the ITO interlayer serves effectively as a barrier for the indiffusion of Ag. Figure 5 shows the light output-current ͑L-I͒ characteristics of the LEDs fabricated with the Ag ohmic reflectors with and without the ITO interlayers ͑annealed at 530°C͒ as a function of the forward drive current.…”

Section: G321mentioning

confidence: 99%

Highly Reflective and Low Resistance Indium Tin Oxide/Ag Ohmic Contacts to p-Type GaN for Flip-Chip Light Emitting Diodes

Hong

Song

Hong

et al. 2005

Electrochem. Solid-State Lett.

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We report on the formation of high-quality Ag contacts to p-GaN by using indium-tin oxide ͑ITO͒ interlayers. The ITO ͑2 nm͒/Ag ͑200 nm͒ contacts give specific contact resistances of 3.26-4.34 ϫ 10 −4 ⍀ cm 2 when annealed at 330-530°C for 1 min in air. The reflectance of the ITO ͑2 nm͒/Ag ͑200 nm͒ is measured to be 85% at 405 nm, which is much better than that of the ITO ͑55 nm͒/Ag ͑200 nm͒ and the single Ag contacts. Light-emitting diodes fabricated with the ITO ͑2 nm͒/Ag ͑200 nm͒ contact gives much higher output power than those with the ITO ͑55 nm͒/Ag and single-Ag reflective contacts.High-brightness GaN-based blue and ultraviolet light-emitting diodes ͑LEDs͒ are of great technological importance for their application in solid-state lighting. The fabrication of high-brightness LEDs requires high light-extraction efficiency as well as high internal efficiency in LED structures. Flip-chip LEDs, where emitted light is extracted through the transparent sapphire substrate, have been demonstrated as one of the promising ways to achieve high light-extraction efficiency, as compared with conventional topemitting LEDs. 1-3 Thus, in this connection, ohmic contacts having highly reflective as well as low contact resistivity are essential for flip-chip LED applications. The most common Ni/Au ohmic contact is a poor reflector at visible wavelengths, e.g., only 31% at 470 nm. 2 An Ag layer is very attractive due to its high reflectance of ϳ92% at 470 nm. 2,4 However, the Ag contact has poor adhesion and agglomeration problems when annealed at elevated temperatures. 2-5 Thus, to realize reliable Ag-based ohmic contacts to p-type GaN, a variety of different schemes, such as Cu-doped indium oxide/Ag, 6 Ni/Ag, 7 Mg-doped indium oxide/Ag, 8 Ni/Au/indium tin oxide ͑ITO͒/Ag, 9 Cu-Ni solid-solution/Ag, 10 Zn-Ni solid-solution/Ag, 11 and Ni/Au/Ag, 12 have been investigated to date. For example, Gessmann et al. 3 investigated omnidirectional reflector ͑ODR͒ to increase extraction efficiency and showed that LEDs made with ODR ͓consisting of GaN, a quarter-wave interlayer of ITO ͑55 nm͒, and Ag ͑200 nm͔͒ give somewhat higher extraction efficiency than those made with conventional Ni/Au contacts. However, their forward voltage and series resistance were much higher than those of the conventional LEDs. In this work, we introduced a thin ITO interlayer to stabilize the Ag reflector and to improve its electrical properties. It is shown that ITO ͑2 nm͒/Ag ͑200 nm͒ contacts become ohmic with the specific contact resistance is as low as ϳ10 −4 ⍀ cm 2 when annealed at 330 and 530°C for 1 min in air. Near UV ͑405 nm͒ GaN-based LEDs were fabricated using the ITO/Ag reflective contacts give forward-bias voltage of ϳ3.3 V at of 20 mA.Metallorganic chemical vapor deposition was used to grow 2 m thick unintentionally doped GaN layers on sapphire ͑0001͒ substrates. This was followed by the growth of 1 m thick GaN:Mg layer ͑n a = 5 ϫ 10 17 cm −3 ͒. The GaN layers were ultrasonically degreased with trichloroethylene, acetone, and methanol for 5 min in e...

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“…Figure 2 shows X-ray diffraction profiles for Ni/Au contacts obtained after holding for 30 min at a) 500 and 550 C in N 2 and b) 550 C in air. In case of N 2 annealing, we observed the formation of a new phase which we identified as Ni 4 N by the Ni 4 N(111) Bragg reflection [8]. The Ni 4 N phase begins to form at 500 C and its growth is clearly shown at the higher temperature of 550 C. The Ni 4 N phase, which is believed to be a high temperature compound, deteriorates the contact resistivity of the Ni/Au layer on p-type GaN films and its formation should be therefore avoided [9,10].…”

Section: Resultsmentioning

confidence: 90%