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1 Beha Uverty Faculty of Egeerg Shoubra Electrcal Egeerg eartmet Frt Year commucato. t emeter Eam ate: 3 0 ECE: Electroc Egeerg fudametal urato : 3 hour K=.38 3 J/K h= J. q=.6 9 C m o =9. 3 Kg [S] =.5 cm 3 [S] m e =.8 m o [S] m h =0.8 m o [S] E g =. e [S] μ =400 cm /. [S] μ = 400 cm /. ε o = F/cm ε r =.7 Eg =. e Soluto Queto ( mark) wer th queto the form of table. Chooe the correct awer (oly oe awer acceted). For trc emcoductor.. (a) ll bod are comlete at 0 K (b) Part of valace electro releaed at hgh T (c) There are ome murte added (d) Both (a) ad (b) The collo due to. May chage both magtude ad drecto of the carrer eed (a) Iozed murte (b) Lattce vbrato (c) Thermal moto (d) rft of artcle 3 the tme betwee collo creaed, the moblty. (a) Rema cotat (b) ecreaed (c) creaed (d) affected oly by the murte cocetrato 4 the dog cocetrato creae above 5, the moblty. (a) Rema cotat (b) affected oly by the murte cocetrato (c) creaed (d) ecreaed 5 Fck low ca decrbe. (a) ffuo heomea (b) rft heomea (c) Both drft ad dffuo (d) No of the above 6 For the fabrcato of Ga jucto. The mot commo method. (a) ffuo (b) Evaorato (c) Etay (d) Io mlatato 7 The learly graded jucto are uually made by (a) ffuo (b) Evaorato (c) Etay (d) Io mlatato 8 The jucto deleto wdth vare a 3 (a) (b) (c) (d) 9 the revere ba voltage creae, the deleto caactace. (a) ecreae (b) Icreae (c) become zero (d) Rema cotat For the actve mode of oerato of bolar jucto trator. The EBJ/CBJ mut be coected a (a) Forward/Forward (b) Revere/Revere (c) Forward/Revere (d) Revere/forward For a bolar jucto trator (BJT), the bae rego (a) Moderately doed (b) ery th (c) Lghtly doed (d) Both(b) ad(c) Mot of the electro the bae of a trator flow (a) Out of the bae lead (b) Ito the collector (c) Ito the emtter (d) Ito the bae uly d b c d a c a a a c d b Page of 9

2 Queto (0 mark) a I a emcoductor, the Ferm level 50 me below the coducto bad. What the robablty of fdg a electro a tate KT below the valace bad edge E at room temerature? b bar of lco 0. mm log ad ha acro ecto of mm. Oe volt mreed acro the bar reult a curret of 8 m. umg that the curret due to electro, calculate:. Cocetrato of free electro ad. The drft velocty. c The dog roce of a S chage t coductvty. There alway a certa ecfc dog level that caue the coductvty to be a mmum. tye emcoductor doed wth that ecfc level. Calculate the mmum value of the coductvty. (T=300 K) (a) Soluto F( E) e EE F KT E E E E KT E F F E E g E e F e F( E) e (b) R 5 3 I 8 L R 6 R m.5cm 3 L q cm vd E cm / ec 700 m / Page of 9

3 (c) q q e h qe qh d t mmum coductvty 0 d d d qh qe d 0 d qe q h e h e h cm cm m m m cm Page 3 of 9

4 Queto 3 (0 mark) a Ela the deedece of moblty o temerature. (ot more tha 6 le) e KT b Prove that: q e c bar of lco of legth cm llumated at oe ed creatg Δ= Δ = cm 3 ece electro ad hole. If the dffuo legth L for the morty hole 4 3 cm ad f all the ece electro ad hole recombe at the other ed of the bar. Calculate ad lot the teady tate ece morty hole dtrbuto Δ() a fucto of the dtace alog the bar. (Ht Ue the aromato, e =+, for <<.) Soluto (a) t hgh temerature (T>50 K) the moblty maly lmted by the lattce vbrato. μ decreae wth creae of T (μ α T 3/ ). t low temerature (T<50 K) the moblty maly lmted by the ozed murte. μ creae wth creae of T (μ α T 3/ ). (b) EF E e kt de E qd d J qμe q 0 d EF E de q EF E def de qμe e kt q d kt kt d d de F 0 d The q μ kt kt μ q T Page 4 of 9

