1. Vat Lieu Ban Dan Nano-i (9-2008)

7/31/2019 1. Vat Lieu Ban Dan Nano-i (9-2008)

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Chng 1: Cc cht bn dn khi

1.1 Mu

1.2 Cu trc tinh th v cu trc vng nng lng ca cc cht bn dnkhi1.3 Cc tnh cht quang, in ca cc cht bn dn khi

1.3.1Tnh cht quang1.3.2Tnh cht in

1.4 ng dng ca vt liu bn dn khi1.5 Cng ngh ch to cc cht bn dn khi1.6 Phn loi cc cht bn dn

Cc cht bn dn c cu trc nan(nanostructured semiconductors)

GS. TS. Phan Hng KhiE-mail: [email protected]


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1.1 M u


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Cht bn dn(ting Anh: Semiconductor) l vtliu trung gian giachtdnin v cht cch in.

Cht bn dnhotngnhmtcht cch innhitthp v c

tnh dninnhit phng.

Gi l "bn dn" (ch"bn" theo ngha Hn Vit c ngha l mtna), c ngha l c thdninmtiukin no ,hocmtiukin khc s khng dnin.

Cht bn dn


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Thnh tuca cng ngh vi intbn dn:

Transitor bn dn ( Bell-lab, 1947) Vi mch tch hp (IC- Integrated Circuit) Cng ngh planar (Texas Instruments, 1958)

MOSFET (RCA- USA, 1960) BnhRAM (IBM, 1966)

Laser bn dn (1970) B vi xl CPU tc 4 GHz

Trung bnh slng transitor/chip tnggpi sau 18 thng

Kch thc linh kin ngy cng b, tingnngiihnvt l Nhiu tnh chtvt l mixuthin


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H. 1.1: Ba nh hoa hc Walter Brattain, William Shockley vJohn Bardeen - nhng ngi c trao tng gii Nobelv Ha hc cho pht minh ca h vo nm 1956. nh minhha t www.porticus.org

H. 1.2: Mu transistor u tin.nh Bell Labs, porticus.org

H. 1.3: 3 mu transistor ca nhng nm thuc th k20. nh Bell Labs, porticus.org


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S bng bn dn trong mt chip:

o Chip u tin ca Intel 4004 (nm 1971) c 2.300 transistor. Cc my tnh IBMPC u tin:

o Loi 8086 (nm 1978): 29.000 transistor.

o Loi i486 (nm 1989): 1.200.000 transistor.

o Pentium III (nm 1999): 9.500.000 transistor.

o Pentium IV (nm 2000): 42.000.000 transistor.

o Penryn (cng b ngy 12/11/2007:): 820.000.000 transistor.

Cc loi chip v cng ngh sn xut:

o 1993: Pentium 800 nm

o 1999: Pentium III 250 nm

o 2002: Pentium IV 130 nmo 2003: Centrino 130 nm

o 2005: Pentium D 90 nm

o 2006: Core 2 Duo 65 nm

o 2007: Core 2 Duo th h sau 45 nm (cn gi l Penryn)


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H. 1.4: S tng trng mt transito trn 1 chip v lng bit trn mt cm2theo nm v

nh lut Moor


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H. 1.5: S tng trng s lng transistor trn cc

mch vi in t theo nm

H. 1.6: nh TEM ca transitor MOS


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H. 1.7: Tin s Moore c trong tay bn gc tpch ln u tin ng bi vit v nh lut cang. (hin ang sng Hawaii)

H. 1.8: K s David Clark ti qun Surrey (Anh), gi cc n phm ca tp ch ElectronicsMagazine trong sut 15 nm qua, k cho c v ni n qung chng i. V by gi, h ang n mngtrc mn tin thng hp dn ca Intel.. Ti dnh c bui sng lc tung c ln v khng nhn thy chng trong sut 15 nm. Khi lin h vi Intel, ti vn khng ngh h s tin li ti,Clark k li.


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H.1.9: Gordon Moore gii thiu mt tm wafer (dnglm chip) ti tr s Intel Santa Clara, California(M).

nhlut Moore (mttrong 7kquanca cng ngh my tnh)

Thin nhin c 7k quan thgiiv hin nhin, chng ta cngmunbitthgiicng ngh cnhngk quan no?nhlutMoore l mttrong7tuyttc trong thgii@ do tp ch CNTT

PCMag bnh chn.

nh lut Moore l mt bc ngot ln trong ngnh cng ngh in t. nh lut c xydngbi Gordon Moore - mt trong nhng sng lp vin catponsnxut chip my tnhniting Intel. nhlut ni rng,tccab vi xl, hay cn gi l slng transistor trnminv inch vung stng ln gpi. iu ny cho n nay vn lun lun ng.

nhlut Moore cng l mtnglc kch thch cho ngnh cng nghipintduy tr sphttrinmnhm trong hng thpk qua.


