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Chapter 1
Introduction
1.1 General
The semiconductor property was first observed in 1833 by Michael Faraday when
he discovered that the electrical resistance of silver sulphide increases with temperature
as compared to a decrease, in metals. The first concept of “semiconductors” was
introduced by !eni"sber"er as “Conductors which have the electron conductivity and
whose resistance is greatly affected by temperature, will be called semiconductor ”#1$, in
year 1%1&. 'hoc(ley, )rattain and )ardeen, in 1%&*, demonstrated their invention of a
point transistor after that a hu"e number of semiconductor+based microelectronic devices
have been fabricated and manufactured throu"hout the world.
ow it is difficult to ima"ine a world without des(top laser printers, cellular
telephones, pa"ers, "lobal positionin", -+/0Ms, players, laser fa2 machine, and
todays combination of different information technolo"ies that to"ether comprises
4nformation superhi"hways. -ompound semiconductor such as 5allium+6rsenide 75a6s
and 4ndium+9hosphide 74n9 have brou"ht about or enabled all of these microelectronic,
optoelectronic, and wireless marvels.
-ompound semiconductors are critical to the success of many technolo"ies that
have opened new mar(ets.. 'ome of the common semiconductor devices are based on
compound semiconductor substrates for such application as hi"h speed di"ital
electronics, hi"h fre:uency analo" electronics, lasers, ;i"ht
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optoelectronic and wireless systems for civilian application. This lar"e "rowth re:uires
newer properties to be e2plored.
'ilicon has a lon" history as a semiconductor material, whereas silicon is the most
popular material used today to ma(e electronic devices, the compounds are considered a
cate"ory of semiconductors that perform functions beyond the physical limits of the
electronic properties of silicon. =hen it comes to li"ht "atherin" or li"ht emittin"
properties, the compounds are unsurpassed by silicon which is a very poor li"ht emittin"
material #>$. The fle2ibility in the properties "ives the compound semiconductors an
added benefit.
1.2 Objectives
The followin" ob?ectives are set for present wor(.
1. To study the properties of the material @inc o2ide.
>. To fabricate a -hemical apor eposition 7- system for deposition of
thin films of Ainc o2ide.
3. To "row thin films of Ainc o2ide and optimiAe the "rowth conditions to yield
"ood :uality films.
&. To characteriAe the films obtained.
>
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1.3 Organization of the thesis.
Chapter 1.
This chapter "ives a brief history of development of semiconductor technolo"y,
ob?ectives of the wor( carried out, and discuss the or"aniAation of thesis report.
Chapter 2.
This chapter contains brief introduction to semiconductors, compound
semiconductors and discuss in details about the material properties and application of
@inc o2ide and compares Ainc o2ide with some of the other competin" compound
semiconductors.
Chapter 3.
This chapter "ives an overview of current "rowth technolo"ies used to deposit
thin films of various semiconductors is "iven. 6 emphasiAe is "iven on -hemical apor
eposition 7-.
Chapter 4.
This chapter deals with details of fabrication of the -hemical apor eposition
7- system and the precursor used for deposition of the films.
Chapter 5.
This chapter "ives e2perimental details involved in film "rowth, and the
techni:ues used for characteriAation of "rown films.
3
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Chapter .
This chapter discus the results obtained after characteriAation of "rown films
durin" the course wor(.
Chapter !.
This -hapter contains conclusion drawn from the wor( carried out durin" the
course wor( and recommendations for future wor(.
&
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Chapter 2
"he Co#pound $e#iconductor% &inc O'ide
2.1 $e#iconductor
'emiconductors are a "roup of material with electrical characteristics between
metals and insulators. The electrical characteristics of semiconductor can be altered to a
dramatic e2tent by several ways includin" dopin", temperature, optical e2citation, stress
and other ways. This as well as other reasons ma(e semiconductors the material of choice
for many electronic devices. -urrent electronic devices such as 4- includin"
microprocessor used in personal computer, lasers, communication devices and a vast
array of other electronic devices are made usin" semiconductors.
Fi"ure >.1B )and dia"ram for -onductors, 'emiconductors, and insulators.
alance band
-onduction band
-onductor
)5
C1e
'emiconductor
alance band
-onduction band
)5
C1De
4nsulator
alance band
-onduction band
D
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'emiconductors are a "roup of materials typically referrin" to "roup 4 elements of the
periodic table or combination of "roup 444 and elements or combination of "roup 44 and
4 elements. )and theory can be used to classify the metals, semiconductors, and
insulators. Metals are class of materials which has valance and conduction band
overlapped, the insulators are those materials with hi"h ener"y band "ap between the
valance band and the conduction band, and semiconductor materials are those materials
with small band "ap typically of the order of 1e as shown in fi"ure 1.1.
'ome elements and many compounds show semiconductor behavior at room
temperature. 'emiconductors from "roup 4 are called elemental semiconductor because
they are composed of only one element. These semiconductors include 'ilicon 7'i and
5ermanium 75e. 'ome compounds of "roup 444 and "roup elements as well as "roup
44 and "roup 4 elements shows semiconductor behavior at room temperature and are
called compound semiconductor .
The elemental semiconductors have achieved a hi"h popularity due to its
relatively simple technolo"y. 0nce "ermanium was most widely used semiconductor
material. 4t was then replaced by silicon due to its superior :uality over "ermanium.
2.2 Co#pound $e#iconductor
The search for new semiconductin" materials with better properties still
continues, and the result is compound semiconductor. The compound semiconductors
show superior properties to silicon. The application of these compound semiconductors in
semiconductor industry is restricted due to relatively comple2 technolo"y re:uired for
"rowth and fabrication of devices and hi"h costs involved. 4n spite of all these reasons,
E
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the compound semiconductors promise to outperform silicon industry by performin" the
tas(s which are beyond the physical limits of silicon.
Most of the studied compound semiconductors come primarily from compounds
of elements from "roup 444 and "roup of periodic table or compounds of elements from
"roup 44 and "roup 4 of periodic table. 'ome 4+4 compounds also e2hibits
semiconductin" properties, but most of them have a small band "ap that limits there use
to infrared detectors and lasers #3$.
Followin" tables "able 2.1 and "able 2.2 shows the possible compounds that can
be formed from 444+ "roup and 44+4 "roup respectively.
"able 2.1% "he 444+ binary compounds 7compound semiconductors are hi"hli"hted
5roup 444 ↓ 5roup
9 6s 'b) ) )9 )6s )'b
6l 6l 6l9 6l6s 6l'b
5a 5a Ga( Ga)s Ga$b
4n 4n In( In)s In$b
0ut of all these compounds only few are potential semiconductors. )oron and
nitro"en compounds, for e2ample, have been included only for sa(e of completeness.
