Low Leakage Current ITO Schottky Electrodes for AlGaN/GaN HEMTs

Keita MATSUDA  Takeshi KAWASAKI  Ken NAKATA  Takeshi IGARASHI  Seiji YAEGASSI  

Publication
IEICE TRANSACTIONS on Electronics   Vol.E91-C   No.7   pp.1015-1019
Publication Date: 2008/07/01
Online ISSN: 1745-1353
DOI: 10.1093/ietele/e91-c.7.1015
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Section on Heterostructure Microelectronics with TWHM 2007)
Category: GaN Process Technology
Keyword: 
ITO,  Schottky gate,  tunnel,  AlGaN/GaN HEMT,  gate leakage current,  

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Summary: 
To reduce the gate leakage current of AlGaN/GaN HEMTs, we selected ITO/Ni/Au for Schottky electrodes and Schottky characteristics were compared with those of Ni/Au electrodes. ITO/Ni/Au and Ni/Au electrodes were deposited by vacuum evaporation and annealed at 350 in nitrogen atmosphere. From the I-V evaluation results of ITO/Ni/Au electrodes, forward and reverse leakage currents were reduced. Schottky characteristics of ITO/Ni/Au electrodes were also improved compared to these of Ni/Au electrodes. In addition, substantial decrease of leakage currents was confirmed after the annealing of HEMTs with ITO/Ni/Au electrodes. This may be explained that ITO/AlGaN interface state became lower by the annealing. By the temperature dependence of I-V curves, clear dependence was confirmed for the gates with ITO/Ni/Au electrodes. On the other hand, small dependence was observed for those with Ni/Au electrodes. From these results, tunnel leakage currents were dominant for the gates with Ni/Au electrode. Thermal emission current was dominant for the gates with ITO/Ni/Au electrode. The larger temperature dependence was caused that ITO/AlGaN interface states were smaller than those for Ni/Au electrode. It was suggested that suppressed AlGaN Schottky barrier thinning was caused by the surface defect donors, then tunneling leakage currents were decreased. We evaluated HEMT characteristics with ITO/Ni/Au electrode and Ni/Au electrode. Id max and Gm max were similar characteristics, but Vth with ITO/Ni/Au electrode was shifted +0.4 V than that with Ni/Au electrode due to the higher Schottky barrier. It was confirmed to have a good pinch-off currents and low gate leakage currents by ITO/Ni/Au electrodes.