Final Main Write Up 29_1 Fabrication of Chemical Vapor Deposition System for ZnO

8/19/2019 Final Main Write Up 29_1 Fabrication of Chemical Vapor Deposition System for ZnO

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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.

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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,

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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

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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"

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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.

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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

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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.

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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%& .

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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.

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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

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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.

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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*$.

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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

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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

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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.

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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


36/77

+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


37/77

+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*


38/77

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


39/77

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%


40/77

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


41/77

+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


42/77

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

&>


43/77

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


44/77

+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

&&


45/77

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


46/77

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


47/77

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


48/77

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-


49/77

. $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


50/77

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


51/77

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


52/77

3. $canning ,lectron 7icroscop- $,7/

The '


53/77

4. 0all #obilit-? resistivit- #easure#ent.

Gall measurements yield the information about the carrier concentration and

mobility. The measurement is based on the Gall


54/77

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.


55/77

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


56/77

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


57/77


58/77


59/77

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%


60/77

.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


61/77

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


62/77

+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>


63/77

/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


64/77

.4. $canning ,lectron 7icroscop-

'


65/77

+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


66/77

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)


67/77

+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*


68/77

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


69/77

!.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%


70/77

6-0=;


71/77


72/77


73/77

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"


74/77


75/77

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


76/77

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


77/77

>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

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Final Main Write Up 29_1 Fabrication of Chemical Vapor Deposition System for ZnO