Metal Oxide Transistors via Polyethylenimine Doping of the Channel Layer: Interplay of Doping, Microstructure, and Charge Transport

Polymer doping of solution-processed In₂O₃ with small amounts of the electron-rich polymer, polyethylenimine (PEI), affords superior transistor performance, including higher electron mobility than that of the pristine In₂O₃ matrix. PEI doping of In₂O₃ films not only frustrates crystallization and controls the carrier concentration but, more importantly, acts as electron dopant and/or scattering center depending on the polymer doping concentration. The electron donating capacity of PEI combined with charge trapping and variation in the matrix film microstructure yields, for optimum PEI doping concentrations of 1.0%–1.5%, electron mobilities as high as ≈9 cm² V⁻¹ s⁻¹ on a 300 nm SiO₂ gate dielectric, an excellent on/off ratio of ≈10⁷, and an application optimal V _T. Importantly, these metrics exceed those of the pure In₂O₃ matrix with a maximum mobility ≈4 cm² V⁻¹ s⁻¹. Furthermore, we show that this approach is extendible to other oxide compositions such as IZO and the technologically relevant IGZO. This work opens a new means to fabricate amorphous semiconductors via solution processing at low temperatures, while preserving or enhancing the mobility of the pristine polycrystalline semiconductor.