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Diy l trao ica Gordon Moore vimts hng tin cng nghquct:

nhlutMoore btnguntu?

o Nm 1965 tp ch Electronics tchcknim 35 nm. Vo thiim,mch vi intlnnht c khong 30 linh kin bn trong. Ti lnngclilchsth thy con sbtut4,8,16...v cnhvytnggpiminm. Lc y ti cng khng nghiu ny thcsl chnh xc v bn thn ti chmunc lm r rngmithstrnn ngy cng tinh vi vrtinhn. Cui cng, ha ra iu m ti vitli chnh xc hncmcbn thn ti c thtin. Mtngibnca ti l gio sCarver Mead thuc hng Cal Tech t lun tn chopht hin ny l nhlut Moore v cthngi ta gi n nhvy. Sut 20 nm ti thm ch

khng thttin sdng ci tn v mi v sau mithychpnhnc. Nm 1975, tithay imtsni dung trong nhlut v mithcginguyn cho nhin nay. Vothiim ny, ti vitmt bi bo vtng lai ca cc linh kin bn dn trong vng 10 nmtip theo. Ti mun trnh by tngvvic cc mch tch hp (IC) s l cha kha to ranhngthitbrtinhn. V th, ti t ra php ngoi suy v sau trthnh nhlut nhnis transistor l xpx 24 thng.

ng cmnhnnhthno v nghaca qu trnh nhn itransistor ny cngnhnhngchim n cho php to ra?

o Ticli bi bo mnh vit v nhnthynhngvnnhcn trong lin quan nmy tnh gia nh. Ti rt ngc nhin khi thy chnh mnh tm ra tnh quy lut nh vy.Thnh thc m ni ti khng bit mnh dbo mtiu mang tnh l thuyt vo nm.


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Mithangingiihn v tc nhn ibng bn dnchmdn.Nhngvtliu

mic thcho php ngnh cng nghip my tnh vtqua ngnggiihn?

o Vibtcvtliu no lm tnguyn tth u c mtgiihncbn m bn khng thlm nhhn. Ti thay i chu k nhn it1 nm ln 2 nm v dndn c ths l 3-4 nm.

bao nhiu lnngita dbo sktthc canhlutMoore v bao nhiu ln ng thc

stin rngiusxy ra?

o Trong 10 nm qua, ti crtnhiu bi bo vitvschmdtcatin trnh nhn itransistor trn chip. C thiim ti nghrng 1 micromet (1 phntriu met) s l giihn cui cng nhng ri mc nhanh chng b vt qua. Sau , ti li tin rng 1/4micromet s l duchmhtnhngmithvntipdin. Giy chng ta angmcdi 1/10 micromet v angtinnmc 1/65. Qu trnh nhn i khng th ko di mimi nhngschmhtschn trong t nht 10-20 nmna v cng l khongthigian m chng ta c thdbo.


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Thg c ththay thsilicon?

o Cth l in ton lngthay cng ngh nano Thcsm ni th ti vnrt hoi

nghi vvicnhngth c khnng thay th hon ton silicon kthuts. Bn c thddng to ra mt transistor ccnhbngnhng cng ngh ny vitnsutrt cao nhngkh c thktni hng t th livi nhau. chnh l vn. Mivic khng nthunch l lm ra mt transistor thtnh.Ti coi cng ngh pht trin xoay quanh mch tch hp IC l phng php cbn xydng cc vi kin trc phc tp. Thay v b thay th, n thc sang xm nhp vo rtnhiu lnhvc khc. Chnghnnhchip gene. Silicon l mt cng nghrtmnh m scn csdngrng ri. Ti chathybtcthg c timnng thay th n.Tuy nhin, iu khng c ngha l nhiu pht minh mis khng thc tch hpli,chnghnvic tch hp cc ng nano carbon vo nhiulp kim loihoctngtnhvy.Du sao, ti vnchathy l mtgii php thay th bng bn dnsilicon.

ng c dbo nhlutg micho 40 nmti?

o Thi, ti xin chu. Mt vng nguytqu cho nh lut Moore ny ri. Tt nhin,cng c th c mtnhlut Moore phin bn 2 nhngngi ra n s khng phi l ti.


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H.1.11: Apple iPhone: my nghe nhc, in thoi ding

H. 1.10: Nintendo Wii l game console thu htnhiu s quan tm nht trong th gii game th.

H.1.12: Lade gip cc my nghe nhc s v a quang hc hin th hnh nh vi nt cao

Cc k quan ca cng ngh my tnh


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15H.1.15: My tnh cm ng b mt ca Microsoft

H. 1.14: Cng ngh mn hnh phngH.1.13: Apple Inc. nh iPod, iTunes, Macsintoshv mi y nht l tn binh iPhone

Cc k quan ca cng ngh my tnh
http://images.google.com.vn/imgres?imgurl=http://www.thetechherald.com/media/images/200811/AppleLogoOld_Alistair_Israel_1.jpg&imgrefurl=http://www.thetechherald.com/article.php/200811/411/ZapMedia-looks-to-take-patent-bite-out-of-Apple&usg=__Of_WzzAKzC3pGSmfBXxmK5cSIUE=&h=400&w=600&sz=14&hl=en&start=23&um=1&tbnid=Q81PAipCXjF5vM:&tbnh=90&tbnw=135&prev=/images%3Fq%3DApple%2BInc.%26ndsp%3D20%26hl%3Den%26rlz%3D1R2SKPB_enVN334%26sa%3DN%26start%3D20%26um%3D1


