Dear Ajay,

The bandgap of GaAs is 1.42 eV and the bandgap of silicon is 1.12 eV, therefore the resulting is a solid sate mixer which is GaAs heavily doped by Si such that the bandgap of this mixer will be weighted average of the GaAs and S. Clustering may be formed if solid solubility of GaAS to silicon is smaller than the Si implanted dose. In addition clustering requiring the annealing at high temperature after implanting.

Best wishes

Thank you Zekry sir, for your valuable reply .

I wanted to ask further , can we use Brus formula here as well to determine the size of this mixed structure (of silicon and GaAs).

Dear Ajay,

another, maybe more likely possibilty for your additional peak, is that you have sub-band-gap absorption due to the formation of Si related defects in your GaAs sample. Such defect level needs to be located within the band-gap to lead to this sub-band-gap absorption, i.e. at energies below the band-gap of GaAs.

Regarding a mixing/alloying of GaAs with Si to form a Ga-As-Si compound and, therefore having a smaller bandgap energy, I don't think that this can be the reason for your observation. The solubility of Si in GaAs is around 0.5at% and, hence, very low. check the Ga-As-Si phase diagram here:

https://link.springer.com/content/pdf/10.1007/BF00180465.pdf

But you need likely a much higher concentration of Si to achieve a bandgap according to your peak energy. Moreover, if you have a higher content of Si than 0.5 at%, then you will form precipiates such as SiAs2 or SiAs. Check the band gaps of the compounds if they fit to your peak.

Best regards