In this article, we report the phase transition region of hydrogenated amorphous (a-Si:H) to nano-crystalline (nc-Si:H) silicon thin films deposited using 27.12 MHz assisted Plasma Enhanced Chemical vapor Deposition (PECVD) process with the approach of plasma diagnosis. This work presents for the first time a study of plasma characteristics using Impedance Analyser (V/I probe) at various applied power (4 W - 40 W), though till now this apparatus has been utilized only to analyse the applied delivered power during processing. On the basis of plasma diagnose, optimum bulk field (5 V/cm); sheath field (1376 V/cm) and minimum sheath width (7.4 x 10-4 cm) observed at 20 W power which provides a visible mark of transition from a-Si:H to nc-Si:H. On account of plasma properties, the deposition was carried out by considering the plasma-surface interaction during growth. The microstructure of the deposited films was characterized using Raman spectra, UV-Vis spectra and conductivity measurements and they were found to be well correlating with the evaluated plasma characteristics. In particular, it was found that at applied power near to the onset of transition regime i.e. at 10 W, preeminent properties of a-Si:H film was observed, predominantly in terms of highest photosensitivity (7.2x103), low photo-degradation and high deposition rate (~1.39 Å/s). On the other hand, volume fraction of crystallites (24 %), wider band gap (2.0 eV) and no photo-degradation observed for the film deposited at 20 W applied power which signifies the existence of crystallites in an amorphous matrix. Copyright © 2017 VBRI Press.