Zinc Selenide (ZnSe) thin films of 500 nm thickness were deposited by electron beam evaporation technique
and irradiated with 8 MeV electron beam for the doses ranging from 0 Gy to 1 kGy. Optical properties
were studied for both irradiated and pristine samples using Ultraviolet-Visible spectrophotometer.
The increase in electron dose tends to decrease in transmittance and increase in refractive index of thin
film. Irradiated thin film exhibits minimum of 67 % transmittance for 800 Gy with very high absorption of
optical energy at 550 nm wavelength. The samples irradiated  800 Gy tends to redeem the pristine properties.
Optical band gap for irradiated thin film were direct and in the range of 2.66 – 2.69 eV

Ganesh, S.

Mahesh, H.M.

Mrudula, K.

Naveen, C.S.

Raghu, P.

Shailaja, J.

SocioEconomic Challenges Journal (Sumy State University)

JOURNAL OF NANO- AND ELECTRONIC PHYSICS ЖУРНАЛ НАНО- ТА ЕЛЕКТРОННОЇ ФІЗИКИ 
Vol. 6 No 4, 04007(4pp) (2014) Том 6 № 4, 04007(4cc) (2014) 
 
 
2077-6772/2014/6(4)04007(4) 04007-1  2014 Sumy State University 
Influence of Electron Irradiation on Optical Properties of ZnSe Thin Films 
 
P. Raghu1, C.S. Naveen1, K. Mrudula1, Sanjeev Ganesh2, J. Shailaja1, H.M. Mahesh1,* 
 
1 Department of Electronic Science, Bangalore University, Jnanabharathi, Bangalore – 560056 Karnataka, India 
2 Microtron Centre, Mangalore University, Mangalagangothri, Mangalore – 574199 Karnataka, India 
 
(Received 05 July 2014; revised manuscript received 17 July 2014; published online 29 November 2014) 
 
Zinc Selenide (ZnSe) thin films of 500 nm thickness were deposited by electron beam evaporation tech-
nique and irradiated with 8 MeV electron beam for the doses ranging from 0 Gy to 1 kGy. Optical proper-
ties were studied for both irradiated and pristine samples using Ultraviolet-Visible spectrophotometer. 
The increase in electron dose tends to decrease in transmittance and increase in refractive index of thin 
film. Irradiated thin film exhibits minimum of 67 % transmittance for 800 Gy with very high absorption of 
optical energy at 550 nm wavelength. The samples irradiated  800 Gy tends to redeem the pristine prop-
erties. Optical band gap for irradiated thin film were direct and in the range of 2.66 – 2.69 eV. 
 
Keywords: E – beam Evaporation, Optical properties, Electron radiation, Thin films, ZnSe. 
 
 PACS numbers: 61.80.Fe, 81.15.Jj, 78.30.Fs, 78.66. – w 
 
 
                                                          
* hm_mahesh@rediffmail.com 
1. INTRODUCTION 
 
Zinc Selenide (ZnSe) is one of the most prominent 
candidate for photovoltaic device as an n-type buffer 
material in CdTe based solar cell due to its wide band 
gap of 2.67 eV [1]. ZnSe thin films have attracted sev-
eral researchers for improving the efficiency of hetero-
junction solar cells. It has an immense potential to use 
as an efficient window/buffer material when CdS 
thickness is relatively small ( 100 nm) in CdS / CdTe 
solar cell. Also, it has wide transmission range from 
450 nm to 21.5 µm with high refractive index of 2.60 at 
550 nm and high electrical resistivity (1012 Ωcm) [2, 3]. 
ZnSe thin films are also used as buffer layers for CIGS 
solar cells which reached the efficiency up to 9.6 % (un-
der AM 1.5 illumination) [4]. It has been reported that, 
by integrating different buffer layers in combination of 
zinc and tin oxide improved CdTe / CdS cell efficiency 
[5-7]. Several researchers has investigated, ZnSe as a 
buffer layer by exploiting the optical properties for re-
placement or along with reduced thickness of CdS  
[8-11]. Ionizing radiation produces the change in physi-
cal properties such as optical, structural, electrical, etc., 
Due to these factors, electron irradiation is included in 
thin film formulations. The functions of electron irradia-
tion include softening films, reducing brittleness, in-
creasing flexibility and ductility. Therefore, present in-
vestigation aims at examining the effects of electron 
irradiation on ZnSe thin films and possibility of using it 
as a buffer layer for solar cells. 
 
