In most recent times, semiconducting materials have become the footing for electronic applications. Because of this, scientists and applied scientists have studied in item about the electrical, conductivity, and structural belongingss of semiconducting materials in order to bring forth semiconducting materials that map efficaciously under assorted temperatures and force per unit areas. The innovation of devices such as incorporate circuits has shown the ability of scientists to make new constructions in the development of semiconducting materials. Continuous research should be done to bring forth higher quality devices. Factors such as the size, lastingness, dependability, lifetime, functionality, and cost of the device have to be considered.
II-VI semiconducting materials are immensely researched during this twenty-four hours and clip. An of import belongings of these semiconducting materials is their energy spreads, which can be varied over a broad scope by changing the mole fraction.
ZnO based semiconducting materials normally become a point of involvement since they offer a broad field of applications runing from optical UV filters and devices like Light Emitting Diode ‘s, optical maser rectifying tubes, ultraviolet Schottky barrier exposure sensors, metal-semiconductor field consequence transistors ( MESFETs ) , high negatron mobility transistors ( HEMTs ) and heterojunction bipolar transistors ( HBTs ) due to a set spread [ 1-3 ] . Due to the big energy set spread and high bond strength, the stuff responds good for high temperature applications, because its intrinsic belongingss are maintained at much higher temperatures. This suggests that ZnO-based power devices can run with less chilling and fewer high cost-processing stairss associated with complicated constructions designed to maximise heat extraction.
ZnO and its belongingss
Most of the II-VI binary compound semiconducting materials crystallize either in three-dimensional Zn sphalerite or hexangular wurtzite construction where each anion is surrounded by four cations at the corners of tetrahedron, and frailty versa. This tetrahedral coordination is typical of sp3 covalent bonding. In add-on, these stuffs besides possess significant ionic character. ZnO is one of the II-VI compound semiconducting materials whose ionicity resides at the boundary line between covalent and ionic semiconducting materials.
ZnO is a promising stuff for the realisation and hereafter of nanotechnology. With its broad band-gap ( 3.37 electron volt ) , high excitonic adhering energy, and high dislocation strength, ZnO can be utilized for electronic and photonic devices, every bit good as for high-frequency applications. The handiness of a native substrate and the possible for room-temperature operations opens the door to ZnO applications including chemical detectors and subscale electronic circuits [ 4 ] .
Figure 1.1: Wurtzite crystal construction of ZnO
It exhibits three crystal constructions viz. , wurtzite, zinc-blende and rocksalt. Thermodynamically, most stable stage of ZnO is wurtzite. While the zinc-blende ZnO construction can be stabilized merely by turning on three-dimensional substrates, the rocksalt ( NaCl ) construction can be obtained at comparatively high force per unit areas. The wurtzite construction has a hexangular unit cell with two lattice parametric quantities, a and degree Celsius, with a=d and c= a?s8/3d,
3d, where vitamin D is the interplanar spacing. And the ratio c/a= a?s8/3 =1.633. A conventional diagram of the wurtzite ZnO construction is shown in Figure 1.1. Table 1.1 shows the basic physical parametric quantities of ZnO [ 5 ]
Table 1.1 Properties of wurtzite ZnO.
Zinc Oxide ( ZnO ) nitrides stuff is a broad set spread semiconducting material stuff with possible applications in optoelectronic every bit good as in electronic devices runing at high power and high temperature conditions. Metal/ZnO contacts, both ohmic and Schottky are of import for these device applications.
One of the serious jobs with these devices is a big electromotive force bead across the semiconducting material metal interface at ohmic contacts, which leads to hapless device public presentation and dependability [ 6 ] . In order to avoid this job, the development of low opposition ohmic contacts is indispensable. Another serious job in Schottky contacts is the high contrary escape currents [ 7 ] . Schottky barrier rectifying tubes with a low forward electromotive force bead, a low contrary escape current, and high dislocation electromotive force etc. , are of import in electronic industry. Thus, farther elaborate surveies are necessary for better apprehension of ohmic and Schottky contact behaviour.
