Photodiode & LED Discription

PHOTO-DIODE AND LED

1. CUÑADO, JeanethT.
GEQUINTO, Leah Jane P.
MANGARING, MeleriaS.
cgmarts@ee12

2. PHOTODIODE
Aphotodiodeisatypeofphotodetectorcapableofconvertinglightinto
eithercurrentorvoltage,dependinguponthemodeofoperation.The
common,traditionalsolarcellusedtogenerateelectricsolarpowerisa
largeareaphotodiode.
OPERATION
•Aphotodiodeisdesignedtooperate
inreversebias.
•Photoelectriceffect.
•Photocurrent.

3. HISTORY & THEORY
•Photodiodetechnologydevelopmentscameoutof
thebasicdevelopmentsofthePNjunctiondiode
thatstartedinthe1940sinearnest.Applications
fortheuseofthePNjunctiondiodewerefound
outsidethebasicuseofrectifyingsignals.
•Photodiodetechnologywasrefinedinthe1950s
andinthelatterpartofthatdecadethePIN
photodiodewasdeveloped.Lightabsorptioninthe
widedepletionareaofthePINstructurewasfirst
investigatedinapaperpublishedin1959by
Gartner.Althoughsiliconhasbeenthefavoured
materialforphotodiodes,germaniumcanalsobe
used,anditsusewasfirstdemonstratedin1962
byRiesz.

4. MATERIALS
STRUCTURE

5. TYPES
1.PINphotodiode
2.PNphotodiode
3.Avalanchephotodiode
4.Schottkyphotodiode
ADVANTAGES &
DISADVANTAGES
+ Advantagesforthe
Photodiodedetectorarehigh
NIRsensitivityandhighspeed.
-Disadvantagesarelimited
amountofpixelsandnoUV
response.

6. CHARACTERISTICS
Photodiodes are similar to
regularsemiconductordiodesexceptthatthey
maybeeitherexposed(todetectvacuum
UVorX-rays)orpackagedwithawindow
oropticalfiberconnectiontoallowlighttoreach
thesensitivepartofthedevice.Manydiodes
designedforusespecificallyasaphotodiodeuse
aPINjunctionratherthanap-njunction,to
increasethespeedofresponse.

7. CHARACTERISTICS

8. SIGNIFICANCE
•Inmostcases,thephotodiodeisusedtodeliver
atriggersignaltoanelectricaldevicewhenitis
eitherexposedtoaUVrayorX-ray.Itmayalso
beusedtodeliverthesametriggersignalwhen
thelightsourceiseitherturnedoffor
thephotodiodeisblockedfromthelightsource.
•Afunctionthataphotodiodecanperformisto
keepanelectricaldeviceoperatingthroughthe
processofconvertinglightintoapowersignalor
voltage.
•Photovoltaicmodeandphotoconductivemode
arenaturallyoccurringreactionstothelight
sourcecreatewhatisreferredtoasa

9. APPLICATIONS
•P-Nphotodiodesareusedinsimilarapplications
to other photodetectors, such
asphotoconductors,charge-coupleddevices,
andphotomultipliertubes.Theymaybeusedto
generateanoutputwhichisdependentuponthe
illumination(analog;formeasurementandthe
like),ortochangethestateofcircuitry(digital;
eitherforcontrolandswitching,ordigitalsignal
processing)..
•Photodiodesareusedinconsumer
electronicsdevicessuchascompact
discplayers,smokedetectors,andthe
receiversforinfraredremotecontrol

10. manyapplicationseitherphotodiodesorphotoconductorsmay
beused.Eithertypeofphotosensormaybeusedforlight
measurement,asincameralightmeters,ortorespondtolight
levels,asinswitchingonstreetlightingafterdark
•Photosensorsofalltypesmaybeusedtorespondtoincident
light,ortoasourceoflightwhichispartofthesamecircuitor
system.Aphotodiodeisoftencombinedintoasingle
componentwithanemitteroflight,usuallyalight-emitting
diode(LED),eithertodetectthepresenceofamechanical
obstructiontothebeam(slottedopticalswitch),or
tocoupletwodigitaloranalogcircuitswhilemaintaining
extremelyhighelectricalisolationbetweenthem,oftenfor
safety(optocoupler).
APPLICATIONS

11. •Photodiodesareoftenusedforaccurate
measurementoflightintensityinscienceand
industry.Theygenerallyhaveamorelinear
responsethanphotoconductors.
•Theyarealsowidelyusedinvariousmedical
applications,suchasdetectorsforcomputed
tomography(coupledwithscintillators),
instrumentstoanalyzesamples(immunoassay),
andpulseoximeters.
•PINdiodesaremuchfasterandmoresensitive
thanp-njunctiondiodes,andhenceareoften
usedforopticalcommunicationsandinlighting
regulation.
APPLICATIONS

12. •P-Nphotodiodesarenotusedtomeasureextremelylowlight
intensities.Instead,ifhighsensitivityisneeded,avalanche
photodiodes, intensified charge-coupled
devicesorphotomultipliertubesareusedforapplicationssuch
asastronomy,spectroscopy,nightvisionequipmentandlaser
rangefinding.
APPLICATIONS

13. EFFECTS
Photodiodesarebasicallyreversebiased
diodeswithopticalwindowsthatallowliketo
shineonthePNjunction.Likeanydiode,the
leakagecurrent(otherwiseknownasa
photodiodes'dark'current)increases
exponentiallywithtemperatureinaccordanceto
WilliamShockley'sideadiodeequation.Thisis
knownasthequantumefficiencyofthe
photodiode.Ifthequantumefficiencyofa
photodiodewillincreasewithtemperature,soas
wellasthethermallyinducednoise.
(According to
temperature…)

14. BreakDownVoltage:
Forsmallactiveareadevices,bydefinitionbreakdownvoltageis
definedasthevoltageatwhichthedarkcurrentbecomes10A.Since
darkcurrentincreaseswithtemperature,therefore,breakdown
voltagedecreasessimilarlywithincreaseintemperature.