75-ANGSTROM GAN CHANNEL MODULATION-DOPED FIELD-EFFECT TRANSISTORS

A III-V nitride modulation doped field effect transistor (MODFET) laye r structure grown by organometallic vapor phase epitaxy (OMVPE) on a s apphire substrate was employed for transistor fabrication, The MODFET layer structure contained a 75 Angstrom GaN channel, 50 Angstrom A(0.1 6)Ga(0.84)N spacer, 20 Angstrom Si doped charge supply layer, 130 Angs trom Al0.16Ga0.84N barrier, and 60 Angstrom Al0.06Ga0.94N cap layer. T he thin channel (75 Angstrom) was chosen to improve the carrier confin ement in the channel. The fabricated MODFET's had 0.25 mu m long gates , and utilized a Au-Si alloy Ohmic metal and a Ti/Pd/Au gate metal. Th e measured transconductance was 40 mS/mm. From the microwave measureme nts on devices with 0.25 mu m long gates, f(t) and f(max) were determi ned to be 21.4 and 77.5 GHz, respectively. (C) 1996 American Institute of Physics.