A big barrier height leads to little escape current and high dislocation electromotive force, which could ensue in improved responsivity and photocurrent to dark current contrast ratio. To accomplish a big Schottky barrier tallness on ZnO, one can take metals with high work maps [ 8 ] .
This work involves the fiction, structural, and electrical word picture of Schottky contact based photodetectors based on ZnO and Ag contactes, and we investigated the consequence of tempering on the behaviour of the I -V characterization [ 9-17 ] .
Aims and Outline of the undertaking
The aims and lineation of this undertaking are written in the undermentioned stairss:
1. To synthesis ZnO on Si by sputtering.
2. To manufacture Ag and Al Schottky contacts on ZnO.
2. To analyze the electric belongingss of these contacts.
3. To analyze the consequence of temperature on the electric belongingss of contacts ( I-V-T ) .
This undertaking contains six chapters. The first chapter provides background information on the ZnO and its belongingss and applications. Theory and literature reappraisal on the metals semiconducting materials contacts, Schottky and ohmic is discussed in the 2nd chapter of this undertaking. Chapter three is about the methodological analysis, experiment and word picture techniques. Consequences of the experiment is in chapter four, while treatment in chapter five. Finally, decisions are collected in chapter six.
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Theory AND LITERATUE REVIEW
ZnO is really of import in industrial application and spatially in photoelectric application, such as photodetector. However, we can non utilize ZnO or other semiconducting materials straight ; we must utilize a contact between semiconducting materials and its applications. Metal/semiconductor contact is really of import and easy to manufacture.
2.2 Metal-semiconductor contacts
The metal semiconducting material contact or metal-semiconductor junction is undeniably an indispensable portion of all semiconducting material devices. In order to organize a dependable and a quality device, an ideal or a high quality metal semiconducting material junction must be formed harmonizing to the design demands of the device. Furthermore, many of the utile belongingss of a p-n junction can be achieved by merely organizing an appropriate metal-semiconductor contact. Basically, metal-semiconductor contacts can be categorized into two types, that is the rectifying metal-semiconductor contact which is tantamount to a p-n junction rectifying tube and the non-rectifying ( ohmic ) metal-semiconductor contact. Two of these metal-semiconductor contacts play an of import function in all the semiconducting material devices because they are evidently attractive due to their fiction simpleness, and are peculiarly utile when high-speed rectification is required.
Fig. 2.1 shows an n-type semiconducting material with a metal work map N„m is brought in contact with a semiconducting material holding a work map N„s, charge transportation occurs until the Fermi degrees align at equilibrium. In Fig. 2.1, it shows the instance where N„m & gt ; N„s with the semiconducting material Fermi degree is ab initio higher than that of the metal before contact is made. To aline the two Fermi degrees, the electrostatic potency of the semiconducting material must be raised, i.e. the negatron energies must be lowered comparative to that of the metal, therefore ensuing in the formation of a depletion part, W near the junction. The positive charge due to unsalaried giver ions within W matches the negative charge on the metal. The electric field and the bending of the sets within W are similar to that of a p-n junction.
The equilibrium contact possible V0, is the possible which prevents farther net negatron diffusion from the semiconducting material conductivity set into the metal while I¦b is the possible barrier tallness, or better known as the Schottky barrier tallness, which act as a barrier for negatron injection from the metal into the semiconducting material conductivity set is N„m- I‡ . Here I‡ is called the negatron affinity, is measured from the vacuity degree to the semiconducting material conductivity set border. Just like in the p-n junction, the possible difference V0 can be decreased or increased by the application of either forward- or reversed-bias electromotive force.
When discoursing about the conveyance mechanisms, which determine the conductivity belongingss of Schottky barriers, it is known that there are assorted ways in which negatron can be transported across a metal-semiconductor junction under forward prejudice.
Fig. 2.1: A Schottky barrier is formed by reaching an n-type semiconducting material with a metal holding a larger work map: a ) set diagrams for the metal and the semiconducting material before connection ; b ) equilibrium set diagram for the junction.
