Controlled tunability of charge carriers is an intriguing technique to modify the electrical behavior of graphene. In this article, we report the photo-induced oxidation and its reversibility in single, bi and tri-layer graphene (S-B-TLG) devices by employing deep ultraviolet (DUV) light treatment in O-2 and N-2 atmosphere, respectively. Oxygen molecules in the presence of DUV light show dissociative adsorption onto the surface resulting a p-type carrier modulation in S-B-TLG devices. Treated graphene samples are characterized by Raman spectroscopy where blue-shift in G and 2D-peak positions is observed by DUV/O-2 treatment without inclusion of any defect. The reverse effect of carrier modulation is observed when DUV/O-2 treated samples are further studied in DUV/N-2 atmosphere. The results of electrical measurements show the shift of Dirac point (DP) towards higher gate voltages (V-g > 0) which confirms a p-type carrier modulation in graphene whereas restoration of DP towards pristine state indicates the de-modulation of carriers in S-B-TLG devices. In addition, UV irradiation induced charge transport mechanism on graphene surface is further interpreted by employing density functional theory calculation and Bader charge transfer analysis. Such experimental and computational insights enhance the probability to understand the defect-free and controlled carrier modulation process, intensifying its applicability in electronic and optoelectronic devices.