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Title: Operation of ohmic Ti/Al/Pt/Au multilayer contacts to GaN at 600 °C in air

Abstract

The high-temperature characteristics (at 600 °C) of Ti/Al/Pt/Au multilayer contacts to gallium nitride (GaN) in air are reported. Microfabricated circular-transfer-line-method test structures were subject to 10 h of thermal storage at 600 °C. Intermittent electrical characterization during thermal storage showed minimal variation in the contact resistance after 2 h and that the specific contact resistivity remained on the order of 10{sup −5} Ω-cm{sup 2}. In addition, the thermally stored multilayer contacts to GaN showed ohmic I-V characteristics when electrically probed at 600 °C. The microstructural analysis with atomic force microscopy showed minimal changes in surface roughness after thermal storage. Observations of the thermochemical reactions after thermal storage using Auger electron spectroscopy chemical depth profiling showed diffusion of Pt and minimal additional Al oxidation. The results support the use of Ti/Al/Pt/Au multilayer metallization for GaN-based sensors and electronic devices that will operate within a high-temperature and oxidizing ambient.

Authors:
 [1];  [1];  [2]
  1. Department of Electrical Engineering, Stanford University, Stanford, California 94305 (United States)
  2. (United States)
Publication Date:
OSTI Identifier:
22310946
Resource Type:
Journal Article
Resource Relation:
Journal Name: Applied Physics Letters; Journal Volume: 105; Journal Issue: 8; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; ALUMINIUM; ATOMIC FORCE MICROSCOPY; AUGER ELECTRON SPECTROSCOPY; DIFFUSION; ELECTRIC CONDUCTIVITY; ELECTRIC CONTACTS; ELECTRONIC EQUIPMENT; GALLIUM NITRIDES; GOLD; HEAT STORAGE; LAYERS; MICROSTRUCTURE; OXIDATION; PLATINUM; ROUGHNESS; SURFACES; TEMPERATURE RANGE 0400-1000 K; TITANIUM

