Deepika Chaudhary; Mansi Sharma; S. Sudhakar; Sushil Kumar
Abstract
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 ...
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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.
Mansi Sharma; Deepika Chaudhary; s. Sudhakar; Preetam Singh; K.M.K. Srivatsa; Sushil Kumar
Abstract
The structural investigation of the a-Si:H material, deposited at different pressures by PECVD process, has been carried out to analyze the signatures of diffused intermediate sort of crystalline phases within the amorphous silicon matrix. Raman characterization along with the Photoluminescence ...
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The structural investigation of the a-Si:H material, deposited at different pressures by PECVD process, has been carried out to analyze the signatures of diffused intermediate sort of crystalline phases within the amorphous silicon matrix. Raman characterization along with the Photoluminescence (PL) and spectroscopic ellipsometry studies were carried out to understand the microstructuree of these films. From Raman analysis the material was found to have indistinguishable crystalline phase, which can also be named as “intermediate amorphous phase” (a phase defined between amorphous and ultra nano-crystalline silicon) with crystalline volume fractions as 56 % and 62 % for 0.23 Torr and 0.53 Torr respectively. Here the contribution of ultra nano-crystallites results in higher crystalline fraction, which is not visibly revealed from the Raman spectra due to its sub nano-crystallite characteristics. For the film deposited at 0.53 Torr stable photo-conductance in conjunction with high photo-response under 10 hour light soaking has been observed, which is as expected due to high crystalline volume fraction. The presence of these phases might be the possible reason for the distinct device characteristics though having nearly the similar electrical properties (photo-response ~104). These studies will help to make improvement in the individual layer properties, other than the interface effect, in the fabrication of efficient p-i-n solar cells.