In the lust two decades the researchers pay attention to the optical properties of semiconductor layers which are used in different electronic devices. The special role of these investigations has the study of electronic states in the semiconductor materials using optical measurements. The important data obtained when some gropes of researchers [1,2] start to investigate the optical spectra modulated by parameters such as: the wavelength, temperature, electrical field… Some particularities of optical spectra, which not founded in the absorption and reflection spectra, it was identified using the modulated spectroscopy.