2. EXPERIMENTAL 
 
2.1 Preparation of Thin Films 
 
The PVD apparatus used for deposition is based on 
a commercial system developed by Hind High Vac. Co., 
Bangalore. ZnSe powder source (99.99 % purity, Sigma 
Aldrich, U.S.A) is brought into the chamber in a mo-
lybdenum crucible in vacuum condition at a pressure of 
2  10 – 5 mbar. Soda lime glass slides of dimensions 
25 mm  15 mm  1.35 mm were used as substrate 
were degreased with soap water followed by ultra-
sonication in double distilled water and ethanol. The 
substrate holder is aided with continuous rotation for 
formation of uniform films on substrate surface. Thin 
films of 500 nm thickness were deposited at constant 
deposition rate of 5-8 A°/sec. Thickness and deposition 
rate were measured using quartz crystal thickness 
monitor (DTM-101).  
 
2.2 Post Deposition Process 
 
The aim of this post-deposition process (such as 
thermal annealing and electron irradiation) is common-
ly used to improve the structural, morphological and 
chemical quality of deposited thin films. Therefore, de-
posited samples were annealed in air ambient at 100° C 
for 3 hrs. After finishing thermal annealing treatment, 
samples were subjected to 8 MeV electron beam irradi-
ation for doses ranging from 200-1 kGy in steps of 
200 Gy, using variable energy Microtron accelerator 
facility available at Microtron Centre, Mangalore Uni-
versity, India. The dose delivered was measured with an 
alanine dosimeter close to the sample, and features of 
Microtron are detailed elsewhere [12, 13]. 
 
2.3 Characterization 
 
Electron irradiated ZnSe thin films of different dos-
es were characterized for optical parameters and were 
compared with unirradiated. Optical investigations of 
thin films were performed using VIS-NIR spectropho-
tometer (Ocean Optics, USA. Model No. USB4000-XR). 
Optical absorption is a useful method for investing the 
induced transition and providing information about band 
structure and optical energy gap of the materials. The 
principle of this technique is that, photons with energies 
higher than band-gap energy will be absorbed [14]. Ab-
sorption coefficient ‘’ can be calculated using relation 
[15], 
 
2.303 1
log
d T

   
    
   
 (1) 
 P. RAGHU, C.S. NAVEEN, ET AL. J. NANO- ELECTRON. PHYS. 6, 04007 (2014) 
 
 
04007-2 
It is also written as a function of incident photon en-
ergy ‘h ’ [16], 
 
     0
P
gh A h E  (2) 
 
Where, Eg is optical band gap, ‘P’ has discrete values 
like 1/2, 3/2, 2 or more depending on whether the transi-
tion is direct or indirect and allowed or forbidden. In the 
direct and allowed cases P  1/2. Value of ‘P’ determines 
the nature of optical transition. The results have been 
analyzed according to the relation (2). A0 is a constant 
and given by, 
 
     
2 2 * 3/2
0 (2 )e rA e neh m m   (3) 
 
Where, m*e and mr are effective and reduced masses 
of charges carriers respectively. The variations of extinc-
tion coefficient (k) with photon can be observed that 
wavelengths regardless of their thickness, values for 
extinction coefficients is calculated using the equation, 
 
 
 

 0
2.303 log 1
4
T
k
d
  (4) 
 
