Abstract
Amorphous gadolinium gallium oxide (GGG) and crystalline gadolinium oxide (Gd 2 O 3 ) have been investigated as dielectrics for fabrication of GaN metal oxide semiconductor field effect transistors. GGG, depoisted by e-beam evaporation in a molecular beam epitaxy (MBE) chamber was found to produce a breakdown field of 12MV/cm indicating a low concentration of defects in the dielectric. MOSFETs fabricated with this dielectric showed modulation at forward voltages up to 3V. Gd 2 O 3 was deposted by molecular beam epitaxy using elemental Gd and an electron cyclotron resonance (ECR) oxygen plasma in an MBE chamber. Both reflection high energy electron diffraction (RHEED) and x-ray diffraction confirm the single crystal nature of the deposited Gd 2 O 3 . However, cross-sectional transmission electron microscopy indicates the presence of a large concentration of dilocations and other structural defects. These defects cause significant leakage in the Gd2O3 and necessitated the addition of an SiO 2 overlayer in order to reduce the gate leakage current in depletion mode devices. Using this double layer structure, devices with modulation at forward voltages up to 7V were obtained, as compared to 3 V. for devices fabricated with GGG. Both dielectrics appear to be stable at temperatures up to 950 - 1000°C as determined by x-ray diffraction and Auger electron spectroscopy.