Design, Fabrication And Characterization Of Gallium Nitride High-Electron-Mobility Transistors
Over the past few years, systems based on gallium nitride high-electron-mobility transistors (GaN HEMTs) have increasingly penetrated the markets for cellular telephone base stations, RADAR, and satellite communications. High power (several W/mm), continuous-wave (CW) operation of microwave HEMTs dissipates heat; as the device increases in temperature, its electron mobility drops and performance degrades. To enhance high-power performance and enable operation in high ambient temperature environments, the AlxGa1[-]xN/GaN epitaxial layers are attached to polycrystalline diamond substrates. e lower surface temperature rise on GaN-on- diamond is directly measured; subsequently, improved electrical performance is demonstrated on diamond versus the native (Si) substrates. Benchmark AlxGa1[-]xN/GaN devices are fabricated on SiC for comparison to diamond, Si, and bulk GaN substrates; the merits and performance of each is compared. In collaboration with Group4 Labs, X-band amplifier modules based on GaN-on-diamond HEMTs have been demonstrated for the first time. Recent efforts have focused on substituting AlxIn1[-]xN barriers in place of AlxGa1[-]xN to achieve higher output power at microwave frequencies and addressing the challenges of this new material system. Ultimately, these techniques may be combined to attain the utmost in device performance.
dissertation or thesis