CMOS-Compatible Approach to Extending the Spectral Response of Oxide Semiconductors

A new technical paper titled “Sputtering-driven formation of interstitial oxygen for intrinsic NIR detection in IGZO phototransistor” was published by researchers at KICET, Korea University, Yonsei University, and Argonne National Lab.

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 (O_i) shallow states. X-ray photoelectron spectroscopy (XPS) and composition-matched density functional theory (DFT) calculations confirmed that these O_i-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.”

Find the technical paper here. February 2026.

Choe, J., Bong, H., Lee, H. et al. Sputtering-driven formation of interstitial oxygen for intrinsic NIR detection in IGZO phototransistor. Sci Rep (2026). https://doi.org/10.1038/s41598-026-40769-z. Creative Commons license.