Orbital matching governs perturbation-driven charge transmission in amorphous IGZO

Abstract

Amorphous indium–gallium–zinc oxide (IGZO) exhibits substantially faster charge transport than its constituent single oxides, yet the microscopic origin of this multiplication advantage remains unclear. To investigate the microscopic origin of this behavior, we employ dynamic ozone perturbation as a probe of charge propagation in IGZO and compare its response with those of ZnO and In2O3. While the single-oxide systems display pronounced slow relaxation components associated with delayed transport from the surface into the bulk, IGZO exhibits a strongly suppressed slow process, yielding transients that are effectively described by a single characteristic timescale. Raman and photoluminescence spectroscopy reveal defect-related sub-gap states associated with ZnO4 structural motifs, suggesting that local structural disorder plays an active role in electronic transport. Besides oxygen-vacancy-related states, the Raman 2LO mode directly points to the involvement of ZnO4-associated defect structures. Rather than representing isolated point defects, these motifs may indicate local coordination distortions that alter the connectivity between neighboring cation environments. Density-functional calculations further show that ozone preferentially adsorbs on In sites, producing localized surface polarization. Partial charge analysis and Wannier-based electronic reconstruction identify an In–O–ZN transport pathway in which orbital-matched ZN–O bridges efficiently relay the surface perturbation into the amorphous network. This identified transport pathway is absent in the corresponding single oxides and provides a direct electronic connection between surface-localized charge accumulation and bulk transport. These results suggest that the enhanced performance of amorphous multiplication oxides extends beyond conventional concepts of band alignment, carrier modulation, and defect engineering. Instead, orbital compatibility between dissimilar cation environments may create emergent transport pathways that qualitatively alter charge propagation. Our findings introduce orbital connectivity as a complementary descriptor for understanding transport in complex amorphous oxide semiconductors.