Int. J. N
depo base laser to 1 morp inves amor film.
Keyw PAC
optoe with solar Thin highe is the area sputt (MB be an nano of tun by ch issue
* ) For
Nanoelectronic
Evalua Raphso
Bassam
1 Univers
2,3,4Unive
Received
Abstrac
Silicon osition (PLD
pressure of r of wavelen
0 pulses h phological
stigation wa rphous struc
words: Nan CS: 78.67.B
1. Introd
Silicon n electronics
sizes of th r cells with n film transi er electron e low cost o
substrates.
tering, hot-w E) methods n excellent ostructured t
ned ion kin hanging the es during de
r corresponde
cs and Materials
ation of en on metho
G. Rasheed ity of Techno rsity of Must
d 4 April 201
ct
thin films D) technique
f 10-4 mbar ngth 1064 n has been u
and optical as carried o cture; the d
noparticles, f; 79.20.Eb duction
nanostructur [1]. Nanoc he order of a
nc-Si layer istors (TFT mobility an of fabricatio Silicon thin wire chemi s [5-7]. Am t choice [8, thin films o netic energy e laser para eposition [1
ence, E-mail: y
s 6 (2013) 97-1
nergy ban d
d1, Hayfa G.
ology, Applie tansiriya, Co 2; Revised 1
have been e. The film within ener nm and 5 ns used. The l properties out using x- deposition p
Optical pro
; 81.15.Fg.
res have attr crystalline s
a few nano rs incorpora Ts) with nc- nd increased on, since th n films can ical vapor d mong them,
,9]. PLD is of several te and ion flu ameters. Th 10-12]. In t
yasmeen_zada 04
nd gap of
. Rashid2, Y ed Science D ollege of Edu 13 June 2012
n prepared ms were depo
rgy range fr s duration, influences s of the Si -ray diffract parameters s
operties lase
tracted much silicon (nc-S ometers emb
ated showed -Si as the a d threshold hin films of be grown b deposition
the pulsed s a conveni echnologica ux density p he use of to this paper w
porous si
Yasmeen Z.
Department, B ucation, Bagh 2; Accepted 1
on sapphir osited in va rom 400 to 8
10 Hz) keep of the la i thin films tion. Result strongly aff
er ablation,
h attention Si) consists bedded in a d high stabil
active layer d voltage sta
nc-Si can b by various d (HW-CVD laser depos ient techniq al relevant m parameters o oxic gases c we report o
m
ilicon usin
Dawood3 *, Baghdad, Ira hdad, Iraq.
12 Dec. 2012
re substrate acuum from 800 mJ. A Q ping the num aser energy
s were inv t shows, tha fect the film
Laser depos
for their po s of an aggr an amorpho
lity and con r exhibited ability [2,3]
be deposited deposition t
), and mole sition (PLD) que for dep materials; it of the depos can be avoi on the struc
ng Newton
, Ahmed T.
aq.
2
e using pul m a silicon t Q-switched umber of pu
y on the s vestigated. S
at film grow m surface to
sition.
ssible appli gregate of c ous matrix.
nversion eff higher perf ]. Another a d directly o techniques, ecular beam ) method is positing hig offers the a sition specie ided, reduci ctural, morp
n-
Hassan4
lsed laser target at a
Nd:YAG lses fixed structural, Structural wn have a opography
ications in rystallites Thin film ficiencies.
formance, advantage ver large-
including m epitaxy s found to gh quality advantage es, simply ing safety phological
98
The deposition process was carried out under 5×10-5 torr at room temperature. The pulsed laser was focused on a rotating target to minimize a pit formation using lenses mounted inside the vacuum chamber. The target mount was fixed at optimum angle of 45°
with the incident laser pulse to reduce the interaction between the laser beam and evaporating materials and to ensure that the maximum of the ejected materials reach's the substrate. Silicon nanoparticales films were deposited on glass substrate under various preparation parameters such as number of pulses and laser energy.
The phases present in the as-deposited films were analyzed by x-ray diffraction in conventional θ–2θ configuration.
The optical transmission and absorption of silicon nanostructured film deposited on glass substrate was examined by CECILE CE-7200 spectrophotometer within the wavelength range (150-1100) nm. The glass substrate was used as a reference sample in the direction of the reference beam to prevent the effect of the reference sample during the measuring process. The estimated data from the transmission spectrum was used to determine the optical band gap graphically of samples prepared under different preparation conditions using the following equation [13, 14]:
α d 1 ln
T
1 (1)
where d and T are the thickness and transmission to the nanostructure films.
3. Result and Discussion
The silicon films thickness deposited by pulse laser ablation (PLD) has been measured optically. Fig. 1 illustrates the effect of the incident laser energies and the number of laser pulses on the film thickness prepared by PLD. A deposited film thickness as a function of laser energy (300-600 mJ) with constant number of pulses (10) pulses.
Increasing laser energy leads to increase in the amount of absorbed energy from the silicon atoms and subsequently increase the number of ejected particles from the target have higher kinetic energy leading to increasing the number of particles reaching the substrate causing increase in the film thickness. This could be attributed to decrease in the laser power density due to removal of the ejected target material and change in the target surface. Schottky contacts were made on (100) polished surface of non-intentionally doped n and p-type GaAs ( ND,NA 21016cm3 ). The ohmicity of back contacts was checked before each experiment.
