Chng 2Di nng lng v

HBK Tp HCM-Khoa -TBMTGVPT: H Trung MMn hc: Dng c bn dn

Di nng lng v nng ht dn

cn bng nhit

Ni dung 1. Vt liu bn dn2. Cu trc tinh th c bn3. Lin kt ha tr

2

3. Lin kt ha tr4. Di nng lng 5. Nng ht dn ni ti6. Cc cht donor v acceptor. 7. Nng ht dn trong bn dn loi N v P

2.1 Vt liu bn dn

3

2.1 Vt liu bn dn

Control of Conductivity is the Key to Modern Electronic Devices

Conductivity, , is the ease with which a given material conducts electricity.

Ohms Law: V=IR or J=E where J is current density and E is electric field. Metals: High conductivity Insulators: Low Conductivity

4

Insulators: Low Conductivity Semiconductors: Conductivity can be varied by several

orders of magnitude. It is the ability to control conductivity that make

semiconductors useful as current/voltage control elements. Current/Voltage control is the key to switches (digital logic including microprocessors etc), amplifiers, LEDs, LASERs, photodetectors, etc...

Classifications of Electronic Materials Electrical/Computer engineers like to classify

materials based on electrical behavior (insulating, semi-insulating, and metals).

Materials Engineers/Scientists classify materials based on bond type (covalent, ionic, metallic, or van

5

based on bond type (covalent, ionic, metallic, or van der Waals), or structure (crystalline, polycrystalline, amorphous, etc...).

In 20-50 years, EEs may not be using semiconductors at all!! Polymers or bio-electronics may replace them! However the materials science will be the same!

Material Classifications based on Bonding Method

Bonds can be classified as metallic, Ionic, Covalent, and van der Waals.

6

Material Classifications based on Bonding Method

7

Material Classifications based on Crystal Structure

Amorphous MaterialsNo discernible long range atomic order (no detectable crystal structure). Examples are silicon dioxide (SiO2), amorphous-Si, silicon nitride (Si3N4), and others. Though usually thought of as less perfect than crystalline materials, this class of materials is extremely useful.

Polycrystalline MaterialsMaterial consisting of several domains of crystalline material. Each

8

Material consisting of several domains of crystalline material. Each domain can be oriented differently than other domains. However, within a single domain, the material is crystalline. The size of the domains may range from cubic nanometers to several cubic centimeters. Many semiconductors are polycrystalline as are most metals.

Crystalline MaterialsCrystalline materials are characterized by an atomic symmetry that repeats spatially. The shape of the unit cell depends on the bonding of the material. The most common unit cell structures are diamond, zincblende (a derivative of the diamond structure), hexagonal, and rock salt (simple cubic).

Material Classifications based on Crystal Structure

9

Conductivities for insulators, semiconductors, and conductors.

10

Element Semiconductors(Cc cht bn dn nguyn t)

Bng phn loi tun hon ca vt liu bn dn

11

Compound Semiconductors(Cc cht bn dn hn hp)

Nhng nm gn y ngi ta s dng nhiu cc cht bn dn hn hp trong nhiu loi dng c bn dn.

C cc cht bn dn hn hp t 2 nguyn t (nh hp), 3 nguyn t (tam hp) v 4 nguyn t (t hp).

12

hp), 3 nguyn t (tam hp) v 4 nguyn t (t hp). Nhiu cht bn dn c cc tnh cht in v quang

khc vi Silicon. c bit l GaAs c dng lm vt liu chnh ch to cc dng c trong cc ng dng quang in t v chuyn mch tc cao

Cc cht bn dn nguyn t v hn hp

13

Cc cht bn dn nguyn t v hn hp (tt)

14

2.2 Cu trc tinh th c bn

15

Khi nim mng v t bo n v Ta s nghin cu vt liu bn dn n tinh

th, m trong cc nguyn t c sp xp tun hon trong khng gian.S sp xp tun hon ca cc nguyn t trong tinh th c gi l mng (lattice).

16

gi l mng (lattice). Trong tinh th, nguyn t s dao ng (do

nhit) quanh 1 v tr c nh. Vi bn dn cho trc, c t bo n v (unit

cell) i din cho ton b mng [tinh th]; bng cch lp li t bo n v trong tinh th ta c ton b mng tinh th.

T bo n v T bo n v c th c c trng bng vector R

(c to thnh t cc vector a, b, c [cc vector ny khng nht thit phi vung gc vi nhau v chiu di ca chng c th bng hay khng bng nhau] v cc s nguyn m, n v p)

R=ma+nb+pc

17

R=ma+nb+pc Cc vector a, b, v c c gi l cc hng s mng

(lattice constants).

