Dual-functional crystalline BeO layer in enhancement-mode ZnO/Si thin film transistors

Integration of oxides with Si opens promising opportunities for novel multifunctional devices and new applications. To optimize the device performances through the hybrid integration, keeping the oxide/Si interface abrupt is critically important and challenging due to the seemingly unavoidable formation of amorphous SiO_x or silicide interfacial layers. Here, we report an interface-engineering approach to this issue by molecular beam epitaxy. A BeO thin layer (∼5 nm) was deposited on Si (111) surface using a two-step process of Be deposition and oxidation. The initially formed BeO served as a template for subsequent homo-epitaxial growth of a 10-nm crystalline BeO layer. The well-defined interface between BeO and Si is clearly discerned by high-resolution transmission electron microscopy, implying the role of crystalline BeO as a barrier layer against oxygen atoms’ diffusion. High-resolution X-ray photoelectron spectroscopy further confirmed that the combined BeO layers sufficiently protect the Si surface from oxidation. A bottom-gate enhancement-mode thin film transistor was established on a ZnO (130 nm)/BeO (70 nm)/Si architecture, where BeO was functionalized both as a diffusion barrier and as a high-k gate insulator. It indicates that this methodology can be potentially extended to hybrid integration of other technologically important crystalline oxides with Si infrastructures.