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1.2. Cu trc tinh th v cu trc

vng nng lng ca cc cht bn dnkhi


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Cu trc tinh th:

Hu ht cc cht bn dn c cu trc tinh th lp phng tp mt (fcc). Chng c 2 nguyn t trongmt c s. To ca hai nguyn t c s l: (000) v ( a/4, a/4, a/4). Nu hai nguyn t cng loi:mng tinh th kim cng (DI) v d: Si, Ge (H. 1.4); nu hai nguyn t khc loi: mng tinh thZinc-Blend (ZB), tn c t theo tn ca tinh th ZnS. GaAs, GaP thuc loI ny (H. 1.5)

Nhiu vt liu bn dn c th c hn mt loi cu trc tinh th. Cc bn dn hp cht trong cGaAs, GaN, ZnS c th c cu trc lp phng hoc cu trc lc gic (hexogonal). SiC c th c cutrc lp phng, hoc mt trong nhiu cu trc lc gic khc. Tinh th lp phng c c trngbi mt thng s mng duy nht, hng s mng a, trong khi tinh th lc gic c c trng bingoi hng s mng a cn bi khong cch gia hai mt lc gic c

H. 1.16: Mng tinh th kim cng(Si, Ge).Mng gm hai mng tinh th Fcc lng vonhau. Mt dch dc theo trc ng cho sovi mng kia mt khong cch l (a/4,a/4,a/4).

H. 1.17: Mng tinh th ZincBlend (GaAs, GaP)


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Tnh cht dn in ca cc vt liu rn c gii thch nh l thuyt vng nnglng.

Nh ta bit, in t tn ti trong nguyn t trn nhng mc nng lng gin on(cc trng thi dng).

Nhng trong cht rn, khi m cc nguyn t kt hp li vi nhau thnh cc khi,th cc mc nng lng ny b ph ln nhau, v tr thnh cc vng nng lng v

s c ba vng chnh.

Cu trc vng nng lng:

Xc nhphnnglngint hay s quan hgiannglng E v vectorsng K E= E(k), thng quagiiphng trnh Schrodinger tmbiuthc:

Trong : H - Haminltonian ca tinh th,

, E - Hm sng v nnglngca tinh th.

EH (1.1)


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y e v h l hai ch s ch in t v l trng, m- khi lng hiu dng, r vector

v tr, reh =re - rh, o v l hng s in mi chn khng v cht bn dn.S dnggn ng khi lng hiu dng ta gii phng trnh trn cho bn dn khi v tmc:

(1.2)

(1.3)

H. 1.21:
http://vi.wikipedia.org/wiki/T%E1%BA%ADp_tin:Semiconductor_band_structure_(lots_of_bands)_Vi.pnghttp://vi.wikipedia.org/wiki/T%E1%BA%ADp_tin:Semiconductor_band_structure_(lots_of_bands)_Vi.png


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Bn dnKim loi

Mc li

Mc li

Vng ho tr

Vng dn

Eg: Vng cm

i lc in tCng thot e

Nng lng chn khng

Cu trc vng nng lng ca kim loi v bn dn

H. 1.22: Gin cc vng nng lng ca kim loi v bn dn


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Vng ha tr (Valence band): L vng c nng lng thp nht theo thangnnglng, l vng m intb lin ktmnhvi nguyn t v khng linhng.

Vng dn (Conduction band): Vng c mcnnglng cao nht, l vng mints linh ng(nh cc intt do) v intvng ny s l intdn, c ngha l chts c khnngdnin khi c inttnti trn vngdn. Tnh dnintng khi mtint trn vng dntng.

Vng cm (Forbidden band): L vng nm gia vng ha tr v vng dn,khng c mcnnglng no do int khng thtnti trn vng cm.Nu bn dn pha tp, c thxuthin cc mcnng lng trong vng cm(mc pha tp). Khong cch giay vng dn v nh vng ha trgi l rng vng cm, hay nnglng vng cm (Band Gap). Ty theo rng vngcmln hay nh m cht c th l dninhoc khng dnin.

Nhvy, tnh dninca cc chtrn v tnh chtcacht bn dn c th lgiimt cch nginnhl thuyt vng nnglngnh sau:


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Kim loi c vng dn v vng ha trph ln nhau (khng c vng cm) do lun lun c int trn vng dn v th m kim loi lun lun dnin.

Cc cht bn dn c vng cm c mtrng xc nh. khng tuyti (0oK), mc Fermi nmgia vng cm, c ngha l ttc cc inttntivngha tr, do cht bn dn khng dnin. Khi tngdnnhit, cc intsnhn c nng lng nhit (kB.T vi kB l hng s Boltzmann) nhng nnglng ny chaintvt qua vng cm nn intvnvng ha tr.Khi tngnhitnmc cao, s c mtsintnhncnnglnglnhnnnglng vng cm v n snhy ln vng dn v chtrntrthnh dn

in. Khi nhit cng tng ln, mtint trn vng dns cng tng ln,do , tnh dnincacht bn dn tngdn theo nhit (hay in trsutgimdn theo nhit). Mt cch gnng, c thvitsphthuccaintrcht bn dn vo nhitnh sau:

vi:R0 l hngs,Eg l rng vng cm. Ngoi ra, tnh dncacht bn dnc th thay inhcc kch thch nnglng khc, vdnh nh sng. Khi chiusng, cc intshp thu nnglngt photon, v c thnhy ln vng dnnunnglngln. y chnh l nguyn nhn dnns thay iv tnh chtca

cht bn dndi tc dngca nh sng (quang-bn dn).

