All‐Oxide Transparent Thin‐Film Transistors Based on Amorphous Zinc Tin Oxide Fabricated at Room Temperature: Approaching the Thermodynamic Limit of the Subthreshold Swing

Abstract

TSOs are ZnO, SnO 2 , Ga 2 O 3 , and In 2 O 3 as well as several related compound materials and alloy systems, due to their broad application potential in the field of optoelectronic devices. [1-3] Especially transparent amorphous oxide semiconductors (TAOSs) have emerged into a thriving distinct area of research over the last few years, and since then, the field has grown rapidly toward, for instance, novel thin-film transistor (TFT) backplanes for next-generation flat-panel displays. [4,5] Alongside their high transparency, TAOSs exhibit a superior, at least tenfold higher free-carrier mobility compared to conventional amorphous silicon thin films and allow homogeneous large-scale deposition at sufficiently low temperatures, enabling the fabrication of transparent devices on flexible substrates. The by far most mature and already widely commercially exploited representative indium gallium zinc oxide (IGZO); however, contains scarce elements such as indium which innovative research is attempting to substitute by material systems consisting of abundant cations only. [6] One suitable candidate that meets these requirements and gained popularity particularly in the recent couple of years is amorphous zinc tin oxide (ZTO). ZTO is composed of earth-abundant, nontoxic elements only and exhibits, in addition to its optical transparency, a reasonably high free-carrier mobility with reported values up to 12.7 cm 2 V −1 s −1 in case of ZTO thin films fabricated at room temperature. [7] The first TFTs implementing amorphous ZTO as channel material have been reported by Chiang et al. back in 2005, followed by numerous studies on ZTO-based TFTs or rather metal-insulator-semiconductor field-effect transistors (MIS-FETs), fabricated using various deposition methods. [8-13] According to previous reports, however, the realization of MISFETs based on amorphous ZTO, including transparent devices, has up to date exclusively been limited to deposition at elevated temperatures or postdeposition annealing treatment in order to achieve sufficient functionality. [8,14-16] As alternatives to MISFET structures, metal-semiconductor fieldeffect transistors (MESFETs), implementing an n-ZTO/AgO x Schottky barrier diode as gate contact, have been reported by

Ultrafast Carrier Dynamics of Amorphous Zinc Tin Oxide Graded Thin Films

“…Meanwhile, Sn is also highly soluble in the ZnO matrix due to their similar ionic radii. The unique characteristics of ZTO, such as tunable band gap, high mobility, excellent mechanical flexibility, and stability, make this ternary oxide compound an essential material for thin-film transistors, photovoltaic cells, battery anode, optical limiters, etc. − Therefore, many research groups have reported their results on the preparation of ZTO thin films via direct current (dc) or radio-frequency sputtering, − atomic laser deposition (ALD), , and solution processes. − Previous results demonstrate that the electrical and optical properties of ZTO films can be fine-tuned by changing the Zn/Sn ratio and the deposition/annealing procedure. − However, no consensus has emerged on the mechanism of carrier transportation and recombination in ZTO because the stoichiometry and defect chemistry of ZTO are complex. A detailed understanding of the carrier dynamics in semiconductor is extremely useful for the development of future optoelectronic systems.…”

Variation in the Bandgap of Amorphous Zinc Tin Oxide: Investigating the Thickness Dependence via In Situ STS

“…Amorphous transparent conducting oxides (a-TCOs) are an alternative to crystalline TCOs that have garnered interest in recent years. − In a-TCOs, the conduction band minimum (CBM) is typically composed of the n s orbital, where n is the primary quantum number. If the radius of the s-orbital is greater than the intercation distance, as happens for n > 4, then strong conduction pathways can exist even in the absence of long-range order in the material. , a-TCO materials such as indium–zinc-oxide grown at room temperature have shown conductivity values comparable to those of crystalline Sn-doped In 2 O 3 (ITO) .…”

(LaCrO3)m/SrCrO3 superlattices as transparent p-type semiconductors with finite magnetization

“…39 Transparent semiconducting oxides are used in various technologies including photovoltaics, 40 infrared plasmonics, 41 and transparent transistors. 42,43 However, many potential applications in electronics and optoelectronics are limited by the lack of p-type materials. [44][45][46] This shortage originates from the facts that for most oxides the valence band edge is formed by the O 2p orbitals and that the high electronegativity of O makes it difficult to introduce shallow acceptors.…”