Study on Al₂O₃/Ge interface formed by ALD directly on epitaxial Ge

Germanium (Ge) has been attracting considerable attention as a high mobility channel material to enhance the performance of CMOS circuits. One of the most important issues for realization of practical Ge-MOSFET devices with superior performances is requirement to improve qualities of gate dielectric/Ge interfaces. In this work, Al₂O₃/Ge structures are fabricated by direct atomic layer deposition (ALD) on epitaxialy grown Ge. We indicate that ALD incubation time is fully suppressed by the ALD on a completely clean Ge surface created by Ge epitaxy on a Ge substrate. Moreover, x-ray photoelectron spectroscopy analyses reveal that unintentional formation of a GeO₂ at the Al₂O₃/Ge interface can be almost avoided by the ALD on the epitaxial Ge whereas the interfacial GeO₂ layer is present for samples exposed to the air before ALD. These results clearly indicate that direct ALD on epitaxial Ge is a very promising method to significantly improve Ge MOSFET performances.