(1.4)


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H. 1.23: Cu trc vng nng lng ca bn dn Si (vng cm xin) v GaAs khi (Vng cmthng)

in tdn

Ltrng L

trng

in tdn


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B. 1.1: Cu trc tinh th v cu trc vng nng lng ca cc cht bn dn kh

Vt liu Cu trc tinhth

rng vngcm (eV)

Hng s inmi

Hng smng (Ao)

Khi lngring (g.cm-3)

C

Si

SiC

Ge

AlN

AlPAlAs

GaN

GaP

GaAs

GaSb

InN

DI

DI

ZB

DI

W

ZBZB

W

ZB

ZB

ZB

W

5,50 I

1,1242 I

2,416 I

0,664 I

6,2 D

2,45 I2,153 I

3,44 D

2,272 I

1,424 D

0,75 D

1,89 D

5,570

11,9

9,72

16,2

= 9,14

9,810,06

|| = 10,4

= 9,5

11,11

13,18

15,69

-

3,5668

5,431

4,3596

5,658

a = 3,111

c = 4,981

5,46365,660

a = 3,5446

c = 5,158

5,4505

5,653

6,0959

a = 3,5446

c = 8,7034

3,5153

2,3290

3,166

5,323

3,255

2,4013,760

6,095

4,138

5,318

5,6137

6,81

DI: Diamond; R: Rocksalt. W: Wurtzite; ZB: Zinc-Blend; *Gap Tnh ti im L; D: vng cmthng (Direct); I: vng cm Xing (Indirect); ||: song song trc C; : Vung gc trc C.


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Vt liu Cu trc tinhth

rng vngcm (eV)

Hng s inmi

Hng smng (Ao)

Khi lngring (g.cm-3)

InP

InAs

InSb

ZnS

ZnS

ZnSe

ZnTe

CdS

CdS

CdSe

CdTe

PbS

PbSe

PbTe

ZB

ZB

ZB

ZB

W

ZB

ZB

W

ZB

W

ZB

R

R

R

1,344 D

0,354 D

0,230 D

3,68 D

3,9107 D

2,822 D

2,394 D

2,501 D

2,50 D

1,751 D

1,475 D

0,41 D*

0,278 D*

0,310 D*

12,56

15, 15

16,8

8,9

= 9,6

9,1

8,7

= 9,38

-

|| = 10,16

= 9,29

10,2

169

210

414

5,8687

6,058

6,479

5,4102

a = 3,8226

c = 6,6205

5,668

6,104

a = 4,1362

c = 6,714

5,818

a = 4,2999

c = 7,0109

6,482

5,936

6,117

6,462

4,81

5,667

5,775

4,079

4,084

5,266

5,636

4,82

-

5,81

5,87

7,597

8,26

8,219

D: Diamond; R: Rocksalt. W: Wurtzite; ZB: Zinc-Blend; *Gap Tnh ti im L; D: vng cm

thng (Direct); I: vng cm Xing (Indirect); ||: song song trc C; : Vung gc trc C.


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Bn dnthun (Pure semiconductor or intrinsic semiconductor)

Huht cc cht bn dnu c cc nguyn tspxp theo cuto tinh th.Hai cht bn dnc dng nhiunht trong kthutchto linh kinint

l Silicium v Germanium. Mi nguyn tca hai cht ny u c 4 intngoi cng kthpvi 4 intca 4 nguyn tkcnto thnh 4 lin ktha tr. V vy tinh th Ge v Si nhitthp l cc cht cch in

H. 1.24:


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Nu ta tngnhit tinh th,nhitnngs lm tngnnglngmtsintv lm gy mtsni ha tr. Cc intcc nib gy ri xa nhau v cth di chuynd dng trong mng tinh thdi tc dngcaintrng. Ti

cc ni ha trb gy ta c cc ltrng (hole). Vphngdinnnglng, tac th ni rngnhitnng lm tngnnglng cc int trong di ha tr.

H. 1.25:


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Khi nng lng ny ln hn nng lng cadi cm (0,7eV ivi Ge v1,12eV ivi Si), in t c thvtdicm vo didnin v cha linhngltrng(trng thi nnglngtrng) trong di ha tr). Ta nhnthys

int trong didninbngsltrng trong di ha tr.

Nu ta gi n l mtint c nnglng trong didnin v p l mtltrng c nnglng trong di ha tr. Ta c:n=p=ni

Ngi ta chng minh crng:

ni2 = A0.T

3. exp(-EG/KT)

Trong : A0 : S Avogadro=6,203.1023T : Nhit tuyt i ( Kelvin)K : Hng s Bolzman=8,62.10-5 eV/0KEG : Chiu cao ca di cm.

(1.5)


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Ta gi cht bn dn c tnh cht n = p l cht bn dn ni bm hay cht bn dn thun.Thng thng ngi ta gp nhiu kh khn ch to cht bn dn loi ny.

