Results and discussion Influence of annealing temperature on surface passivation The effective lifetimes

of the samples annealed at different temperatures in air are shown in Figure 2. The effective lifetime change is the ratio of the effective lifetime after annealing to that of the effective lifetime before annealing. The ratio was used instead of the actual value because the effective lifetimes of the six as-deposited samples (before annealing) were not strictly identical, which rendered meaningless the observation of the absolute value of the effective lifetime after annealing. The effective lifetime change initially increased with increased annealing temperature and then rapidly decreased below unity. This result indicated that passivation collapsed at annealing temperatures higher than 700°C. The optimum annealing temperature was around 500°C in air, which was higher than the reported 400°C to 450°C when annealed Proteasome inhibitor in N2[15]. KU-60019 purchase learn more Figure 2 Influence of annealing temperature on Al 2 O 3 passivation. Corona charging measurement was performed to observe the field-effect and chemical passivation mechanisms. Q f and the lowest lifetime can be extracted from the resulting measurement curve, as described in the section ‘Corona charging measurement.’ Figure 3a shows the measured data, and Figure 3b shows the Q f and the minimum effective lifetime change (lowest lifetime after annealing

vs. as-deposited value) as a function of the annealing temperature. Q f significantly increased to 1012 cm-2 after annealing at 400°C compared with Q f of about 1011 cm-2 before annealing (Figure 1). Q f increases from 2.5 × 1011 cm-2 at 300°C, reaches the highest point of about 2.5 × 1012 cm-2 at 500°C, and thereafter decreases to 8 × 1011 Atorvastatin cm-2. Q f did not significantly change

when the annealing temperature was higher than 600°C. Meanwhile, the effective lifetime of the sample annealed at 300°C was slightly enhanced (Figure 2), i.e., 1.2 times greater than that of the as-deposited sample. This result indicated that Q f of 2.5 × 1011 cm-2 did not significantly affect surface passivation. The chemical passivation variation at 300°C to 500°C was similar to Q f based on the minimum lifetime in the corona charging measurement. The chemical passivation effect increased with increased annealing temperature before 500°C and quickly decreased thereafter. This variation was related to the hydrogen release from the film found by Dingemans [16]. Figure 3 Corona charging measurement of samples. (a) Before and after annealing. (b) Fixed charge density and minimum effective lifetime change after annealing at different temperatures. Notably, Q f reached 1012 cm-2 after annealing at 750°C, and this value was almost one magnitude higher than that of the as-deposited sample. However, the effective lifetime was low (Figure 2) because of the poor chemical passivation at 750°C in Figure 3b of the minimum lifetime change value.