342 Journal of Non-Crystalline Solids 119 (1990) 342-346 North-Holland EFFECT OF RF POWER ON THE STRUCTURE AND RELATED GAP STATES IN HYDROGENATED AMORPHOUS SILICON Suvarna BABRAS, S.V. RAJARSHI, R.O. DUSANE and V.G. BHIDE School of Energy Studies, Department of Physics, University of Poona, Pune-411 007, India S.T. KSHIRSAGAR National Chemical Laboratory, Pashan Road, Pune-41l 008, India Received 12 June 1989 Revised manuscript received 27 December 1989 The intricate relationship between the structure and processing parameters in a-Si : H is not well understood. The effect of variation in rf power on the structural, optical and electronic properties of glow discharge deposited hydrogenated amorphous silicon (a-Si:H) has been studied using deep level transient spectroscopy (DLTS), photoluminescence (PL), spectroscopic ellipsometry and Raman spectroscopy. The DLTS results show a predominant increase in the gap state density around 0.5 eV below the conduction band, which is also supported by the decrease in the intensity of the PL peak around 0.8 eV with rf power. Ellipsometry results show an overall decrease in the value of e2, while the energy corresponding to the c2 peak position remains constant. Significant modifications of spectral features are observed in the Raman spectra of film deposited at higher rf powers. These results suggest that the a-Si : H films grown at higher rf power are less dense and have larger vacancy or void concentration. It is proposed that such structural defects lead to the observed energy levels in the gap and associated physical properties of the a-Si : H films. 1. Introduction Since the first reports on hydrogenated amor- phous silicon appeared, our understanding of the various aspects of a-Si:H has been continuously growing [1-6]. It is almost established that varia- tions in the electronic properties of a-Si:H thin films can occur due to variations in the material preparation technique or post preparation treat- ments. The point which is more important and more basic however is to justify these variations in electronic properties on the basis of structural aspects [7]. Questions such as the identification of defects such as point defect or vacancies and correlating them with the specific electronic prop- erties have still not been addressed in detail. It is with this view in mind that we have studied the effect of the variation of a particular process parameter on the a-Si:H film properties by em- ploying both the electrical and structural char- acterization techniques. From the correlation of these results we attempt to identify a particular type of defect and associate with it a specific energy level within the gap. Of the various process parameters involved in the glow discharge deposition of a-Si:H which affect the properties of the a-Si : H films, we have varied the rf power applied to the plasma, with other parameters being held constant. For a capacitively coupled rf glow discharge deposition process where Sill 4 is used as a source gas, an increase in rf power leads to an increase in the deposition rate [8], an aspect of considerable tech- nological importance [9]. The variation of physical properties of the a-Si : H films as a function of rf power has been previously studied [10,11]. These results show that the spin density characteristic of the dangling bond increases with increasing rf power. Lucovsky et al. [12] showed from IR spec- troscopy that the hydrogen bonding configuration did not remain as monohydride at high rf powers, but also showed the presence of dihydride species 0022-3093/90/$03.50 © 1990 - Elsevier Science Publishers B.V. (North-Holland)