Germanium metal-insulator-semiconductor capacitors with rare earth La2O3 gate dielectric

In this work, we investigate La2O3 as a gate dielectric candidate for Ge devices, using metal-insulator-semiconductor (MIS) structures. When the deposition temperature increases, the electrical characteristics improve with regard to dispersion in accumulation, hysteresis, stretch out, leakage current and interface state density D-it. By analyzing the CV data for films with different oxide thickness we find that the dielectric constant of La2O3 has a medium k-value of about 11. The same data indicate that there is no interfacial layer, which is confirmed by high resolution transmission electron microscopy (HRTEM) observations. These results suggest that a strong reaction with the Ge substrate may take place so that a La-Ge-O compound may form over the entire film thickness reducing the k-value. This reaction layer could be responsible for the reduction of Dit indicating good passivating properties. However, it may limit gate oxide scaling in future Ge MOS devices.