The electronic structure and the interface formation at the interface region between pentacene and $\mathrm{Hf}{\mathrm{O}}_2$ are investigated using x-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and x-ray emission spectroscopy (XES). The measured C $1s$ XPS spectra of pentacene indicate that chemical bonding occurs at the interface between pentacene and $\mathrm{Hf}{\mathrm{O}}_2$. The carbon of pentacene reacts with oxygen belonging to $\mathrm{Hf}{\mathrm{O}}_2$ and band bending occurs at the interface due to a redistribution of charge. The determined interface dipole and band bending between pentacene and $\mathrm{Hf}{\mathrm{O}}_2$ are 0.04 and $0.1\mathrm{eV}$, respectively. The highest occupied molecular orbital (HOMO) level is observed at $0.68\mathrm{eV}$ below the Fermi level. This chemical reaction allows us to grow a pentacene film with large grains onto $\mathrm{Hf}{\mathrm{O}}_2$. We conclude that high performance pentacene thin film transistors can be obtained by inserting an ultrathin $\mathrm{Hf}{\mathrm{O}}_2$ layer between pentacene and a gate insulator.

• Received 23 June 2005

DOI:https://doi.org/10.1103/PhysRevB.72.205328