Low resistance ohmic contacts to <i>n</i>-GaN and <i>n</i>-AlGaN using NiAl

Ingerly, D. B.; Chen, Y.; William, R; Takeuchi, Tetsuya; Chang, Y. A.

doi:10.1063/1.126983

Cited by 21 publications

(16 citation statements)

References 23 publications

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“…19 This can be attributed to the formation of NiAl at the metal semiconductor interface. 19 An XRD scan of the Ti/Al/Ni/Au contains a peak that corresponds to the formation of a NiAl compound at the interface which has a very high melting temperature of 1639°C.…”

Section: Resultsmentioning

confidence: 99%

Ohmic Contact to High-Aluminum-Content AlGaN Epilayers

Srivastava

Hwang

Islam

et al. 2009

Journal of Elec Materi

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We report on the effect of dry etching and the combination of metal stacks used to form ohmic contacts on silicon-doped high-Al-content (>60%) n-AlGaN layers for deep-ultraviolet light-emitting diodes. The contact characteristics are compared for as-grown and plasma-etched n-AlGaN samples. The Ti/Al/Ti/ Au contacts to as-grown n-AlGaN were linear, with a specific contact resistivity of 5 9 10 À5 X-cm 2 . The same metallic layer combinations yielded nonlinear contacts on the plasma-etched surface of the n-AlGaN layers. However, when Ni was used as the barrier layer instead of titanium, the contacts to plasma-etched AlGaN surfaces became linear, with a specific contact resistivity of 5 9 10 À4 X-cm 2 .

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Section: Resultsmentioning

confidence: 99%

Ohmic Contact to High-Aluminum-Content AlGaN Epilayers

Srivastava

Hwang

Islam

et al. 2009

Journal of Elec Materi

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“…The nitrides of Sc, Y and La are semiconductors 99 and hence not interesting from a metal contact point of view. Except for two studies of NiAl 21 and Pd/Al 7 contacts, all studies of ohmic contact formation to n-AlGaN have so far been on Tibased contacts 7-20 and both the ohmic and Schottky studies have only been performed on n-Al x Ga 1-x N with x ≤ 0. 35. In systems where slow kinetics are dominating the changes towards equilibrium, the systems might not reach thermodynamic equilibrium during annealing, i.e., the contact might not end up forming the phase in equilibrium with both AlGaN and N 2 at a specific partial pressure.…”

Section: Potential Stable Contacts To Alganmentioning

confidence: 98%

“…Studies on contacts to AlGaN or AlGaN/GaN HFETs have been based on the Ti/Al, [7][8][9][10][11][12][13][14][15][16][17][18][19][20] NiAl, 21 and Pd/Al 7 metallization schemes with different overlayers for the ohmic contacts and on Ti, 22 Ni, [22][23][24] Pd, 25 Re, 26 Ir, 14,17,19 Pt, 16,25 Pt/Ti, 14 Au, [27][28][29] and WSiN 14 for the Schottky contacts. The choice of systems has been highly motivated by successful contact formation to GaN by these metallization schemes, and the studies have mainly been concerned with optimizing the electrical properties, i.e., low contact resistivity or high barrier heights, and thermal stability on nAl x Ga 1-x N with x ≤ 35%.…”

Section: Introductionmentioning

confidence: 99%

Phase equilibria in transition metal Al-Ga-N systems and thermal stability of contacts to AlGaN

Schweitz

Mohney

2001

Journal of Elec Materi

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As a first step in predicting the phase equilibria in TM-Al-Ga-N systems, where TM denotes a transition metal from the first three transition series, phase equilibria are calculated in the TM-Al-N systems, and the condensed phases in equilibrium with both AlN and N 2 gas are discussed with respect to the position of the transition metal in the periodic table, temperature, and nitrogen pressure. Possible phases for use as stable electrical contacts to AlGaN are identified using these predictions, similar previous predictions for the TM-Ga-N systems and experimental findings. fraction increases, the electronic properties of the existing contacts change due to an increasing band gap and decreasing electron affinity of AlGaN, and new metallization schemes may have to be developed to accomplish good contact formation to Al x Ga 1-x N with x > 35%. New metallization schemes may also turn out to yield contacts to Al x Ga 1-x N with x ≤ 35% with superior properties to the existing contacts.The phase equilibria in the TM-Ga-N systems, where TM denotes a transition metal from the first three transition series, have previously been estimated. 30 As a first step in understanding the TM-AlGa-N systems, this article discusses the phase equilibria in the TM-Al-N systems. There are fortunately more experimentally available phase diagrams for these systems 31-42 than for the TM-Ga-N system; 30,43-47 however, many of the diagrams are not available for the conditions of most interest for processing contacts and devices. Thus, calculated ternary phase diagrams have to be used in many cases. Such an approach has been taken for systems composed of transition metals and Al-As, 48,50 In-P, 51,52 and In-As; 48,49 however, the same simple approach that has been used to calculate the ternary phase diagrams is not possible for the TM-Al-Ga-N systems due to lack of information about quarternary phases and the predominance of solution phases in the TM-Al-Ga and AlGa-N systems.This paper presents simple ternary phase diagram calculations of the TM-Al-N systems. These calcula-

