Group 4 Four Probe

8/17/2019 Group 4 Four Probe

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AimTo determine Resistivityof a semiconductor using

four probe method.



LIST OF EXPERIMENT

1. To Determine The Value of “g !" !ar Pen#ulum an# Fin# The Ra#iu$ of%"ration.&. To $tu#" Moment of Inertia of a '"(heel.). To Stu#" the Ma$$ S*ring S"$tem.

+. To Stu#" The Re$ol,ing Po(er of a Tele$-o*e.

. To Fin# The /a,elength of a So#ium Light0 !" Ne(ton$ Ring.

2. To Fin# The /a,elength of a So#ium Light0 !" Fre$nel$!i*ri$m.3. To Fin# The /a,elength of Mer-ur" %reen Light !" Di4ra-tion %ratingu$ing

S*e-trometer.

5. To Fin# The S*e-i6- Rotation of 7ane Sugar !" Polarimeter.



Apparatus Required8Four *ro9e $etu* :;nalogue or #igital

t"*e<

8O,en an# it$ $u**l"

8Sam*le of $emi-on#u-tor :%e-r"$tal<

8 Thermometer



. Combo Box and Sliders •Select Material > Thi$ i$ u$e# to $ele-t $emi-on#u-tor material for #oing the$imulator. • Range of Current > One -an -hoo$e the range of -urrent for the -urrent $our-e.

• Current Slider > It range$ from 1m; to &??m;. :Note@The #i,i$ion$ in the $li#er i$6Ae# a$ 1??<. If &?m; -urrent i$ $ele-te# in the -om9o 9oA0 the $li#er ,alue (illrange from ?m; to &?m;0 (ith an inter,al of ?.&m; an# if the ,alue i$ &??m; in the-om9o 9oA0 $li#er ,alue -hange$ from ?m; to &??m; (ith an inter,al of &m;. •Range of oven > Thi$ -om9o 9oA i$ u$e# to 6A the teme*rature to a *arti-ular range. • !ven> O,en i$ u$e# to ,ar" the teme*rature u*to &??? 7. Set !utton B It i$ u$e# to 6A the tem*erature in the o,en. Run !utton B ;fter $etting the tem*erature0 u$ing run 9utton (e -an $tartheating the o,en

/ait !utton B It i$ u$e# to $to* heating the o,en at a *arti-ular tem*erature. Mea$ure !utton> It i$ u$e# to #i$*la" the *re$ent tem*erature of the o,en.



Four Probe A four point probe is a simple apparatus for measuring

the resistivity of semiconductor samples. By passing a

current through two outer probes and measuring the

voltage through the inner probes allows the

measurement of the substrate resistivity.



THEORY AND FORMULA USED

At a constant temperature, the resistance, R of a conductor isproportional to its length L and inversely proportional to its area ofcross section A.

(1)Where ρ is the resistivity of the conductor and its unit is ohmmeter.

A semiconductor has electrical conductivity intermediate inmagnitude beteen that of a conductor and insulator. !emiconductordiffers from metals in their characteristic property of decreasingelectrical resistivity ith increasing temperature



According to band theory, the energy levels of semiconductors can begrouped into to bands, valence band and the conduction band. "n thepresence of an e#ternal electric field it is electrons in the valence bandthat can move freely, thereby responsible for the electricalconductivity of semiconductors. "n case of intrinsic semiconductors,the $ermi level lies in beteen the conduction band minimum andvalence band ma#imum. !ince conduction band lies above the $ermilevel at %&, hen no thermal e#citations are available, the conductionband remains unoccupied. !o conduction is not possible at %&, andresistance is infinite. As temperature increases, the occupancy of

conduction band goes up, thereby resulting in decrease of electricalresistivity of semiconductor

1. Resistivity of semiconductor by four probe method1. 'he resistivity of material is uniform in the area of

measurement.. "f there is a minority carrier inection into the semiconductor bythe current* carrying electrodes most of the carriers recombinenear electrodes so that their effect on conductivity is negligible.+. 'he surface on hich the probes rest is flat ith no surfaceleaage



1. -. 'he four probes used for resistivity measurementcontact surface at points that lie in a straight line.. 'he diameter of the contact beteen metallicprobes and the semiconductor should be small

compared to the distance beteen the probes./. 'he boundary beteen the current carryingelectrodes and the bul material is hemispherical andsmall in diameter.0. 'he surface of semiconductor material may beeither conducting and non*conducting. A conducting

boundary is one on hich material of much loerresistivity than semiconductor has been plated. Anon*conducting boundary is produced hen thesurface of the semiconductor is in contact ithinsulator.



