Figure 9
Hemispherical reflectance spectra of black silicon micro-nano hybrid structures obtained for different processes and micro structures. (a) Reflectance results of six samples with nanostructures, (b) reflectance results of single micro structures and silicon surface with no treatment. As shown in (a), six lines are presented, and the reflectivity values of the samples are illustrated. Taking the forbidden energy gap of silicon into consideration, silicon can usually absorb light with wavelengths below 1100 nm. Therefore, wavelengths between 300 nm and 1100 nm are analyzed. As can be inferred from the figure, except for the wet-pit sample (red line) and the dry-flat sample (purple line), the reflectance of the samples decreases slightly with wavelength from 300 nm to 400 nm, remains stable for wavelengths from 400 nm to 1000 nm and increases dramatically for wavelengths from 1000 nm to 1100 nm. The wet-pit sample shows little fluctuation for wavelengths from 300 nm to 700 nm but strongly increases from 700 nm to 1100 nm. The dry-flat sample presents a peak in the wavelength range from 300 nm to 1100 nm, which may originate from the effect of light diffraction. Fluctuations can be seen at wavelengths near 820 nm because the UV-3600 instrument changes light sources from infrared to visible light. Reflectance results of single micro structures and silicon surface with no treatment are shown in (b). It can be inferred that silicon with no treatment indicated high reflectance that far surpassed other rough surfaces with single micro structures. The micro pits and tips were only fabricated by ICP without nano structures and the process of them were the same as the No. 1, No. 2, No. 4, and No. 5 samples in first process step.
