EFFET DE LA FREQUENCE DANS LA DETERMINATION DES PROPRIETES OPTOELECTRONIQUES DU SILICIUM AMORPHE HYDROGENE PAR LA TECHNIQUE DE PHOTOCOURANT CONSTANT EN REGIME PERIODIQUE (AC-CPM)

Abstract

We present in this article the relationship between the optical excitation frequency and the optical and electronic properties of amorphous semiconductors in particular hydrogenated amorphous silicon a-Si:H. The optical absorption coefficient α (hν) and the density of states (DOS) of undoped Intersolar ISB4 sample, which is prepared by plasma enhanced chemical vapour deposition (PECVD), are measured by the constant photocurrent method in periodic mode (AC-CPM). We have also developed a computer program to model AC-CPM taking into account all the possible thermal and optical transitions between the localized states in the gap and the extended states in the conduction and valence band. The defect pool model for the electronic density of states is incorporated in our modelling. To validate our simulation results, we have measured α (hν) for several frequencies. Then the measured absorption spectrums are converted into electronic density of states within the mobility gap of the sample. Our measurements and our modelling results show that the optical absorption coefficients are underestimated as frequency increase. We affect this underestimate to the mode used to determine the optical absorption coefficient. Furthermore, Our results showed us that the reconstruction of the density of the occupied states within the gap mobility of the material is better for high frequencies than for low frequencies.