Graded Composite Hf02/Al2O3 Dielectric AlGaAs/InGaAs MOS-HEMTs for Low Gate Leakage and High Power Application

Composite HfO2/Al2O3-dielectric In0.2Ga0.8As/Al0.24Ga0.76 As metal–oxide semiconductor high-electron-mobility transistors (MOS-HEMTs) by using RF sputtering/ozone water oxidization, respectively, are investigated.  In comparison with a conventional Schottky-gate device on the same epitaxial structure, an Al2O3 liner was chemically formed for the present MOS-HEMT to improve interfacial quality and decrease gate leakages. Moreover, a high-k HfO2 layer was further deposited on the Al2O3 liner to enhance the gate modulation capability. The present MOS-HEMT with the devised HfO2/Al2O3 dielectric stack has demonstrated excellent switching characteristics, including superior subthreshold slope (S.S.) of 70 mV/dec and high drain–source current (Ids) on–off ratio of up to 6 orders. Improved direct-current (DC), radio-frequency (RF), and high-temperature device performances of the present designs are also comprehensively studied in this work.