3. RESULTS AND DISCUSSION 
 
Figure 1 illustrates transmittance spectra of 
500 nm ZnSe thin films – deposited and irradiated with 
different dose (200 Gy-1 kGy). At 550 nm, unirradiated 
ZnSe thin film exhibits high transmittance of 75 %, as 
the dose increased from 200 Gy to 1 kGy the transmit-
tance has been decreased upto 800 Gy and at 1 kGy 
dose transmittance has been increased slightly (Fig. 2). 
This attributes to improvement in absorption after ir-
radiation from 200 Gy to 800 Gy. The width of trans-
mission edge shifted towards lower energy with in-
creasing irradiation doses. Hence the influence of irra-
diation directly affects the absorption of thin film. 
Figure 3 represents optical absorption spectra of 
ZnSe films deposited on glass substrate. Absorption coef-
ficient was calculated from transmittance spectra for the 
film irradiated with different electron dose. The varia-
tion in absorption coefficient with wavelength reveals a 
 
400 500 600 700 800 900 1000 1100
20
30
40
50
60
70
80
T
ra
n
sm
it
ta
n
ce
 (
%
)
Wavelength (nm)
  unirradiated
  200 Gy
  400 Gy
  600 Gy
  800 Gy
  1000 Gy
 
 
Fig. 1 – Transmittance spectra of irradiated ZnSe thin films of 
500 nm thickness) 
0 200Gy 400Gy 600Gy 800Gy 1kGy
55
60
65
70
75
80
T
r
a
n
sm
it
ta
n
c
e
 (
%
)
Dose 
 500nm
 
 
Fig. 2 – Transmission versus Dose of irradiated ZnSe Thin films 
 
400 500 600 700 800 900 1000
0
1000000
2000000
3000000
4000000
A
b
s
o
rp
ti
o
n
 (

)
Wavelength
  unirradiated
  200 Gy
  400 Gy
  600 Gy
  800 Gy
  1000 Gy
 
 
Fig. 3 – Absorption coefficient versus wavelength of ZnSe 
thin films 
 
very low absorption of energy in visible region and high 
absorption in shorter wavelengths. The spectra also con-
firm that, as the irradiated dose increases there is an 
increase in absorption at 550 nm. This attributes to the 
decreased transparency of thin film. 
The direct band to band transition energies and tail 
width of pristine and irradiated film is represented in 
table 1. Pristine film has direct band gap of 2.68 eV 
which is equal to standard bulk band gap [17]. Optical 
band-gap value for de posited film for different dose var-
ies in the range of 2.66-2.69 eV. This variation in optical 
band gap trend is because of increase in irradiation en-
ergy. The free atoms are responsible for creating several 
overlapping levels resulting in more energy inturn create 
multiple overlapping bands within thin films [18]. This 
phenomenon can be explained by Urbach tail which sig-
nifies characteristic phenomena of absorption curve with 
respect to photon energy (Fig. 4) 
If structure of thin film has disorderness, we can es-
timate the level using Urbach energy [19] which results 
in lean-in transmittance spectra towards minimum pho-
ton energy. Tail width of thin films can be calculated by 
slope of straight line portion of plot (Fig. 4). The mini-
mum tail width of 0.56 eV revealed by 600 Gy. Whereas, 
1 KGy irradiated film exhibits higher tail width of 
1.02 eV which is almost equal to pristine sample. 
 INFLUENCE OF ELECTRON IRRADIATION ON OPTICAL PROPERTIES… J. NANO- ELECTRON. PHYS. 6, 04007 (2014) 
 
 
04007-3 
Table 1 – Variation of Band gap and tail width of irradiated ZnSe thin films 
 
Sl. №. Electron Dose (Gy): Pristine 200 400 600 800 1000 
1 Band Gap (eV): 2.68 2.69 2.68 2.69 2.66 2.67 
2 Tail Width (eV): 1.03 0.87 0.85 0.56 0.90 1.02 
 
2.50 2.55 2.60 2.65 2.70 2.75
13.75
13.80
13.85
13.90
13.95
14.00
14.05
14.10
14.15
14.20
14.25
ln
 (

)
h (eV)
 200 Gy
 400 Gy
 600 Gy
 800 Gy
 1 Gy
 Pristine
 
 
Fig. 4 – Variation of ln() versus photon energy of ZnSe thin 
films 
 
This behavior highlights that higher dose can retain the 
properties of un-irradiated thin film. This is also evident 
from figure 3 that absorption has increased for lower 
dose and there after decreases, which inturn replicates 
better transmittance property. 
 
