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.