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“…3,6,8,90 Ohmic contact to n-type Al x Ga 1-x N.-For n-type Al x Ga 1-x N, ohmic contacts can be easily formed by using Ti/Al-based or V/Albased metal schemes. [91][92][93][94][95][96][97][98][99][100][101][102][103][104][105][106] The Ti/Al-based metal schemes are generally used as contacts to n-Al x Ga 1-x N, producing contact resistivities of 10 −4 −10 −6 cm 2 after annealing at high temperatures. [91][92][93][94][95][96] The ohmic contact formation was explained by the formation of AlN and TiN phases, generating donor-like nitrogen vacancies (V N ) and hence increasing donor concentrations near the surface region.…”

Section: Ohmic Contacts For Deep Uv Ledsmentioning

confidence: 99%

Review—Group III-Nitride-Based Ultraviolet Light-Emitting Diodes: Ways of Increasing External Quantum Efficiency

Park

Kim

Cho

et al. 2017

ECS J. Solid State Sci. Technol.

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There is a rapidly growing demand for highly efficient ultraviolet (UV) light sources for a wide variety of applications. In particular, state-of-the-art AlGaN deep UV light-emitting diodes (DUV LEDs) exhibit inadequately low external quantum efficiencies (EQEs). The low efficiencies are attributed to the inherent material properties of high-Al-content AlGaN including strained epitaxial layers, low carrier concentrations, and strong transverse magnetic (TM)-polarized light emission. Extensive efforts have been made to tackle these challenging issues and technological developments have been achieved and enabled the fabrication of reasonable EQE LEDs. In this review, recent advances in the growth of high-quality AlGaN epitaxial layers, transparent and reflective ohmic contacts, and light extraction for AlGaN-based UV LEDs are reviewed. Al x Ga 1-x N-based ultraviolet light-emitting diodes (UV LEDs) are of technological importance because of their applications in numerous areas such as water purification, biological analysis, sensing, epoxy curing, high-density optical storage, white light illumination, UV adhesives, 3-dimensional (3D) printer and UV-coating.1,2 These applications are made possible because of their wide bandgap energy range in the UV spectrum, which spans from 6.2 eV (AlN) to 3.4 eV (GaN), namely, from UV-A (320-400 nm), UV-B (290-320 nm) to UV-C (200-290 nm).3-7 The external quantum efficiency (EQE) of Al x Ga 1-x N-based UV LEDs decreases rapidly as the molar fraction (x) of Al increases, namely, as the wavelength decreases, as illustrated in Figure 1. 8 Thus, a great deal of effort has been made in order to improve the EQE of UV LEDs. The effort notwithstanding, however, the EQE of AlGaN-based UV LEDs is still insufficiently low. The typical EQE of UV LEDs, specifically in the UV-C spectral range (100-280 nm), is less than 5% and decreases down to 10 -6 % for 210-nm AlN-based UV LEDs. 4 These low EQEs are associated with the intrinsic material properties of Al x Ga 1-x N.1,2 Figure 2 exhibits a schematic diagram of a typical AlGaN UV LED structure grown on a sapphire substrate. The structure consists of a Si-doped n-type AlGaN, an Al x Ga 1-x N/Al y Ga 1-y N multiple-quantum well (MQW) active region, an AlGaN-based electron-blocking layer (EBL), a Mg-doped p-type AlGaN, and a Mg-doped p-type GaN. Almost every layer in the structure poses different technical issues, which limit the efficiency of UV LEDs, as shown in Figure 2. First, increasing the Al content generally results in a poor crystallinity of AlGaN epilayers, causing a poor internal quantum efficiency (IQE). Second, both n-type and ptype doping efficiencies of AlGaN are difficult to increase because the ionization energies of acceptor (Mg) and donor (Si) dopants largely increase with increasing Al content. The low doping efficiency causes several technological problems: (i) a poor electrical efficiency (EE) attributable to high-resistance contacts on resistive n-type and p-type AlGaN; (ii) current crowding causing non-uniform current in...

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Low resistance ohmic contacts to n-GaN and n-AlGaN using NiAl

Cited by 21 publications

References 23 publications

Ohmic Contact to High-Aluminum-Content AlGaN Epilayers

Ohmic Contact to High-Aluminum-Content AlGaN Epilayers

Phase equilibria in transition metal Al-Ga-N systems and thermal stability of contacts to AlGaN

Review—Group III-Nitride-Based Ultraviolet Light-Emitting Diodes: Ways of Increasing External Quantum Efficiency

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