400 500 600 700 800 900 1000
0.00
0.02
0.04
0.06
0.08
0.10
0.12
E
x
ti
n
c
ti
o
n
 C
o
-e
ff
ic
ie
n
t 
(k
)
Wavelength (nm)
  unirradiated
  200 Gy
  400 Gy
  600 Gy
  800 Gy
  1000 Gy
 
 
Fig. 5 – Variation of Extinction Coefficient vs wavelength of 
irradiated ZnSe Thin films 
 
The extinction coefficient (k) is directly related to ab-
sorption of light. In the case of polycrystalline films, ex-
tra absorption of light occurs at grain boundaries [20]. 
This leads to non-zero value of ‘k’ for photon energies 
smaller than the fundamental absorption edge [21]. This 
is further confirmed by figure 5. 
 
0 200 400 600 800 1000
1.6
1.8
2.0
2.2
2.4
R
e
fr
a
c
ti
v
e
 I
n
d
e
x
 (
n
)
Dose (Gy)
  500 nm
 
 
Fig. 6 – Variation of refractive index versus dose rate of 
500 nm ZnSe thin films 
 
The refractive index ‘n’ of the deposited films is eval-
uated from envelope technique is shown in figure 6. The 
maximum refractive index is found to be 2.21 for 600 Gy 
irradiated film. All values were found to be wavy nature, 
while higher energy dose will retain the value of pristine 
sample. 
 
4. SUMMARY 
 
Electron irradiation on 500 nm ZnSe thin films was 
found to induce changes in optical properties depending 
on irradiation dose: irradiation leads to decrease in 
transparency of thin film while higher dose of 1 KGy 
leads to decrease in absorption with increase in trans-
parency equal to pristine sample. The film posses direct 
transition with optical band gap in the range of 2.66-
2.69 eV and also exhibit maximum refractive index for 
600 Gy and minimum for 1 KGy dose. The decrease in 
transmittance and refractive index after 800 Gy (i.e., for 
1 KGy and above) has to be investigated. 
 
AKNOWLEDGEMENTS 
 
Authors would like to express their sincere thanks 
to BRNS-DAE, Govt. of India for the financial support 
vide major research project (Sanction No: 
2011/34/19/BRNS/0080) under which this work has 
been carried out. 
 
 
 
 
 
 
 
 
 
 P. RAGHU, C.S. NAVEEN, ET AL. J. NANO- ELECTRON. PHYS. 6, 04007 (2014) 
 
 
04007-4 
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Influence of electron irradiation on optical properties of ZnSe thin films