6luminum compounds are not very stable and usually disinte"rate with time. The si2
most important semiconductors are 5a9, 5a6s, 5a'b, 4n9, 4n6s, and 4n'b.
Most of the 444+ semiconductors have Ainc blend crystal structure.
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atoms has four valance electrons. This su""ests that the bondin" has a covalent character.
Gowever, since the elements of "roup 444 are more electropositive, and those of "roup
are more electrone"ative than "roup 4 elements, the bondin" in 444+ compounds has a
partial ionic character as well, as an effect the band "ap of 444+ compound
semiconductors is lar"er than those of "roup 4 elemental semiconductors.
"able 1.2% The 44+4 )inary -ompounds 7compound semiconductors are hi"hli"hted
Group II ↓ Group *I
0 ' 'e Te@n @n 0 &n$ &n$e &n"e
-d -d0 Cd$ Cd$e Cd"e
G" G"0 G"' G"'e G"Te
The crystal structure of 44+4 "roups shows variations and is rather comple2. -d'
and -d'e crystalliAe in the hcp7HH wurtAite structure, and @nTe and -dTe in Ainc blend,
where as @n' and @n'e can e2ist in both these forms. The bondin" in these structures is
mi2ture of both ionic and covalent types. This is because the avera"e number of valance
electrons per atom is still four, but 4 atoms are considerably more electrone"ative than
"roup 44 atoms, and this introduces ionicity.
The technical importance of these compound semiconductors is that they provide
a wider choice of band "ap in comparison to elemental semiconductors. 'ome of them
8
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have band "ap which corresponds to visible spectrum of radiation and finds applications
in li"ht emittin" diodes.
6 ma?or problem with compound semiconductors is that there preparation in
sin"le crystal form is difficult, also due to difference in vapor pressure of these materials.
0ne material may vaporiAe more rapidly than other, causin" e2cess of other type of
atoms. These other type of atoms may "et trapped interstitially in the lattice or may
precipitate out to form a second phase.
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2.3 "he &inc O'ide
@inc 02ide is an 44+4 "roup semiconductor material. The material is "ainin"
much attention in recent years, due many of its useful and hi"hly fle2ible properties. @inc
o2ide has a wide direct band "ap and a he2a"onal wurtAite crystal structure.#&$.
+igure 2.2B =urtAite crystal structure.
The @inc o2ide wurtAite structure, as show in fi"ure 1.>, consists of one
he2a"onal lattice containin" the @inc atoms and one he2a"onal lattice containin" the
o2y"en atoms. The two sub lattices interpenetrate into each other.
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2.4 &inc O'ide #aterial properties
@inc o2ide has molecular mass of 81.38% amu 7HH, and its specific "ravity at
room temperature is D.E&> "Kcm3. @inc o2ide has a meltin" point of >>DIL 7HH. @inc
o2ide crystal has cell parameters as a.3>Dnm and c.D>Inm at room temperature and
room temperature linear thermal e2pansion coefficients are
a+a2is direction &.*D
c+a2is direction >.%>
The electron mass is I.>8 and the hole mass is 1.8.7HH #D$
@inc 02ide has many interestin" properties, which ma(es it very attractive candidate for
future semiconductor industry. 'ome of the important properties are listed below.
2.4.1 ,nerg- band gap
@inc o2ide has a band "ap of 3.&e #E$, which falls in ultra+violate re"ion in
electroma"netic spectrum. The band "ap is direct in natureN this "ives it many interestin"
applications in optoelectronic devices.
2.4.2 Che#ical $toichio#etric/ stabilit-
@inc o2ide li(e many other o2ides, is chemically stable#*$. This is important
property for decidin" the life of the device manufactured.
2.4.3 ,'citon binding energ-
6n e2citon is a bound state of an electron and a hole in an insulator or
semiconductor, in other words, a -oulomb correlated electron hole pair. The bindin"
11
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ener"y associated with such a pair is called e2citon bindin" ener"y. The e2citon play very
important role in optical properties of semiconductor and enhances the li"ht emission
properties.
The @inc o2ide has hi"hest e2citon ener"y of EI me #8$, which is very lar"e as
compared to other competitors li(e 5a which has e2citon bindin" ener"y of >% me#%$.
4t can be noted here that e2citon bindin" ener"y for @inc o2ide is greater than the thermal
noise of 26meV at room temperature, it mean e2citons in Ainc o2ide are stable at room
temperature.
2.4.4 0ardness
@inc o2ide is hardest of 44+4 semiconductor materials. 4t has a hardness of &.D on
mohs scale #1I$. This indicates that its performance will not be de"raded as easily as the
other compounds throu"h the appearance of defects.
2.4.5 "ransparent nature
;i(e all metal o2ides, @inc o2ide is transparent in nature for visible li"ht #11$. The
deficiency of o2y"en atoms in the Ainc o2ide provides free char"e carriers and the
material acts li(e an electric conductor. )y properly controllin" o2y"en content, one can
control the electrical conductivity of @inc o2ide. This conductivity and transparent
behaviour "ives the material a very interestin" and rare combination of properties.
1>
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2.4. +erroelectric effect
The ferroelectric effect is an electrical phenomenon whereby certain ionic crystals
may e2hibit a spontaneous dipole moment. The term ferroelectricity refers to the
similarity with ferroma"netism, in which a material e2hibits a permanent ma"netic
moment. @inc o2ide can be made ferroelectric by ma(in" ternaries with it with
Man"anese #1>$. Thus it finds application in ma"netic sensors and most importantly
upcomin" field of spintronics.
2.4.! (iezoelectric effect
9ieAoelectric effect is the property of certain crystals of "eneratin" an electric
char"e when placed under mechanical stress, or of bein" deformed when an electrical
char"e is placed across it. Gi"h 9ieAoelectric -Km > #13$is observed in @inc
o2ide. This is amon" hi"hest of all semiconductors.
2.4. onto'icit-
@inc o2ide is an echo friendly chemical and has a lon" history of application in
medical field and cosmetics due to its ability to absorb the O radiation comin" from
sun. The material is also constantly used in various ointments and sunscreens. Thus, it
can be e2pected to be haAard free for nature.
Many other interestin" properties have been observed li(e "ood adhesion with
many material surfaces, /adiation resistance to P, Q, and R radiations etc.
Gere is comparison of (ey properties of @inc o2ide with those of competin"
compound semiconductor materials currently in useB
13
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"able 2.3% 9roperties of some of the -ompound 'emiconductors.
