Non-monotonic Size Dependence of Electron Mobility in Indium Oxide Nanocrystals Thin Film Transistor

Abstract

Indium oxide nanocrystals (In 2 O 3 NCs) with sizes of 5.5 nm-10 nm were synthesized by hot injection of the mixture precursors, indium acetate and oleic acid, into alcohol solution (1-octadecanol and 1-octadecence mixture). Field emission transmission electron microscopy (FE-TEM), High resolution X-Ray diffraction (Xray), Nuclear magnetic resonance (NMR), and Fourier transform infrared spectroscopy (FT-IR) were employed to investigate the size, surface molecular structure, and crystallinity of the synthesized In 2 O 3 NCs. When covered by oleic acid as a capping group, the In 2 O 3 NCs had a high crystallinity with a cubic structure, demonstrating a narrow size distribution. A high mobility of 2.51 cm 2 /V·s and an on/off current ratio of about 1.0 × 10 3 were observed with an In 2 O 3 NCs thin film transistor (TFT) device, where the channel layer of In 2 O 3 NCs thin films were formed by a solution process of spin coating, cured at a relatively low temperature, 350°C. A size-dependent, non-monotonic trend on electron mobility was distinctly observed: the electron mobility increased from 0.43 cm 2 /V·s for NCs with a 5.5 nm diameter to 2.51 cm 2 /V·s for NCs with a diameter of 7.1 nm, and then decreased for NCs larger than 7.1 nm. This phenomenon is clearly explained by the combination of a smaller number of hops, a decrease in charging energy, and a decrease in electronic coupling with the increasing NC size, where the crossover diameter is estimated to be 7.1 nm. The decrease in electronic coupling proved to be the decisive factor giving rise to the decrease in the mobility associated with increasing size in the larger NCs above the crossover diameter.

Ferroelectric/Dielectric Double Gate Insulator Spin-Coated Using Barium Titanate Nanocrystals for an Indium Oxide Nanocrystal-Based Thin-Film Transistor

“…New strong bands appearing at 1558 and 1435 cm –1 were attributed to the asymmetric and symmetric COO – stretching band, and no C–N stretching band was observed, indicating that oleic acid was successfully modified on the surface of BT NCs. In general, several reaction parameters, including the concentration of the precursors, the nature of the solvent, surfactants, , and the reaction time, played a significant role in the morphology of the BT NCs. Table lists the shape, average particle size, and lattice parameters of BT NCs obtained from the mixture in which 1-butanol was replaced with other alcohols with different polarities (ε).…”

“…Oleic acid-capped In 2 O 3 nanocrystals (In 2 O 3 NC, 5.3 nm size) were synthesized following our previously reported procedure. , …”

Solution‐processed Tetrafluoroborate‐capped In2O3 Nanocrystal Thin‐Film Transistors

“…Synthesis of In 2 O 3 NC followed our previously published hot injection method with a slight modification . Briefly, a 250 mL three‐neck flask containing ODA (25.45 g) and ODE (150 mL) was degassed at 120 °C.…”

“…Previously, we investigated two types of surface engineering‐utilization of shorter organic ligands or inorganic ligands for the semiconducting oxide nanocrystal to increase the mobility of In 2 O 3 NC TFT devices. Replacing long chain oleic acid (OA) ligand of the In 2 O 3 NC by short ligand such as β‐alanine, benzoic acid, 4‐aminobenzoic acid, and 2‐aminopyridine has been investigated to decrease the interdistance; however, these NC TFTs exhibited low mobility under the NCs thin film annealing conditions in the low temperature range 150–350 °C. As for the 350 °C annealing condition, oleic acid, β‐alanine, benzoic acid, 4‐aminobenzoic acid, and 2‐aminopyridine ligands, in their In 2 O 3 NC TFT devices, showed the mobilities of 0.4, 2.2, 3.1, 2.6, and 9.5 cm 2 /V/s, respectively .…”

“…Replacing long chain oleic acid (OA) ligand of the In 2 O 3 NC by short ligand such as β‐alanine, benzoic acid, 4‐aminobenzoic acid, and 2‐aminopyridine has been investigated to decrease the interdistance; however, these NC TFTs exhibited low mobility under the NCs thin film annealing conditions in the low temperature range 150–350 °C. As for the 350 °C annealing condition, oleic acid, β‐alanine, benzoic acid, 4‐aminobenzoic acid, and 2‐aminopyridine ligands, in their In 2 O 3 NC TFT devices, showed the mobilities of 0.4, 2.2, 3.1, 2.6, and 9.5 cm 2 /V/s, respectively . This is because a part of organic ligands still survived on the NC surfaces, obstructing the charge transport through NC solids, owing to the high decomposition temperature of those organic capping ligands.…”