The fabrication of AlGaN/GaN high electron mobility transistors (HEMTs) emp
loys strong spontaneous and piezoelectric polarization. The material was gr
own by OMVPE at 1050 degrees C and 75 Torr. The Hall measurements yielded a
pproximate to 1 x 10(13)/cm(2) electron sheet density, with 1200 to 1600 cm
(2)/Vs electron mobility for 300 Angstrom Al0.3Ga0.7N/GaN on sapphire at 30
0 K. The process steps for mesa isolation, Ohmic and Schottky contacts are
presented. The frequency response and drain-source breakdown voltage have b
een determined experimentally. The average electron transit velocity, deter
mined from cut-off frequency, is 1.2 x 10(7) cm/s, and the breakdown electr
ic; field is estimated to be 3 MV/cm. On sapphire substrates, large periphe
ry devices yielded 1.8 W/mm at 75% power-added efficiency and small periphe
ry devices yielded 3.3 W/mm at 36% power-added efficiency at 4 GHz. Perform
ance limitations due to electron trapping during HEMT operation are include
d. Predictions:of >20 W/mm microwave output power are presented for these d
evices on SiC substrates.