Dissolution of n-type CdTe samples has been investigated under illumination in 2 M H2SO4 solution. A Te-0 layer is formed which leads to a decay of the photocurrent. This enrichment has been investigated by cyclic voltammetry and by X-ray photoelectron spectroscopy (XPS). Photons are absorbed within the Te-0 layer leading to a decrease of the photocurrent and to a characteristic modification of the spectral response that can be used as an in situ probe of the presence of such a layer.