Material-rystal
'tructure
;attice
parameters
a c
)and+
"ap
D D.>1 3.3* 1.8% D% 8.*D@n' =urtAite 3.8> D.>E 3.8I 1.D% 3I %.EI
@n'e@inc
blendD.EE >.* 1.>% >I %.1I
5a6s@inc
)lendD.ED 1.&3 ++ &.> 1>.%
5a =urtAite 3.1% D.18 3.3% >.>& >1 8.%IEh+'ic =urtAite 3.18 1D.1> >.8E 3.1* ++ %.EE
4ndeed @inc o2ide has a uni:ue combination of hi"h values for ener"ies of band
"ap ener"y, cohesion and e2citon stability.
1&
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2.5 )pplications
The enormous potential for use of @inc o2ide in optoelectronic applications can
be e2plained with reference to above mentioned properties and table >.3. 6lthou"h the
material has a lon" history of applications in electrical and electronic industry, but it is
"ainin" lar"e attention these days in field of semiconductors. 'ome of them are
mentioned here
2.5.1 ight e#itting devices.
ue to a band "ap of 3.& e @inc o2ide finds applications as ultra+violet li"ht
source. 4mplementation of ;i"ht
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2.5.4 $ensors.
The @inc o2ide can be used as sensor for sensin" various parameters li(e
-hemical sensors #>D$B 'ensor for o2y"en content or alcohol content. 'urface
resistivity of the material is very sensitive to 02y"en or alcohol content, due to this
dependence on o2y"en it can act li(e a "ood 02y"en sensor or alcohol detectors.
Mechanical 'ensorB 'ensor for mechanical forces, pressures etc. The @inc o2ide
shows lar"eKhi"h pieAoelectric effect and can be used as mechanical sensor and also finds
application in M
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2.5.! 7aterial for $pintronics.
The @inc o2ide shows ferroma"netism if doped with Ma"nesium o2ide. Thus Ainc
o2ide can have both ferroelectric as well as semiconductin" properties this ma(es
material suitable for spintronics applications.
2. )dvantages of &inc o'ide over other se#i conducting #aterials
The material e2hibits a "ood combination of attractive uni:ue properties,
fle2ibility, and stability. This all "ives the material a leadin" ed"e over other materials.
'ome of them bein" as followsB
2..1. 0igh e'citon binding energ-.
The @inc o2ide has hi"h e2citon bindin" ener"y, which is D% me at room
temperature. 4n fact it has hi"hest e2citon bindin" ener"y in the class of 44+4 and 444+
semiconductor materials. The hi"h e2citon bindin" ener"y "ives the @inc o2ide superior
optical properties and the e2citonic stimulated li"ht emission can be obtained up to a
temperature of DDI
2..2. 8and gap can tailored
One of key advantage of using compound semiconductor is the
band gap of material can be tailored [16]to desired values depending
on the requirements. For Zinc oide this is achieved by making ternary
!ith other elements like magnesium "band gap #.$e%& .
1*
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2..3. arger operating te#perature range
The Ainc o2ide has a lar"e band "ap. This enables the device fabricated from Ainc
o2ide to with stand a wide temperature ran"e as compared to other semiconductor
material li(e silicon.
2..4. 9adiation resistant
The @inc 02ide is radiation resistant to P, Q, and R radiations#1*$. This "ives Ainc
o2ide strate"ic importance in nuclear war fare, space applications where radiation levels
are very hi"h. The Ainc o2ide is even more radiation resistant than 5a7HHsame #1*$.
2..5. o6 :ar; Current
The hi"h band "ap of material "ives it advanta"e of very low dar( current. This
ma(es detectors fabricated from @inc o2ide to "ive superior spectral response for ultra
violate radiation.
2... arge $hear 7odulus
The Ainc o2ide has very lar"e shear modulus of &D.D 5pa as compared with 18.3D
for @n'e, 3>.EI for 5a6s, D1.3* for 'i. This indicates stability of the Ainc o2ide crystal.
18
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Chapter 3.
Gro6th "echnologies
3.1 Introduction
eposition technolo"y can well be re"arded as the ma?or (ey to creation of
devices such as computers, since microelectronic solid state devices are all based on
material structures created by thin film deposition.
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processes are especially suitable if polysilicon, polycides, or refractory metals are to be
deposited.
3.2 Classification of deposition technologies
There are a lar"e number of deposition technolo"ies for material formation #18$.
'ome of important and especially useful in thin film deposition methods are listed
bellowB
,vaporative 7ethods
acuum
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Gas (hase Che#ical (rocesses
-hemical apor deposition7-
6tmospheric+pressure -
;ow+pressure -
Metal+0r"anic -
9hoto+enhanced -
Thermal formin" 9rocesses
Thermal o2idation
Thermal polymeriAation
i
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resistance+heated filaments, electron beams, crucible heated by conduction, radiation, or
rf+induction, arcs or lasers. 6dditional complications may include hi"h vacuum, precise
substrate motion 7to ensure uniformity and need for process monitorin".
7olecular bea# epita'- 78,/ % M)>
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4n $puttering process the e?ection of surface atoms from an electrode surface by
momentum transfer from bombardin" ions to surface atoms, forms an epi layer. 'ince the
surface atoms comes out and thus this process can also be used for etchin", or surface
cleanin". 5rowth of c+a2is oriented films usin" sputterin" have been reported7HH.#>1$
4n (las#a process, the fact that some chemical reactions are accelerated at a
"iven temperature in presence of ener"etic reactive+ion bombardment, is the basis of
processes for surface treatments such as plasma o2idation,and plasma nitridin" etc.
5rowth of @n0 nanotubes and nano wires have been reported usin" this techni:ue.7HH
#>>$
3.2.3. Gas (hase Che#ical (rocess
Method of film formation by purely chemical processes in "as phase or vapor
phase includes chemical vapor deposition and thermal o2idation. Che#ical *apor
:eposition 7C*: is a material synthesis process whereby constituents of vapor phase
react chemically near or on a substrate surface to form a solid product. The deposition
technolo"y has become one of the most important mean for creatin" thin film and coatin"
of a very lar"e variety of materials essential to advanced technolo"y7HH#>3$, particularly
solid state electronics where some of the most sophisticated purity and composition
re:uirements must be met. The main feature of - is its versatility for synthesiAin"
both simple and comple2 compounds with relatively ease and at "enerally low
temperatures. )oth chemical composition and physical structure can be tailored by
control of reaction chemistry and deposition conditions.
>3
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Thin films that can be prepared by - cover a tremendous ran"e of elements
and compounds. 0r"anic, or"anometallic and inor"anic reactants can be used as startin"
materials. 5ases are preferred because they can be easily metered and distributed to
reactor. ;i:uid and solid reactants must be vaporiAed without decomposition at suitable
temperature and transported usin" a suitable "as throu"h heated tubes to the reaction
chamber.
