GaAs enhancement-mode MOSHEMT with Pt/ ZrO₂ /Ti/Au composited gate structure

The properties of a GaAs enhancement-mode metal-oxide-semiconductor high electron mobility transistor (E-MOSHEMT) were demonstrated using an electron-beam deposited Pt/ ZrO₂ composited gate structure. X-ray photoelectron spectroscopy was conducted to measure the binding energies of ZrO₂ thin films with various postannealing temperatures, and its structural properties remained stable up to 600°C. A 20 nm thick Pt metal layer between AlGaAs and ZrO₂ was used as a buried metal to control the device threshold voltage (Vth) for the enhancement-mode operation. By calculating the capacitance-voltage (C-V) measured curves, the dielectric constant of ZrO₂ was 12.6 and the voltage shift of the C-V hysteresis phenomena can be reduced to 4.5 mV after 400°C postannealing. Measured load-pull power results have also shown that ZrO₂ E-MOSHEMT achieved a better power added efficiency at a high input swing owing to the gate leakage current reduction. The electron-beam evaporated Pt/ ZrO₂ /Ti/Au composited gate MOSHEMT is suitable for high volume production due to its in situ insulator and metal gate deposition in the same chamber.