Sputtering-driven formation of interstitial oxygen for intrinsic NIR detection in IGZO phototransistor

TL;DR

A new method uses sputtering to create oxygen defects in IGZO, enabling efficient near-infrared detection without extra materials.

Contribution

A defect-engineering approach using sputtering geometry to enable intrinsic NIR sensitivity in IGZO without dopants or heterostructures.

Findings

Off-axis sputtered IGZO shows pronounced NIR response due to interstitial oxygen defects.

The optimized device achieves high responsivity and detectivity under 850 nm illumination.

The method is scalable and compatible with large-area fabrication, with low device variation.

Abstract

Amorphous indium gallium zinc oxide (a-IGZO) is a promising wide-bandgap semiconductor for large-area optoelectronics; however, its intrinsic insensitivity to sub-bandgap photons typically necessitates extrinsic dopants or heterostructures for near-infrared (NIR) photodetection. Here, we report a heterostructure-free and dopant-free broadband phototransistor that achieves intrinsic NIR sensitivity through geometry-driven defect engineering during sputter deposition. Amorphous IGZO thin films with a nominal In: Ga: Zn atomic ratio of ≈ 1:2:1 were deposited using on-axis (vertical) and off-axis (horizontal) sputtering configurations. While on-axis IGZO only exhibited visible-light photosensitivity, off-axis IGZO displayed a pronounced NIR response, enabled by the formation of interstitial oxygen (Oi) shallow states. X-ray photoelectron spectroscopy (XPS) and composition-matched density functional theory (DFT) calculations confirmed that these Oi-induced defect states lie 0.1–0.5 eV above the valence band maximum (VBM), effectively narrowing the optical bandgap and enabling sub-gap absorption and photogating under 850 nm illumination. The optimized a-IGZO phototransistor achieves a responsivity of 42.5 A W-1, an external quantum efficiency of 6.2 × 103%, and a specific detectivity of 8.3 × 1011 Jones, all without plasmonic, hybrid, or quantum-dot sensitizers. Moreover, the off-axis process exhibits < 10% device-to-device variation across 5 samples, confirming its robustness and compatibility with large-area fabrication. To validate its practical utility, the off-axis IGZO device was further employed to quantify the sugar content (Brix) of coffee samples under NIR illumination, showing a clear correlation between photocurrent and concentration. This work demonstrates a simple, scalable, and CMOS-compatible approach to extending the spectral response of oxide semiconductors, opening new opportunities for cost-effective broadband photodetectors and integrated photonic systems.

The online version contains supplementary material available at 10.1038/s41598-026-40769-z.

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