Investigation of Ge nanocrytals in a metal-insulator-semiconductor structure with a HfO2∕SiO2 stack as the tunnel dielectric

A metal-insulator-semiconductor (MIS) structure containing a HfO2 control gate, a Ge nanocrystal-embedded HfO2 dielectric and a HfO2∕SiO2 stack layer as tunnel oxide, was fabricated by an electron-beam evaporation method. High-resolution transmission electron microscopy study revealed that the HfO2∕SiO2 stack layer minimized Ge penetration, leading to the formation of Ge nanocrystals that are self-aligned between the tunnel oxide and the capping HfO2 layer. Influence of different annealing conditions on the formation and distribution of Ge nanocrystals was studied. Current–voltage (I–V) and capacitance–voltage (C–V) measurements revealed promising electrical characteristics of the MIS structure, and relatively high stored charge density of 1012cm−2 was achieved.