In situreflectance difference spectroscopy (RDS) has been performed during growth and nitrogen-doping of ZnTe thin films fabricated by molecular beam epitaxy. The doping level of the ZnTe samples can be determined by evaluating the RD spectra in the vicinity of theE1andE1+&Dgr;1transitions. RDS features in this spectral range were used to optimize online the doping performance of the N-plasma cell. Furthermore, doping-induced surface processes have been investigated, like surface saturation with activated N species and surface Fermi level pinning occurring at ambient pressure. ©1998 American Institute of Physics.