S-doped amorphous hydrogenated silicon (a-Si,S:H) thin films were prepared by conventional PECVD method on corning glass substrates. The prepared thin films were subsequently annealed in vacuum (~ 2 × 10 – 6 Torr) in the temperature range from 100 °C to 500 °C. The annealing effects at room temperature were examined by means of optical transmission spectra of the films in the wavelength range 300-1100 nm. Dispersion in optical constants such as transmittance, bandgap and refractive index were observed. Tailoring in optical constants was observed with respect to doping concentrations as well as the annealing temperatures.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3097

Gupta, H.

Kumar, A.

Kumar, R.

Mehra, R.M.

Pal, Pankaj K.

Purohit, L.P.

Electronic Sumy State University Institutional Repository

JOURNAL OF NANO- AND ELECTRONIC PHYSICS ЖУРНАЛ НАНО- ТА ЕЛЕКТРОННОЇ ФІЗИКИ Vol. 5 No 1, 01020(2pp) (2013) Том 5 № 1, 01020(2cc) (2013)   2077-6772/2013/5(1)01020(2) 01020-1  2013 Sumy State University Short Communications  Optical Dispersion In Annealed Thin Films of S-doped a-Si:H Alloys  L.P. Purohit1,*, H. Gupta1, Pankaj K. Pal1, A. Kumar2, R. Kumar1, R.M. Mehra3  1 Department of Physics, Gurukula Kangri University, 249404 Haridwar, India 2 Department of Mathematics & Statistics, Gurukula Kangri University, 249404 Haridwar, India 3 School of Engineering & Technology, Sharda University, Greater Noida, India  (Received 30 December 2012; published online 28 March 2013)  S-doped amorphous hydrogenated silicon (a-Si,S:H) thin films were prepared by conventional PECVD method  on corning glass substrates. The prepared thin films were subsequently annealed in vacuum (~ 2 × 10 – 6 Torr) in the temperature range from 100 C to 500 C. The annealing effects at room tempera-ture were examined by means of optical transmission spectra of the films in the wavelength range 300-1100 nm. Dispersion in optical constants such as transmittance, bandgap and refractive index were ob-served. Tailoring in optical constants was observed with respect to doping concentrations as well as the annealing temperatures.  Keywords:  a-Si:H thin films, Doping concentrations, Annealing temperatures, Transmittance, Optical constants.   PACS numbers: 71.55 Jv, 71.55. Jv, 81.05. Gc, 81.40 Tv                                                                * lppurohit@gmail.com 1. INTRODUCTION  Hydrogenated amorphous silicon thin films and its alloys are the promising candidates for the realization of advanced opto-electronic devices. The doping in hy-drogenated amorphous silicon and its impact on the devices has been studied by several groups, for exam-ple, tetrahedrally coordinated elements: C and Ge [1], helogen elements: F and Cl [2]. So far carbon doped hydrogenated amorphous silicon (a-Si, C:H) has emerged as leading contender in large bandgap alloys in amorphous silicon based photovoltaic devices by serving as photon energy absorbing window layers in multi-junction cells [3]. However, the long-term stabil-ity and the efficiency of the material have not been solved due to the photoinduced degradation in a-Si:H thin films, which is associated with light-induced meta-stable Si dangling-bond defect [4, 5]. The selection of Se and S as the doping element, terminate the silicon dan-gling bonds in the same way as hydrogen [6]. Anneal-ing studies have emerged as an important tool that provide an insight to the various material property es-pecially hydrogenated amorphous silicon thin films [6].  2. EXPERIMENTAL  The a-Si,S:H thin films were prepared using PECVD method of H2Se and H2S vapor mixed with silane gas (SiH4) decomposition on 7059 corning glass at the substrate deposition temperature of 230 C. The thicknesses of the films were ranged from 0.24 to 5.44 m. The absence of sharp peaks in X-ray diffrac-tion pattern confirmed the amorphous nature of the films. The samples were annealed at the temperatures of 100 C, 200 C, 300 C, 400 C and 500 C, respec-tively, in vacuum furnace for an hour and then the transmittance response of these samples was subse-quently measured after each annealing process. The optical transmission measurements were performed on S-doped a-Si:H thin films using a Shimadzu spectro-photometer (3700 UV-VIS-NIR).  