AVS 45th International Symposium
    Electronic Materials and Processing Division Tuesday Sessions
       Session EM+SE-TuM

Invited Paper EM+SE-TuM1
Gallium Nitride Structures for High Power Microwave Amplification

Tuesday, November 3, 1998, 8:20 am, Room 316

Session: Critical Issues in Widebandgap Semiconductors
Presenter: L.F. Eastman, Cornell University
Authors: L.F. Eastman, Cornell University
K. Chu, Cornell University
N. Weimann, Cornell University
J. Smart, Cornell University
J.R. Shealy, Cornell University
Correspondent: Click to Email
Among the wide band-gap materials Gallium Nitride has yielded the best frequency response and efficiency for microwave amplifiers. Wurtzite Al@sub x@Ga@sub 1-x@N/GaN/SiC HEMT structures, with x < .50, yield a high two-dimensional electron gas density of ~ 1 x 10@super 13@/cm@super 2@ with no intentional doping, due to the piezoelectric effect. The drain-source breakdown voltage at pinchoff rises linearly with gate length, being > 200 V for 1 µm gates due to the 3-4 MV/cm breakdown field strength. Using SiC substrates having > 3 W/cm°K thermal conductivity, up to 20 W/mm periphery will be possible. The normalized drain current is > 1 A/mm, yielding a high normalized optimum load of ~ 200 ohm-mm for 1 µm gates. Large periphery HEMT's with reasonable load resistances will allow power levels > 100 W, with efficiency above 60%, for frequencies < 12 GHz. The impact of dislocations, with density of .5 - 2.0 x10@super 9@/cm@super 2@ for GaN on SiC, on electron mobility has been determined analytically, and is in the range of 1,500-2,000 cm@super 2@/V-s. These dislocations line up in the growth direction and thus do not substantially limit the electron mobility in vertical FET's such as the Static Induction Transistor (S.I.T.) The theoretical value of the peak electron velocity for GaN is 2.7 x 10@super 7@cm/s and is reached at 150-200,000 V/cm. Short gate (.15µm) HEMT's have unity current gain frequency of ~ 70 GHz, and unity power gain frequency of 140 GHz. Due to the large bandgap, operation with channel temperatures > 200°C is possible with no substantial reduction in performance.