Electrical properties of La2O3 and HfO2/La2O3 gate dielectrics for germanium metal-oxide-semiconductor devices

Germanium metal-insulator-semiconductor capacitors with La2O3 dielectrics deposited at high temperature or subjected to post deposition annealing show good electrical characteristics, especially low density of interface states Dit in the 1011eV−1cm−2 range, which is an indication of good passivating properties. However, the κ value is estimated to be only about 9, while there is no evidence for an interfacial layer. This is explained in terms of a spontaneous and strong reaction between La2O3 and Ge substrate to form a low κ and leaky La–Ge–O germanate over the entire film thickness, which, however, raises concerns about gate scalability. Combining a thin (∼1nm) La2O3 layer with thicker HfO2 degrades the electrical characteristics, including Dit, but improves gate leakage and equivalent oxide thickness, indicating a better potential for scaling. Identifying suitable gate dielectric stack which combines good passivating/interfacial properties with good scalability remains a challenge.