Thermally stable Ru-Si-O gate electrode for AlGaN/GaN HEMT

Eliana Kaminska Anna Piotrowska Artur Szczesny 1,5Radoslaw Lukasiewicz 1Andrian V. Kuchuk Krystyna Golaszewska Renata Kruszka Adam Barcz Rafał Jakieła 4Elzbieta Dynowska 3Anna Stonert 2Andrzej Turos 2,4

1. Institute of Electron Technology (ITE), al. Lotników 32/46, Warszawa 02-668, Poland
2. Soltan Institute for Nuclear Studies, Hoża 69, Warszawa 00-681, Poland
3. Polish Academy of Sciences, Institute of Physics, al. Lotników 32/46, Warszawa 02-668, Poland
4. Institute of Electronic Materials Technology (ITME), Wólczyńska 133, Warszawa 01-919, Poland
5. Warsaw University of Technology, Institute of Microelectronics & Optoelectronics (imio), Koszykowa 75, Warszawa 00-662, Poland


Reliable Schottky contact for AlGaN/GaN high electron mobility transistor (HEMT) should use low resistivity, large work function metal. Moreover, the metallisation for this application should withstand high-temperature treatments during device processing (realisation of self-aligned HEMT) without change of structure, electrical conductivity and composition, and be stable in contact with the semiconductor. Recently, several studies have demonstrated the applicability of RuO2 as Schottky contact to n-GaN. Ru and RuO2 are high melting point materials, characterised by low resistivity and work function > 5 eV.
With an eye on high temperature applications we have chosen to study thermally stable, electrically conducting, amorphous Ru-Si-O films being a combination of conducting RuO2 and SiO2. We compare Ru, RuO2 and Ru-Si-O Schottky contacts fabricated on n-GaN and AlGaN/GaN HEMT heterostructure. Ti/Al ohmic contacts were prepared for this study. Ru, RuO2 and Ru-Si-O layers were deposited by sputtering, using either Ru or RuSi target, in a mixture of Ar and O2. Heat treatments were done at 400-10000C in either O2 or N2 flow. The electrical properties of contacts were extracted from I-V and C-V characteristics. Contact microstructure was analysed by high-resolution XRD, SIMS and RBS.
Crucial point during the deposition was to optimise the O2/Ar ratio and the working pressure with regard to thin film resistivity and stress.
Of three investigated metallisations, Ru films yielded the lowest potential barriers. Although barrier heights of RuO2 and Ru-Si-O Schottky contacts were very similar, amorphous Ru-Si-O contact exhibited significantly lower reverse leakage current and superior thermal stability. We will discuss in detail the behaviour of Ru-based contacts in terms of electronic interactions at either crystalline or amorphous metallisation/semiconductor interface.
Work supported by the grant from the State Committee for Scientific Res.3 T11B 008 026.

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Presentation: poster at E-MRS Fall Meeting 2004, Symposium C, by Eliana Kaminska
See On-line Journal of E-MRS Fall Meeting 2004

Submitted: 2004-05-20 20:25
Revised:   2009-06-08 12:55
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