Thermally Co-Evaporated p-type Zn-doped CuI Thin Film Transistors

Abstract

To meet the ever-growing demand for transparent displays, the development of transparent materials has been the focus of much commercial and academic research. Metal oxides are a promising option due to their excellent transparency and electrical properties. Regrettably, the majority of available metal oxide semiconductors are n-type. For resolving these differences, copper iodide has been proposed as a viable p-type material owing to its high optical transparency, electrical conductivity, and the possibility of low-temperature synthesis. However, the uncontrolled carrier concentration from copper vacancies is a severe issue making its practical use as a transistor hard. Zn2+ (hole suppressor) can be a powerful solution. [1] In addition, a patterning process for implementing a complex circuit is indispensable. A thermal evaporation method was selected because it is highly reproducible and uniform, can control film thickness, and doesn’t require any solvent (especially toxic type). In addition, film fabrication without heating (merit for applications on flexible electronics), easy multi-stacking, and large-scale are too. Using the thermal evaporation process, we can control film formation according to the deposition rate adjustment. In addition, the doping concentration is adjusted through the difference in deposition rates between the dopant and the main material. The thermally evaporated Zn-doped CuI TFTs show high electrical properties (SS of 146mV/dec, µsat of 6cm2V-1s-1, Ion/Ioff of about 3.3x106, Vth of 2.45V). We focused on two things. One is that multiple stacking is easy [2], and the other is that the Fermi level increases as the amount of dopant (Zn2+) increases. [1] It is to lower the valence band offset by introducing a copper film between gold and zinc-doped copper iodide films. This may reduce the charge barrier. Here, we made a CuI single-layer TFT, and a Zn-doped CuI single-layer TFT. In the end, we combined it to create a heterojunction CuI/Zn-doped CuI TFTs and give ideas for it.