Many variants of - are in use, some areB
1. o6 (ressure Che#ical *apor :eposition (C*:/ B /eactor operates at a low
pressure 7typically I.1 to 1I torr for ;9- system. 4n ;9-, particle
contamination is reduced and film uniformity and conformality are better than
conventional 6tmospheric 9ressure -hemical apor eposition 769-.
eepin" reactor at low pressure minimiAes autodopin", a ma?or problem in
6tmospheric 9ressure -hemical apor eposition 769-.7HH#>&$
>. (hoto ,nhanced Che#ical *apor :eposition (0C*:/% 9G- is based
upon the activation of reactants in the "as phase or vapor phase by
electroma"netic radiation, usually short wave ultra violate radiation. 'elective
absorption of photons by reactant molecules or atoms initiates the process by
formin" reactive free radical species that then interact to form a desired film
product.
>&
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3.2.4. i*$.
>E
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Chapter 4
+abrication of Che#ical *apor :eposition
$-ste#
4.1 Introduction
-hemical apor eposition 7- has established itself as an important epita2ial
crystal "rowth techni:ue #>8$ yieldin" hi"h :uality ;ow imensional 'tructures 7;'
for fundamental semiconductor physics research and useful semiconductor devices, both
electronic and photonics. The "rowth of compound semiconductors results by introducin"
metered amount of the precursors into a :uartA tube that contains a substrate placed on a
heated susceptor. The reaction ta(es place close to the heated substrate or in many cases
on the substrate itself to produce the thin film. - is attractive as it may be used for the
deposition of very hi"h crystalline :uality layers and can be scaled up for the mass
production with relative ease. 6nother important feature of - system is the hi"h
"rowth rates that can be attained #>%$. 4t can produce heterostructures, multi+:uantum
wells 7MS= and super lattice 7'; with very abrupt switch on and switch off transitions
in composition as well as in dopin" profiles in continues "rowth by rapid chan"es of the
"as composition in the reaction chamber.
4.2 "he C*: s-ste# :esign
To obtain @inc o2ide thin films on a substrate, a - system was fabricated at
-6T 4ndore. The system is desi"ned to use @inc acetylacetonate as precursor. The
>*
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precursor bein" solid, a carrier "as is needed to carry its vapors to reaction chamber. The
carrier "as used here is itro"en "as from a hi"h purity 7%%.%%DU nitro"en cylinder.
The setup is divided in three ma?or parts
1. /eaction chamber.
>. -onnectin" lines
3. )ubbler
&.>.1 9eaction Cha#ber
/eaction chamber provides an isolated environment for reactants where they react
to produce re:uired product.
There are two types of reactors
1 ertical reactors
> GoriAontal reactors
+igure 4.1% 6 ertical /eactor
/eactant"ases
9roduct
"ases
'ubstrate
Geater
>8
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ertical reactors is a system in which fresh process "as enters the process space
throu"h a central port as shown in fi"ure &.1 and mi2es with the depleted "as as it flows
radially outwards over the wafer surface . The fresh process "as stimulates a current
which flows from the center of the plate, reacts at substrate surface, and flows toward the
e2haust of the reaction chamber.
+igure 4.2% 6 GoriAontal /eactor
4n horiAontal reactor the process "as flows horiAontally over the substrate. The
front side is e2posed to fresh supply of reactants whereas rear side "ets lower
concentration of reactants, this leads to uneven thic(ness of coatin". To avoid this tiled
substrates are used. 6 horiAontal reactor "eometry is shown in fi"ure &.>.
For the present system a vertical reactor is desi"ned, due to its relative ease in
fabrication, simple to use, and better uniformity of coatin" with relatively less efforts.
9roduct
"ases
'ubstrate
Geater /eactant"ases
>%
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The reaction chamber consists of
1. /eaction chamber wall
>. Geater and its support.
The ma?or roll of the reaction chamber body is
1 To prevent the reactants from interactin" with outside environment.
> To provide proper structure for inlet and outlet of reactants.
3 To maintain proper concentrations of reactants surroundin" the heater,
where they react.
+igure 4.3% The ertical /eactor 5eometry Osed in - 'ystem Fabricated
4nlet for precursor@n7acac
>
4nlet for02y"en
0utlet for9roduct"ases
/eactor base
Threadedholes forscrew
V0 /in"
/eactor body
3I
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The reactor has two inlets, one for precursor other for o2y"en. There is one outlet
for e2haust of waste "ases as shown in fi"ure. 6t the ?unction of inlets, the "ases are
mi2ed and travel downwards. The reactor body is (ept in a conical shape ne2t to the
entrance of the "ases so as to provide a streamline flow of "ases. The mi2ture propa"ates
downwards where a heater with the substrate is placed.
The reactor chamber is made up of :uartA. )esides bein" transparent, :uartA has
the advanta"e that it can withstand hi"her temperature, which ma(es it possible to "o to
hi"her "rowth temperatures as compared to "lass durin" deposition.
The reactor is cleaned in or"anic solvent, acid washed for W hour and finally
cleaned in water and or"anic solvents before assembly. The assembly of the reactor
chamber and the heater are shown in the fi"ure &.3.
+igure 4.4% The Geater 'tand Osed in The /eactor.
6n aluminum stand is used to (eep the heater vertical. The stand consists of an
annular rin" which is supported by four rods , as shown in the fi"ure &.&. 0ver the rods
there is a threaded dis( that holds the heater.
31
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The heater is positioned in middle of the reactor. This allows the "ases to mi2
properly prior to reaction, and this also maintains a safe distance from e2haust, as some
uneven flow may be present near e2haust.
The stand is mounted over a nylon base, which supports the :uartA reactor wall.
This ?oint is made air ti"ht by usin" an V0 rin" in the flan"ed couplin".
+igure 4.5% The Geater 5eometry Osed in /eactor.
=e have used an '' resistive heater. The heater has cylindrical "eometry as
shown in the fi"ure &.D and has a diameter of >.D inches, which ma(es ma2imum
allowable substrate siAe up to > inches. The heater is mounted in vertical fashion. The
heater has an inbuilt +type thermocouple. The temperature of heater can be increased
without dama"in" up to 8IIL- in o2y"en ambient.
