Effect of Pd or Pt addition to Ti/Al ohmic contact materials for <i>n</i>-type AlGaN

Murai, Shunta; Masuda, Hideyuki; Koide, Yasuo; Murakami, Masanori

doi:10.1063/1.1471931

Cited by 37 publications

(22 citation statements)

References 12 publications

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“…The Mo reacts with the Ga of the AlGaN layer and causes the generation of Ga vacancies at the AlGaN surface. It has been reported that Ga outdiffusion enhanced by reacting Pd or Pt reduces contact resistance [5]. However, Pd and Pt have a high work function, so diffusion to the semiconductor with hightemperature annealing results in a Schottky contact.…”

mentioning

confidence: 99%

Al‐free Ti/Mo/Ta/Au‐based n‐type ohmic contact with a smooth surface for AlGaN/GaN power HEMTs

Ohki

Kanamura

Takahashi

et al. 2005

phys. stat. sol. (c)

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We have demonstrated an Al-free Ti/Mo/Ta/Au-based n-type ohmic contact for high power AlGaN/GaN high electron mobility transistors (HEMTs). Our fabricated ohmic contact has an extremely smooth surface morphology and almost the same specific contact resistance (ρ c ) of 9.1 × 10 -6 Ωcm 2 as conventional Ti/Al-based contacts. We have found that Mo, which is generally inserted as a barrier layer, has the effect of reducing contact resistance. Moreover, we have applied this ohmic technique to fabricate an AlGaN/GaN HEMT and obtained sufficient transconductance (g m ) of 210 mS/mm.1 Introduction AlGaN/GaN high electron mobility transistors (HEMTs) are promising devices for high power applications, such as a power amplifier in wireless base stations [1][2][3][4]. The requirements of ohmic electrode for high power devices are low contact and sheet resistance, smooth surface and edge, and high reliability and reproducibility. Conventional ohmic contacts for AlGaN/GaN HEMTs have Ti/Al-based structures (e.g., Ti/Al/Ti/Au and Ti/Al/Ni/Au) with high-temperature annealing at over 800 °C. These ohmic contacts provide low contact and sheet resistance, so they are widely used. However, their surface and edge are extremely rough because of the low melting point of Al. A rough surface and edge morphology results in poor reliability and reproducibility due to nonuniformity of the applied electric power. Moreover, an ohmic electrode containing Al may show poor reliability due to the electromigration of Al. In this paper, we report on a new Al-free ohmic contact that better satisfies the ohmic electrode requirements for high power devices.

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mentioning

confidence: 99%

Al‐free Ti/Mo/Ta/Au‐based n‐type ohmic contact with a smooth surface for AlGaN/GaN power HEMTs

Ohki

Kanamura

Takahashi

et al. 2005

phys. stat. sol. (c)

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“…1. It was shown that the as-deposited sample exhibited a non-linear I-V characteristic due to the large work function of the p-GaN (>7.5 eV) [27,28]. However, the linearity of the I-V curves becomes improved with increasing annealing temperature.…”

Section: Resultsmentioning

confidence: 96%

“…More recently, promising approaches using Ni-based alloys such as Ni-La, Ni-Zn, Ni-Mg, and Ni-Cu produced very low specific contact resistivity in 10 −5 ∼10 −6 cm 2 range, depending on metal schemes [15][16][17][18]. From those approaches, Ni/Au is although being used as p-contact electrode for conventional InGaN/GaN LEDs, various Pt-and Pd-based ohmic contact such as Pt/Ni/Au, Pt/Ru, Pt, Pt/Au, Ti/Pt/Au, Pd/Au, Pd/Ni, Pd/Pt/Au, Pt/Pd/Au, and Pd/Ag/Au/Ti/Au also have been investigated significantly due to the fact that those metals have large work functions and easily react with gallium during an annealing process [7,13,[19][20][21][22][23][24][25][26][27][28][29]. The specific contact resistivities of both the Pt-and Pd-based ohmic contacts are typically in the range of low 10 −3 ∼10 −5 cm 2 .…”

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confidence: 99%

Structural and electrical properties of low resistance Pt/Pd/Au contact on p-GaN

Yoon

Kim

2006

J Electroceram

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We have investigated electrical and structural properties of Pt/Pd/Au ohmic contact on p-type GaN:Mg (2.5 × 10 17 cm −3 ) using Auger electron spectroscopy (AES) and glancing angle x-ray diffraction (GXRD) analysis. It was shown that the specific contact resistivity improved with increasing annealing temperature. The annealing of the contact at 600 • C for 2 min in flowing N 2 atmosphere resulted in a specific contact resistivity of 3.1 × 10 −5 cm 2 . Both GXRD and AES depth profile results show that Ga 3 Pt 5 , Ga 2 Pd 5 , and Au 7 Ga 2 phases are formed at the interface region between metal and GaN when annealed at temperatures 600 • C. Possible explanation is suggested to describe the annealing dependence of the specific contact resistivity of the Pt/Pd/Au contacts.

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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%

“…[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. 92,98,104 However, Ti/Al-based contacts had a tendency to form Schottky behavior as the Al mole fraction increases, 104,105 while V/Al-based schemes provided lower contact resistance due to the formation of vanadium nitride (VN).…”

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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Effect of Pd or Pt addition to Ti/Al ohmic contact materials for n-type AlGaN

Cited by 37 publications

References 12 publications

Al‐free Ti/Mo/Ta/Au‐based n‐type ohmic contact with a smooth surface for AlGaN/GaN power HEMTs

Al‐free Ti/Mo/Ta/Au‐based n‐type ohmic contact with a smooth surface for AlGaN/GaN power HEMTs

Structural and electrical properties of low resistance Pt/Pd/Au contact on p-GaN

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

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