Quantum confinement effects in amorphous In–Ga–Zn–O thin-film transistors with quantum well channel

We confirmed that quantum confinement effects are clearly observed even in a disordered material. Employing amorphous In–Ga–Zn–O (a-IGZO) thin-film transistors (TFTs) with quantum well channels, it was observed that field-effect mobility–gate voltage relations exhibited plateaus when the well thickness was 5 nm or less. Device simulation incorporating the quantum confinement effects reproduced the well-thickness dependence of the plateau onset voltage, verifying that the quantized electronic levels in the a-IGZO well dominate the TFT characteristics and, thus, the electron transport is free electron like with a coherent length of ∼5 nm. The field-effect mobility did not exceed the drift mobility of bulk a-IGZO, which is different from amorphous silicon superlattice TFT.