Dear All,
Fano interference is usually observed between the zone-folded transverse acoustic (FTA) phonon modes and the electronic continuum in n-type 4H-SiC. In our n-type 4H-SiC samples, the FTA (-) and FTA(+) modes are noticed at 197.4 cm-1 and 205.7 cm-1 respectively (at room temperature).
I'm trying to fit the these modes according to reference Mitani et. al. JAP 2012. But quite unsuccessful in fitting these modes.
1. Before fitting both FTA (-) and FTA(+) modes in a single fitting function, I first tried by fitting FTA(+) mode separately. (I subtracted background to a minimum then performed fitting), but did not succeed.
2. I have also normalized to unity after background subtraction, but again not succeeded.
3. I initialized the parameters as per the reference plots given in Mitani et. al. 2012. It did not work out.
4. I would be grateful if someone could find the mistake that I'm doing in the fitting methodology. I am also attaching the raw excel data file for your reference. Someone please try fitting the given data.
5. Also, in literature, I'm unable to find the fitting parameters for a 4H-SiC sample with specific dopant/carrier concentration.
Compared to the literature that you posted, the ability to fit to your spectrum properly is limited by two issues. First, your spectral resolution is too low. You should decrease the step size by a factor of two or three at least. Secondly, your signal to noise is too low. The peak at 197.4 cm-1 is only about a factor of two above the noise level. It needs to be at least a factor of three or more. You should acquire the spectrum for at least a factor of twice as long. Faced with these two issues, I am not surprised that you are entirely unsuccessful to fit your spectrum.
Dear Professor,
Thank you for your reply.
I would like to know if it is really due to low S/N or the confusion regarding real or complex nature of the asymmetric parameter q.
The resolution and S/N in the spectrum are both below what I consider adequate for curve fitting. When the equation is programmed improperly, curve fitting will also fail. To test for this case though, you should be able to generate a theoretical curve using fixed parameters. Does the theoretical curve behave as expected as you vary the parameters?
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