I am trying to estimate the band gap of semiconductor material using valence band spectra obtained from ultraviolet photoelectron spectroscopy. Is there any book/reference which describe the analysis process?
Just from a UPS you can't determine the band gap. Either you have to perform electropositive doping, see section 3.3.3 of Article Properties of non-IPR fullerene films versus size of the bui...
and references therein. However, that works only for semiconductors for which you can be sure that electrons really just get transferred to the LUMO without further ado. Otherwise you can combine UPS+IPE (Inverse PhotoEmission), use STS (scanning tunneling spectroscopy) or determine the optical bandgap from UV-Vis measurements.
UPS is used to determine the valence band edge only. To calculate the band gap of semiconducting materials, you can use absorbance or transmittance spectra from UV-Vis measurements.