Electronic Sumy State University Institutional Repository

JOURNAL OF NANO- AND ELECTRONIC PHYSICS ЖУРНАЛ НАНО- ТА ЕЛЕКТРОННОЇ ФІЗИКИ Vol. 6 No 4, 04007(4pp) (2014) Том 6 № 4, 04007(4cc) (2014)   2077-6772/2014/6(4)04007(4) 04007-1  2014 Sumy State University Influence of Electron Irradiation on Optical Properties of ZnSe Thin Films  P. Raghu1, C.S. Naveen1, K. Mrudula1, Sanjeev Ganesh2, J. Shailaja1, H.M. Mahesh1,*  1 Department of Electronic Science, Bangalore University, Jnanabharathi, Bangalore – 560056 Karnataka, India 2 Microtron Centre, Mangalore University, Mangalagangothri, Mangalore – 574199 Karnataka, India  (Received 05 July 2014; revised manuscript received 17 July 2014; published online 29 November 2014)  Zinc Selenide (ZnSe) thin films of 500 nm thickness were deposited by electron beam evaporation tech-nique and irradiated with 8 MeV electron beam for the doses ranging from 0 Gy to 1 kGy. Optical proper-ties were studied for both irradiated and pristine samples using Ultraviolet-Visible spectrophotometer. The increase in electron dose tends to decrease in transmittance and increase in refractive index of thin film. Irradiated thin film exhibits minimum of 67 % transmittance for 800 Gy with very high absorption of optical energy at 550 nm wavelength. The samples irradiated  800 Gy tends to redeem the pristine prop-erties. Optical band gap for irradiated thin film were direct and in the range of 2.66 – 2.69 eV.  Keywords: E – beam Evaporation, Optical properties, Electron radiation, Thin films, ZnSe.   PACS numbers: 61.80.Fe, 81.15.Jj, 78.30.Fs, 78.66. – w                                                             * hm_mahesh@rediffmail.com 1. INTRODUCTION  Zinc Selenide (ZnSe) is one of the most prominent candidate for photovoltaic device as an n-type buffer material in CdTe based solar cell due to its wide band gap of 2.67 eV [1]. ZnSe thin films have attracted sev-eral researchers for improving the efficiency of hetero-junction solar cells. It has an immense potential to use as an efficient window/buffer material when CdS thickness is relatively small ( 100 nm) in CdS / CdTe solar cell. Also, it has wide transmission range from 450 nm to 21.5 µm with high refractive index of 2.60 at 550 nm and high electrical resistivity (1012 Ωcm) [2, 3]. ZnSe thin films are also used as buffer layers for CIGS solar cells which reached the efficiency up to 9.6 % (un-der AM 1.5 illumination) [4]. It has been reported that, by integrating different buffer layers in combination of zinc and tin oxide improved CdTe / CdS cell efficiency [5-7]. Several researchers has investigated, ZnSe as a buffer layer by exploiting the optical properties for re-placement or along with reduced thickness of CdS  [8-11]. Ionizing radiation produces the change in physi-cal properties such as optical, structural, electrical, etc., Due to these factors, electron irradiation is included in thin film formulations. The functions of electron irradia-tion include softening films, reducing brittleness, in-creasing flexibility and ductility. Therefore, present in-vestigation aims at examining the effects of electron irradiation on ZnSe thin films and possibility of using it as a buffer layer for solar cells.  2. EXPERIMENTAL  2.1 Preparation of Thin Films  The PVD apparatus used for deposition is based on a commercial system developed by Hind High Vac. Co., Bangalore. ZnSe powder source (99.99 % purity, Sigma Aldrich, U.S.A) is brought into the chamber in a mo-lybdenum crucible in vacuum condition at a pressure of 2  10 – 5 mbar. Soda lime glass slides of dimensions 25 mm  15 mm  1.35 mm were used as substrate were degreased with soap water followed by ultra-sonication in double distilled water and ethanol. The substrate holder is aided with continuous rotation for formation of uniform films on substrate surface. Thin films of 500 nm thickness were deposited at constant deposition rate of 5-8 A°/sec. Thickness and deposition rate were measured using quartz crystal thickness monitor (DTM-101).   2.2 Post Deposition Process  The aim of this post-deposition process (such as thermal annealing and electron irradiation) is common-ly used to improve the structural, morphological and chemical quality of deposited thin films. Therefore, de-posited samples were annealed in air ambient at 100° C for 3 hrs. After finishing thermal annealing treatment, samples were subjected to 8 MeV electron beam irradi-ation for doses ranging from 200-1 kGy in steps of 200 Gy, using variable energy Microtron accelerator facility available at Microtron Centre, Mangalore Uni-versity, India. The dose delivered was measured with an alanine dosimeter close to the sample, and features of Microtron are detailed elsewhere [12, 13].  