Gallium nitride MIS-HEMT using atomic layer deposited Al2O3 as gate dielectric
J. Vac. Sci. Technol. A, vol. 31, no. 01A140 (2013).
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Metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs) were fabricated with an AlGaN/GaN heterostructure. The ALD-deposited Al2O3 layer served as gate dielectric under the gate electrode and as passivation layer in the access region. Different processing routes were tested and confirm that choosing the optimum order of processing steps is required to take full advantage of MIS-HEMT capabilities. Gate leakage currents as low as 2×10-10 A/mm at VGS=-20V were measured. They are 4 orders of magnitude lower compared to the Schottky reference. Also, drain leakage went down to 10-8 A/mm and thus reduced by 3½ decades compared to the Schottky-type. The corresponding on/off-ratio rates 108. The subthreshold swing improved considerably from 180mV/dec for the Schottky type to 90mV/dec for the MIS-HEMT. Breakdown voltage is >200V for a gate-drain distance >4 µm. From S-parameter measurements ft=18GHz and fmax=72GHz were extrapolated.
a Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik, Gustav-Kirchhoff-Straße 4, D-12489 Berlin, Germany
b SENTECH Instruments GmbH, Schwarzschildstraße 2, 12489 Berlin, Germany