5 (c) Cotuty equato (o lght/teady tate) Note (the lght aborbed very mall rego.e at =0 ad creatg a ece of morty carrer of cm 3 but the em coductor doe ot eoe to lght 0 L Th equato ha a oluto a: L ( ) Ce C e L Note L = cm ad L = 4 3 cm ce L L L e whe The ( ) C ( ) C ( ) L L or C C ()=(C C ) ( ) L ** t = 0 = o = e C +C = I ** t =L =0 e (C +C ) 0.(C C )=0 II By olvg (I) ad (II) C =5.5 C = 4.5 cm -3 3 =0 X= = cm ( ).5 5 Thu for /L << the dtrbuto become lear ot eoetal a how Page 5 of 9

6 Queto 4 (8 mark) a For the how abrut jucto drve a ereo for the electrc feld the rego < <. b efe: the barrer otetal ad the derve the ereo for the barrer otetal (bult otetal) term of the dog cocetrato c abrut lco jucto at zero ba ha doat cocetrato of N = 7 cm 3 ad N = 5 5 cm 3. T = 300 K.. Calculate the Ferm level o each de of the jucto wth reect to the trc Ferm level.. Calculate the bult otetal.. eterme the eak electrc feld for th jucto. (a) ψ() d E ( ) ρ ( ) d d ε d ψ Soluto E 0 de() d E() E() E 0 de() d E() E E E() E ma E(0) (b) Barrer otetal: whe the tye materal ut cotact wth the tye materal, free electro from tye dffue ad cro the jucto ad combe wth hole the tye materal leavg behd (+ve o) the urface of the tye. Whle ( ve o) o the tye reg. Thee otve ad egatve o createe a electrc feld whch tur roduce a electrcc otetal (barrer otetal) that revet more electro from crog the jucto. ervato: traght forward utl: o KT NN l q

7 (c) d abrut lco jucto at zero ba ha doat cocetrato of N = 7 cm 3 ad N = 5 5 cm 3. T = 300 K. v. Calculate the Ferm level o each de of the jucto wth reect to the trc Ferm level. v. Calculate the bult otetal. v. eterme the eak electrc feld for th jucto. de: 5 KT KT N 5 EF E l l 0.06l 0.33e q q.5 de: 7 KT P KT N E EF l l 0.06l 0.408e q q.5 b 7 5 KT NN 5 l 0.06l q.5 N N N E E ma (0) b cm0.46m ma (0) / 4 cm E E Page 7 of 9

8 Queto 5 (0 mark) b RN a Gve that:. q N N N rve a ereo for the deleto caactace of the +, ad the draw the relato betwee the recrocal of the quared of the caactace ad the revere voltage. b deal oe ded lco + jucto ha uform dog o both de of the abrut jucto. The dog relato N = 50 N. Gve that: b = 0.75, R =, T = 300 K ad the cro ectoal area of the jucto = 5 5 cm, eterme:. N ad N., for R =. The jucto caactace. c half wave rectfer wth a traformer couled ut how the adjacet fgure. raw the waveform o ad. Calculate the value of (), o (), averge ad F out. Soluto (a) b R N q N N N for N N dq d C... d d R C ( b R ) C ( ) ( b R ) C b R b R R. (b) b KT NN 50N l 0.06l q.5 50N l.5 50N N N 50N cm cm 7 3 Page 8 of 9

9 SN ( S P ) N 03. rm ( S )3. 0 oavg OUTf 50 f Hz b R (0.75 ) 4.86 cm.86m C C ( ) b (0.75 ) C 5.55 F / cm R C C F F (c) Page 9 of 9