Mt s t bo n v tinh th lp phng c bn

Cc t bo n v khc nhau da trn cc t bo n v lp phng: t bo n v lp phng n gin (SC), t bo n v lp phng tp trung bn trong (BCC), v t bo n v lp phng tp trung b mt (FCC)

18

Cu trc mng tinh th kim cng Silicon v germanium c mt cu trc tinh th kim

cng. Cu trc silicon thuc v lp nhng t bo n v lp

phng tp trung b mt. T bo n v silicon gm c tm nguyn t silicon.

Cu trc c th c nhn thy nh hai mng tinh th con (b mt) thm nhp nhau vi mt mng con c

19

con (b mt) thm nhp nhau vi mt mng con c i ch bi mt mng con khc bng khong cch dc theo ng cho bn trong khi lp phng

Hu ht nhng cht bn dn III/V tng trng theo mng tinh th zincblende, m ng nht vi mt mng tinh th kim cng ch c iu mt trong s nhng mng tinh th con t bo lp phng tp trung b mt c nguyn t gallium (Ga) v nhng nguyn t arsenic (As) khc.

Cu trc mng tinh th kim cng (tt)

20

Cc mt phng tinh th v ch s Miller Cc tnh cht tinh th theo nhng mt phng khc

nhau th khc nhau v nhng tnh cht in, nhit, v c c th ph thuc vo hng tinh th.

Cc ch s [Miller] dng nh ngha nhng mt phng trong tinh th.

Th d: Xc nh mt phng tinh th Mt phng giao vi cc trc ta ti a, 3a, v 2a.

21

Mt phng giao vi cc trc ta ti a, 3a, v 2a. Ly nghch o ca cc ta ny ta c 1, 1/3 v 1/2. Ba s nguyn nh nht c cc t s 6, 2 v 3. Nh vy mt phng ny c th c xem nh mt phng (623).

Cc qui c nh ngha ch s Miller: (hkl) : mt mt phng [hkl] : hng tinh th l im trong mng tinh th gn

gc ta nht theo hng mong mun. {hkl} : h cc mt phng tng ng i xng

Cc mt phng tinh th v ch s Miller (tt)

22

Khi c ta m th ghi s dng tng ng v c ng gch trn con s, th d hng tinh th c ta -1,-1,1 th ngi ta ghi l .

Cc mt phng tinh th v ch s Miller (tt)

23

Cc ch s Miller thng gp: (a) cc mt phng tinh th, v (b) cc vector hng

Th d mt s hng tinh th

Cc mt phng tinh th v ch s Miller (tt) Trong cc mng tinh th lp phng, hng [hkl] vung gc vi mt phng (hkl).Th d: h mt phng {100} l:

24

2.3 Cc lin kt ha tr(Valence bonds)

25

(Valence bonds)

Lin kt ng ha tr v lin kt ionTrong cc dng c bn dn c th gp cc lin kt sau: Lin kt ng ha tr (covalent bonding) Lin kt ion (ionic bonding)

26

Trong bn dn nguyn t dng cc lin kt ng ha

tr; cn trong bn dn hn hp th s dng c lin kt ng ha tr v lin kt ion.

Na MgK Ca

Rb SrCs Ba

O FS Cl

Se BrTe I

C NSi P

Ge AsSn Sb

B

Al

Zn GaCd In

Li Be He

Ne

Ar

Kr

Xe

1A 2A

2B

3A 4A 5A 6A 7A

8A

The periodic tableThe periodic table

Cs BaFr Rd

Te I

Po At

Sn SbPb Bi

Cd InHg Ti

Xe

Rn

Groups 3B,4B,5B,6B7B,8B,1B lie in here

A section of the periodic table

Lin kt ion do lc ht tnh in gia cc ion tch in dng v m (gia 1A v 7A).

Qu trnh ny dn n chuyn in t v to thnh cc ion c tch in; ion tch in dng do nguyn t mt in t v ion tch in m do nguyn t c thm in t.

Lin kLin kt ion (t ion (Ionic bondingIonic bonding))

28

Tt c cc hn hp ion l cht rn n tinh th nhit phng.

NaCl v CsCl l cc th d tiu biu cho lin kt ion.

Cc tinh th ion th c im nng chy cao, rn dn v c th ha tan c trong cc cht lng thng thng.