Fig. 2.2 shows the instance for an n-type semiconducting material under forward prejudice. The reverse procedures occur under contrary prejudice. The mechanisms are:
emanation of negatrons from the semiconducting material over the top of the barrier into the metal ;
quantum-mechanical tunneling through the barrier ;
recombination in the space-charge part ;
recombination in the impersonal part ( hole injection ) .
Fig. 2.2 Transport procedures in a forward-biased Schottky barrier.
It is possible to do practical Schottky barrier rectifying tubes in which procedure ( a ) is the most of import and such rectifying tubes are by and large referred to as ‘nearly ideal ‘ . Procedures ( B ) , ( degree Celsius ) , and ( vitamin D ) cause departures from this ideal behavior.
On the other manus, the ohmic or non-rectifying metal-semiconductor contact is formed when the charge induced in the semiconducting material in alining the Fermi degrees is provided by bulk bearers ( Fig. 2.3 ) .
Fig. 2.3 ( a ) Ohmic metal-semiconductor for an n-type semiconducting material ( N„m & lt ; N„s ) , and ( B ) the equilibrium set diagram for the junction.
For illustration, for an n-type semiconducting material with the instance of N„m & lt ; N„s as shown in Fig. 2.3 ( a ) , the Fermi degrees are aligned at equilibrium by reassigning negatrons from the metal to the semiconducting material. This raises the semiconducting material negatron energies ( lowers the electrostatic potency ) relation to the metal at equilibrium Fig. 2.3 ( B ) . In this instance, the barrier to electron flow between the metal and the semiconducting material is little and easy overcome by a little electromotive force. No depletion part occurs in the semiconducting material in these instances since the electrostatic possible difference required to aline the Fermi degrees at equilibrium calls for accretion of bulk bearers in the semiconducting material.
For metal-semiconductor contacts, the ohmic contact is needed for connexions to other devices or circuit elements because of its additive current-voltage ( I-V ) features in both biasing waies ( with minimum opposition and no inclination to rectify signals ) , the Schottky contact, besides operation as a rectifying junction, poses an advantage in fast-switching application over the p-n junction opposite number. The Schottky barrier rectifying tube is a bulk bearer device. This fact means that there is no diffusion electrical capacity associated with a forward-biased Schottky rectifying tube. The riddance of the diffusion electrical capacity makes the Schottky diode a higher frequence device than the p-n junction rectifying tube. Furthermore, when exchanging a Schottky rectifying tube from forward to change by reversal prejudice, there is no minority bearer stored charge to take, as is the instance in the p-n junction rectifying tube. Since there is no minority bearer storage clip, the Schottky rectifying tubes can be used in fast- shift applications. A typical shift clip for a Schottky rectifying tube is in the picosecond scope, while for a p-n junction it is usually in the nanosecond scope.
2.3 Thermoionic emanation theoretical account
The forward I-V features was analyzed utilizing standard thermionic emanation relation for negatron conveyance from a metal-semiconductor with low doping concentration and the equation is given by [ 1-7 ]
( 2.1 )
where Vd is the electromotive force across the rectifying tube, n the ideality factor, K is the Boltzman invariable, and Is is the impregnation current given by
( 2.2 )
where Q is the electron charge, T the temperature, S the contact country, A** effectual Richardson invariable and i?¦b the Schottky barrier tallness. The value of i?¦b can be deduced straight from the I-V curves if the effectual Richardson invariable, A** is known. Eqs ( 1 ) can be eventually rewritten as
( 2.3 )
Here, the secret plan of ln [ Iexp ( qV/kT ) ] vs. V will give a consecutive line with the incline = q/nkT and y-intercept at lnIs. And from this value of Is we can cipher the value of Schottky barrier height i?¦b from Eqs ( 2 )
( 2.4 )
The theoretical value of A** is 32.4 A cm-2K-2 based on the effectual mass of ZnO ( m* = 0.27me ) and from A** =4i?°e m* K2 / ( h3 ) =120 ( m*/me ) .
Or in easy manner at V & gt ; 3kT/q we can simplified the theoretical account to [ 8 ]
( 2.5 )
In add-on, by take the logarithmic this equation go
( 2.6 )
We can easy to cipher Is from the y-intercept and n from the incline.