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X )eni"n nature
X easy to handle
X oesnt catch fire spontaneously 7as M@n,
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furnace in this application, the outer surface temperature is not more than DIL-N if
furnace temperature was maintained at 1>IL -. -ontrollin" the current throu"h the
heatin" coil controlled the temperature of furnace. 6 9T1II sensor was used to measure
the temperature. The sensor is placed on the body of the bubbler to be placed inside the
furnace. 6 di"ital 0 0FF controller was used to control the temperature with accuracy
of 3L-. 4nside the furnace there is a constant temperature Aone where the bubbler can be
placed.
9recursor
-opper pipe
'teelcontainer
Geatin" coil4nlet
0utlet
3D
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+igure 4.% 6 )ubbler Osed for 'olid olatile 9recursor.
4nitially the bubbler was made of steel container. 0n the top two :uarter+inch
copper tube were braAed throu"h as shown in the fi"ure &.8. itro"en "as enters from one
of the copper tube into the bubbler where it "ets saturated by precursor vapors. 0ther
copper tube carries out this saturated "as. This tube is maintained at hi"h temperature by
windin" (anthal tape over it.
This (ind of setup for bubbler was very cumbersome and slow in response also
refillin" of precursor was difficult. To overcome all these problems, a bubbler with a
different heatin" scheme was redesi"ned.
4t is important to note that here the bubbler is re:uired to maintain at temperature
well below 1DIL- 7around 11IL-. 4t is (nown that Teflon tapes could withstand more
than this temperature.
3E
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+igure 4.=% The )ubbler esi"n Osed for - Fabricated.
Thus the furnace was replaced by directly windin" (anthal tape over metal
bubbler and usin" Teflon tapes for isolation. 6 new bubbler was desi"ned with a
cylindrical body. 6t the top two :uarter+inch tubes are braAed as before. Ferule connecters
are attached at outlets of these :uarter inch tubes, and a W inch tube is also braAed which
can be used to refill the precursor. 6t the time of wor(in" this W inch tube was sealed as
shown in fi"ure &.%.
5as outlet5as inlet
9recursorinlet
anthaltape
''container
Temperature-ontroller
3*
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0ver the vertical walls of the container a thic( layer of Teflon tape is wound.
0ver this layer (anthal tape is wound. The tape is wrapped around very carefully by
(eepin" it ti"ht enou"h, but if tape is stressed very ti"ht then it may cut the Teflon tape
beneath and may short with metal which is below the Teflon layerN =hereas if (anthal
tape is not ti"ht enou"h then on heatin" it may e2pand and may loose the "ripe and "et
loosened. 6lso the spacin" between ad?acent (anthal tape windin"s is maintained
constant. This is important for uniform heatin".
4t is difficult to solder (anthal tapes to copper wires, thus the copper wire was
press fitted to ma(e electric connection. To isolate the (anthal tape another layer of
Teflon tape is wound. This layer prevents any electric shoc(s and prevents (anthal tape
from e2ternal temperin".
9T1II is used as temperature sensor. 4t is placed at bottom plate of cylinder. The
position of sensor is chosen such that it is placed away from heatin" coils, the censor lies
?ust below precursor and thus "ives the temperature of precursor more accurately, also
center of bottom plate is a symmetric point and the temperature will be unbiased to
distance from heatin" coil.
&.>.3. Gas lines.
5as flows in the system are mana"ed throu"h "as lines or lines. 5as flows
throu"h cylinder to bubbler, and then bubbler to reaction chamber, are maintained
throu"h lines. There are many ?oints in line, ?oints are "enerally vulnerable to lea(a"es
and thus these ?oints decide the pressure it can handle lea( free.
38
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The line carryin" precursors, which are solid at room temperature, are vulnerable
to cho(in" problem. Maintainin" the temperature of the line more than bubbler
temperature solves the problem. % The ;ayout ia"ram.
4n the system Y inch copper tube are employed as lines. Ferules are employed for
connections as they can handle low pressures without considerable lea(s.
/e"ulator
0Z[5<
4T/ 0
5<
/otameter
)ubbler)ubbler
/eaction-hamber
Geated line
5as-ylinder
3%
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The outlet of nitro"en cylinder is split into two lines usin" a VT connector. I°-, and thus Teflon tape can be used here. Teflon tape is wound over copper
pipe to form a thic( layer. Then (anthal tape is wind evenly over this Teflon layer. 0ver
this (anthal tape another layer of Teflon is wind to prevent shoc( and e2ternal
disturbance to (anthal tape. The electrical connections are done as for bubbler.
This techni:ue cannot be directly applied at ?oints, valves. 4t was observed that if
these ?oints are not heated, the precursor starts settlin" on the internal walls, which may
lead to cho(in" of lines. To heat these ?oints a (anthal tape mesh is used. First a piece of
(anthal tape is wound by Teflon tape of sufficient thic(ness. This ma(es the tape
electrically insulatin". 6 mesh 7net is made out of this (anthal tape as shown in
fi"ure &.11 and now this net can be placed surroundin" ?oints. 6nd electrically these net
are placed in series with other heatin" coil on copper pipes. This prevents settlin" of
precursor inside the tubes.
&I
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+igure 4.11% The Teflon -oated anthal Tape Mesh Osed for Geatin".
To (eep wirin" handy banana pin connectors are used to ?oin ad?acent mesh etc.
Teflon winded-anthol tape
&1
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The ?oint between "lass reactor and copper tube carryin" precursor cannot be
done usin" either ferule or flarin". 6 =ilson seal arran"ement is used. -opper tube is
braAed to the couplin", the "lass tube alon" with V0 rin" are put inside as shown in the
fi"ure &.1> .i.
+igure 4.12 % The -ouplin" Osed to -onnect 6 5lass Tube and 6 -opper Tube.
The V0 rin" is pressed ti"htly between the two threaded metal bloc(s as shown in
fi"ure &.1>.ii This V0 rin" then isolates the "lass rod from outside environment.
)raAin"
-oppertube
-oppertube
V0 /in"
5lasstube
Threadin"
i ii
&>
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4.3. Control and 7onitoring
6part from these bloc(s a control system is needed to control the temperatures of
various units as mentioned. This is done usin" an 0 0FF di"ital controller. The
controller has a least count of I.1°- for 9T1II temperature sensor and 1 °- for +type
thermocouple input. The set point can be set with accuracy of 1°-. The controller drives
output throu"h a relay. The relay can handle a ma2imum current of 36mp at >>I rms.
The controller displays the process temperature and this allows one to monitor the
temperatures of substrate and bubbler. 6lthou"h the di"ital 0 0FF controller has
hysteresis option to avoid race around condition 7hi"h speed switchin" of output relay,
but it is not re:uired to use it for the system as the heatin" and coolin" processes are slow
enou"h to avoid hi"h fre:uency switchin", also the 9T1II is placed away from heatin"
coil, this distance adds a delay in control mechanism and further decreases the fre:uency
of switchin". 4n the case of lines the sensor is placed at a point, where while heatin",
lowest temperature is observed, this ensures sufficient hi"h temperature in line so that
precursor dont condense at any point in the line. The connection dia"ram is shown in
fi"ure &.13.
