n, k data for pnc-Si
We haven’t talked much about the optical properties of pnc-Si, but I thought it would be good to share some of the index and dispersion data I’ve collected using the ellipsometer. Below are plots of index of refraction (n) and extinction coefficient (k) vesus energy. The index is a measure of the optical density. The extinction coefficient is a measure of the energy loss due to absorption.
I’ve plotted an amorphous silicon sample I measured as well as a single crystalline sample (from reference) for comparison. As you can see in the index plot, pnc-Si has a shape “half-way” between the amorphous and single crystal curve. The “bump” in both the pnc-Si and c-Si curve is due to the optical absorption at the bandgap energy. The k plot clearly shows the bandgap energies for all three materials. Our measured amorphous and pnc-Si bandgaps are in agreement with literature (1.5 eV for amorphous and 2.2 eV for nano-crystalline). We should note that the 2.2 eV is a secondary absorption edge (primary is at 1.1 eV) but because our samples are so thin that we do not pick up the primary.
your results make sense- the pnc-Si is similar to crystalline Si with a significant broadening factor of the resonances in your curves- that’s what is expected in nanocrystalline matetials, as the dephasing time decreases due to interface scattering etc compared to single crystal Si.