2.4 Seriess Resistance
At big currents at that place will a electromotive force bead across the series opposition. The big series opposition is attributed to the big spacing between the contacts. We can cipher the series opposition Rs from the Cheung map
( 2.7 )
( 2.8 )
a secret plan of H ( I ) V. I will give a consecutive line with the y-axis intercept equal to ni?¦b and the incline of this secret plan is the series opposition.
2.5 Ag and Al-ZnO contact
Because the work map of Ag larger than ZnO as we see in table 1.1, Ag used in contact with ZnO to organize schottky contact, see figure 2.4
Schottky contacts are required for some UV sensors, transistor devices, and for material features of ohmic and Schottky contacts to n-type ZnO have been reported in the literature utilizing Ag [ 9-11 ] and Al every bit good as others, where the features of the contacts were reported for a given metal and ZnO stuffs. Aluminum has typically resulted in ohmic behaviour with specific changeless electric resistance.
Recently, Allen et al [ 12 ] measured the ideality factor N to be 1.1 and the SBH to be 0.77 electron volt for a Ag/ZnO SBD produced on the O-polar surface of ZnO. Besides Sheng et al [ 13 ] declared that the ideality factor of Ag/ZnO varied from 1.37 at 265 K to 1.29 at 340 K.
Figure 2.4 Ag-ZnO schottky contact.
Table 2.1: Valuess of work maps and electronegativities for some common metals
( electron volt ) . ( Rhoderick and Williams, 1988 )
2.4 Theory of Characterization Techniques
2.4.1 Scaning Electron Microscopy ( SEM )
SEM is an negatron microscope which utilizes an negatron beam to bring forth a exaggerated image of a sample. The negatrons interact with the atoms that make up the sample bring forthing signals that contain information about the sample ‘s surface topography.
In SEM, negatrons are thermionically emitted from an negatron gun ( tungsten fibril ) through a series of lenses to be focused and scanned across the sample. The beam, which typically has an energy runing from a few hundred electron volts to 40 keV base on ballss through braces of scanning spirals or braces of deflector home bases in the negatron column, typically in the concluding lens, which deflect the beam in the ten and Y axes so that it scans in a raster manner over a rectangular country of the sample surface. Through uninterrupted random dispersing events that primary beam efficaciously fills a tear shaped interaction volume with a battalion of electronic excitements. Fig 2.4 shows the schematic of SEM.
Fig 2.4: Schematic of SEM.
2.4.2 X-Ray Diffraction ( XRD )
XRD is a powerful, non-destructive technique to analyse crystalline constructions with high truth. The interplanner spacing vitamin D values for a peculiar stuff and for a peculiar construction are alone. From this, information about the crystal features such as structural belongingss ( lattice parametric quantities, strain, grain size, epitaxy, stage composing, preferable orientation order-disorder transmutation, thermic enlargement ) , atomic agreement and thickness of the stuff can be obtained.
X-ray diffraction is based on constructive intervention of monochromatic X raies and a crystalline sample. X raies are generated by a cathode beam tubing, filtered to bring forth monochromatic radiation, collimated to concentrate, and directed toward the sample. The interaction of the incident rays with the sample produces constructive intervention ( and a diffracted beam ) when conditions satisfy Bragg ‘s Law:
( 2.9 )
This jurisprudence relates the wavelength of electromagnetic radiation to the diffraction angle and the lattice spacing in a crystalline sample. These diffracted X raies are so detected, processed and counted. By scanning the sample through a scope of 2I? angles, all possible diffraction waies of the lattice should be attained due to the random orientation of the powdery stuff. Conversion of the diffraction extremums to d-spacing allows designation of the mineral because each mineral has a set of alone d-spacing as mentioned above. This is achieved by comparing of d-spacing with standard mention forms. Fig 2.5 shows the diffraction of X raies by a crystal.Fig 2.6 shows the conventional for XRD.
Fig 2.5: Diffraction of X raies by a crystal.
Fig 2.6: Schematic of XRD.
