Valence and conduction band offsets in sputtered HfO2/InGaZnO4 heterostructures

Abstract

Amorphous InGaZnO4 (a-IGZO) thin film transistors have been demonstrated on a variety of substrates, including flexible template like paper, tape and polyethylene terephthalate. Charge trapping at the a-IGZO/dielectric interface has been identified as a primary source of instability in these transistors. The valence and conduction band offsets are important parameters of these interfaces and should be sufficiently large to inhibit the injection of electrons and holes into the dielectric where they can cause threshold shifts and gate leakage. In this paper we report on the determination of band offsets in the HfO2/InGaZnO4 heterostructure using X-Ray Photoelectron Spectroscopy. The valence band offset was determined to be ∼0.38 eV ± 0.03 eV, while the conduction band offset was determined to be 2.26 eV. The HfO2/InGaZnO4 system has a nested or straddling gap (type I) alignment. We compare these bad offsets to previously reported values for HfO2 and other dielectrics on a-IGZO.