Effects of sputtering-deposition inclination angle on the IGZO film microstructures, optical properties and photoluminescence

IGZO/PET specimens were respectively prepared with 0°, 15°, 30°, 45°, and 60° as the inclination angle of the thin film deposition. The ntype conductivity was identified in these specimens. The following parameters, including the film thickness and morphologies of the top and lateral surfaces, the mechanical properties, chemical compounds and their primary lattices in X-ray diffraction (XRD) patterns, and the X-ray photoelectron spectrometries (XPS) for Ga2p, Ga3d, In3d, Zn2p, and O1s are presented. IR is defined as the intensity ratio of the InGaO₃(ZnO)₃ peak value to the sum of the peak values of InGaO3(ZnO)3 and InGaZnO4. Decompositions of the O1s and Ga3d spectra provide nearly Gaussian profiles of Ga-Ga, In4d, Ga-O, O₁, O₂, and O₃. The O₂ intensity ratio IR_O2, which is defined as the ratio of O₂ peak intensity to the peak intensity sum of O₁ and O₂, was evaluated for these five specimens. Depth profiles of the distributions of O, Zn, Ga, and In ions were obtained by secondary ion mass spectrometry (SIMS), and the slope (Go) of the O-ion profile in the decaying region was obtained as a function of inclination angle. Increases in the inclination angle can effectively reduce surface roughness. The peak intensities of Ga2p, Ga3d, In3d, Zn2p, and O1s formed in the specimen preparations with a nonzero inclination angle were always lower than those of the IGZO_0° specimen. Although an increase in inclination angle can raise the IR_O2 value, a nonzero inclination angle yielded an IR value lower than that of the IGZO_0° specimen. Moreover, the IR_O2 value increased with (negative) Go decrease as the response. The combined result of increasing IR_O2 and the In-O and Ga-O bonds, and decreasing the IGZO film thickness can increase light transmission. Specimens with a larger surface roughness result in a higher reflection. The IR parameter for the specimens with a nonzero inclination angle has a value smaller than that of the IGZO_0° specimen; as such, an increase in IR is advantageous for increasing the n-type conductivity. The decreasing rate of extinction coefficient k with respect to wavelength in the visible light region increases significantly with increasing IR_O2. IR and IR_O2 are therefore the governing factors of the peak intensities for the three decomposed profiles of microphotoluminescence (PL). Increasing IR and IR_O2 or decreasing film thickness is advantageous for increasing the PL peak intensities. Increases in the product values of IR and IR_O2 are favorable for increasing the peak intensities of violet and ultraviolet.