H. 1.26


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Bn dn thun (Intrinsic Semiconductor):

Mt trng thi hiu dng

2 1/2(m*dos)3/2(EEc)1/2N(E) =

2 h3

Nng ht ti thun

ni = pi = 2(kBT/2 h2)3/2 (me*mh*)3/2 exp(-Eg/2kBT)

EFi = (Ec + Ev)/2 + 3/4kBTln(mh*/me

*)

Vt liu Mt trng thi

hiu dng vng dn(Nc)

Mt trng thi

hiu dng vng hotr (Nv)

Nng ht ti

thun (ni = pi)

Si (300K)

Ge (300K)

GaAs (300K)

2,78x1019 cm-3

1,04x1019 cm-3

4,45x1017 cm-3

9,84x1018cm-3

6,00x1018 cm-3

7,72x1019 cm-3

1,50x1010 cm-3

2,33x1013 cm-3

1,84x10196cm-3

(1.6)

(1.7)

(1.8)


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Cht bn dn pha tp

Cht bn dnloi p (hay dng nghatingVit l bn dndng) c tpcht lcc nguyn tthuc nhm III, dninchyubng cc ltrng(vittt chochting Anhpositive', ngha l dng).

Cht bn dnloi n (bn dn m - Negative) c tpcht l cc nguyn t thuc

nhm V, cc nguyn t ny dng 4 electron to lin kt v mt electron lpngoi lin ktlnglovi nhn, y chnh l cc electron dn chnh

C thgii thch mt cch nginv bn dn pha tpnhvo l thuyt vngnnglngnh sau: Khi pha tp,sxuthin cc mc pha tpnm trong vngcm, chnh cc mc ny khin cho intd dng chuyn ln vng dnhocltrngd dng di chuynxung vng ha trto nn tnh dncavtliu.V th,chcn pha tpvi hm lngrtnhcng lm thay iln tnh chtdnincacht bn dn.


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Cht bn dnloi N: (N - type semiconductor)

Gis ta pha vo Si thunnhng nguyn tthuc nhm V cabng phn loitun

hon nh As (Arsenic), Photpho (p), Antimony (Sb). Bn knh nguyn tca As gnbng bn knh nguyn tca Si nn c th thay thmt nguyn t Si trong mngtinh th. Bnin tca As kthpvi 4 in tca Si ln cn to thnh 4 niha tr, Cn dlimtintca As. nhitthp,ttc cc intca ccni ha tr u c nng lng trong di ha tr, tr nhng in t tha ca Askhng toni ha tr c nng lng ED nm trong dicm v cch dydninmtkhangnnglngnhchng 0,05eV.

H. 1.27


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Gis ta tngnhitca tinh th,mtsni ha trb gy, ta c nhngltrngtrong di ha tr v nhngint trong didningingnh trong trnghpca cc cht bn dnthun. Ngoi ra, cc intca As c nnglng ED cngnhnnhitnngtr thnh nhngint c nnglng trong didnin. Vth ta c th coi nh hu ht cc nguyn t As u b Ion ha (v khang nnglnggia ED v didninrtnh),ngha l ttc cc int lc u c nnglng ED uctngnnglngtr thnh intt do.0,05eV.

Nu ta gi NDl mt nhng nguyn t As pha vo(cn gi l nhng nguyn t cho donor atom).Ta c:

n = p + ND

Vi n - mt in t trong di dn in; p - mt ltrng trong di ha tr.

Ngi ta cng chng minh c: n.p = ni2 (n < p)

ni: mt in t hoc l trng trong cht bn dnthun trc khi pha.

Cht bn dn nh trn c s in t trong di dn innhiu hn s l trng trong di ha tr gi l cht bndn loi N.

(1.9)

H. 1.28


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Cht bn dnloi P: (P - type semiconductor)

Thay v pha vo Si thunmt nguyn tthuc nhm V, ta pha vo nhng nguyn tthuc nhm III nh Indium (In), Galium (Ga), nhm (Al),... Bn knh nguyn t Ingn bng bn knh nguyn t Si nn n c th thay th mt nguyn t Si trong

mng tinh th. Ba intca nguyn t In kthpvi ba intca ba nguyn tSi kcnto thnh 3 ni ha tr, cn mtintca Si c nng lng trong diha tr khng tomtnivi Indium. Gia In v Si ny ta c mt trang thi nnglngtrng c nnglng EA nm trong dicm v cch di ha trmtkhongnnglngnhchng 0,08eV.

H. 1.29


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Thay v pha vo Si thun mt nguyn t thuc nhm V, ta pha vo nhng nguyn tthuc nhm III nh Indium (In), Galium (Ga), nhm (Al),... Bn knh nguyn t In gnbng bn knh nguyn t Si nn n c th thay thmt nguyn t Si trong mng tinh th.Ba intca nguyn t In kthpvi ba intca ba nguyn t Si kcnto thnh3 ni ha tr, cn mtintca Si c nnglng trong di ha tr khng tomtni

vi Indium. Gia In v Si ny ta c mt trang thi nnglngtrng c nng lng EAnm trong dicm v cch di ha trmtkhongnnglngnhchng 0,08eV.

