Fabrication and characterization of gallium nitride electronic devices

Gallium nitride (GaN)-based high electron mobility transistors (HEMTs), metal oxide semiconductor field effect transistors (MOSFETs), and Schottky rectifiers were fabricated and characterized. Novel dielectric materials Gd ₂O₃ and ScO were evaluated as potential gate dielectrics for GaN MOS applications. The devices presented herein show tremendous potential for elevated temperature, high frequency, and/or high voltage operation.; AlGaN/GaN HEMTs were grown by MOCVD on sapphire and SiC substrates and by RF-MBE on sapphire substrates. Devices were fabricated with gate lengths from 100 nm to 1.2 μm. Drain current density approached 1 A/mm and extrinsic transconductance exceeded 200 mS/mm for small gate periphery devices. For the shortest gate length, a unity-gain cutoff frequency (f_T) of 59 GHz and a maximum frequency of oscillation (f_max) of 90 GHz were extracted from measured scattering parameters. The experimental s-parameters were in excellent agreement with simulated results from small-signal linear modeling. Large signal characterization of 0.25 x 150 μm2 devices produced 2.75 W/mm at 3 GHz and 1.7 W/mm at 10 GHz. Devices fabricated on high thermal conductivity SiC substrates exhibited superior high temperature performance and a reduced density of threading dislocations.; Novel gate dielectrics Gd₂O₃ and ScO were grown by gas source molecular beam epitaxy (GSMBE). Current-voltage (I-V) and capacitance-voltage (C-V) data were collected from MOS capacitors to evaluate the bulk and interfacial electrical properties of the insulators. Single crystal Gd₂O ₃ was demonstrated on GaN, but the resultant MOSFET exhibited a large gate leakage attributed to defects and dislocations in the oxide. MOSFETs with a stacked gate dielectric of Gd₂O₃/SiO₂ were operational at a drain source bias of 80 V and a gate bias of +7 V.; Bulk GaN templates grown by hydride vapor phase epitaxy (HYPE) were used to fabricate vertical geometry Schottky rectifiers. Size- and temperature-dependent I-V characteristics are reported. These devices show significant improvements in forward turn-on voltage, on-state resistance, and reverse recovery characteristics relative to previously reported devices fabricated on GaN layers grown on sapphire.