$ig sho the resistivity probes on a die of material. "f theside boundaries are ade2uately far from the probes,

the die may be considered to be identical to a slice. $or thiscase of a slice of thicness and the resistivity is computed as

()'he function, f(3!) is a divisor for computing resistivity hichdepends on the value of and !

We assume that the si4e of the metal tip is infinitesimal andsample thicness is greater than the distance beteen theprobes,

(+) Where 5 6 the potential difference beteen inner probes involts." 6 7urrent through the outer pair of probes in ampere.! 6 !pacing beteen the probes in meter



Experimenta setup



Pro!edure1. !elect the semiconductor material from the combo bo#.

. !elect the source current from the slider. Restrict the sliderbased on the range of current.

+. !elect the Range of oven from the combo bo#.

-. !et the temperature from the slider.

. 7lic on the Run 8utton to start heating the oven in aparticular interval, from the default %7 to the temperaturethat e set already 7lic on the Wait button to stop heating.

/. 7lic on the !et button to display the temperature that eset in the oven.



0. 7lic on the 9easure button to display the present temperaturein the oven.

:. !elect the range of voltmeter from the combo bo#.

;. 9easure the 5oltage using 5oltmeter.

1%.7alculate the Resistivity of semiconductor in e5 for the giventemperature using e2uation () and (+).

11. A <raph is plotted ith 'emperature along #*a#is and resistivityof semiconductor along y*a#is.



O!SERV;TIONS7on$tant -urrent C m;Di$tan-e tra,elle# 9et(een *ro9e$0S0

C ?.& -m

Thi-ne$$ of -r"$tal :(< C ?.? -m



O9$er,ation$S. NO. TEMP T

:<

VOLT;%E

V:mV<

:1T< A

1???

βαα·ρρρρρρ ρρ

ln : <

1. )+) 2.! 2."#$ .%!2 &.#'%

&. )+1 2#.( 2.")2 ."% &."!

). ))5 22.' 2."'" .")( &.!$

+. ))3 2).' 2."!( ."( &.)"

. )) 2'.2 2."%$ #.#) &.#2"

2. ))) 2$.# 2.) #.$ &.'%



S. NO. TEMP T:<

VOLT;%EV:mV<

:1T< A1???

*esistivity ρ

ln : <

3. ))1 2!.2 ).) #."! ."#

G. )&5 2!." ).2# #.#2! .##%

5. )&3 2(.( ).$% #.#$" .#'(



"AL"ULAT#ONS

F:/S< C 2.??

C :VH&H).1+H?.&< :1??H1>2H2<

C VH1).?G) 1????

Eg C :&<H$lo*e of gra*h

$lo*e C :ln < ::1T<H1???< C ).22

Eg C ?.2&5 eV



Per-entage error C G.32 J

;,erage Re$i$ti,it" C 1.?)1G Km



"RA#$

&.2

&.#$

&.#

&.$

.$

.#

.#$

.2

&.#$

&.#

&.(

&.)

.#

.$

."

.#2

.#$

1/T*1000

.ln(ρ)

2."#$ 2.")2 2."'" 2."!( 2."%$ ).) ).2# ).)" ).$%



RESULT

1< Ta9le $ho($ ,ariation of re$i$ti,it"(ith tem*erature.

&< Re$i$ti,it" of %e -r"$tal a$ afun-tion of tem*erature i$ $ho(n inthe gra*h.

)< 7al-ulate# ,alue of Eg C ?.2&5 eV

+< Per-entage Error C G.32 J

< Re$i$ti,it" of $emi-on#u-tor C1.?)1G Km



Appi!ations OF Four Probe Met$od

%&The Measurement of SheetResistivity

The sheet resistivity of the top emitter layer is very easy to measureexperimentally using a "four point probe". A current is passed through theouter probes and induces a voltage in the inner voltage probes. The junction between the n and p -type materials behaves as an insulating layer and the cellmust be kept in the dark .



Using the voltage and current readings from the

probe[

!here The typical emitter sheet resistivity of silicon

solar cells lies in the range #-$## %&' .(n typical usage the current is set to ).* mA sothat the resistivity is simply the voltage readingin m+



2)Measurement of Bulk Resistivity

The measurement of bulk resistivity is similar to that of sheet

resistivity except that a resistivity in cm- is reported using the wafer thickness, t

!here t is the layer&wafer thickness in cm

The simple formula above works for when the wafer thickness

less than half the probe spacing t s&/0 1or thicker samplesthe formula becomes

!here s is the probe

spacing.



PRE"AUT#ONS AND SOUR"ES OF

ERROR



%#%L#O&RAPHY

• (((.google.-o.in

• ; ha

•(((.(ii*e#ia.org• In#u Praa$h

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THAN' YOU

Group 4 Four Probe

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