The metallic elements have only up to the valence electronsin their outer shell will lose their electrons and become positiveions, whereas electronegative elements tend to acquireadditional electrons to complete their octed and becomenegative ions, or anions.

Ionic bondingIonic bonding

29

Na Cl

This typical curve has a minimum at equilibriumdistance R0

R > R0 ; the potential increases

gradually, approaching 0 as Rthe force is attractive

V(R)

0 R

Repulsive

Ionic bondingIonic bonding

30

the force is attractive

R < R0; the potential increases

very rapidly, approaching at small radius.

the force is repulsive

R

rR

0 R0

Attractive

Lin kLin kt t ng ng hha a trtr((Covalent bondingCovalent bonding))

Cc cht bn dn nguyn t Si, Ge v kim cng c lin kt bng c ch ny v chng thun ng ha tr.

Lin kt ny l do dng chung cc in t.(mi

31

Lin kt ny l do dng chung cc in t.(mi cp in t to nn lin kt ng ha tr) Cc cht rn c lin kt ng ha tr th c im nng chy cao, rn v khng ha tan trong cc cht lng thng thng. Cc bn dn hn hp s dng c cc lin kt ng ha tr v lin kt ion.

Comparison of Ionic and Covalent BondingComparison of Ionic and Covalent Bonding

32

Th d lin kt ng ha tr vi cc cht c 4 in t ha tr

33

- nhit thp cc in t c rng buc theo mng tinh th t din tng ng.- Khi nhit cao hn th cc dao ng nhit s lm gy cc lin kt ng ha tr.

34

2.4 Cc di nng lng(Energy bands)

35

(Energy bands)

Nhng mc nng lng ca 1 nguyn t c cch ly

hiu nhng tnh cht ca nhng cht bn dn, ta cn phi hiu nhng tnh cht ca nhng nguyn t to thnh chng.

Theo m hnh ca Bohr th nguyn t gm c mt li, m v c bn cha ton b khi lng ca nguyn t. V gn nh khng c khi lng. Hu nh mi khi lng c tp trung trong li c ng knh nh 10-15 m , khi so snh vi ng knh v 10-10 m = 0.1 nm = 1(ngstrom).

36

= 0.1 nm = 1(ngstrom). Li gm c nhng neutron v nhng proton. Li mang in tch

dng. V (v in t) mang in tch m v c nhng in t trn cc qu o trong v. Nhng ton b nguyn t th khng c in tch hay trung ha in.

Nhng in t nh nhng v tinh. Chng quay xung quanh li trn qu o nht nh. Nhng in t c lm n nh trn nhng qu o ca chng do s cn bng ca nhng lc ly tm v Coulomb.

Nguyn t Hydrogen Do s cn bng gia lc ly tm v lc

tnh in, tn ti mt lin h vn tc in t v bn knh ca li. Vn tc ca mi in t lin h vi bn knh qu o vi tm li. V mt in t c th c nhng nng lng khc nhau, n c th c nhng bn knh khc nhau n li ca

37

nhng bn knh khc nhau n li ca nguyn t. Tuy nhin, m hnh c nhng vn sau: Theo in ng hc c in, ht c tch in

trn qu o dn n to thnh mt lng cc t m bc x nng lng. Do mt mt nng lng, ht s b ht nhiu hn vo li, m dn n ng i nh hnh xon c. Cui cng ht s ri vo li ca nguyn t.

gii quyt vn ny, ng Bohr ngh tin sau: cc mc nng lng ca nguyn t v bn knh qu o c lng t ha. Cc mc nng lng c cho php ca nguyn t Hydrogen c cho bi:

Nguyn t Hydrogen (tt)

38

vi EB l nng lng Bohr v n l s lng t nguyn tc(principle quantum number). Nng lng Bohr c cho bi:

vi aB l bn knh Bohr, q l in tch in t (l in tch c bn) v 0 l hng s in mi chn khng. Nhng nng lng in t gia nhng mc nng lng En khng c cho php.

Khi nhng nng lng in t c lng t ha v nhng bn knh ca nhng mc nng lng (energy levels) cng c lng t ha.

Nhng mc nng lng ca mt nguyn t l duy nht. S to thnh hay tch ra ca nhng mc nng lng ny cho php

to thnh nhng di nng lng (enery bands). Nhng nng lng, m gia nhng nng lng c nh

ngha, c gi l nhng di nng lng cm (forbidden energy

Nguyn t Hydrogen (tt)

39

ngha, c gi l nhng di nng lng cm (forbidden energy bands) hay nhng di cm.

