Direct Observation of Hole Current in Amorphous Oxide Semiconductors under Illumination

Hole current was directly observed in oxide semiconductors under illumination. Two stacks were fabricated, with In-Ga-Zn-O (IGZO) as the channel and SiO2 or SiNx as the gate insulator. X-ray photoelectron spectroscopy confirmed the IGZO/SiNx interface has no hole barrier while the IGZO/SiO2 interface has a significant one. This was used to analyze hole generation in IGZO by illuminating light at various wavelengths. As a result, a threshold wavelength, where holes start to emerge in the channel, was found to exist. Negative bias-illumination-temperature stress experiments showed that no additional threshold voltage shift exists at wavelengths longer than this threshold wavelength.