Are There High-Density Deep States in an Atomic-Layer-Deposited Indium–Gallium–Zinc Oxide Thin Film?

It has been well recognized that high-density deep states exist in indium–gallium–zinc oxide (IGZO) thin films. Many of the device characteristics of IGZO transistors, such as negative bias illumination stability (NBIS), are understood to be related to these deep states. However, in this work, it was found that the deep-state density (NtD) of atomic-layer-deposited (ALD) IGZO transistors can be an ultralow value (<2.3 × 1012/cm3) by the proposed NBIS-free light-assisted I–V measurements so that the deep states do not affect the I–V characteristics even in the subthreshold region. This work also reveals that NBIS is not related to the photoexcitation of electrons in the deep states. Our results suggest that the existence of deep states and the impact of deep states on ALD IGZO transistors may need to be revisited.