Ngi ta thng dng n v ca nng lng l eV (electronvolt). i lng eV l n v nng lng tng ng in t c c khi th ca n tng thm 1V (1eV=1.6 x 10-19AVs=1.6 x 10-19J).

Bn knh Bohr c cho bi:

vi h l hng s Planck v me l khi lng ca in t.

M hnh nguyn t ca Bohr c th kt hp vi l thuyt quang t (photon) ca Einstein. Hiu s nng lng gia 2 mc nng lng n v m (nng lng photon) c cho bi:

En ng vi mc nng lng cao hn. Chuyn tip t mc nng lng cao hn xung thp hn dn

Nguyn t Hydrogen (tt)

40

Chuyn tip t mc nng lng cao hn xung thp hn dn n mt nng lng. Nng lng c gii phng di dng photon, vi f l tn s ca nh sng c pht x. Tn s f v bc sng tng ng ca nh sng c cho bi:

Nhng di nng lng Ta chuyn vic kho st t nguyn t n sang kho st cht rn. Vi mt nguyn t cch ly, cc in t c cc mc nng lng ri rc.

Khi s p cc nguyn t cch ly c gom li vi nhau to thnh cht rn, qu o ca cc in t ngoi cng ph lp nhau v tng tc vi nhau. S tng tc ny bao gm nhng lc ht v y gia cc nguyn t. Nhng lc ht gia cc nguyn t gy ra s dch cc mc nng lng. Thay v to thnh nhng mc n, nh trong trng hp n nguyn t, p mc nng lng c to thnh. Nhng mc nng lng gn nhau. Khi p ln, nhng mc nng lng khc nhau to thnh mt di lin tc. Nhng mc v do nhng di c th m rng ln nhiu eV ty theo khong cch gia cc nguyn t v phn t.

41

Cu trc di nng lng ca bn dn By gi chng ta chuyn t m t tng qut cu trc di

nng lng trong cht rn sang trng hp c th hn ca silicon. Mt nguyn t silicon cch ly c 14 in t. Trong 14 in t, c 10 in t chim nhng mc nng lng su hn. Do , bn knh qu o nh hn lc tch gia nhng phn t trong tinh th. 10 in t b lin kt cht vi cc nguyn t.

42

nguyn t. Bn in t di ha tr cn li c lin kt yu vi li v c

th tham gia vo cc phn ng ha hc. Do , chng ta c th tp trung vo lp v ngoi cng (mc n=3). Mc n=3 gm cc lp v con 3s (n=3 v l=0) v 3p (n=3 v l=1). Lp v con 3s c 2 mc trng thi cho php trn 1 nguyn t v c hai trng thi c lp bi 1 in t ( 0oK). Lp v con 3p c 6 trng thi cho php v 2 trong cc trn thi ny c lp bi nhng in t cn li.

Biu din s ca nguyn t silicon cch ly

43

S to thnh nhng di nng lng trong silicon theo hm khong cch gia cc nguyn t trong mng tinh th.

44

Khe nng lng (bandgap) y ca di dn c gi l EC v nh ca di ha tr

c gi l EV. Hiu s nng lng gia y di dn v nh di ha tr c gi l khe nng lng EG.

Khe nng lng EG = EC EG gia y di dn v nh di ha tr bng b rng di cm. EG l nng lng cn ph v lin kt trong bn dn cho mt in t

45

cn ph v lin kt trong bn dn cho mt in t trong di dn v mt l trng trong di ha tr.

S thiu ht mt in t trong di ha tr c coi l mt l [trng t do]. S thiu ht trong di ha tr c th c lp bng in t ln cn, m dn n s dch chuyn v tr thiu ht, xem nh l di chuyn. L c in tch dng. C hai in t v l gp phn vo to nn dng in.

Nu 1 in t c kch thch vo di dn, n c th di chuyn t do trong tinh th, t in t c th c xem nh mt ht trong khng gian t do. S truyn lan ca in t t do c th c m t bng hm sng, l li gii ca phng trnh Schrdinger. Hm sng cho in t t do c cho bi

Gin nng lng-momentum

46

vi k l vector sng c phng trnh sau:

p l momentum (m-mn) ca in t. Do biu thc ny, nng lng in t c th c cho

trc theo hm ca vector sng. Ta ni v biu din khng gian k. Cc di nng lng lc ny c th c xc nh theo hm ca vector k.