XRD with nano silico nano scatte nano and b found energ energ laser
Fig.
F To study D as shows constant nu oparticles si
on, and thi oparticles ar ering angle oparticles si
becomes br d to be (3.1 gy. Further gy .which m r energy.
2: X-Ray di
Fig. 1: Thick y the crysta in Fig. 2 o umber of pu izes indicat is figure d re amorpho e (25.5°) w
ze was (4.1 roader for
2 nm). This r, Fig. 2 sh may be due
iffraction of
kness of samp allinity of si of Si films ulses. It is o tes the degr
oes not sh ous. It was when the las 1 nm).This p
higher lase s may be du hows that th to amount o
Si nanoparti 300
mples prepare ilicon nano deposited b observed tha ree of crys how any pe s found tha ser energy
peak shifts er energy (8 ue to the for he peak in of small sili
icles films pr
mJ.
0mJ
Int. J. Nano
d by LA vers ostructure fi
by PLD un at the large stallinity of eaks and w
at the broa of (300 m
towards a 800 mJ), w rmation of a
tensities in icon particl
repared by PL
oelectronics and
sus laser ene lms, sampl der differen
broad back f deposited we conclude ad peak wa J) was use smaller sca where the na
a smaller pa creases wit es in the de
LD at laser e
d Materials 6 (2
ergies.
les were an nt laser ene kground rela films is am de that indi
as position ed and the attering ang nanoparticle articles size th increase eposited film
energy. 300 m 80
2013) 97-104
99 alyzed by ergies and ated to the morphous ividual Si
ed at the estimated gle (21.5°) size was e at higher
the laser m for high
mJ & 800 00mJ
100 particles the partic
Fig. 3: T F absorptio explains samples.
laser ene an ejecte depends higher la particles substrate absorptio
from the su cles deposit
The effect of ig. 4 illust on coefficie the relation It is obviou rgy plays a ed materials completely aser energy of higher k and this w on coefficien
urface subs ed on substr
f preparation trates the e ent, were th
n between us that the l a significant s of two sta y on the las . Therefore kinetic ener will lead to nt.
trates these rate.
parameters o effect each he samples p the photon aser energy t role in the ates; molten
ser energy.
e, one could rgy which e o increases
e particles h
on the transm of the las prepared by n energy w y will be inc
laser-targe n and vapor Big amoun d expect th enable the p s film thick
have high e
mission spect ser energy y laser abla with absorpt
creasing the et interaction
ized materi nt of vapori at higher la particles to kness and
nergy and l
tra for differe and numb ation techni
ion coeffici e absorption
n. This inter al. The rati ized materi aser energy reach and d consequent
lead to incr
rent laser ene ber of pulse
ique. This f ient of pre n coefficient eraction pro
io of these al is obtain y produces
deposited o tly increase
reases
ergy.
es on figure
pared t. The duces states ned at
small on the es the
Fi
nano energ of at estim line inter by N The a
(αhυ) pulse takin the w the a
“best wher y0=-7 b=-3
plus may
ig. 4: Effect o In order ostructures p gy band gap toms in the mated in this of the plot section poin Newton-Rap
analysis of u Step 1 U )2 vs. (hυ) es).This beh ng advantag window.
Step 2 F aid of Matl t” fitting to
0 ax
y y re,
7.057*1011, .499*1011 , Step 3 Fi
TM ‘ softwa Step 4 C be done ‘an
Step 5 Fi
of preparatio r to réali prepared fil p of these s crystal latt s work by t t (αhυ)² ve nt between hson metho using this m Using a grap (for sampl havior may b ge of any ge
inding the “ ab or Sigm
experiment
3 2 cx bx
x
a=8.807*
c=0.4929 inding the “ are .
Calculating f nalytically’
inding the ‘
on parameter se the ele lms. It is ve samples. Th tice and the two method ersus (hυ).
the straigh od [15, 16].
method were phing utility
e prepared be represen eneral know
“best fitting ma-plot softw
tal data pair
3
*1011, 9*1011
“roots”, if ne first and sec or ‘numeric intercepts’,
rs on the abso ectrical an
ery importa his value de e structure o ds; Tradition The optica ht line and p
e summarize y to genera
with laser nted in term wledge one h
g” or “good ware packa rs (αhυ)2 an
Cubic eq
eeded. This cond deriva cally’.
, using “Adv
Int. J. Nano
orption coeff nd optical
ant to study epends on th
of the prepa nal method al band gap photon ener
ed as follow ate the beha energy=40 s of xy-plan have about d fitting” eq age .It is fo
d (hυ):
quation:
s may be do atives of y=
vantage plu
oelectronics and
ficient for dif specificatio y and calcu
he arrangem ared film. T
by extrapo p (Eg) repr rgy axis and
ws:
avior of exp 00 mJ and n ne abbreviat
the function quation. Thi ound to be c
ne using ‘M
=f(x) for the us TM “softw
d Materials 6 (2
fferent laser ons of th ulate the val
ment and di The energy olation of th resents the d the secon
perimental d number of tion, i.e. y=f n to help in is may be d cubic equat
Matlab’ or ‘a e cubic equa ware.
