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High Frequency AlGaN/GaN MODFET's

  • L. Eastman (a1), K. Chu (a1), W. Schaff (a1), M. Murphy (a1), N. G. Weimann (a1) and T. Eustis (a1)...

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 × 107 cm/s and in some cases well under that value. This compares with theoretical predictions of ~ 2.0 × 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 Ω-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.

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[1] Burm, J., Chu, K., Schaff, W.J., Eastman, L.F., Asif Khan, M., Chen, Q., Yang, J.W., Shur, M.S., IEEE Electron Dev. Lett. 18, 141-143 (1997).
[2] Wu, YF, Keller, S, Kozodoy, P, Keller, B P, Parikh, P, Kapolnek, D, Denbaars, S P, IEEE Electron Dev. Lett. 18, 290-2 (1997).
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[4] Khan, M. A., Chen, Q., Shur, M. S., Dermott, B. T., Higgins, J. A., Burm, J., Schaff, W., Eastman, L. F., Electron. Lett. 32, 357-358 (1996).

Keywords

High Frequency AlGaN/GaN MODFET's

  • L. Eastman (a1), K. Chu (a1), W. Schaff (a1), M. Murphy (a1), N. G. Weimann (a1) and T. Eustis (a1)...

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