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Homework Feb.20,2013

ThishomeworkisintendedforyoutoworkonwhileIamawayfortheFulbright-

NehruconferenceinCochi.Itisalittlecomplicated,andyoumustpayclose

attentiontoyourunits,butintheendIthinkitwillturnouttobesimpleenough.

Considerthefollowingdataforthecapacitanceofthespacechargelayerfortwo

samplesofthesamesemiconductorwiththesamerelativepermittivity,but

differentdopantconcentrations.Thesesemiconductorsareratherhighlydoped

(whichshouldgiveyouahintaboutthepossibleanswersinunitsofpercubiccentimeter!).

Potential(Voltsvs

Ag/AgCl)

Semicond.1,SCFarads Semicond.2,SCFarads

0.10 0.001042572 0.002146694

0.05 0.001080844 0.002241679

0.00 0.001125801 0.002363597-0.05 0.001177694 0.00248452

-0.10 0.001239394 0.002599376

-0.15 0.001311934 0.002742042

-0.20 0.001397542 0.002886751

Therelativepermittivityofthemediumis12.0.Thepermittivityoffreespaceis

8.854x10-12F/m.Beverycarefulofunitsandofsurfacearea!Therelationship

betweentheMott-Schottkyslopeandthedonordensity(thisisann-type

semiconductor)isasfollows:

m =2

NdeA

20

1) Calculatethedonordensityofeachsemiconductor.Whichismorehighlydoped?

2) Ifthismaterialishematite(Fe2O3),whatpercentageofallFeatomsinthestructureisadonordopantforthemosthighlydopedsample?

3) Whatistheflatbandpotentialofeachsample?4) GiventhatthepH=13.6forthesemeasurements,whatistheflatband

potentialofhematiteatpH7ontheSHEscale?