A comparison of gallium gadolinium oxide and gadolinium oxide for use as dielectrics in GaN MOSFETs

摘要

[[abstract]]Amorphous gadolinium gallium oxide (GGG) and crystalline gadolinium oxide (Gd2O3) have been investigated as dielectrics for fabrication of GaN metal oxide semiconductor field effect transistors. GGG, deposited by e-beam evaporation in a molecular beam epitaxy (MBE) chamber was found to produce a breakdown field of 12 MV/cm indicating a low concentration of defects in the dielectric. MOSFETs fabricated with this dielectric showed modulation at forward voltages up to 3 V. Gd2O3 was deposited 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 Gd2O3. However, cross-sectional transmission electron microscopy indicates the presence of a large concentration of dislocations and other structural defects. These defects cause significant leakage in the Gd203 and necessitated the addition of an SiO2 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 7 V 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