H. 1.30


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nhitthp (T=00K), ttc cc intu c nnglng trong di ha tr. Nu tatngnhitca tinh ths c mtsin t trong di ha trnhnnng lng vvtdicm vo didnin,ngthicng c nhngintvtdicm ln chimchnhngltrng c nnglng EA.

H. 1.31


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Nu ta gi NA l mtnhng nguyn t In pha vo (cn cgi l nguyn tnhn), ta cng c:

p = n + NA

p: mtltrng trong di ha tr.n: mtint trong didnin.

Ngi ta cngchng minh c:

n.p = ni2 (p>n)

ni l mtinthocltrng trong cht bn dnthuntrc khi pha.Cht bn dnnh trn c s l trng trong di ha trnhiuhnsin t trongdidnincgi l cht bn dnloi P.

Nhvy, trong cht bn dnloi p, httiinas l ltrng v httiinthius l int.

(1.10)

(1.11)


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Cht bn dnhnhp:

Ta cng c th pha vo Si thunnhng nguyn t cho v nhng nguyn tnhnc cht bn dnhnhp. Hnh sau l snnglngcacht bn dnhnhp.

Trong trnghpcht bn dnhnhp, ta c:

n+NA = p+ND

n.p = ni2

Nu ND > NA => n>p, ta c cht bn dnhnhploi N.Nu ND < NA => n


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H. 1.33: Cc mc tp cht trong bn dn Si v GaAs


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Vng thun

Vng ngoi lai

Vng lnh

Mt in t (cm-3)

Nhit (K)

H. 1.34: S thay i mt in t theo nhit ca bn dn Si c nng tp cht cho (Donor)1015 cm-3

H. 1.35: Mc fermi ca Si v GaAs c nng tp 1015 cm-3ph thuc vo nhit


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H. 1.36: S ph thuc in tr sut cu Si v GaAs vo nng pha tp nhit phng

in tr sut

nng pha tp (1015 cm-3


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1.3. Cc tnh cht quang,in ca cc cht bn dn

khi


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Bc sng (m)

Nng lng Photon (eV)

0.01 0.1 0.2 0.39 1 1.5 6 10 40 100 10000.3 0.77

Rt xa Xa Gn Trung bnh Xa Rt xa

Tm Xanh L cy Vng Cam

0.39 0.45 0.492 0.577 0.597 0.622 0.77

100 10 1 0.1 0.01 0.001

c hc 1.24

= = = m

h h (eV)

T ngoi Nhn thy Hng ngoi

1.3.1.Cc tnh cht quang

(1.14)


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E2

E1

E2

E2

E2

E1

h 12

h 12

h21

h 12h 21

(ng pha)

a) Hp th

c) Pht x cng bc

b)Pht x ngu nhin

Mt ht ti iu kin cn bng nhit

H s pht x cwngx bc + H s pht x ngu nhin= H s hp th

n2/n1 = exp-(E2-E1)/kT = exp- h 12/kT

B21n2 h 12 + A21n2 = B12n1 h 12

(1.15)

(1.16)


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Tc pht x cng bc B2 = h 12 Tc pht x ngu nhin A21

pht x cng bc vt hn hn pht x ngu nhin, mt nng lngphoton h 12 phi ln. c mt ny, ngi ta dng bung cnghng quang hc (optical resonator cavity) tng trng photon. Ta c:

Tc pht x cng bc B21 n2 = x

Tc hp th B12 n1

pht x cng bc cc photon tri hn hp th photon, chng ta phi cmt in t mc nng lng cao nhiu hn so vi mt in t mc nng lng thp hn. Trng thi ny gi l trng thi o mt (population inverse).

(1.17)

(1.18)


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Ega) b) c)

Et

Ev

Ec

h

H. 1.37: Hp th quang trong cc cht bn dn a)h = Eg, b) h > Eg, v c) h


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d (x)

(x + x) - (x) = x = - (x) x; where = f ( ).

dx

d (x) x = - (x); (x) = (0)exp( x);

dx

(x) = 0exp( x); y (x) = 0 at x = 0 and (W) = (0)exp( W);

(x) (x + x)0

x

W0

0exp( x);

0 x WH. 1.38: Hp th quang a) Bn dn khi chiu sng, b) S tt dn ca chm

phton theo hm Exp.

a) b)

(1.18)

(1.19)

(1.20)

0,711,52361

Nng lng


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490,2 0,6 1 1,4 1,8

,,

10

102

103

104

105

106

GaP

GaAs

InP

Ga0,3In0,7As0,64P0,36

InGaAs

SiGe

(cm-1)

H. 1.39: H s hp th camt s cht bn dn

photon (eV)

Bc sng photon ( m)


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1.3.2.Tnh cht in

Di tc dng ca in trng, cc in t v trng l di chuyn vi vn tc trungbnh

Vn = nnE v vp = p pE

Sintv ltrng di chuyn thay i theo mithiim, v timithiim cmtsintv ltrngc sinh ra di tc dngcanhitnng. Sintsinh

ra trong minvthi gian gi l n v trong khi di tc sinh to g. Nhngintny c i sng trung bnh chuyn in t c th gp mt l trng c cng nnglng v ti hpviltrng ny. Nugi n l mtint, trong mtnvthigian sintb n. Ngoi ra, trong cht bn dn, mti v sti hp l n/sphnbcamtintv ltrng c th khng u, do c skhuch tn cainttvng c nhiuintsang vng c t int.

