Figure 5b,c shows the EDS mappings of aluminum and silicon, respectively. White and black signals show a maximum and minimum value, respectively. Note that the signal of aluminum was detected on the bottom of SiNWs after Al2O3 deposition, although the signal was not detected before the deposition. However, the Al intensity Salubrinal research buy around the bottom was weaker than the one at the top. From a SEM image, the shape of SiNWs around the top is needle-like and the gap between SiNWs is about several hundred nanometers, although the gap around the bottom is about several ten nanometers (not shown). Therefore,

the intensity of Al is higher around the top. These results also suggest that the Al2O3 film macroscopically covered SiNWs from the top to the bottom. To investigate the microscopic structure of the interface between Forskolin a SiNW and Al2O3, TEM and HAADF-STEM observations were carried out. Figure 6a,b shows a schematic diagram on how to fabricate the sample for HAADF observation and a HAADF image of the SiNW

cut into a round slice at the bottom of the SiNW, respectively. The contrast of a HAADF Enzalutamide image is proportional to the square of the atomic number and becomes brighter with increasing atomic number. The contrast between the SiNW and Al2O3 is very clear in the figure. It should be noted that there is no gap at the interface. In Figure 6c, the uniform thickness of Al2O3 can be seen and is about 30 nm, which is enough for the passivation of crystalline silicon solar cells [29]. The uniform deposition on the SiNW arrays is due to the excellent surface coverage of ALD techniques. From these results, the Al2O3 film deposited by the ALD method was able to cover the SiNW arrays up to the bottom. Since the fine interface between a SiNW and Al2O3 was formed and dangling bonds on the surface were modified by oxygen, the minority carrier lifetime in the SiNW arrays was improved. Figure 3 Transient response of excess carrier density in a SiNW array on bulk silicon. (a) Linear scale. (b) Logarithmic scale. Figure 4 Cross-sectional SEM image Progesterone of an a-Si:H thin film deposited

on a SiNW array. Figure 5 SEM image and EDS mapping of SiNW without and with Al 2 O 3 . (a) Cross-sectional SEM image of SiNWs without and with Al2O3. EDS mappings of (b) Al and (c) Si corresponding to the SiNWs shown in (a), respectively. Figure 6 HAADF-STEM and TEM images of the SiNW with Al 2 O 3 . (a)The procedure on how to measure the HAADF-STEM image. (b) Cross-sectional HAADF-STEM image of a SiNW cut into a round slice at the bottom of the SiNW array. (c) Cross-sectional TEM image of the interface between the SiNW and Al2O3. For further improvement of carrier lifetime, annealing of the SiNW arrays embedded in Al2O3 was carried out. It was reported that negative fixed charge density at the interface of Al2O3/p-type c-Si increased from 1.3 × 1011 to 2.45 × 1012 cm−2 by annealing at 400°C [36].