Improvement in carrier mobility through band-gap engineering in atomic-layer-deposited In-Ga-Zn-O stacks

This paper reports the performance improvement of heterojunction channel field-effect transistor using an atomic-layer-deposited InGaZnO (IGZO) channel on basis of a band alignment. The heterojunction stack consisted of a 5 nm-thick In0.61Ga0.16Zn0.23O confinement layer (CL) and a 2 nm-thick In0.52Ga0.32Zn0.15O barrier layer (BL). Band-gap engineering through cation composition and thickness modulation of each layers allowed free electron diffusion from the In0.52Ga0.32Zn0.15O BL to the In0.61Ga0.16Zn0.23O CL and carriers confinement in CL, leading to the improvement in field-effect mobility. The control transistor with 5 nm-thick IGZO CL layer had a mobility of 33.4 cm2/Vs, whereas the heterojunction transistor with 2 nm-thick IGZO BL exhibited a higher mobility of 50.7 cm2/Vs as well as low gate swing of 89 mV/decade as a result of carrier transporting boosting. Moreover, the corresponding heterojunction channel transistors exhibited better gate bias stability due to the mitigation of gap states creation and passivating behavior by introducing the 2 nm-thick IGZO BL. •2DEG formation of a-IGZO stack using ALD route is demonstrated on a high-k HfO2 dielectric film.•The Ga fraction in IGZO barrier layer plays a pivotal role in the band alignment.•Significant boosting of mobility and stability is observed for the transistor with heterojunction IGZO stack.