2.3 Characterization  Electron irradiated ZnSe thin films of different dos-es were characterized for optical parameters and were compared with unirradiated. Optical investigations of thin films were performed using VIS-NIR spectropho-tometer (Ocean Optics, USA. Model No. USB4000-XR). Optical absorption is a useful method for investing the induced transition and providing information about band structure and optical energy gap of the materials. The principle of this technique is that, photons with energies higher than band-gap energy will be absorbed [14]. Ab-sorption coefficient ‘’ can be calculated using relation [15],  2.303 1logd T           (1)  P. RAGHU, C.S. NAVEEN, ET AL. J. NANO- ELECTRON. PHYS. 6, 04007 (2014)   04007-2 It is also written as a function of incident photon en-ergy ‘h ’ [16],       0Pgh A h E  (2)  Where, Eg is optical band gap, ‘P’ has discrete values like 1/2, 3/2, 2 or more depending on whether the transi-tion is direct or indirect and allowed or forbidden. In the direct and allowed cases P  1/2. Value of ‘P’ determines the nature of optical transition. The results have been analyzed according to the relation (2). A0 is a constant and given by,       2 2 * 3/20 (2 )e rA e neh m m   (3)  Where, m*e and mr are effective and reduced masses of charges carriers respectively. The variations of extinc-tion coefficient (k) with photon can be observed that wavelengths regardless of their thickness, values for extinction coefficients is calculated using the equation,     02.303 log 14Tkd  (4)  3. RESULTS AND DISCUSSION  Figure 1 illustrates transmittance spectra of 500 nm ZnSe thin films – deposited and irradiated with different dose (200 Gy-1 kGy). At 550 nm, unirradiated ZnSe thin film exhibits high transmittance of 75 %, as the dose increased from 200 Gy to 1 kGy the transmit-tance has been decreased upto 800 Gy and at 1 kGy dose transmittance has been increased slightly (Fig. 2). This attributes to improvement in absorption after ir-radiation from 200 Gy to 800 Gy. The width of trans-mission edge shifted towards lower energy with in-creasing irradiation doses. Hence the influence of irra-diation directly affects the absorption of thin film. Figure 3 represents optical absorption spectra of ZnSe films deposited on glass substrate. Absorption coef-ficient was calculated from transmittance spectra for the film irradiated with different electron dose. The varia-tion in absorption coefficient with wavelength reveals a  400 500 600 700 800 900 1000 110020304050607080Transmittance (%)Wavelength (nm)  unirradiated  200 Gy  400 Gy  600 Gy  800 Gy  1000 Gy  Fig. 1 – Transmittance spectra of irradiated ZnSe thin films of 500 nm thickness) 0 200Gy 400Gy 600Gy 800Gy 1kGy556065707580Transmittance (%)Dose  500nm  Fig. 2 – Transmission versus Dose of irradiated ZnSe Thin films  400 500 600 700 800 900 100001000000200000030000004000000Absorption ()Wavelength  unirradiated  200 Gy  400 Gy  600 Gy  800 Gy  1000 Gy  Fig. 3 – Absorption coefficient versus wavelength of ZnSe thin films  very low absorption of energy in visible region and high absorption in shorter wavelengths. The spectra also con-firm that, as the irradiated dose increases there is an increase in absorption at 550 nm. This attributes to the decreased transparency of thin film. The direct band to band transition energies and tail width of pristine and irradiated film is represented in table 1. Pristine film has direct band gap of 2.68 eV which is equal to standard bulk band gap [17]. Optical band-gap value for de posited film for different dose var-ies in the range of 2.66-2.69 eV. This variation in optical band gap trend is because of increase in irradiation en-ergy. The free atoms are responsible for creating several overlapping levels resulting in more energy inturn create multiple overlapping bands within thin films [18]. This phenomenon can be explained by Urbach tail which sig-nifies characteristic phenomena of absorption curve with respect to photon energy (Fig. 4) If structure of thin film has disorderness, we can es-timate the level using Urbach energy [19] which results in lean-in transmittance spectra towards minimum pho-ton energy. Tail width of thin films can be calculated by slope of straight line portion of plot (Fig. 4). The mini-mum tail width of 0.56 eV revealed by 600 Gy. Whereas, 1 KGy irradiated film exhibits higher tail width of 1.02 eV which is almost equal to pristine sample.  