The approximate effective lifetime τ eff of a symmetrically PD0325901 solubility dmso passivated silicon wafer can be expressed as 1/τ eff = 1/τ b + 2S eff/W, where τ b is the bulk lifetime, W is the crystalline silicon (c-Si) wafer thickness, and S eff is the effective SRV. The bulk lifetime was estimated at about 1 ms using the I2 passivation method to determine S eff. Figure 4 shows that S eff was linear with 1/Q f 2 for negative Q f values >6.8 × 1011 cm-2, except for the sample annealed at 750°C. The linear relationship of samples annealed between 400°C and 700°C indicated that passivation was dominated by field-effect passivation (Q f). Thus, the sample annealed at 300°C (dislocated line) indicated that Q f of 2.5

× 1011 cm-2 was too low to dominate surface passivation, which confirmed the conclusion drawn from Figure 3. This result also agreed with the simulation of Hoex et al. for p-type c-Si [5]. Based on

the dislocation of the sample annealed at 750°C, a high interface trap density was inferred to destroy the field-effect passivation and increase S eff. Figure 4 Plot of S eff and 1/ Q f 2 with the linear fit for annealing temperatures. The annealing temperatures are between 400°C to 700°C (Q f> 6.8 × 1011cm-2). The slightly bent linear fit line was due to the logarithmic X- and Y-axes. DBAR analysis at different annealing temperatures DBAR analysis was performed at the Beijing Slow Positron Beam (Institute of High Energy Physics, Chinese Academy of Sciences, Beijing, China). A positron beam generated from a Na22 radioactive source was used, and the energy of the positrons was modulated between 0 and 10 keV to obtain the PD-332991 incident energy profile of positron annihilation. The energy region of the S parameter ranged from 510.24

to 511.76 keV, whereas the W parameter ranged from 504.2 to 508.4 and from 513.6 to 517.8 keV. Thus, the total energy region of the peak ranged from 504.2 to 517.8 keV. The vacancy defects in the alumina films were mainly Al vacancies, O vacancies, http://www.selleck.co.jp/products/Paclitaxel(Taxol).html and clusters of vacancies (voids) [13, 17, 18]. O vacancies with a positive charge (F+- and F2+-type defects) have difficulty trapping positrons because of their identical charge. Nobuaki Takahashi et al. [19] calculated the defect energetics using first-principle calculations and found that the oxygen vacancy has a much higher formation energy than the aluminum vacancy [19], further supporting the view that few positrons are trapped in charged O vacancies. Therefore, Al and neutral O vacancies (F center) are crucial to the annihilation results in the present study. Figure 5a,b shows the measured S and W parameters as a function of the incident positron energy for samples annealed at different temperatures for 10 min. In Figure 5a, the shapes of the three curves are similar because the deposition conditions of the three films were identical, and the substrates on which these films grew were also the same.