In-gap states of an amorphous In–Ga–Zn–O thin film studied via high-sensitivity ultraviolet photoemission spectroscopy using low-energy photons

Abstract

Low-density electronic states in the energy gap of an amorphous In–Ga–Zn–O film control device performance. Herein, density of states (DOS) distribution from valence band to the in-gap states of 1014 cm−3 eV−1 level was determined using high-sensitivity UV photoemission spectroscopy. Exponential tail states accompanying two energetically-localized states were directly observed as reported previously. The observed slope of the exponential tail state was different from the Urbach energy derived using photothermal deflection spectroscopy, indicating the importance of directly observing the DOS of in-gap states.