Silicon Nanotexture Surface Area Mapping Using Ultraviolet Reflectance

Abstract

The enhanced surface area of silicon nanotexture is an important metric for solar cell integration as it affects multiple properties including optical reflectance, dopant diffusion, and surface recombination. Silicon nanotexture is typically characterized by its surface-area-to-projected-area ratio or enhanced area factor (EAF). However, traditional approaches for measuring EAF provide limited statistics, making correlation studies difficult. In this article, silicon's dominant ultraviolet reflectance peak, R(E2), which is very sensitive to surface etching, is applied to EAF spatial mapping. A clear decay correlation between R(E2) and EAF is shown for multiple textures created using reactive ion etching and metal catalyzed chemical etching. This correlation is applied to R(280 nm) reflectance mapping to yield accurate, high-resolution full-wafer EAF spatial mapping of silicon nanotextures. R(280 nm) mapping is also shown to be sensitive enough to correlate the impact of nanotexture spatial variation on post-diffusion sheet resistance. Finite-difference time-domain simulations of several nanoscale pyramid textures confirm a decay band for R(E2) versus EAF, consistent with our measurements. We suggest that R(E2) mapping may prove useful for other silicon nanotexture properties and applications where EAF is important.

Plasma Focused Ion Beam Tomography for Accurate Characterization of Black Silicon Validated by Full Wave Optical Simulation

“…Therefore, our group's previous work has extended the use of E1 and E2 peaks into a 2D mapping for surface texturing. [ 44 ] The FDTD simulation results show that the reflection for both RIE1 and RIE2 are well scattered at E1 and E2 peaks, which explains the root cause of the excellent optical behavior of BSi.…”

“…Our group reported previously that the UV reflectance behavior is particularly sensitive to surface nanoetching. [ 44 ] As such, an UV reflectance map can be used to quickly monitor texturing variation. Therefore, Table 2 also shows the deviation of FDTD simulated Reflection(%) to the measured Reflection(%) in the UV (250–400 nm) only range.…”

Wetting Properties of Black Silicon Layers Fabricated by Different Techniques

“…The most successful and widely used techniques are reactive ion etching (RIE), metal-assisted chemical etching (MACE), and laser-induced etching (LIE). [19][20][21][22][23][24] Most research on BSi focuses on optical, structural, and electronic properties (as reviewed in ref. [25]).…”

Properties of Black Silicon Layers Fabricated by Different Techniques for Solar Cell Applications

“…The most successful and widely used methods are reactive ion etching (RIE), metal-assisted chemical etching (MACE), and femtosecond laser-induced processing (LIP). [22][23][24][25][26] These techniques yield varying structures and, consequently, different properties of BS layers. Therefore, it is very important to compare different fabrication techniques and determine the resulting properties of BS.…”