Figure 3

Optical properties of nanostructure-engineered SnO₂ thin films. (a) Room temperature (RT) optical absorption spectra of the SnO₂ thin films. A strong absorption tail was observed in the 400 °C annealed sample. With increasing annealing temperatures, the absorption edges significantly blueshift and approach the bandgap of bulk SnO₂ as a result of enhanced crystallization. As a reference sample, the bulk-like crystalline SnO₂ film was deposited directly at 600 °C. (b) RT photoluminescence (PL) spectra of the SnO₂ thin films. The ultraviolet (UV) emission is much sharper in the 400 °C annealed samples compared with the others. As the annealing temperature increases, the UV emission becomes weaker, and eventually it is replaced by a broad band in the visible region, which is characteristic of the bulk SnO₂. The inset shows the PL spectrum with fine structures of the 400 °C annealed sample measured at 10 K.