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Au-free recessed Ohmic contacts to AlGaN/GaN high electron mobility transistor: Study of etch chemistry and metal scheme

Niranjan, S and Guiney, I and Humphreys, CJ and Sen, P and Muralidharan, R and Nath, DN (2020) Au-free recessed Ohmic contacts to AlGaN/GaN high electron mobility transistor: Study of etch chemistry and metal scheme. In: Journal of Vacuum Science and Technology B: Nanotechnology and Microelectronics, 38 (3).

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Official URL: https://doi.org/10.1116/1.5144509


The authors study the effect of etch chemistry and metallization scheme on recessed Au-free Ohmic contacts to AlGaN/GaN heterostructures on silicon. The effect of variation in the recess etch chemistry on the uniformity of Ohmic contact resistance has been studied using two different etch chemistries (BCl3/O2 and BCl3/Cl2). Experiments to determine the optimum recess etch depth for obtaining a low value of contact resistance have been carried out, and it is shown that near-complete etching of the AlGaN barrier layer before metallization leads to the lowest value of contact resistance. Furthermore, two metal schemes, namely, Ti/Al and Ti/Al/Ti/W, are investigated, and it is found that the Ti/W cap layer on Ti/Al leads to low contact resistance with a smooth contact surface morphology. The effect of maintaining unequal mesa and contact pad widths on the extracted values of contact resistance and sheet resistance using the linear transfer length method (LTLM) has been studied. This is important as LTLM structures are used as monitors for process control during various steps of fabrication. It is shown that the extracted contact resistance and sheet resistance values are reliable when the mesa width is equal to the contact pad width. Finally, a possible mechanism for carrier transport in the Ohmic contacts formed using this process has been discussed, based on temperature dependent electrical characterization, and the field emission mechanism is found to be the dominant mechanism of carrier transport. A low Ohmic contact resistance of 0.56 � mm, which is one of the lowest reported values for identical metal schemes, and good contact surface morphology has been obtained with moderate post-metal annealing conditions of 600°C. © 2020 Author(s).

Item Type: Journal Article
Publication: Journal of Vacuum Science and Technology B: Nanotechnology and Microelectronics
Publisher: AVS Science and Technology Society
Additional Information: Copyright of this article belongs to AVS Science and Technology Society
Keywords: Aluminum alloys; Aluminum gallium nitride; Contact resistance; Electric contactors; Etching; Gallium alloys; Gallium nitride; High electron mobility transistors; III-V semiconductors; Metallizing; Metals; Morphology; Ohmic contacts; Semiconductor alloys; Sheet resistance; Surface morphology, AlGaN/GaN heterostructures; AlGaN/GaN high electron mobility transistors; Annealing condition; Dominant mechanism; Electrical characterization; Field emission mechanism; Possible mechanisms; Temperature dependent, Chemical resistance
Department/Centre: Division of Interdisciplinary Sciences > Centre for Nano Science and Engineering
Date Deposited: 06 Apr 2021 07:06
Last Modified: 06 Apr 2021 07:06
URI: http://eprints.iisc.ac.in/id/eprint/65219

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