Can you check whether the shift is identical for both Ga and As? In that case it might indicate a local charging effect (which is often accompanied by an intensity decay).

One may investigate this further using Raman Scattering based on the changes in the Couple Plasmon LO-Phone mode that is impacted by the ion implementation energy. See for example:

Raman scattering studies of reactive ion-etched MBE, IEEE Journal of Quantum Elect, Vol: 25 Issue: 5

(https://ieeexplore.ieee.org/abstract/document/27992)

Reactive Ion Etching of MBE GaAs: A Raman Scattering Study, SPIE Proceedings Volume 0946, Spectroscopic Characterization Techniques for Semiconductor Technology III; (1988) https://doi.org/10.1117/12.947423

Thank you Weippert sir and Baharam sir .

The XPS spectra of Ga signal in implanted GaAs sample shifted by 0.51 eV w.r.t unimplanted sample and As signal in implanted sample shifted by 0.48 eV w.r.t unimplanted sample.

If it's 0.51 vs. 0.48 eV, that's within the resolution / statistical margin to claim it is a charging effect.

OK, Weippert Sir.

Thanks for immediate reply.

But at the same time , I am getting a very good signal of Si2p with intensity double than Ga and As signal. What does this mean ? Does it mean accumulation of silicon clusters ?

Well, that's hard to say in "remote diagnosis". You should consider two things: 1) Does the Si2p peak also have an enhanced binding energy (e.g. when you compare it to a strongly conducting Si wafer)? Then you made a rather insulating Si-rich GaAs/Si mixed compound 2) If it's not charging as well, you probably made a conducting layer (or something similar) that may have insulated the top domains atop the substrate, but conducts rather well on it's own. For a deeper analysis, you might consider using SPEM or an EDX-capable REM.

Thanks a lot Weippert sir , for your valuable input.