Gin nng lng-momentum (tt)

47

TD v gin nng lng - momentum

48

Gin nng lng-momentum [cgl gin di nng lng] ca(a) bn dn gin tip (Td: Si ) v (b) bn dn trc tip (Td: GaAs)

49

GaAs c gi l bn dn trc tip v n khng cn s thay i momentum chuyn in t t di ha tr sang di dn. Si c gi l bn dn gin tip v n cn s thay i momentum chuyn in t t di ha tr sang di dn.

S dn in trong kim loi, bn dn v cht cch in

50

Schematic energy band representations of conductor, semiconductor, and insulator.

51

52

2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning is a trademark used herein under license.

Schematic of band structures for (a) metals, (b) semiconductors, and (c) dielectrics or insulators. (Temperature is 0 K.)

Ngi ta phn loi vt liu theo: Tnh dn in thng qua in dn sut [S/m hay

S/cm] ca n Ch :

dn in ca bn dn gia cch in v dn in. in dn sut ca bn dn c th thay i do n ph thuc vo: nhit

, cu trc, thun khit, nh sng

Min (di) nng lng th phn chia vt liu s chnh

53

Min (di) nng lng th phn chia vt liu s chnh xc hn cch trn.TD: Mt s bn dn c bn: Si, Ge, (thuc nhm IV) dng

ch to diode, transistor v IC. Mt s bn dn phc hp: GaAs, ZnS (thuc nhm III-V v

II-VI tng ng) dng ch to cc dng c tc cao, cm bin bc x,..

L thuyt min nng lng (hay di nng lng) [Energy band theory]

M hnh nguyn t Bohr. Cc in t ha tr l cc in t lp ngoi cng

ca nguyn t v n tham gia lin kt ha tr vi cc nguyn t ln cn trong mng tinh th.

54

nguyn t ln cn trong mng tinh th. Cc in t trong mt nguyn t nhng mc nng

lng ri rc. Trong mng tinh th cc nguyn t gn nhau to

thnh cc di nng lng, gia nhng di nng lng c in t (di cho php) l nhng di nng lng khng c in t (di cm).

Th d v m hnh di nng lng

55

56

2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning is a trademark used herein under license.

The energy levels broaden into bands as the number of electrons grouped together increases.

Br

o

o

k

s

/

C

o

l

e

,

a

d

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.

The simplified band structure for sodium. The energy levels broaden into bands. The 3s band, which is only half filled with

57

2

0

0

3

B

r

o

o

k

s

/

C

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only half filled with electrons, is responsible for conduction in sodium.

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2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning is a trademark used herein under license.

(a) At absolute zero, all of the electrons in the outer energy level have the lowest possible energy. (b) When the temperature is increased, some electrons are excited into unfilled levels. Note that the Fermi energy is unchanged.

Br

o

o

k

s

/

C

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a

d

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.

The band structure of carbon in the diamond form. The 2s and 2plevels combine to

59

2

0

0

3

B

r

o

o

k

s

/

C

o

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a

d

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levels combine to form two hybrid bands separated by an energy gap, Eg.

60

Phn loi vt liu theo khe nng lng

61

Mt s thut ng thng dng trong l thuyt di nng lng:

Mt s thut ng thng dng trong l thut di nng lng: NV: mt trng thi hiu dng ca di ha tr, y l s l ti a trn 1

n v th tch m ta c th tm thy trong ton b vng ha tr. NC: mt trng thi hiu dng ca di dn, y l s in t ti a trn

1 n v th tch m ta c th tm thy trong ton b di dn. n: nng in t (electron concentration) l s in t trn 1 n v th

62

n: nng in t (electron concentration) l s in t trn 1 n v th tch trong di dn.

p: nng l (hole concentration) l s l trng trn 1 n v th tch trong di ha tr.

Ch : n v p cn c gi l cc nng dt dn (carrier concentration) v chng l nhng ht mang in tch t do v chuyn ng theo in trng to thnh dng in.

2.5 Nng ht dn ni ti(Intrinsic concentrations)

63

(Intrinsic concentrations)

Cc tnh cht vt liu v ht dn Bn dn thun v bn dn c pha tp cht (Intrinsic and extrinsic

Semiconductors) Vt liu c xem l bn dn thun (cn gi l bn dn ni ti hay tinh khit)

nu vt liu cha mt lng tp cht tng i nh. Vt liu c xem l bn dn c pha tp cht (cn gi l bn dn ngoi lai)

nu vt liu cha mt lng tp cht tng i ln.

