1. UMKB Defect States Distribution in Microcrystalline Silicon by the Constant Photocurrent Method in the ac-mode T. Tibermacine 1, M. Ledra 1, N. Ouhbab 1 and A. Merazga 2 1 Université Mohammed Khider, Laboratoire des Matériaux Semi-conducteurs et Métalliques, 2 Physics Department, Faculty of Sciences, Taif University, Saudi Arabia. FIRST INTERNATIONAL CONFERENCE ON NEW MATERIALS AND ACTIVE DEVICES - NMCA’2011 - UNIVERSITY OF OUM EL-BOUAGHI Measured ac absorption coefficient at 60Hz. Extracted DOS distribution using the measured ac absorption spectrum at 60 Hz.RESULTS Absolute ac-CPM  (h ) spectrum measured at 5 Hz frequency.  (h ) determined from the transmittance and  (h ) for crystalline silicon are both shown for comparison. Microcrystalline silicon  c-Si:H - 00c 354 sample - CONCLUSION In the present work, the electronic properties of microcrystalline silicon films have been studied by using constant photocurrent technique in ac regime. By analyzing the measured absorption coefficients, we have found that the density of valence band-tail states falls exponentially towards the gap with a typical band-tail width of 63 meV. A schematic picture of the density of states in energetic sense has been obtained. Our study indicates then that the constant photocurrent method is able to extract the density of localized states in highly-crystalline  c-Si:H films. ABSTRACT Recently, hydrogenated microcrystalline silicon (µc-Si:H) has attracted much interest in optoelectronic applications. It offers a higher stability against light degradation and a wider absorption bandwidth extending into the near infrared. The electronic properties and performance of µc-Si:H films are correlated with the deposition parameters and the structural properties. Therefore, the detailed knowledge of the gap density of states (DOS) in µc-Si:H is of great importance to understand the transport mechanism. The Constant Photocurrent Method in the ac-mode (ac-CPM) as a powerful technique is used to determine the defect Density Of States (DOS) in µc-Si:H. The absorption coefficient spectrum, ac-  (h ), is measured under ac-CPM conditions at 60Hz, then it is converted by the CPM spectroscopy into a DOS distribution covering a portion in the lower energy range of occupied states. We have found that the density of valence band-tail states falls exponentially towards the gap with a typical band-tail width of 63 meV.. Laboratory of Metallic and Semiconducting Materials - LMSM - University of Biskra PRINCIPLE  Incident photon flux  is adjusted to maintain photocurrent I ph constant over the range of photon energy:  (h )=constant/  (h )  Highly sensitive technique (  (h ) down to 10 -2 cm -1 )  Can be configured into DC or AC illumination WHAT ARE WE GOING TO OBTAIN?  Absorption coefficient spectrum curve both in DC and AC modes  Density of states distribution D(E) EXPERIMENTAL SET-UP Dundee Laboratory Scotland - UK - PERSPECTIVE WHAT WE WOULD LIKE TO DO IN THE NEAR FUTURE! Laboratory of Metallic and Semiconducting Materials - LMSM - University of Biskra