Charge carrier lifetime dependence on annealing conditions in copper oxide thin films: A transient absorption study Learnmore Shenje, Dr Suzanne Ullrich

Ultrafast transient absorption spectroscopy has been used to study charge carrier dynamics in Copper(I) and Copper(II) oxide thin films as a function of annealing conditions. 16 samples were deposited on glass substrates and then subsequently annealed at temperatures 150 to 380 C for periods ranging from 2 to 24 hrs. Clear evidence of oxidation from the copper (I) to the copper (II) phases was observed by steady state and time-resolved spectroscopies as well as x-ray diffraction. Thin film transient absorption spectra were recorded by exciting the samples across the band gap and probing subsequent carrier dynamics with a white light continuum. The mixed Cu₂O/CuO thin film transient spectra were compared to those of pure Cu₂O and CuO to investigate the influence of annealing conditions on the films’ optical properties. All samples showed multi-exponential decay kinetics with a fast component (ranging from 0.2 – 0.5 ps) and a long-lived component (>1 ns); an additional 0.8 to 3 ps intermediate time constant was observed in mixed Cu₂O/CuO and pure CuO films. These kinetics are attributed to carrier relaxation in the conduction band, trapping and recombination.