2013) 97-104
101 energy.
he silicon lue of the istribution band gap he straight value of nd method
data pairs pulse=10 f(x). Then n choosing down with tion yield
advantage ation, this
102
Usually this numerical method used for solving nonlinear algebraic equations. Here, we adapted the basic idea of this method:
o
oWhen the real root x1 is known, then one may easily compute the functional f(x1).
Drawing a line tangent to the curve at point x1 , then the tangent line intersect the x-axis at a point , say x2 , which play a significant important in evaluating Eg values.
ooEvaluating intersection point of tangent line with x-axis:
) (
) (
1 '
K K K
K
f x
x x f
x
(2) Where,
xk+1 = approximate root after k+1 iterations.
xk = approximate root after k iterations.
f(xk) = functional value at xk.
f ′(xk) = first derivative value of the functional at xk. k = 1,2,3,……
As a result, intersection points gives a range of Eg values due to the cases a. f(x) and f '(x)
[3.5375, 2.8653, 1.6453, 1.1454, ….]
b. f(x) and f ''(x)
[3.5375, 1.754, 1.6658 , 1.0258, ….]
c. f '(x) and f ''(x)
[3.965, 3.0439, 1.5632, …….]
The average value of Eg = 1.6248 eV, this gives an indication that this method still gives an approximated Eg value.
Using the two methods to find the optical band gap energy. Fig. 5 shows the effect of different laser energies on the optical band gap of the silicon nanostructure films, It was found that the optical band gap energy is highly affected by the incident laser energy. When low laser energy (300) mJ is employed, low number of large size silicon nanoparticales were ablated from the target and the estimated band gap energy was (1.6 eV, 1.53 eV) as shown in Fig. 5a. Increasing the incident laser energy to (400) mJ leads to increase the laser power density and this leads to increase the number of small size nanoparticles ejected from target and reaching the substrate surface, therefore the optical band gap increases. This band gap reaches (1.7 eV, 1.625 eV) as shown in Fig. 5b. By increasing the incident laser energy Fig.
5c & d, this means we will gain a high number of small size silicon nanoparticles rather than large size nanoparticles and this will leads to increases the value of optical band gap energy and reaches (1.9 eV, 1.78 eV) at higher energy. The observed shift in the band-edge can be
attrib Acco of ba
This to the of na subst analy estim laser that t to the the g amor
buted to the ording to th and gap (cha
Fig. 5:
4. Conclu
Silicon sa technique i e following anosilicon f trate edge w ysis (Newto mation for t
r energy wh the band ga e quantum c grain size d rphous.
decreasing he quantum ange from i
: Optical ban
usions
amples con is considere g features: g films produc while large on-Raphson the band ga hile the abso ap increases confinemen decreases w
g in the parti confinemen ndirect to q
nd gap to the
nstituting sil ed as an exc good thickne
ced by laser particles ar n method) f ap energy.
orption incre s with incre nt effect. X- with increas
icles size ac nt two proc quasi direct)
samples pre
licon nanos cellent techn
ess, size an r ablation re re located at
for the opti The film tr eased with asing the la -ray diffract sing the las
Int. J. Nano
ccording to ess will hap ), and the se
epared under
structure w nique to fab nd structural
eveals that t the film c ical propert ransmission increasing t aser energy tion for the er energy a
oelectronics and
the quantum ppen; the fir econd enlarg
different las
was produce bricate silic l control. A
small partic enter. It is f ties give an n decreases the laser en
duo to size films prepa and the film
d Materials 6 (2
m confinem rst change t ge in the ba
ser energies.
ed by LA t con nanopar A surface mo
cles are pla found that n n accurate s with incre nergy. It is a e reduction ared by LA m structure
2013) 97-104
103 ment effect.
the nature nd gap.
technique.
rticles due orphology ced at the numerical and good easing the also found
according show that becomes
104
[8] H. Chen, C. Jia, X. Zhang, W. F. Zhang, Vacuum, 85 (2010) 193
[9] T. Seto, T. Orii, M. Hirasawa, N. Aya, Thin Solid Films, 437 (2003) 230 [10] L. M. Kukreja, B. N. Singh, P. Misra, P. O. CAT, Indore, INDIA (2006)
[11] E. T. Salem: (Ph.D.) Thesis, Dep. of Applied Physics, University of Technology, (2006)
[12] M. Oszwaldowski, T. Berus, J. Rzeszutek, J.Alloys, compunds, 78 (2004) 6823 [13] R. A. Swady, Int. J. Namoelectronics and Materials, 4 (2011) 59
[14] B. Bendjemil, Int. J. Namoelectronics and Materials, 2 (2009) 173 [15] L. V. Zhigilei, A. M. Dongare Tech. Science Press CMES, 3 (2004) 539
[16] N. F. Habubi, K. A. Mishjil, H. G. Rashid, B. G. Rasheed, IJAP Lett., 1 (2008) 21
