International Journal of Soft Computing and Engineering (IJSCE) ISSN: 2231-2307, Volume-2, Issue-6, January 2013 516 Retrieval Number: F1176112612/2013©BEIESP Published By: Blue Eyes Intelligence Engineering & Sciences Publication Effect of Post-Deposition Annealing on Hydrogenated Amorphous Silicon Thin Films Grown At High Power by Pecvd Aravind Kumar, Pawan Kumar, Parmender Kumar, Kapil Malik, P. N. Dixit Abstract- The crystallization of hydrogenated amorphous silicon layers (a-Si:H) [1,2] deposited by plasma enhanced chemical vapor deposition (PECVD) is of great interest. Generally, laser or metals are used to induce crystallization in a- Si:H films. We have found that films deposited at high rf power (> 0.2 W/cm2) by PECVD technique shows some crystallites embedded in a-Si:H matrix and their after its vacuum thermal annealing at 250 and 300 o C helps to further enhancement of crystallite size. These films were characterized using , UV-VIS spectrometry, Raman Spectra, of these films were measured as a function of temperature in the range of 300 o C to 250 o C. Keyword: Amorphous silicon, Thin Films, Growth PECVD. I. INTRODUCTOIN Plasma Enhanced Chemical Vapor Deposition (PECVD) of Silane has evolved as an elegant technique for the deposition of the hydrogenated amorphous silicon (a-Si:H) and related alloys. a-Si:H films have attracted considerable attention because of their outstanding optical properties [3- 4]. This material is in use in photovoltaic and large area electronic devices at commercial level. However, low deposition rate and stability are the limitation of this material. Enhancement of the deposition rate should be achieved with maintaining the device quality of the material. Attainment of high rate of deposition could be possible by various approaches, such as (a) containment of the plasma by the use of earth shields so the reactive species do not diffuse out of the Inter-Electrode space & enhancement of the density of ionized species by an increase of power input to the plasma, in a careful way, so that gas phase polymerization reaction are avoided (b) Increase of the plasma excitation frequency (c) use of higher silane radicals. Normally to deposit the device quality a-Si:H films lower power density (less than 20 mW/cm2) is used. In the present investigation we have chosen high power density deposited a-Si:H films for our study. Manuscript received On December. 2012. Aravind Kumar, Department of Physics Kalindi College East Patel Nager New Delhi-110008., India. Pawan Kumar, Department of Physics Gurukula Kangri Vishwavidyalaya, Haridwar-249404, India. Parmender Kumar, Department of Physics Gurukula Kangri Vishwavidyalaya, Haridwar-249404, India. Kapil Malik, Department of Physics Gurukula Kangri Vishwavidyalaya, Haridwar-249404, India. P.N. Dixit, Plasma Processed Materials Group National Physical LaboratoryDr. K.S. Krishnan Road, New Delhi-110 012 II. EXPERIMENTAL PROCEDURE It is well known that sustaining plasma by RF excitation is rather easy. It is because electrons in the plasma respond instantaneously to the RF field and absorbs energy from the field via inelastic collision with gas molecules in the bulk, thereby, gaining sufficient energy to ionize the gas. In this section a detailed study of RF plasma (13.56 MHz) produced a-Si:H films by using silane ( SiH 4 ) as the feed gas has been made. For this study a 13.56 MHz source RF plasma Model RF 5S) was used to excite the plasma. Substrates were placed on the anode of the research reactor. The partial pressure of SiH 4 is adjusted with the help of Mass Flow Controller (MFC). In order to increase the deposition rate (r d ), systematic variation of applied RF Power to the cathode was varied systematically at different pressures. The deposition condition were as follows: (1) Pressure(0.1-1.0 Torr, (2) substrate temperature, 3000 o C, (3) SiH 4 flow rate, 40.0 sccm, (4) power density varied from 16 to 180 mW cm -2 . The thicknesses of the films, was measured by a talystep (Rank-Taylor Hobson), were in the range 1.5 μm. Optical, electrical and structural measurements were carried out on samples as per procedure discussed. We have designated the sample deposited at 1W power as HR-031, and 21W power as HR-022. III. DEPOSITION RATE The deposition rate of the films was calculated from the measured thickness divided by deposition time. Thicknesses of the films were estimated by talystep (Rank-Taylor Hobson) measurement equipment. Variation of deposition rate of a-Si:H films as a function of Power as shown in the Fig (1.1) The variation of deposition rate r d (A 0 /s) with variation of applied power. It is clear that r d increases monotonically with increase of applied power. Normally to deposit the device quality a-Si:H films low power density (less than 20 mW/cm 2 ) is preferred. The deposition rate increases from 2.9 to 13 A 0 /s with the increases of applied power from 1W to 21W. Increases of the applied power enhance the dissociation and ionization of silane radical and thus resulting increase of the flux of deposition precursors to the substrate surface. IV. OPTICAL PROPERTIES Investigations of the optical properties of semiconductors are among the most important sources of information on the band structure, the frequencies of the optical modes of the phonon spectrum and other properties of the semiconductors.