Modulation-Doped In₂O₃/ZnO Heterojunction Transistors Processed from Solution

This paper reports the controlled growth of atomically sharp In₂O₃/ZnO and In₂O₃/Li-doped ZnO (In₂O₃/Li-ZnO) heterojunctions via spin-coating at 200 °C and assesses their application in n-channel thin-film transistors (TFTs). It is shown that addition of Li in ZnO leads to n-type doping and allows for the accurate tuning of its Fermi energy. In the case of In₂O₃/ZnO heterojunctions, presence of the n-doped ZnO layer results in an increased amount of electrons being transferred from its conduction band minimum to that of In₂O₃ over the interface, in a process similar to modulation doping. Electrical characterization reveals the profound impact of the presence of the n-doped ZnO layer on the charge transport properties of the isotype In₂O₃/Li-ZnO heterojunctions as well as on the operating characteristics of the resulting TFTs. By judicious optimization of the In₂O₃/Li-ZnO interface microstructure, and Li concentration, significant enhancement in both the electron mobility and TFT bias stability is demonstrated.