Structural and electrical characteristics of lanthanum oxide gate dielectric film on GaAs pHEMT technology

In this study, a high dielectric constant lanthanum oxide thin film (La₂O₃) was fabricated as a gate dielectric on GaAs pHEMTs to reduce the effect of the gate leakage caused by continuing the constant field-scaling trend of MOS technology. The chemical compositions and the crystalline structure at different annealing temperatures were observed by X-ray photoelectron spectroscopy (XPS) and x-ray diffraction (XRD) respectively, and the results reveal its significant thermal stability. By fabricating the capacitor, the dielectric constant of La₂O₃ with annealing at 400square was calculated to be 21.6 which is higher than the sample without annealing. In addition, transistors with two different gate materials were successfully fabricated, Pt/La₂O₃/Ti/Au gate and the conventional Pt/Ti/Au gate. The DC results shown the oxide-device performed higher turn-on and breakdown voltage, exhibited better RF characteristic, and the gate leakage current was at least one order lower than the conventional device. Therefore, La₂O₃ is a potential candidate high-k material as the gate dielectric which can enhance the performance while scaling down the device dimension and overcome the thermal effect applied for high power applications.