Annealing is a heat intervention that is given to a stuff to change its belongingss such as strength and hardness. Annealing is used to bring on ductileness, relieve internal emphasiss, refine the construction and better cold working belongingss. In the semiconducting material industry, silicon wafers are annealed, so that dopant atoms, normally boron or P, can spread into permutation places in the crystal lattice, ensuing in drastic alterations in the electrical belongingss of the semiconducting stuff.
Annealing occurs by the diffusion of atoms within a solid stuff, so that the stuff progresses towards its equilibrium province. Heat is needed to increase the rate of diffusion by supplying the energy needed to interrupt bonds. The motion of atoms has the consequence of redistributing and destructing the disruptions in metals and ( to a lesser extent ) in ceramics. This change in disruptions allows metals to deform more easy, so additions their ductileness. Mechanical belongingss, such as hardness and ductileness, alteration as disruptions are eliminated and the metal ‘s crystal lattice is altered.
2.3 Energy Dispersive X-ray Analysis ( EDX )
One of the most utile characteristics of SEM analysis is Energy Dispersive X-ray Analysis ( EDX ) . An accoutrement to an SEM, this analytical tool allows coincident non-destructive elemental analysis of a sample. The negatron beam in an SEM has an energy typically between 5,000 and 20,000 negatron Vs ( electron volt ) . The energy keeping negatrons in atoms ( the binding energy ) ranges from a few electron volt up to many kVs. Many of these atomic negatrons from one of the innermost shells are dislodged as the incident negatrons beam strikes the surface of a conducting sample, therefore ionising atoms of the sample, i.e. this leaves the atom in an aroused province with a vacancy near the nucleus of the atom. Relaxation to the original province follows by an negatron from an outer shell of the atom that falls inward to make full the vacancy. The difference in energy between the two energy provinces is released in the signifier of an x-ray. Because the emitted X ray has energy equal to the difference between two aggressively defined degrees feature of the atom, it is called a characteristic X ray. Unlike the x-ray continuum, characteristic X raies have distinct energies, which serve to clearly place the atom type involved in the passage. They provide the fingerprint, or signature for designation of about any component in the periodic tabular array.
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This chapter will lucubrate on fiction processes undertaken to get micron ( micrometer ) sized contacts on ZnO by using Al and Ag metallization as suggested in earlier chapters. The fiction procedure is segregated into wafer cleansing, sputtering for ZnO, metal deposition, contact forms definition and I-V measurings.
3.1 Cleaning wafer with RCA method
In this experiment n-type, Si ( 100 ) was selected as substrates to sputter ZnO thin movies on its surface. Therefore surface cleaning on the Si wafers were carried out before any fiction procedure is initiated to take any taint on the wafers.
Presently stairss utilizing in Nor Lab cleaned Si wafers:
Cleaning Si in H2O/NH4OH/H2O2 in ratio 5:1:1 in glass cup at temperature 75oC for 10min.
Cleaning in HF: H2O in ratio 1:50 in plastic greenhorn for 10 to 15 sec.
Finally in H2O/HCL/H2O2 in ratio 6:1:1 at temperature 75oC for 10min.
The sample was rinsed in deionized H2O after each measure.
SiO2 as buffer bed on Silicon:
To heighten the growing of ZnO on Si ( 100 ) , and to cut down the mismatch between ZnO and Si the SiO2 was utilizing as a buffer bed, By tempering the Si ( 100 ) sample in furnace at 1100oC for 3hr with O2 flow.
R F Sputtering for ZnO
Assorted deposition techniques such as reactive vaporization, solution growing, spray pyrolysis, metallo organic chemical vapor deposition, ion beam spatter, dc/rf magnetron sputtering etc. were employed for the readying of ZnO movies. Among these methods, dc reactive magnetron sputtering received much attending because of sputtering from elemental mark in the presence of reactive gas for readying ofcompound movies with high energy of sputtered species, low force per unit area operation and low substrate temperature rise, made it as an attractive technique to lodge movies on different substrates. When compared to other physical deposition techniques, magnetron sputtered movies have better adhesion and greater uniformity over big countries. The physical belongingss of ZnO movies prepared by dc reactive magnetron sputtering chiefly depend on the sputtering parametric quantities such as substrate temperature, oxygen partial force per unit area and sputtering force per unit area apart from the target-substrate distance, sputtering power and deposition rate. In this work, we use n-type Si ( 100 ) as a substrate. See figures 3.1 and 3.2.