/otameters are employed to control and monitor the flow of "ases. The rotameters
used has a ran"e of I+> lpm.
&3
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+igure 4.13% The -onnection ia"ram.
)ubbler-u7acac
>
/eaction-hamber
Geated line
)ubbler @n7acac
>
9T1II
9ower for bubbler -ontroller
To +typeThermocouple
9ower forheater
9ower forline
heater 9T1IIFor line
temperature.sensin"
>>I
&&
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Chapter 5
,'peri#ental :etails
5.1. Introduction
The - setup built provides the necessary conditions re:uired to obtain thin
films of @inc o2ide. The system provides an environment, where the re:uired "rowth
parameters can be ad?usted to obtain "ood :uality films. 6fter the setup is fabricated, it is
re:uired to set all the "rowth parameters to proper values to obtain @inc o2ide films. This
is done by "rowin" films with systematic variations in "rowth conditions to obtain
optimal :uality films.
5.2. Gro6th para#eters
For the system fabricated, there are five parameters that can be controlled as
mentioned below.
1. 8ubbler "e#perature
The bubbler temperature "overns the vapor pressure of the precursor material and
thus amount of precursor comin" out with the carrier "as. The @inc 6cetylacetonate melts
at 1>&o- and thus bubbler temperature is varied between %D o- to 1>I o-, as to avoid
meltin" of precursor.
&D
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2. $ubstrate "e#perature
The substrate temperature is one of the most important "rowth parameter. The
reaction temperature at the substrate decides the reaction dynamics at the surface. The
precursor reacts at temperatures above >DI o- in o2y"en to "ive Ainc o2ide. The
temperature of substrate has to be maintained above >DI o-.
3. ine "e#perature
The temperature of lines carryin" precursor vapors has to be maintained at a temperature
more than that of bubbler temperature to ensure the precursor dont condense or deposit
inside the line. The line temperature doesnt play any role in film "rowth and is not
critical parameter. The temperature of heated line is maintained at 1>I o- as bubbler
temperature is not supposed to be more than this.
4. O'-gen +lo6
02y"en is re:uired for crac(in" @inc 6cetylacetonate. The flow rate of o2y"en decides
the amount of o2y"en present in the reaction chamber. The presence of o2y"en vacancies
in the film "overns the resistivity of the film obtained. The o2y"en flow rates is
maintained in a ran"e of I to > liters per minute 7lpm
5. itrogen +lo6
The flow rate of the nitro"en controls the amount of precursor enterin" the reaction
chamber. The nitro"en flow rate is maintained between .D to > lpm.
&E
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urin" the wor( more than DI films were "rown. The "rowth conditions of some
of the important films "rown are "iven as followsB
"able 5.1% 5rowth. 9arameters for 'ome of The Films eposited.
'ample
umber
02y"en
Flow
7lpm
itro"en
Flow
7lpm
)ubbler
Temperature
7o-
'ubstrate
Temperature
7o-'33 > .D 1I8 &II'&3 > .D 1I8 DII'&D > .D 1I8 &DI'DI > .D 1I8 DDI
'&* > .D 1I8 EII'>I > .D 11I &>I
5.3. "he se
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2. Clean the substrates
The substrates are acid washed usin" followin" procedureB
The substrates are washes usin" deter"ent soapN this removes any "rease or oil
layer present on the substrate. The substrate then is (ept in concentrated G-l acid to
remove any metallic or other dust particles. The substrate is then boiled in
trichlroethylene 7T-
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. $top o'-gen flo6 and nitrogen flo6
The o2y"en flow is turned off after the "rowth is over. The nitro"en flow is
stopped after the bubbler temperature falls down to DIo-. This is done to avoid any
settlement of precursor in the tubes.
!. $top line heating
6fter nitro"en flow is turned off the line heatin" is stopped. 6s there is no
precursor comin" out from bubbler into the lines, it is safe to turn off the line heatin".
5.4 Characterization techni
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0ne can observe a hump in absorption spectra near band ed"e for @inc o2ide, this is due
to e2citons.
The spectrometer O+31I19- was used for ta(in" measurements. The
spectrometer was used in transmittance mode, and a absorption spectrum in the
wavelen"th ran"e of >III\ to 3II\ is recorded.
The transmission spectrum can be used to obtain the film thic(ness of the film.
The film thic(ness can be calculated usin" followin" formula
−
=
>1
11>
λ λ µ
nd
DI
=here
d is film thic(ness
n is no of frin"es observed
µ is refractive inde2 of the film.
λ1wavelen"th of first
minimaKma2ima
]> is wavelen"th of last
minimaKma2ima
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2. @9a- diffraction
Z+/ay diffraction is a non+destructive tool to characteriAe microstructural
properties of semiconductor thin films such as crystallite siAe, strain and crystallo"raphic
orientation. The hi"h resolution Z+/ay diffraction #3I$ techni:ue has become essential
tool for characteriAin" semiconductor.
The machine used for Z+/ay analysis is PAalytical !"Pert MR#. The -opper
α line was used 7λ 1.D&ID Å for Z+/ay diffraction. The machine was used in θ "$θ
mode to observe diffraction pattern.
arious characteristic pea(s of @inc o2ide were observed and Full =idth at Galf
Ma2imum 7F=GM was measured.
The mean "rain siAe can be calculated usin" ebye 'cherrer formulaB
θ
λ
cos%. %
d =
>> Crctn &'HM % ∆−∆=
D1
=hered is mean "rain siAe
] is wavelen"th of Z+/ay used.) is corrected F=GM^ is )ra"" diffraction an"le
=here) is corrected F=GM_F=GM is observed F=GM in
radians
_-rctn is correction factor for theinstrument used
=hered is mean "rain siAe
] is wavelen"th of Z+/ay used.) is corrected F=GM in radians^ is )ra"" diffraction an"le
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3. $canning ,lectron 7icroscop- $,7/
The '
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4. 0all #obilit-? resistivit- #easure#ent.
Gall measurements yield the information about the carrier concentration and
mobility. The measurement is based on the Gall
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The Gall mobility can be calculated as
l
w
*
*
% E
E
%neE
(
E
*
H
c
)
y
)
)
)
) 11 ==−== µ
The measurements were made by a four probe method in the an+der+9aaw
"eometry, and substrates are cut in rectan"ular shape.
