Effect of annealing on performance of ZnO thin film transistors

Effects of thermal annealing on the structural and electrical properties of ZnO thin films for boosting their piezoelectric response

“…32 In other reports, the decrease in the electrical resistivity was explained by the improvement of crystallinity, the decrease of defect density or the decrease of grain boundary density, which helps to reduce the scattering of charge carriers and thus enhance the charge carrier mobility. 30,35 In our case, the electrical resistivity increases when the annealing temperature is increased to 800 °C, which could be due to more oxygen adsorption creating the depletion zone at the grain boundary at higher annealing temperature. Besides, the decrease in the density of defects that can act as shallow donors such as carbon impurities 51 could also be one of the reasons, which is suggested by the decrease of C-C bond signals in Raman spectra (Figure 4).…”

“…The similar pore formation in ZnO thin films after thermal annealing has been reported in Refs. 31,35,36 . These pores could affect the electrical properties of ZnO thin films.…”

“…By increasing annealing temperature, some reports have shown that the resistivity of ZnO increases, 32,50 while other reports have shown that it decreases. 30,35 The increase in the electrical resistivity was explained by i) the atoms relocated during thermal annealing in such a way that a reduced amount of defects that act as shallow donors in ZnO occurs, thus leading to a decrease in the charge carrier density, 50 or by ii) the oxygen adsorbed at the grain boundary after thermal annealing under oxygen atmosphere, creating depletion zones that decrease the charge carrier density and hamper the movement of charge carriers. 32 In other reports, the decrease in the electrical resistivity was explained by the improvement of crystallinity, the decrease of defect density or the decrease of grain boundary density, which helps to reduce the scattering of charge carriers and thus enhance the charge carrier mobility.…”

“…At 1000°C, the increase in the electrical resistivity is due to a significant impact of pores that interrupted the charge carrier motion. 35 Piezoelectric characterization that the annealed thin films have a higher piezoelectric amplitude than the as-grown thin film. Also, the thin films annealed at higher temperatures have a larger number of area with higher piezoelectric amplitude than the thin films annealed at lower temperatures.…”