Spectroscopic Investigation on the Origin of Photoinduced Carrier Generation in Semiconducting InGaO and InGaZnO Films

We investigated the electronic structures of defective semiconducting InGaO and InGaZnO films using X-ray photoelectron spectroscopy. The defects were created intentionally using an intensive Ar-ion bombardment on the films. After Ar bombardment, a subgap state emerged above the valence band edge, which decreased the band gap to <2 eV, suggesting the possibility of electron−hole pair creation even under visible light illumination. Also, the defect states were found to have metal sp characters, being related to oxygen deficiencies in the n-type semiconducting oxides. Therefore, eliminating the oxygen deficiency in the semiconducting oxide films is essential for preventing the photoinduced degradation in thin-film field effect transistors.