The PL peak for bulk 3C-SiC is 2.3eV approximately. But the peak for Polycrystalline SiC(bulk) sample is observed to be near 2.8eV. So a shift is observed. I am interested to know the reason behind this massive shift.
Laser wavelength: He-Cd 325nm at Room temperature, 10K
Detector: CCD
Hi, have you irradiate the sample at one single power, or you observe these behavior, at lower power densities. may be your sample has non linear effects. like Raman, Brillouin, etc. Like cristal KTP on Green laser use 805nm laser to emit 532nm. 2nd question the sample has temperature controlled stage?
Best Regards.
Hee Jun Lee,
The reason that 3C-SiC has a different PL peak from poly crystalline SiC is that the two have different stacking structures. The differences in stacking structure change the brillouin zones, and is reflected in the direct and indirect band gaps. As I understand it, PL measurement of an indirect band-gap will have a lower intensity because the detection efficiency is much lower since the excitation lifetime is so much longer. So look for changes in intensity as well as change in peak location for hints as to what might be going on. I found a paper that talks about the changes in stacking structure, "Theory of electronic and optical properties of 3C-SiC".
I hope this is helpful.
Sincerely,
George Peterson
A possible explanation comes from a size-dependence of the band structure of your crystals. The smaller the average crystal size in your polycrystal, the larger the expected band gap involved in the PL transitions. It would be interesting to know the average SiC crystal size in your polycrystalline sample... micrometer or nanometer range?
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