INFLUENCE OF ELECTRON IRRADIATION ON OPTICAL PROPERTIES… J. NANO- ELECTRON. PHYS. 6, 04007 (2014)   04007-3 Table 1 – Variation of Band gap and tail width of irradiated ZnSe thin films  Sl. №. Electron Dose (Gy): Pristine 200 400 600 800 1000 1 Band Gap (eV): 2.68 2.69 2.68 2.69 2.66 2.67 2 Tail Width (eV): 1.03 0.87 0.85 0.56 0.90 1.02  2.50 2.55 2.60 2.65 2.70 2.7513.7513.8013.8513.9013.9514.0014.0514.1014.1514.2014.25ln ()h (eV) 200 Gy 400 Gy 600 Gy 800 Gy 1 Gy Pristine  Fig. 4 – Variation of ln() versus photon energy of ZnSe thin films  This behavior highlights that higher dose can retain the properties of un-irradiated thin film. This is also evident from figure 3 that absorption has increased for lower dose and there after decreases, which inturn replicates better transmittance property.  400 500 600 700 800 900 10000.000.020.040.060.080.100.12Extinction Co-efficient (k)Wavelength (nm)  unirradiated  200 Gy  400 Gy  600 Gy  800 Gy  1000 Gy  Fig. 5 – Variation of Extinction Coefficient vs wavelength of irradiated ZnSe Thin films  The extinction coefficient (k) is directly related to ab-sorption of light. In the case of polycrystalline films, ex-tra absorption of light occurs at grain boundaries [20]. This leads to non-zero value of ‘k’ for photon energies smaller than the fundamental absorption edge [21]. This is further confirmed by figure 5.  0 200 400 600 800 10001.61.82.02.22.4Refractive Index (n)Dose (Gy)  500 nm  Fig. 6 – Variation of refractive index versus dose rate of 500 nm ZnSe thin films  The refractive index ‘n’ of the deposited films is eval-uated from envelope technique is shown in figure 6. The maximum refractive index is found to be 2.21 for 600 Gy irradiated film. All values were found to be wavy nature, while higher energy dose will retain the value of pristine sample.  4. SUMMARY  Electron irradiation on 500 nm ZnSe thin films was found to induce changes in optical properties depending on irradiation dose: irradiation leads to decrease in transparency of thin film while higher dose of 1 KGy leads to decrease in absorption with increase in trans-parency equal to pristine sample. The film posses direct transition with optical band gap in the range of 2.66-2.69 eV and also exhibit maximum refractive index for 600 Gy and minimum for 1 KGy dose. The decrease in transmittance and refractive index after 800 Gy (i.e., for 1 KGy and above) has to be investigated.  AKNOWLEDGEMENTS  Authors would like to express their sincere thanks to BRNS-DAE, Govt. of India for the financial support vide major research project (Sanction No: 2011/34/19/BRNS/0080) under which this work has been carried out.           P. RAGHU, C.S. NAVEEN, ET AL. J. NANO- ELECTRON. PHYS. 6, 04007 (2014)   04007-4 REFERENCES  1. W.S. Lour., C.C. Chang, Solid-State Electron. 39 No 9, 1295 (1996). 2. G. Grebe, G. Roussos, H. J. Schulz, J. Phys. C 9, 4511 (1976). 3. G. Jones, J. Woods, J. Phys. D 9, 799 (1976). 4. A. Rumberg, Ch. Sommerhalter, M. Toplak, A. Jager Wal-dau, Ch. M. Lux Steiner, Thin Solid Films 362, 172 (2000). 5. X. Wu, P. Sheldon, National center for photovoltaics reviews meeting, report No NREL/CP-520-25656, 1 (1998). 6. G. Gordillo, Photovoltaic specialist Conference – (Conference Record of the Twenty-Ninth IEEE:2002), 644 (IEEE: 2002). 7. D.M. Sharafat Hussain, Nowshad Amin, Chalc. Lett. 8 No 3, 187 (2011). 8. P. Raghu, C.S. Naveen, J Shailaja, S. Ganesh, S.I. 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Zinc Selenide (ZnSe) thin films of 500 nm thickness were deposited by electron beam evaporation technique and irradiated with 8 MeV electron beam for the doses ranging from 0 Gy to 1 kGy. Optical properties were studied for both irradiated and pristine samples using Ultraviolet-Visible spectrophotometer. The increase in electron dose tends to decrease in transmittance and increase in refractive index of thin film. Irradiated thin film exhibits minimum of 67  transmittance for 800 Gy with very high absorption of optical energy at 550 nm wavelength. The samples irradiated > 800 Gy tends to redeem the pristine properties. Optical band gap for irradiated thin film were direct and in the range of 2.66 - 2.69 eV. Â© 2014 Sumy State University

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Influence of electron irradiation on optical properties of ZnSe thin films

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