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Comparison of ZnO metal–oxide–semiconductor field effect transistor and metal–semiconductor field effect transistor structures grown on sapphire by pulsed laser deposition

2005; American Institute of Physics; Volume: 23; Issue: 3 Linguagem: Inglês

10.1116/1.1924613

1520-8567

C. J. Kao, Yong Wook Kwon, Young-Woo Heo, D. P. Norton, S. J. Pearton, F. Ren, G. C.,

Semiconductor materials and devices

ZnO thin film field effect transistors with 1.5–20μm gate width were fabricated using either a metal gate [metal–semiconductor field effect transistor (MESFET)] or a metal–oxide–semiconductor (MOS) gate. In both cases we found that use of a thick (∼0.8–0.9μm) ZnO buffer was necessary on the sapphire or glass substrate prior to growing the active layers in order to reduce gate leakage current. Source/drain contacts of e-beam deposited Ti∕Al∕Pt∕Au showed specific contact resistances of 2.18×10−6Ωcm2 without annealing and the interdevice isolation currents were ∼10μA at 40V bias. The MOS structure with 50nm (Ce,Tb)MgAl11O19 gate dielectric showed a 1 order of magnitude lower gate leakage current than the MESFET, due to the relatively low barrier height of metals on n-type ZnO (0.6–0.8eV). Good drain–source current characteristics were obtained from MOS gate structures using P-doped ZnO channels, whereas the metal structures showed very poor modulation.