3.1 Diagram of a simplified DC magnetron spatter used for this survey
3.2 Picture of the equipment in the lab
Check the Film in SEM and EDX
To look into the morphology of the surface of ZnO thin movie Scanning negatron microscope SEM was used, and to demo the ratio and pureness of ZnO movie EDX word picture was used.
X-ray diffraction of ZnO thin movie
As we, see in chapter two X ray is a good manner to look into the quality of ZnO thin movie. In our work after spirting ZnO on Si ( 100 ) , the movie was characterized by x-ray diffraction.
To heighten the belongingss of thin movie we annealed it at 900oC in furnace see figure 3.3.
Figure 3.3 Annealing furnace.
Evaporate Al and Ag on the part of the surface of ZnO
First Al was evaporated by utilizing thermic vaporizing system and 2nd Ag was evaporated on another part of ZnO movie, utilizing these stairss:
Beginning of Al and Ag ( 99.999 % pure ) in the signifier of farinaceous ( 0.040 ” in diameter ) was cut into little pieces and loaded onto a tungsten melting pot in the vacuity chamber. 2 tungsten melting pots can be at the same time loaded into the chamber but merely 1 beginning on the crucible can be melted at a clip.
The vacuity chamber was evacuated and the force per unit area inside the chamber was brought down to between 2.0-x10-5 to 3.4×10-5 millimeter of mercury before the beginning was heated.
The wolfram melting pot was heated with 5.0A DC current for 1 minute. Al beginning was melted immediately at this current degree.
After 1 minute, the shutter was opened to let deposition of Al onto the ZnO movie.
The shutter was opened to let deposition of Al onto the ZnO movie.
The shutter was opened for 5 proceedingss and the warming current was turned off instantly after that every bit good.
After lodging Al, the crucible containing Ag is rotated and ready to be melted. Step 4 to 7 was repeated except the wolfram melting pot was heated with 5.0 a DC current for 1 minute.
During the deposition force per unit area inside the chamber reached 8.0×10-5 millimeter of mercury.
Vacuum in the chamber was eventually released and the wafer was taken out for the following processing measure.
Figure 3.4 Diagram of the evaporator used for this survey
Figure3.5 Picture of the equipment in the lab
Finally after evaporate Ag and Al, the movie was annealed at 900oC, to acquire schottky contacts, we repeat the experiment in different manner, but this was the good manner to acquire Schottky.
3.8 I-V-T measurings with different temperature
The basic equipment required to execute device electrical trials is the parametric analyser system shown in figure 3.6 with the capableness of positioning needle like investigations on the contact constructions and using the right electromotive force, current and mutual oppositions to the device. All the devices measurings are made in fundamentally the same manner. A electromotive force is applied to the constituent contact investigation and the attendant current flowing between the contacts is measured with ammeter. The consequences are so exhibited on the show screen or the proctor. In add-on, we make all measurings at different temperature get downing from room temperature ( 300K ) up to ( 523K ) . We repeated this measure more times to acquire a good schottky.
Figure 3.6 Parametric Analyzer ( I-V System )
In this chapter, we will offer our informations and consequences of word picture of ZnO thin movie. The quality and the belongingss of ZnO thin movie synthesis by dc-sputtering techniques will be shown in this chapter. In add-on, the consequences of the contacts of Ag/ZnO/Al will be offered.
4.1 Scaning Electron Microscope ( SEM ) and EDX of ZnO thin movie
The scanning negatron micrograph ( SEM ) image of the representative ZnO movie deposited on Si substrate is shown in figure 4.1 ; we can see the surface morphologies of ZnO movie and the grain size.
Figure 4.1 SEM image of ZnO thin movie growing by dc/ R degree Fahrenheit spatter.