Citation Formats

Hou, Minmin, E-mail: mmhou@stanford.edu, Senesky, Debbie G., and Department of Aeronautics and Astronautics, Stanford University, Stanford, California 94305. Operation of ohmic Ti/Al/Pt/Au multilayer contacts to GaN at 600 °C in air. United States: N. p., 2014. Web. doi:10.1063/1.4894290.
Hou, Minmin, E-mail: mmhou@stanford.edu, Senesky, Debbie G., & Department of Aeronautics and Astronautics, Stanford University, Stanford, California 94305. Operation of ohmic Ti/Al/Pt/Au multilayer contacts to GaN at 600 °C in air. United States. doi:10.1063/1.4894290.
Hou, Minmin, E-mail: mmhou@stanford.edu, Senesky, Debbie G., and Department of Aeronautics and Astronautics, Stanford University, Stanford, California 94305. Mon . "Operation of ohmic Ti/Al/Pt/Au multilayer contacts to GaN at 600 °C in air". United States. doi:10.1063/1.4894290.
@article{osti_22310946,
title = {Operation of ohmic Ti/Al/Pt/Au multilayer contacts to GaN at 600 °C in air},
author = {Hou, Minmin, E-mail: mmhou@stanford.edu and Senesky, Debbie G. and Department of Aeronautics and Astronautics, Stanford University, Stanford, California 94305},
abstractNote = {The high-temperature characteristics (at 600 °C) of Ti/Al/Pt/Au multilayer contacts to gallium nitride (GaN) in air are reported. Microfabricated circular-transfer-line-method test structures were subject to 10 h of thermal storage at 600 °C. Intermittent electrical characterization during thermal storage showed minimal variation in the contact resistance after 2 h and that the specific contact resistivity remained on the order of 10{sup −5} Ω-cm{sup 2}. In addition, the thermally stored multilayer contacts to GaN showed ohmic I-V characteristics when electrically probed at 600 °C. The microstructural analysis with atomic force microscopy showed minimal changes in surface roughness after thermal storage. Observations of the thermochemical reactions after thermal storage using Auger electron spectroscopy chemical depth profiling showed diffusion of Pt and minimal additional Al oxidation. The results support the use of Ti/Al/Pt/Au multilayer metallization for GaN-based sensors and electronic devices that will operate within a high-temperature and oxidizing ambient.},
doi = {10.1063/1.4894290},
journal = {Applied Physics Letters},
number = 8,
volume = 105,
place = {United States},
year = {Mon Aug 25 00:00:00 EDT 2014},
month = {Mon Aug 25 00:00:00 EDT 2014}
}
  • Radiation effects in the Au-Ti-Al-Ti-n-GaN multilayer metallization subjected to irradiation with {sup 60}Co {gamma}-ray photons in the dose range 4 x 10{sup 6}-2 x 10{sup 7} Gy are considered, and the effect of radiation on the initial contact structures and the structures subjected to a rapid thermal annealing (RTA) at high-temperature in the nitrogen atmosphere is studied. Irradiation does not significantly affect the properties of structures that were not subjected to the heat treatment. An RTA at 700 deg. C brings about a deterioration of the contact-layer morphology. The morphological and structural transformations in the contact metallization due to themore » RTA are enhanced by irradiation with {gamma}-ray photons. The combined radiation-thermal treatment is conducive to the mass transfer between contacting layers. In addition, after {gamma}-ray irradiation with the dose of 2 x 10{sup 7} Gy, the oxygen-impurity atoms appear over the entire contact's structure and are observed in a large amount in the near-contact GaN region.« less
  • The physical mechanism of low-thermal-budget Au-free ohmic contacts to AlGaN/GaN heterostructures is systematically investigated with current-voltage, high-resolution transmission electron microscopy, and temperature-dependent contact resistivity characterizations. With a low annealing temperature of 600 °C, pre-ohmic recess etching of the AlGaN barrier down to several nanometers is demonstrated to be an effective method to reduce the contact resistance between Ti/Al/Ti/W ohmic metals and AlGaN/GaN heterostructures. However, further over recess of the AlGaN barrier leads to only sidewall contact to 2D electron gas channel and thus degraded contact performance. It is verified by temperature-dependent contact resistivity measurements that field emission (tunneling) dominates the currentmore » transport mechanism in Au-free ohmic contacts with AlGaN barrier partially and over recessed, while both field emission and thermionic emission contribute to traditional Ti/Al/Ni/Au ohmic contacts to AlGaN/GaN heterostructures that annealed at high temperature (850 °C)« less
  • Transmission electron microscopy has been applied to characterize the structure of Ti/Al and Ti/Al/Ni/Au Ohmic contacts on {ital n}-type GaN ({approximately}10{sup 17} cm{sup {minus}3}) epitaxial layers. The metals were deposited either by conventional electron-beam or thermal evaporation techniques, and then thermally annealed at 900{degree}C for 30 s in a N{sub 2} atmosphere. Before metal deposition, the GaN surface was treated by reactive ion etching. A thin polycrystalline cubic TiN layer epitaxially matched to the (0001) GaN surface was detected at the interface with the GaN substrate. This layer was studied in detail by electron diffraction and high resolution electron microscopy.more » The orientation relationship between the cubic TiN and the GaN was found to be: {l_brace}111{r_brace}{sub TiN}//{l_brace}00.1{r_brace}{sub GaN}, [110]{sub TiN}//[11.0]{sub GaN}, [112]{sub TiN}//[10.0]{sub GaN}. The formation of this cubic TiN layer results in an excess of N vacancies in the GaN close to the interface which is considered to be the reason for the low resistance of the contact. {copyright} {ital 1996 American Institute of Physics.}« less
  • The temperature dependences of the contact resistivity {rho}{sub c} of Au-TiB{sub x} Al-Ti-n{sup +}-n-n{sup +}-GaN-Al{sub 2}O{sub 3} ohmic contacts have been studied before and after microwave treatment followed by nine-nonth room-temperature sample storage. The temperature dependences of {rho}{sub c} of initial samples were measured twice. The first measurement showed the temperature dependence typical of ohmic contacts; the repeated measurement in the temperature region above 270 K showed a {rho}{sub c} increase caused by metallic conductivity. After microwave treatment, the metallic conductivity in the ohmic contact is not observed. This is presumably associated with local heating of metal Ga inclusions undermore » microwave irradiation and the formation, due to high chemical activity of liquid gallium, of compounds of it with other metallization components. In this case, the temperature dependence of {rho}{sub c} is controlled by ordinary charge transport mechanisms. After nine-nonth room-temperature storage, the temperature dependence of ?c is described by the tunneling mechanism of charge transport.« less
  • A metallization scheme has been developed for obtaining low ohmic contacts to n-GaN with a low contact resistance. The metal contact is a Ti/Al/Ti/Au composite with layers that are respectively 30, 100, 30, and 30 nm thick. Contacts with a specific contact resistivity {rho}{sub s}, as low as 6.0{times}10{sup {minus}7}{Omega}cm{sup 2} for a doping level of 1.40{times}10{sup 20}cm{sup {minus}3} were obtained after annealing the sample for 30 s at 750{degree}C in a rapid thermal annealer. The Ti placed on top of the traditional Ti/Al contact appears to have the advantage of tying up the excess Al; therefore it does notmore » form a mottled contact. Some of the additional Ti{endash}Al intermetallic alloys that are formed also have beneficial effects. The Ti{endash}Au layer forms a robust upper portion of the composite, which enables the contacts to have high-temperature applications. {copyright} 2001 American Institute of Physics.« less