Electronic structure and origin of intrinsic defects in sputtered HfTiO₂ alloy dielectric on GaAs surface

In this work, we have investigated the electronic structure and electrical properties of sputter-deposited high-k dielectrics grown on p-GaAs substrate with post-deposition annealing at 500 °C/N₂ ambient. Capacitance-voltage results show that co-sputtered amorphous-HfTiO₂ alloy dielectric can reduce interfacial dangling bonds. HRTEM and AR- X-ray photoelectron spectroscopy results confirmed the formation of a thin interfacial layer during sputter deposition. At the atomistic level, the surface reaction and electronic interface structure were investigated by density-functional theory (DFT) calculations. Using the HSE functional, theoretical calculations of bulk HfO₂, a-TiO₂, and HfTiO₂ band gaps are found to be 5.27, 2.61, and 4.03 eV, respectively. Consequently, in the HfTiO₂/GaAs interface, the valance band offset is found to be reduced to 1.04 eV compared to HfO₂/GaAs structure valance band offset of 1.45 eV. Reduction in border trap density (~10¹¹ V/cm²) was observed due to Ti atoms bridging between As-dangling bonds. The angle-resolved XPS analysis further confirmed Ti-O-As chemical bonding with very thin (~20 Å) dielectric layers.