Experimental and theoretical evidence for hydrogen doping in polymer solution-processed indium gallium oxide

Area of Science:

• Materials Science
• Solid-State Physics
• Semiconductor Devices

Background:

• Aqueous solution-processed indium gallium oxide (IGO) thin-film transistors (TFTs) are promising for low-cost electronics.
• Enhancing the field-effect electron mobility of IGO TFTs is crucial for device performance.
• Understanding the mechanisms behind mobility enhancement in metal oxide semiconductors is an active research area.

Purpose of the Study:

• To investigate the origin of the significant electron mobility enhancement in IGO TFTs achieved by adding polyvinyl alcohol (PVA).
• To elucidate the role of PVA in modifying the microstructure, electronic structure, and charge transport properties of IGO films.
• To establish a pathway for high-performance, stable metal oxide semiconductor electronics using green solvent processing.

Main Methods:

• Utilized a comprehensive suite of experimental techniques: extended X-ray absorption fine structure (EXAFS), resonant soft X-ray scattering (R-SoXS), ultraviolet photoelectron spectroscopy (UPS), Fourier transform-infrared (FT-IR) spectroscopy, time-of-flight secondary-ion mass spectrometry (ToF-SIMS), and composition-/processing-dependent TFT property measurements.
• Employed advanced spectroscopic methods including high-resolution solid-state 1H, 71Ga, and 115In NMR spectroscopy, specifically 71Ga{1H} rotational-echo double-resonance (REDOR) NMR.
• Performed theoretical calculations using discrete Fourier transform (DFT) analysis combined with ab initio molecular dynamics (MD) liquid-quench simulations.

Main Results:

• Polyvinyl alcohol (PVA) addition resulted in a >70-fold increase in field-effect electron mobility, reaching 7.9 cm²/Vs.
• PVA facilitated optimal hydrogen doping, evidenced by a Ga···H distance of ~3.4 Å and a conversion of Ga coordination from six- to four-coordinate.
• These changes effectively suppressed deep trap defect localization and reduced metal-oxide polyhedral distortion, leading to enhanced electron mobility.

Conclusions:

• Hydroxyl polymer doping, specifically PVA, offers an effective method for hydrogen doping in green solvent-processed metal oxide films.
• The observed reduction in deep trap defects and polyhedral distortion is directly linked to the improved electron mobility in IGO TFTs.
• This study demonstrates a viable strategy for developing high-performance, ultra-stable metal oxide semiconductor electronics using simple binary compositions and environmentally friendly processing.