AlGaN/GaN based MOSHFETs with Different Gate Dielectrics and Treatments
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AlGaN/GaN based MOSHFETs with Different Gate Dielectrics and Treatments D. Mistele*, T. Rotter, Z. Bougriouaa**, I. Moermanna, K.S. Röverb, M. Seybothc, V. Schweglerc, J. Stemmer, F. Fedler, H. Klausing, O.K. Semchinova, J. Aderhold, and J. Graul Laboratory for Information Technology, University of Hannover, Schneiderberg 32, D-30167 Hannover, Germany a INTEC Ghent University – IMEC, St. Pietersnieuwstraat 41, B-9000 Ghent, Belgium b Institute for Semiconductor Technology, University of Hannover, Appelstr.4A, D-30167 Hannover, Germany c Department of Optoelectronics, University of Ulm, Albert-Einstein-Allee 45, 89071 Ulm, Germany
ABSTRACT AlGaN/GaN based hetero field effect transistors (HFETs) were capped with different dielectrics, characterized, and tested for DC performance. As dielectrics we use SiO2 and photoelectrochemical (PEC) grown AlxGa2-xO3. Combination of this two dielectrics show best performance with respect to gate leakage current and controllability of the drain current ID. The MOSHEFTs work also at positive gate voltages in accumulation, which is also demonstrated in a broad transconductance peak. The PEC oxidation shows low density of interface states Dit and the insulating properties depend strongly on the PEC conditions. Pre-treatments before the SiO2 deposition result in varying threshold voltages |Vth| and it seems that (NH4)Sx pre-treatment leaves the surface in best conditions. Comparison of Ti/Al and Ti/Al/Ti/Au as source/drain contacts for AlGaN/GaN HFETs are done and the annealing behavior of Ti/Al/Ti/Au is displayed resulting in contact resistance as low as RC = 2 Ωmm after annealing at 850°C in N2. INTRODUCTION AND MOTIVATION In recent years research was strongly intensified in AlGaN/GaN based high temperature / high power electronics. Reasons for this are the physical properties of wide-bandgap semiconductors such as chemical and temperature stability and good thermal dissipation. But also specific properties of the AlGaN/GaN system are very important, especially the polarization effects resulting in the formation of a 2DEG at the heterointerface [1] and the high electron drift velocity [2] compared to other semiconductor systems. As transistor devices first GaN-based HBTs were realized, before MESFETs, MODFETs, and HFETs (HEMTs) were fabricated owing excellent device characteristics especially with respect to high frequency/high power applications [3]. As the last transistor type MOSFETs were fabricated [4]. Low gate leakage currents (several orders of magnitude), higher IDmax, and *
Email: [email protected] current address: CRHEA-CNRS, Rue Bernard Gregory, 06560 Valbonne, France
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I6.51.1
positive gate biasing resulting in a broad transconductance peak are advantages of MOSFETs [5,6,7]. As gate dielectrics typically SiO2[6], Si3N4[8], AlN[9], or Gdx(Ga2-xO3)[10,11] are used. Usually interface states or traps at the dielectric/semiconductor interface are an obstacle necessary to overcome especially for III-V semiconductor systems. The present study examines SiO2
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