3. RESULTS AND DISCUSSION  Fig. 1 shows the typical transmission spectra for the gas ratio of H2S / SiH4  1 × 10 – 4 with respect to an-nealing temperatures from 100 to 500 C in vacuum for an hour. The maximum transmittance was observed at annealing temperature of 300 C for all samples.    Fig. 1 – Transmission spectra of a-Si, S:H thin films with respect to annealing temperature from 100 to 500 C  The variation of absorption coefficient with anneal-ing temperatures as well as doping concentrations for a-Si, S:H is shown in Fig. 2. The maxima and minima of the fringes in the transmission spectra were used to calculate the optical constants [7]. Optical bandgap, Eg, of a-Si, S:H thin films have been estimated from the transmission spectra which was taken in the wave-length range from 300-1100 nm after each heat treat-ment for all the samples. The optical bandgap of the films has been calculated using the Tauc’s relation:  L.P. PUROHIT, H.GUPTA, PANKAJ K. PAL, ET AL.  J. NANO- ELECTRON. PHYS. 5, 01020 (2013)   01020-2   (B / hν)(hν − Eg)γ, B is the proportionality constant, hν is the photon energy. The variation of band gap for all S-doped a-Si:H thin films versus annealing temper-ature, as well as doping concentrations, are shown in Fig. 3.    Fig. 2 – Absorption coefficient versus annealing temperature (C) of a-Si, S:H thin films with respect to doping ratios  S-4 (H2S / SiH4  10 – 4); S-5 H2S / SiH4  1.1 × 10 – 5); S-7 (H2S / SiH4 = 6.8 × 10 – 7)  The value of band gap was observed the highest at the annealing temperature of 300 C for all the doping concentrations.    Fig. 3 – Variation of bandgap versus annealing temperature at a typical wavelength of 750 nm for a-Si, S:H thin films  The variation of refractive indices of S-doped a-Si:H thin films at typical wavelength,  = 750 nm, versus annealing temperature is shown in Fig. 4. The values of n were observed the lowest at around the annealing temperature of 300 C for all S-doped samples. The decrease in refractive index with S- doping in a-Si:H might be due to the increase in internal strain. Optical absorption measurements show that the incorporation of S in a-Si:H films increases the bandgap of the mate-rial and the results in increased disorder and higher defect densities [7]. It might be expected that the an-nealing can remove many of the defects which are re-sponsible for the performances in the devices. Thus, it appears that there is an improvement in the quality of a-Si, S:H films up to annealing temperature of 300 C and deterioration beyond this temperature. Finally, it is suggested that the annealed S-doped a-Si:H films at 300 C in vacuum for an hour, could be a viable alter-native to a-Si, C:H as a wide band gap semiconductor materials.    Fig. 4 – Variation of Refractive indices versus nnealing tem-perature at a typical wavelength of 750 nm a- Si, S:H thin films  4. CONCLUSION  The films were subsequently annealed, and anneal-ing temperature was optimized to 300 C for better opti-cal constants of S-doped a-Si:H thin films. The disper-sion of optical properties, viz. transmittance, absorption coefficient and refractive indices were observed. It is also seen that the incorporation of S in a-Si:H films increases the bandgap of the material and results in increased disorder and higher defect densities.   REFERENCES  1. J. Chevallier, H. Wieder, A. Onton, C.R. Guarnieri, Solid State Commun. 24, 867 (1977). 2. S.A. Dallal, S. Kalem, J. Bourneix, J. Chevallier, M. Tolemonde, Philos. Mag. B 50, 493 (1984). 3. M. Hossain, J. Roberto, S. Perez, J.M.R. Rivera, K. Gangopadhyay, S. Gangopadhyay, J. Mater. Sci. 20, 412 (2009). 4. V. Nadazdy, R. Durny, M. Zeman, J. Non-Cryst. Solids 352, 1059 (2006). 5. J. Melskens, G.V. Elzakker, Y. Li, M. Zeman, Thin Solid Films 516, 6877 (2008). 6. S.K. Sharma, J. Baveja, R.M. Mehra, phys. stat. sol. (a) 194, 216 (2002). 7. G.A.M. Amin, Opt. Mater. 29, 562 (2007).   