Xt mtmu bn dn khng u c mtintc phn bnhhnh v. Timtim M trn titdin A, sinti ngang qua titdin ny (do skhuch tn)tlvi dn/dx, vidin tch caintv vititdin A.

(1.22)


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1.4 ng dng ca vt liu bn dn khi


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Phm cht linh kin mong mun Cu trc vng nng lng cn c

Linh kin in t phtcng sut cao

Linh kin in ttn s cao

Linh kin pht sng

Lade thng tin ng di(1,55 m, 1,3 m)

ng dng hin th

, xanh l cy, xanh bin

Pht sng ngn cho cc b nhquang v my in

Nhn m/ghi nh nhit

Vng cm rng(GaN, SiC,C)

Khi lng hiu dng nh, phncch cc valley ln (InAs, InGaAs)

Vt liu c vng cm thng(AIIIBV)

rng vng cm khong 0,8 eV(InGaAsP)

rng vng cm t 1,6 3,6 eV

(AlGaAs, InGaN)

Vng cm rng(GaN, AlN)

Vt liu vng cm hp(InSb, HgCdTe)


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1.5. Cng ngh ch to cc cht bn dn k


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Cc khu cng ngh c bn ch to vt liu bn dn

vt liu ban u

Bn dn a tinh th

Bn dn n tinh th

Phin

Si/SiO2 GaAs/Ga, As

Chng ct v lng ng Tng hp

Nui n tinh th Nui n tinh th

Mi, ct, nh bng Mi, ct, nh bng


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1.5.1 Cng ngh ch to cc cht bn dn khi Si

a) Vt liu ban u:

CtSiO2c t vo l nung vi cc cacbon di dng than, cok.., xy raphn ng:

SiC (rn) + SiO2(rn) Si (rn) + SiO (hi) + CO (hi)

Si to ra c cht lng luyn kim c sch khong 98%.Bc tip theo Si c nghin nh v x l trong HCl to thnhtrichlorosilane (SiHCl)3:

Si (rn) + 3HCl (hi) (300oC) SiHCl3 + H2(hi)

nhit phng (SiHCl)3 dng lng (nhit si 32oC). Bng cch chng ctc th loi mt s tp cht. Sau khi chng ct lm sch, (SiHCl)3 cho phn ngtrong kh H2 to thnh Si a tinh th c sch in t (EGS)

(SiHCl)3 (hi)+ H2 Si (rn) + 3HCl (hi)


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c) Phng php nng chy vng


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c) Phng php nng chy vng

Thanh atinh Si

Cun tcao tn

n tinh

th Si

Mm Si

G

Vng

nng

chy

H. 1.41: M t nguyn l nui n tinh th bng Phng php nng chy vng


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H. 1.42: Phin Si c ct, mi, nh bng t thi n tinh th

1.5.2 Cng ngh ch to cc cht bn dn khi GaAs


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a) Vt liu ban u:

Ga, As: sch ho hc

Gin pha h Ga - As

200

400

600

800

1000

1200

1400

(T1, x) T1

810oC

Cl C m

29,5

Pha lng Pha lng

Ga + Pha lng GaAs + As

GaAs + Ga

GaAs + Pha lng

Tb s

x

% nguyn t As

To(C)

0 10 20 30 30 50 60 70 80 90 100

H. 1.43:

b) Nui n tinh thGaAs:


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Mm tinh th GaAs nng chy

Vng 2 Vng 1

As

600

800

1000

1200

12421260 oC

610620 oC

To(C)

Phng php Bridgman

Phng php Czochralsski (tng t nh nui tinh th Si)

H. 1.44: M t nguyn l nui n tinh GaAs th bng phng phpBridgman


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1.6. Phn loi cc cht bn dn

Group IV (Elemental) Crystalline


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Group IV (Elemental) Crystalline

Materials (Periodic Table, Column IV)

C (carbon)Diamond Structure: Kim cng(diamond!!),bn dn (semiconductor)

Graphite: kim loi (metal), dng thng dng nht (most common form)Fullerenes(buckminsterfullerene):bucky balls, nanotubes, .

Clathrates(new form ?):bn dn (semiconductor), hp cht (compounds),recent research

Si (silicon)

Diamond Structure:bn dn (semiconductor), dng thng dng nht(common form)

Clathrates(new form):bn dn (semiconductor), cc hp cht(compounds), nghin cu mi (recent research)

Group IV Materials


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Group IV Materials

Ge (germanium)Diamond Structure

:semiconductor, common form

Clathrates(new form)semiconductor, compounds, current research

Sn (tin)Diamond Structure (gray tin or -Sn): semimetal

Body Centered Tetragonal Structure (white tin or -Sn): metal,common form

Clathrates(new form): semiconductor, compounds, current research

Pb (lead)Face Centered Cubic Structure:metal

Group IV Materials


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(Diamond Structure Band Gaps)

Khe nng lng gim rng vng cm (Decreasing bandgap)Eg -Khong cch gia cc nguyn t t ng (increasing interatomic distance)

C 6 eV

Si 1.1 eV

Ge 0.7 eV

Sn Bn kim loi (semimetal) 0 eV

Pb Kim loi, khng phi cu trc kim cng (metal, not

diamond structure!)