To look into the being of Zn and O ratio we characterized the movie by utilizing EDX techniques. The spectrum is shown in figure 4.2
Figure. 4.2 EDX of ZnO thin movie growing by dc/ R degree Fahrenheit spatter.
4.2 X-ray Diffraction Data of ZnO/Si thin movie
The crystalline constructions of sample ( ZnO/Si ) movie was so examined by x-ray diffraction analysis ( XRD ) , which is a good technique to look into the quality of the crystalline construction. XRD informations are shown in figure 4.3.
We can see two extremums located at 2i?± = 34.4o and 69.3o. The first extremum represents the contemplation of hexangular ZnO ( 0002 ) and the 2nd represents the substrate Si ( 100 ) .
Figure 4.3 XRD of deposited ZnO movie on Si ( 100 ) utilizing dc spatter.
4.3 I-V measurings of Ag/ZnO/Al contacts
To analyze the electric belongingss of this contact, I-V-T measurings were used. The forward and contrary of I-V-T word picture of Ag/ZnO/Al thin movie are shown in figure 4.4 and figure 4.5. The measurings were taken at different temperatures started from room temperature up to 573K.
Figure 4.4 I-V of forward and contrary of Ag/ZnO/Al contacts at different temperature in logarithmic graduated table.
Figure 4.5 I-V of forward and contrary of Ag/ZnO/Al contacts at different temperature.
In add-on, for more information we plot forwarded and rearward behaviour individually at different temperatures in logarithmic graduated table as shown in figure 4.6 and 4.6.
Figure 4.6 Forward I-V of Ag/ZnO/Al contacts at different temperature.
Figure 4.7 Reverse I-V of Ag/ZnO/Al contacts at different temperature.
Figures from 4.8 to 4.12 show the I-V for Ag/ZnO/Al contacts at different temperature individually.
Figure 4.8 I-V of forward and contrary of Ag/ZnO/Al contacts at T= 300K
Figure 4.9 I-V of forward and contrary of Ag/ZnO/Al contacts at T= 323K
Figure 4.10 I-V of forward and contrary of Ag/ZnO/Al contacts at T= 373K
Figure 4.11 I-V of forward and contrary of Ag/ZnO/Al contacts at T= 423K.
Figure 4.12 I-V of forward and contrary of Ag/ZnO/Al contacts at T= 523K.
4.4 Barrier highs and the ideality factor computations
From the thermoionic emanation theoretical account equations 2.1, 2.5 and 2.6 a secret plan of ln ( I ) vs. V can be shown. The secret plans give consecutive lines with a incline = q/nkT and y-intercept at lnIs. From the value of Is we can cipher the value of Schottky barrier height i?¦b from Eqs ( 2.4 ) . We repeat the secret plan for all measurings at different temperature, ( see figures 4.13 – 4.18 ) . The values of Schottky barrier tallness i?¦b, impregnation currents and ideality factor N were calculated and shown in table.1.
Figure 4.13 secret plan of ln ( I ) vs. Voltage for Ag/ZnO/Al contacts at temperature T=300K
4.14 secret plan of ln ( I ) vs. Voltage for Ag/ZnO/Al contacts at temperature T=323K
Figure 4.15 secret plan of ln ( I ) vs. Voltage for Ag/ZnO/Al contacts at temperature T=373K
Figure 4.16 secret plan of ln ( I ) vs. Voltage for Ag/ZnO/Al contacts at temperature T=423K
Figure 4.17 secret plan of ln ( I ) vs. Voltage for Ag/ZnO/Al contacts at temperature T=473K
Figure 4.18 secret plan of ln ( I ) vs. Voltage for Ag/ZnO/Al contacts at temperature T=523K.
4.5 Series Resistance Calculations
At big currents through the junction there will be a electromotive force bead across the series opposition. The big series opposition is attributed to the big spacing between the contacts. We calculated the series opposition Rs from the Cheung map equation ( 2.7 ) and from equation ( 2.8 )
Using the n value determined from the incline of Equ.2.6, a secret plan of H ( I ) V. I will give a consecutive line with the y-axis intercept equal to ni?¦b and the incline of this secret plan is the series opposition. All computations of Rs are in table 4.1.
