Very Low Sheet Resistance AlN/GaN High Electron Mobility Transistors

C.Y. Chang(1), T.J. Anderson(2), F. Ren(2), S.J. Pearton(1), A.M. Dabiran(3), A.M. Wowchak(3), B. Cui(3), and P.P. Chow(3)

1.Department of Materials Science Engineering, University of Florida, Gainesville, FL
2.Department of Chemical Engineering, University of Florida, Gainesville, FL 32611
3. SVT Associates, Inc., Eden Prairie, Minnesota 55344

Index term: AlN/GaN HEMTs, ozone treatment

AlN/GaN high electron mobility transistor (HEMT) structures with a 3.5 nm AlN barrier were grown with a rf plasma-assisted molecular beam epitaxy (MBE) system on sapphire and SiC substrates, resulting in high electron mobility of >1800 cm2/V s and 2DEG carrier density of 2.8×1013 cm-2. A near record-low sheet resistance of ~167 ohm/sq was achieved using Ti/Al based Ohmic metallization annealed at 850 °C for 30s. The sheet resistance of AlN/GaN structure is about 57% lower than a AlGaN/GaN structure. UV ozone treatment was used to oxidize the AlN surface layer and this oxide layer served as the gate oxide layer and a protective layer during the device fabrication. AlN/GaN HEMTs exhibited a drain current density of 1.3 A/mm at gate voltage of +4 V and excellent pinch-off characteristics at gate voltage of -4 V. The current gain cut-off frequency, fT, and maximum frequency of oscillation, fmax, were 19.6 GHz and 30.9 GHz, respectively for 0.4× 200 μm2 gate HEMTs.

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