64

nu vt liu cha mt lng tp cht tng i ln. Bn dn cn bng nhit

Ta gi s ang xt bn dn thun v b qua cc nh hng ca tp cht vi bn dn. Ngoi ra ta gi s bn dn cn bng nhit, ngha l bn dn khng b tc ng bi cc kch thch bn ngoi nh nh sng, p sut hay in trng. Bn dn c gi nhit khng i trn ton b mu th (ngha l khng c gradient nhit trong cht bn dn).

Nng ht dn trong bn dn

65

Bn dn thun cn bng nhit

66

Mt trng thi Ta c th tnh cc mt trng thi bng phng trnh

Schrdinger. Tuy nhin ta s khng bn v vic suy ra hm mt trng thi. SV c th c thm trong ph lc H ca sch Semiconductor Devices, tc gi M.S Sze.

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vi NC l mt trng thi in t v NV l Mt trng thi l Mt trng thi c xc nh bi mt tham s vt liu, l

khi lng hiu dng ca in t (me) hay l (mh). Do , mt trng thi ca in t v l thng khc nhau.

Mc (hay nng lng) Fermi EF v nng ht dn cn bng

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Thng k Fermi-Dirac vi nh hng ca nhit

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Phn b Fermi-Dirac ca in t Fe(E) v l Fh(E).

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Cn bng nhit Cht bn dn cn bng nhit, nu nhit mi v tr ca tinh th l nh nhau, dng in tng cng qua vt liu bng 0, v cht rn khng b chiu sng. Ngoi ra ta cn gi s rng khng c phn ng ha hc tham d. Do nng lng Fermi trn ton vt liu l nh nhau:

EF = EF(x, y, z) = const

Nng lng Fermi trong cht rn

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Phn b Boltzmann

72Ch : Cc phng trnh trn ch p dng cho bn dn iu kin cn bng (kcb).

Nng ht dn ni ti

73

Nng ht dn ni ti ni

74

Biu din n & p qua ni

75

TD cc gi tr NC, NV v ni ca 1 s bn dn thng dng ( 300oK)

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2.6 Cht Donor v cht AcceptorBn dn c pha tp cht

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Bn dn c pha tp chtBn dn loi P v bn dn loi N

Cht cho in t (donor) v cht nhn in t (acceptor)

Khi bn dn b pha tp cht (vi 1 lng ln tp cht) th ngi ta gi n l bn dn ngoi lai hay bn dn c pha tp cht. Trong phn ny ta s xt nh hng ca cc acceptor v donor ln cc tnh cht ca vt liu. Ta s tp trung xt pha tp cht cho silicon.

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(a) Mng tinh th Si loi N vi pha tp cht bng cc nguyn t donor As hay P (arsenic hay phosphorus). (b) Mng tinh th Si loi P vi pha tp cht bng cc nguyn t acceptor B (boron).

Donors When a semiconductor is

doped with impurities Extrinsic semiconductor The impurity energy level are

introduced N-type Si with donor

Arsenic atom with five valence

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Arsenic atom with five valence electron Covalent bonds with its four neighboring Si atoms The fifth electron

Relatively small bonding energy to its host arsenic atom Be ionized to become a conduction electron

The arsenic atom is called a donor Silicon become n-type

Because the addition of the negative charge carrier

Acceptors P-type Si with acceptor

Boron atom with three valence electron An additional electron is

accepted to form four covalent bonds around the boron

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the boron A positive charged

hole is created in the valence band

Boron is an acceptor

Gin di nng lng ca bn dn loi N v bn dn loi P

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Nng lng ion ha ca cc tp cht trong Si v GaAs

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2.7 Nng ht dn trong bn dn loi N v P

83

dn loi N v P

Bn dn loi N

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Quan h gia nng in t n v nng l trong bn dn

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Nng ht dn trong bn dn N

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Nng ht dn trong bn dn P(NA > ND)

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Bn dn c b chnh (Compensated Semiconductor)

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nh hng ca nhit n nng ht dn (Td: Si loi N, xt nn)

At low temperature Thermal energy not sufficient to ionize all

donor impurities Some electron are frozen at the donor

level Electron density less than the donor

concentration As the temperature increased

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As the temperature increased The condition of complete ionization is

reached nn=ND

As the temperature is further increased Electron concentration the same over a wide temperature range Extrinsic region

As the temperature is increased even further The intrinsic carrier concentration becomes comparable to the donor concentration The semiconductor become intrinsic This temperature depend on ND and Eg

Bn dn suy bin v khng suy bin

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