Table 4.1. Schottky barrier tallness, Saturation currents, ideality factor and series opposition at different temperature.
T ( K )
Is ( A )
i?¦B ( electron volt )
Rs ( I© )
This chapter will offer a broader position in apprehension and construing the physical constructions and the electrical belongingss of the contacts based on the word picture informations. The consequence of temperature on I-V measurings of Ag and Al on ZnO movie. Barrier tallness of the contact and ideality factor will be calculated.
5.1 ZnO thin Film Quality
From SEM image figure 4.1, we see homogeneous distributions of ZnO grains on the surface of Si ( 100 ) , and from EDX spectrum figure 4.2, we can see merely Zn and Oxygen ( O ) , which indicate that the ZnO thin movie was a high quality.
XRD spectrum of ZnO thin movie has two extremums at 2i?±= 34.4o and 69.3o for contemplation from the plane h-ZnO ( 0004 ) and Si ( 100 ) severally. This ideated that merely a individual crystal of ZnO on Si substrate. The mean size of ZnO crystals has been calculated from Scherrer expression where D is the mean size of the crystal, K is a changeless peers 0.9, i?¬ is the incident x-ray moving ridge and i?? is given by i??= i?°/2 [ FHWM * i?°/180 ] . The value of D was 15.1nm.
5.2 Effect of Temperature on Schottky barrier tallness and ideality factor
The contact belongingss obtained from the I-V-T features ( frontward and change by reversal ) of Ag/ZnO/Al as map of temperature are shown in Fig.4.1 and 4.2. It is observed that the features of Al/Ag/ZnO Schottky contacts are unvarying over different contacts. The forward I-V-T features was obey the standard thermionic emanation relation equation 2.1 and curves obtained for the I-V-T measurings indicate a really strong temperature dependance of the Ag/ZnO/Al Schottky rectifying tubes, and thermionic emanation becomes the dominant procedure.
The barrier tallness and the ideality factor are plotted as a map of temperature in Fig. 5.1 and fig. 5.2. The secret plan shows that the ideality factor exhibits a decreasing with increasing temperature, while the barrier height addition with increasing temperature which indicate that the thermionic emanation was dominant [ 1,2 ] . In add-on, we can see the rectifying tube was stable with temperature increasing.
In Fig 5.3 the secret plan between impregnation current and temperature show that as temperature addition the impregnation current addition which indicate that the conduction addition with temperature, and this significance that this device better on high temperature than low.
Figure 5.1. Barrier tallness as a map of temperature in the temperature scope ( 300-523 K ) for the Ag/ ZnO/Al Schottky rectifying tube after tempering at 900C.
Figure 5.2. Ideality factor as a map of temperature in the temperature scope ( 300-523 K ) for the Ag/ ZnO/Al Schottky rectifying tube after tempering at 900C
From figure 5.3, we can see the reverse relation between barrier tallness and ideality factor. This indicates that as barrier tallness addition the contacts between metal and semiconducting material enhancing.
Figure 5.3 Plotting of Barrier height vs. Ideality factor of Ag/ZnO/Al at different temperatures.
4.2 Seriess Resistance
Figure 5.4 shows the relation between series opposition and temperature for Ag/ZnO/Al contacts. We can see the lessening of opposition as temperature addition enchantress indicates that this rectifying tube operate at high temperature than at low temperature. Figure 5.5 shows the relation between impregnation current and temperatures ; we can see the impregnation current was addition as temperature addition, which indicates the opposition was decreased. Figure 5.6 shows the relation between impregnation current and series opposition.
Figure 5.4. Seriess opposition as a map of temperature in the temperature scope ( 300-523 K ) for the Ag/ ZnO/Al Schottky rectifying tube after tempering at 900C.
Figure.5.5 Saturation Current as a map of temperature in the temperature scope ( 300-523 K ) for the Ag/ ZnO/Al Schottky rectifying tube after tempering at 900C.
Figure 5.6. Saturation current vs. series opposition for the Ag/ ZnO/Al Schottky rectifying tube after tempering at 900C.