+igure 5.2%6n 6rbitrary 'hape Osed for van der 9auw Measurements
;et
G
4
1
&
3
>
D&
=here* c is potential difference in 2
direction.* H is Gall volta"e.l is len"th across which * c is
measured.w is the width of sample. E ) is electric field in 2 direction.
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i(
+l
+l i( ,
* R =,
Then the resistivity of the sample can be calculated as followsB
f R Rd
+=
>>ln
&1,3>3&,>1π ρ
=here f is determined from a transcendental e:uationB
=
+
−
f h
f
-
- >lne2p
>
1arccos
>ln1
1
Gere S / >1,3&K/ 3>,&1, if this ratio is "reater than unityN otherwise S / 3>,&1K / >1,3&
The Gall coefficient / G is calculated as
+
= >13,&>&>,31 R R
%
d R
H
4n order to minimiAe errors, it is useful to avera"e over current and ma"netic field
polarities.
Then
[ 77778
113,>&13,&>&>,13&>,31 % R % R % R % R
%
d R H +−++−−+=
87878787 13,&>13,>&&>,31&>,13 % R % R % R % R −−−+−−−+
DD
=here
4i? is current enterin" in contact i
and leavin" from contact ?
(l is ( +l
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The measurements were carried out for at room temperature. These measurements
were done usin" two iethley >3E 'ource+measurement units.
5. (hotolu#inescence (/
The 9; measurements were made at room temperature. The e2citation source
used was Ge+-d laser 7] 3>Dnm. The emitted li"ht was dispersed usin" a I.Dm
monochromator and detected usin" a 9hoto multiplier Tube.
DE
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Table E.1B The Film Thic(ness -alculated Osin" 6bsorption Frin"es.
'ample
eposition
Temperature
7o-
Film thic(ness
calculated
7nm
&II7'33 484
&DI7'&D 321
DII7'&3 490
DDI7'DI 373
D%
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.2. @9a- :iffraction
Z+/ay iffraction of films "rown at deposition temperature &DIo-, DIIo-, DDIo-,
and EIIo- was done to observe the effect of "rowth temperature on the crystalline :uality
of the film. The Z+/ay diffraction of the samples is as shown in fi"ure E.3.
+igure .3 B -omparison of -rystalline Suality 6s 6 Function of 5rowth Temperature
=e find that the film deposited at &DIo- is predominantly oriented alon" the c
a2is `stron" 7II> pea( but the other pea(s, li(e 71II and 71I1 are also visible 7-9'
no. 8I+II*D. 6t a deposition temperature of DIIo-, the film obtained is mainly oriented
alon" the c a2is and only a very small si"nature of 71I1 pea( is observed. 6t a deposition
temperature of DDIo-, the film is observed to be stron"ly c a2is oriented. Fi"ure E.& is a
EI
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plot of the calculated value of 47II>K4 for different deposition temperatures. The value
of 47II>K4 is an indication of the de"ree of orientation of the film. For the values of
47II>K4 close to 1, the films are hi"hly c a2is oriented.
Fi"ure E.&B ariation of 47II>K4 with eposition Temperature
=e also find another Z+ray pea(, which is assi"ned to the 7>II pea( of the @n0 >
phase 7-9' no.13+I311. 6t a deposition temperature of EIIo-, we find that the
crystalline :uality reduces drastically resultin" in very low intensity Z+/ay pea(s.
4t can be seen that, as temperature is increased the sharpness of the pea( increases,
this is reflected by decrease in F=GM as shown in the Fi"ure E.D, fi"ure E.D shows
variation of F=GM with deposition temperature. This indicates improvement in
crystalline :uality of the film and increase in the "rain siAes.
E1
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+igure .5B ariation of F=GM with eposition temperature.
The "rain siAes for above mentioned films are calculated, and are "iven in table
E.>
"able .2% 5rain 'iAe 6s -alculated from F=GM.
eposition Temperature
7o-
5rain siAe
7nm
&DI >&&
DII 3>I
DDI 3%>
.3. 0all and resistivit- #easure#ents
E>
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/esistivity and Gall measurement for samples "rown at temperature &DIo-, and
DIIo-, and DDIo- ta(en. The lowest resistivity of D.821I+> ohm cm was observed for
sample "rown at DIIo-, also the sample showed a hi"hest mobility of 3cm>K'ec7HH
amon"st the four samples mentioned.
Change this part after looking at the data.
ariation of resistivity of the sample with deposition temperature is as shown in
Fi"ure E.E.
+igure .B ariation of /esistivity =ith eposition Temperature.
4t can be seen that optimal deposition temperature for "rowin" the films of lower
resistivity is in ran"e of &DIo- to DIIo-.
E3
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.4. $canning ,lectron 7icroscop-
'
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+igure .B Gi"hli"htin" he2a"onal structure
Gere one can observe he2a"onal crystallite structure, which is e2pectedly due to
wurtAite structure of @inc o2ide.
ED
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E.D. (hotolu#inescence
Fi"ure E.% "ives the /T 9hotoluminescence 79; data for the samples deposited at
different temperatures where it is found that the most intense 9; is observed in the
sample deposited at &DIo-.
+igure .=B /oom temperature 9; data of @n0 films deposited at different substratetemperatures. )eyond D1Inm, the data is ma"nified by a factor of 1I indicatin" the
absence of deep centre luminescence.
EE
400 500 600 700 800
0.0
0.2
0.4
0.6
0.8
1.0
Laser Plasma Lines
! 10
P L
" n t e n s i t # $ a
u %
&a'elength $nm%
(eposition temperature
450o)
500o)
550o)
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+igure .1>B The /oom temperature 9; intensity ma2ima as a function of depositedtemperatures.
Thus it is found that althou"h the crystalline :uality of the @inc o2ide layers
improve with increase in deposition temperature, the 9; intensity reduces. This is most
probably due to the "eneration of non+radiative carrier recombination centers at hi"h
"rowth temperatures that reduce the 9; intensity. 6nother si"nificant observation in the
/T 9; data for all the samples is that, none of the films have any luminescence from deep
centers in the visible part of the spectrum. 1I 9; of the sample deposited at &DI o- also
shows no visible 9; from the deep centers in the visible part of the spectrum.
E*
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Chapter !