Optical Dispersion In Annealed Thin Films of S-doped a-Si:H Alloys

SocioEconomic Challenges Journal (Sumy State University)

JOURNAL OF NANO- AND ELECTRONIC PHYSICS ЖУРНАЛ НАНО- ТА ЕЛЕКТРОННОЇ ФІЗИКИ 
Vol. 5 No 1, 01020(2pp) (2013) Том 5 № 1, 01020(2cc) (2013) 
 
 
2077-6772/2013/5(1)01020(2) 01020-1  2013 Sumy State University 
Short Communications 
 
Optical Dispersion In Annealed Thin Films of S-doped a-Si:H Alloys 
 
L.P. Purohit1,*, H. Gupta1, Pankaj K. Pal1, A. Kumar2, R. Kumar1, R.M. Mehra3 
 
1 Department of Physics, Gurukula Kangri University, 249404 Haridwar, India 
2 Department of Mathematics & Statistics, Gurukula Kangri University, 249404 Haridwar, India 
3 School of Engineering & Technology, Sharda University, Greater Noida, India 
 
(Received 30 December 2012; published online 28 March 2013) 
 
S-doped amorphous hydrogenated silicon (a-Si,S:H) thin films were prepared by conventional PECVD 
method  on corning glass substrates. The prepared thin films were subsequently annealed in vacuum 
(~ 2 × 10 – 6 Torr) in the temperature range from 100 C to 500 C. The annealing effects at room tempera-
ture were examined by means of optical transmission spectra of the films in the wavelength range 300-
1100 nm. Dispersion in optical constants such as transmittance, bandgap and refractive index were ob-
served. Tailoring in optical constants was observed with respect to doping concentrations as well as the 
annealing temperatures. 
 
Keywords:  a-Si:H thin films, Doping concentrations, Annealing temperatures, Transmittance, Optical 
constants. 
 
 PACS numbers: 71.55 Jv, 71.55. Jv, 81.05. Gc, 81.40 Tv 
 
 
                                                             
* lppurohit@gmail.com 
1. INTRODUCTION 
 
Hydrogenated amorphous silicon thin films and its 
alloys are the promising candidates for the realization 
of advanced opto-electronic devices. The doping in hy-
drogenated amorphous silicon and its impact on the 
devices has been studied by several groups, for exam-
ple, tetrahedrally coordinated elements: C and Ge [1], 
helogen elements: F and Cl [2]. So far carbon doped 
hydrogenated amorphous silicon (a-Si, C:H) has 
emerged as leading contender in large bandgap alloys 
in amorphous silicon based photovoltaic devices by 
serving as photon energy absorbing window layers in 
multi-junction cells [3]. However, the long-term stabil-
ity and the efficiency of the material have not been 
solved due to the photoinduced degradation in a-Si:H 
thin films, which is associated with light-induced meta-
stable Si dangling-bond defect [4, 5]. The selection of Se 
and S as the doping element, terminate the silicon dan-
gling bonds in the same way as hydrogen [6]. Anneal-
ing studies have emerged as an important tool that 
provide an insight to the various material property es-
pecially hydrogenated amorphous silicon thin films [6]. 
 
2. EXPERIMENTAL 
 
The a-Si,S:H thin films were prepared using 
PECVD method of H2Se and H2S vapor mixed with 
silane gas (SiH4) decomposition on 7059 corning glass 
at the substrate deposition temperature of 230 C. The 
thicknesses of the films were ranged from 0.24 to 
5.44 m. The absence of sharp peaks in X-ray diffrac-
tion pattern confirmed the amorphous nature of the 
films. The samples were annealed at the temperatures 
of 100 C, 200 C, 300 C, 400 C and 500 C, respec-
tively, in vacuum furnace for an hour and then the 
transmittance response of these samples was subse-
quently measured after each annealing process. The 
optical transmission measurements were performed on 
S-doped a-Si:H thin films using a Shimadzu spectro-
photometer (3700 UV-VIS-NIR). 
 
3. RESULTS AND DISCUSSION 
 
Fig. 1 shows the typical transmission spectra for the 
gas ratio of H2S / SiH4  1 × 10 – 4 with respect to an-
nealing temperatures from 100 to 500 C in vacuum for 
an hour. The maximum transmittance was observed at 
annealing temperature of 300 C for all samples. 
 