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Cc cht bn dn n cht(Elemental Semiconductors)

Mainly, Column IV elements

C (diamond), Si, Ge, Sn (gray tin or -Sn)

Tetrahedrally bonded in diamond crystal structure.

Each atom has 4 nearest-neighbors.Bonding: sp3 covalent bonds.

Also! Some Column V & Column VI elements are

semiconductors! P, 3-fold coordinated lattice

S, Se, Te 5-fold coordinated lattices


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II VI Compounds


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II-VI Compounds(Periodic Table Columns II & VI)

Column II Column VIZn O

Cd S

Hg Se

Mn sometimes Tenot used Po

ZnO, ZnS, ZnSe, ZnTe; CdS, CdSe, CdTe

HgS, HgSe, HgTe, some compounds with Mn.

II VI C d


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II-VI Compounds

Applications: IR detectors, LEDs, switches

ZnO, ZnS, ZnSe, ZnTe; CdS, CdSe, CdTeHgS, HgSe, HgTe (semimetals); compounds with Mn

Bandgap decreases & interatomic distance increases as we

go down the periodic table

Large bandgaps! Except for Hg compounds, which aresemimetals with zero gaps.

Tetrahedral coordination! Some zincblende & some

wurtzite crystal structures.

Bonding: Charge separation due to valence difference islarge.

More ionic than covalent!

IV-IV Compounds


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p(Periodic Table Column IV)

Column IV

CSi

Ge

Sn

SiC

Other compounds: GeC, SnC, SiGe, SiSn, GeSn cannot be

made or cannot be made without species segregation or are

not semiconductors.

SiC: zincblende (semiconductor), & hexagonal close

packed (large gap insulator).

Also MANY other crystal structures!

IV VI Compounds


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IV-VI Compounds(Periodic Table Columns IV & VI)

Column IV Column VI

C O

Si S

Ge Se

Sn Te

Pb

PbS, PbTe, PbSe, SnS

Others: SnTe, GeSe, cant be made, cant be madewithout segregation, arent binary compounds, or arentsemiconductors.


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IV-VI Compounds

Applications: IR detectors, switches

PbS, PbTe have zincblende crystal structure

Others: 6-fold coordination

~ 100% ionic bonding

Small bandgaps (IR detectors)

I VII Compounds


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I-VII Compounds(Periodic Table Columns IV & VI)

Mostly insulators: NaCl, CsCl,

No tetrahedral coordination! 6 or 8 fold coordination.

~ 100% ionic bonding

NaCl and CsCl crystal structures

Large bandgaps


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Hp cht oxide (Oxide Compounds)

a s l cht in mi c rng vng cm ln(Most aregood insulatorswith large bandgaps)

C t cht bn dn oxide: CuO, Cu2O, ZnO

Cha c hiu tt(Not well understood)C rt t ng dng(Very few applications) Except for ZnO (ultrasonic transducer)

nhit thp mt s oxide tr thnh siu dn La2CuO4(Tc~ 135K)

Mt s cht bn dn khc


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Mt s cht bn dn khc(Some Other Semiconductor Materials)

Alloy mixturesof elemental materials (binary alloys):SixGe1-x ,... (0 x 1)

Alloy mixturesof binary compounds (ternary alloys):

Ga1-xAlxAs, GaAs1-xPx, (0 x 1)

Alloy mixturesof binary compounds with mixtures onboth sublattices (quaternary alloys):

Ga1-xAlxAs1-yPy, .., (0 x 1, 0 y 1)

Vary x & y varies bandgap & other properties.

BANDGAP ENGINEERING!

Exotic Semiconductors


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Exotic Semiconductors Layered compounds: PbI2, MoS2, PbCl2,

Covalent bonding within layersweak Van Der Waals bonding between layers

Effectively 2 dimensional solids

Electronic & vibrational properties have ~ 2 dimensional

character.

Organic semiconductors

Polyacetyline: (CH2)n

Great promise for future applications(Has been said for 25 years!)

Not well understood

Other Semiconductors


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Other Semiconductors

Bn dn t(Magnetic semiconductors)

Cc hp cht c cha Mn & / or Eu v cc ion t khc(& other magnetic ions)

Va c tnh cht bn dn va c tnh cht t (Bothsemiconducting & magnetic)

EuS, CdxMn1-xTe, Cc b bin iu quang hc (Optical modulators)

Cc cht bn dn khc (Others)

I-II-(VI)2 & II-IV-(V)2 compounds

AgGaS2, ZnSiP2, ., Tetrahedral bonding

Cc hp chtV2-(VI)3

As2Se3.


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Cu hi n tpchng 1:

1. Cu trc tinh th v cu trc vng nng lng ca cc cht bndn khi Si, AIIIBV vAIIBVI.

2. Tnh cht quang ca cc cht bn dn khi.

3. Tnh cht in ca cc cht bn dn khi.

4. Cc phng php chtovtliu bn dnkhi

5. Phn loi cc cht bn dn

Documents

1. Vat Lieu Ban Dan Nano-i (9-2008)