Conclusions and 9eco##endations
!.1. Conclusion
6 wor(in" 'in"le 'ource -hemical apor eposition 7''- system for
deposition of @inc o2ide thin films was successfully fabricated durin" the course of this
wor(. @inc o2ide films are deposited usin" the above+mentioned fabricated - system,
under various deposition conditions. Osin" this system, some "rowth parameters have
been optimiAed. The Z+ray, optical absorption, photoluminescence, ' pea( width decreases, indicatin" the formation of lar"er
siAe "rains at hi"her deposition temperatures. =e thus find that inspite of havin" oriented
films with lar"er "rain siAes at hi"h deposition temperatures 7DDIo-, the optical
properties de"rade with deposition temperature, possibly due to the formation of certain
non+radiative recombination centers at hi"h deposition temperatures. Furthermore, we
find that a second undesirable phase @n0> is formed at DDIo- deposition temperature.
E8
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!.2. $cope of future 6or;
This thesis discusses the fabrication of - system, and optimiAation of certain
parameters to obtain "ood :uality films. 6s future wor( followin" wor( is su""ested
X 0ptimiAe flow rates.
X Ose it for multiple materials to "et ternary and :uaternary semi conductin"
materials.
X Ose different substrates.
E%
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6-0=;
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D.D. 5rowth parameters &D
D.E. The se:uence of operations 47
D.D -haracteriAation techni:ues. &%
E. 6bsorption spectrum&%*. Z+/ay diffraction D1
8. 'cannin"
%. Gall mobility, resistivity measurement. D3
1I. 9hotoluminescence DE
-hapter E /esults and iscussionE.E. 6bsorption spectrum D*
E.*. Z+/ay iffraction EI
E.8. Gall and resistivity measurements E3
E.%. 'cannin"
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List of Tables
TableNo.
Title PageNO.
The 444+ binary compounds8
The 44+4 binary compounds%
9roperties of some of the -ompound 'emiconductors.1D
5rowth. 9arameters for some of the films deposited.&8
The Film Thic(ness -alculated Osin" 6bsorption Frin"esEI
5rain 'iAe 6s -alculated from F=GM E3
*D
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9eferences
1. 5 )usch,E&
>. 6pplied 9hysics ;etters, olume 8>, 4ssue 18, pp. >%%E+>%%8 7>II3, ery
efficient li"ht emission from bul( crystalline silicon, Trup(e, Thorsten3. M.'. Tya"i ,”introduction to 'emiconductor materials and devices”,p" E3,ohn=iley 'ons.
&. iandon" [e,'hulin 5u et al.,”The "rowth and annealin" of sin"le crystalline @n0films by low+pressure M0-”,ournal of -rystal 5rowth,>&3,7>II>,1D1+1DE
5. 'al'o datasheet
E. [.ashiwaba,F.atahira et al. ”Getero+epita2ial "rowth of @n0 thin films byatmospheric pressure - methode” ournal of -rystal 5rowth ,vol >>17>III&31+&3&
*. 9. 'amarase(ara, 6.5.. isantha et al. ” Gi"h 9hoto+olta"e @inc 02ide ThinFilms eposited by - 'putterin"” ,-hines ournal of 9hysics ol. &I, o. >
8. .M. Gvam,” *pti+al ain an- "n-u+e- ./sorption from !+itoni+ole+ules in n*”, oli- tate )ommun, $1978% 987%. ournal of -rystal 5rowth >D* 7>II3 >DD+>E> D, umber 3 Februay 1,1%E>
11. T. Minami, G. anto et al ,” Gi"hly -onductive and Transparent 6luminumoped @inc 02ide Thin Films 9repared by /F Ma"netron 'putterin"”,pn. .6ppl. 9hys. ol. >3 71%8& ;>8I+;>8>
1>. '. . 9earton, . 9. orton et al. ”/ecent advances in processin" of
@n0”, .. acuum 'cience Technolo"y ), ol. >>, o. 3, May+un >II&13. F. )ernardini and . Fiorentini ,” ,'pontaneous polariAation and pieAoelectricconstants of 444+ nitrides”,9hysical /eview ) olume DE, umber 1E 1D0ctober 1%%*+44
1&. . M. )a"nall, [. F. -hen et al “0ptically pumped lasin" of @n0 at roomtemperature”,6ppl. 9hys. ;ett. *I 71*, >8 6pril 1%%*
1D. 'atoshi Masuda, en itamura et al.” Transparent thin film transistors usin" @n0as an active channel layer and their electrical properties ”,ournal of 6pplied9hysics ,ol %3,number 3, 1 February >II3
1E. '. (irchner )h. *ruber+ et al., -O%/ gro!th of ZnO usingvarious oygen precursors,+0ournal of 'rystal *ro!th 2$"334&352
1*. .-. ;oo( “/ecent advances in @n0 materials and devices ”Materials 'cienceand II1 38338*
18. 5handhi, '.., ;'4 Fabrication 9rinciples, ohn =iley sons1%. Gand boo( of thin film eposition 9rocesses and Techni:ues .. 'chue"raf >I. [. -hen, . M. )a"nall,etal.” 9lasma assisted molecular beam epita2y of @n0 on
c +plane sapphireB5rowth and characteriAation”,ournal of 6pplied 9hysics ol8&, no *, 1 0ct 1%%8
*E
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>1. '.G. eon", .=. ;ee, et al.” eposition of aluminum+doped Ainco2ide films by/F ma"netron sputterin" and study of their structural, electrical and optical properties”, Thin 'olid Films &3D 7>II3 *88>
>>. Zian+Gua @han",'u+[uan Zie,” /ational esi"n and Fabication od @n0 anotubes from anowire Templates in a Microwave 9lasma 'ystem”, . 9hys.-hem. ) >II3,1I*, 1I11&+1I118
>3. handboo( p" no ect>&. =. ;ee, -. eon",” Fabrication and application potential of @n0 nanowires "rown
on 5a6s7II> substrates by metalor"anic chemical vapour deposition”, anotechnolo"y 1D 7>II& >D&>D%
>D. G. [uan, [. @han",” 9reparation of well+ali"ned @n0 whis(ers on "lass substrate
by atmospheric M0- ”,ournal of -rystal 5rowth,>E3 7>II& 11%+1>&>E. .;eaf, -. Fry et al.,” /oom temperature chemical vapor deposition of c+a2is
@n0”, ournal of -rystal 5rowth >*& 7>IID &1>&1*>*. =.T. 'eebera, M.0. 6bou+Gelala, et al.,” Transparent semiconductin" @n0B6l
thin Flms prepared by spray pyrolysis” , Materials 'cience in 'emiconductor9rocessin" > 71%%% &D+DD
>8. @iba ami ,” /eactor esi"n -onsiderations for M0- 5rowth of ThinFilms”, 4&I 7>II> 11>+11E
3I. dhundo31. .0leyni(, M.6dam et al.,” Metalor"anic -hemical vapor phase deposition of
@n0 with different 0+precursors, ournal of -rystal 5rowth, >&8, 7>II3 1&+1%
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