High Frequency AlGaN/GaN MODFET's
L. Eastman, K. Chu, W. Schaff, M. Murphy, N. G. Weimann
Dept. Electrical Engineering, Cornell University
T. Eustis
Dept. Material Science, Cornell University
This article was received on Tuesday, June 10, 1997 and
accepted on Tuesday, August 12, 1997. Abstract
Short-gate MODFET's of AlGaN/GaN on Sapphire have been
fabricated and characterized with gate lengths in the .12 - .25 µm range.
Values of ft = 50 GHz and fmax = 100 GHz have been
obtained. Analyzing the performance, the average electron transit velocity is
shown to be 1.25 x 107 cm/s and in some cases well under that value.
This compares with theoretical predictions of ~ 2.0 x 107 cm/s. The
electron scattering effects of dislocations, which are charged, are modeled to
explain the lower mobility. Ion bombardment or dry etching is used for mesa
isolation. Ti/Al/Ti/Au sintered for 100 seconds at 800 °C is used to
yield ohmic contacts of .5 - 1.0 
-mm. Pt/Au Schottky gates are used. A
high breakdown voltage, exceeding 100 V even for short gate MODFET's,
shows that ten times higher load resistance values are possible, compared with
GaAs MODFET's. Normalized output power levels well over 10 W/ mm are
thus projected for GaN MODFET's on SiC substrates, where the thermal
conductivity is about 5W/cm-°C. with future integrated traveling-wave,
power-combining circuits, output power > 100 W at 10 GHz is predicted.
Outline
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Cite this article as: MRS Internet J. Nitride Semicond. Res. 2, 17(1997).
last updated Tuesday, December 22, 1998 12:16:09 AM.© 1997-1998 The Materials Research Society
