Band alignment at the SiO2/HfO2 interface: Group IIIA versus group IIIB metal dopants

Using density functional theory (DFT) we examine the effect of Al and La incorporation on the electronic properties of the interface in the SiO2/HfO2 high-k gate stacks recently introduced into the advanced modern field effect transistors (FETs). We show that La and Al doping have opposite effects on the band alignment at the SiO2/HfO2 interface: while the Al ions, which substitute preferentially for Si in the SiO2 layer, promote higher effective work function (EWF) values, the substitution of La for Hf decreases EWF. The analysis of the electronic structure of the doped interface suggests a simple relation between the electronegativity of the doping metal, screening properties of the interfacial layer, and the band offset, which allows predicting qualitatively the effect of the high-k gate stack doping with a variety of metals on its EWF.