A new method is described whereby a pulsed ArF excimer laser can be used to clean GaAs substrates prior to thin film deposition by pulsed-laser deposition (PLD). The laser is used to create excited hydrogen, which effectively removes contaminants from the GaAs surface. The cleaning process involves hydrogen, photoelectrons, and photons, and is termed HEP to reflect the involvement of these three types of particles. ZnSe films have been epitaxically deposited by PLD on GaAs substrates cleaned by the HEP process. X-ray diffraction data show that GaAs substrates treated by excited hydrogen are very good for epitaxial growth of ZnSe. ZnSe films were synthesized at 320 degrees C under different Ar pressures to understand the effects of ambient gas pressure on film quality and morphology. Introduction of an ambient gas (Ar) improved film duality and morphology. The full width at half maximum of the x-ray theta rocking for the (004)-ZnSe peak for the best film grown, at 20 mTorr and 320 degrees C, was 0.04 degrees. X-ray and atomic force microscopy results are reported for several ZnSe films deposited on GaAs substrates cleaned by the HEP process. The results are compared with those of ZnSe films synthesized on GaAs substrates that were thermally treated, but were not treated by the HEP process.