Application of atomic layer deposited Al_2O_3 as charge injection layer for high-permittivity dielectrics

摘要

The current transport through (Ba,Sr)TiO_3 (BST)/Al_2O_3 bilayer structures with Pt electrodes is studied using current-voltage measurements. Due to its low permittivity compared to BST the Al_2O_3 layer, which is deposited by atomic layer deposition (ALD), enables electron injection by tunneling at low thickness, such that transport becomes limited by the bulk conductivity of BST. A current rectification of up to 106 is observed at an Al_2O_3 thickness of 1.8 nm, indicating that hole transport does not contribute to the current. The measurements are complemented by the determination of the energy band alignment at the interface using photoelectron spectroscopy. A Fermi level pinning in the Al_2O_3 layer, which seems to be characteristic for ALD films, leads to a significant modification of the energy band alignment. This pinning does not prohibit electron injection, which relies on the potential drop across the Al_2O_3 layer.