Specific space charge zones on the substrate side of (100) ZnSe/GaAs interfaces, corresponding to strong band bending, were investigated within the vibrational and optical energy ranges by using combined Raman scattering and photoreflectance. While the conventional Raman set-up provides surprisingly an unperturbed Raman response, micro-Raman measurements performed at the near-interface on a cleaved (110) face show the activation of a theoretically forbidden LOGaAs mode, attributed to the expected electric-field-induced Raman scattering (EFIRS). Besides, the observation of Franz-Keldysch oscillations above the fundamental gap of GaAs by photoreflectance provides experimental evidence of another nature for strong interfacial static electric fields and provides an estimation of their average value. These are in good agreement with the activation of EFIRS effects.