 
 
Fig. 1 – Transmission spectra of a-Si, S:H thin films with 
respect to annealing temperature from 100 to 500 C 
 
The variation of absorption coefficient with anneal-
ing temperatures as well as doping concentrations for 
a-Si, S:H is shown in Fig. 2. The maxima and minima 
of the fringes in the transmission spectra were used to 
calculate the optical constants [7]. Optical bandgap, Eg, 
of a-Si, S:H thin films have been estimated from the 
transmission spectra which was taken in the wave-
length range from 300-1100 nm after each heat treat-
ment for all the samples. The optical bandgap of the 
films has been calculated using the Tauc’s relation: 
 L.P. PUROHIT, H.GUPTA, PANKAJ K. PAL, ET AL.  J. NANO- ELECTRON. PHYS. 5, 01020 (2013) 
 
 
01020-2 
  (B / hν)(hν − Eg)γ, B is the proportionality constant, 
hν is the photon energy. The variation of band gap for 
all S-doped a-Si:H thin films versus annealing temper-
ature, as well as doping concentrations, are shown in 
Fig. 3. 
 
 
 
Fig. 2 – Absorption coefficient versus annealing temperature 
(C) of a-Si, S:H thin films with respect to doping ratios  
S-4 (H2S / SiH4  10 – 4); S-5 H2S / SiH4  1.1 × 10 – 5); S-7 
(H2S / SiH4 = 6.8 × 10 – 7) 
 
The value of band gap was observed the highest at 
the annealing temperature of 300 C for all the doping 
concentrations. 
 
 
 
Fig. 3 – Variation of bandgap versus annealing temperature 
at a typical wavelength of 750 nm for a-Si, S:H thin films 
 
The variation of refractive indices of S-doped a-Si:H 
thin films at typical wavelength,  = 750 nm, versus 
annealing temperature is shown in Fig. 4. The values of 
n were observed the lowest at around the annealing 
temperature of 300 C for all S-doped samples. The 
decrease in refractive index with S- doping in a-Si:H 
might be due to the increase in internal strain. Optical 
absorption measurements show that the incorporation 
of S in a-Si:H films increases the bandgap of the mate-
rial and the results in increased disorder and higher 
defect densities [7]. It might be expected that the an-
nealing can remove many of the defects which are re-
sponsible for the performances in the devices. Thus, it 
appears that there is an improvement in the quality of 
a-Si, S:H films up to annealing temperature of 300 C 
and deterioration beyond this temperature. Finally, it 
is suggested that the annealed S-doped a-Si:H films at 
300 C in vacuum for an hour, could be a viable alter-
native to a-Si, C:H as a wide band gap semiconductor 
materials. 
 
 
 
Fig. 4 – Variation of Refractive indices versus nnealing tem-
perature at a typical wavelength of 750 nm a- Si, S:H thin 
films 
 
4. CONCLUSION 
 
The films were subsequently annealed, and anneal-
ing temperature was optimized to 300 C for better opti-
cal constants of S-doped a-Si:H thin films. The disper-
sion of optical properties, viz. transmittance, absorption 
coefficient and refractive indices were observed. It is also 
seen that the incorporation of S in a-Si:H films increases 
the bandgap of the material and results in increased 
disorder and higher defect densities. 
 
 
REFERENCES 
 
1. J. Chevallier, H. Wieder, A. Onton, C.R. Guarnieri, Solid 
State Commun. 24, 867 (1977). 
2. S.A. Dallal, S. Kalem, J. Bourneix, J. Chevallier, 
M. Tolemonde, Philos. Mag. B 50, 493 (1984). 
3. M. Hossain, J. Roberto, S. Perez, J.M.R. Rivera, 
K. Gangopadhyay, S. Gangopadhyay, J. Mater. Sci. 20, 
412 (2009). 
4. V. Nadazdy, R. Durny, M. Zeman, J. Non-Cryst. Solids 
352, 1059 (2006). 
5. J. Melskens, G.V. Elzakker, Y. Li, M. Zeman, Thin Solid 
Films 516, 6877 (2008). 
6. S.K. Sharma, J. Baveja, R.M. Mehra, phys. stat. sol. (a) 
194, 216 (2002). 
7. G.A.M. Amin, Opt. Mater. 29, 562 (2007).  
 


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Optical Dispersion In Annealed Thin Films of S-doped a-Si:H Alloys

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