Chế tạo và khảo sát tính chất của lớp chuyển tiếp p n trên cơ sở màng mỏng zno và khả năng ứng dụng của chúng

DAI HOC QUdc GIA HA NOI
TRUdNG DAI HOC KHOA HOC TU NHI^N
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ã ô ã

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CHE TAO VA KHAO SAT TINH CHAT CUA LOP CHUY^N
TI^P p-n TREN CO SO MANG M 6 N G ZnO VA KHA
NANG U N G DUNG CUA CHUNG
M a so: Q T - 08 - 16

CHU TRI D £ TAI:

PGS. TS. Ta Dinh Canh

CAC CAN BO THAM GIA: CN. Nguyin Viet Tuyen

HA N 6 I - 2008


BAO CAO

TOM TAT

De tai:

CHE TAG VA KHAO SAl TJNH CHAT CUA LQP CHUY^N
TI^P p-n TREN CO Sd M A N G M 6 N G ZnO VA KHA
N A N G U N G DUNG CUA CHUNG
Ma so: QT - 08 - 16
Chu tri de tai:

PGS. TS. Ta Dinh Canh

Can bo tham gia:

CN. Nguyin Viet Tuyen

1. Muc tieu de tai:
Trong cac hop chat ban dan, ZnO la chat ban dan c6 do rong vomg
cam Ion (-'3,3eV a nhiet do phong), do ben vung va nhiet do nong chay cac,
gia thanh re. ZnO thiromg dugc dung lam vat lieu cho cac Hnh kien quang
dien tir. ZnO c6 hieu suat lucmg tu phat quang c6 the dat tai gan 100%, ma
ra trien vong trong viec che tao laser ZnO nhiet do phong. Mang mong ZnO
CO do dan dien va do truyen qua quang hoc cao trong mien anh sang nhin thay
dugc umg dung lam dien cue trong suot cho pin mat trai chat lirgmg cao va gia
thanh ha. Cac mang ZnO dan dien trong suot con dirge su dung trong cac man
T

t

'

/

hinh tinh the long, cac cOra so dien tir, cac thiet bj quang hoc uon dugc, cac

gu^ong phan xa nhiet de phii va kho phu, tham chi hot ZnO con c6 ung dung
trong che tao kem chong nang. Dae biet, trong nhiJng nam gan day, cac nha
khoa hoc tren the gicri dang tap trung nghien curu vat lieu ZnO cau true nano


vai nhieu hy vgng trong viec che tao mot the he linh kien mai c6 nhieu tinh
chat UTJ viet so vai cac mau khoi.
2. Noi dung nghien ciifu:
De thuc hien dirge muc tieu neu d tren, d^ tai da giai quyet dugc eac vSih
de sau:
+ Che tao mang ZnO c6 chat liigng cao bang phuofng phap phun xa r.f.
magnetron tren thiet bj Univex - 450 cua hang Leybold.
- Lam chu dugc thiet bi Univex - 450 cua hang Leybold.
- Che tao bia ZnO va ZnO pha tap tiT bot ZnO va b6t In203 cua
hang Merck bang phuofng phap gdm tmyen thong tren cac thiet bi cua du an
OPEC.
+ Che tao mang In+Al bang phuong phap boc bay nhi^t trong chan
khong.
3. Cac ket qua dat dirac:
+ Dua cac thiet bi che tao mang mong bang phun xa catdt Univex-450
va boc bay nhiet trong chan khong Univex-300 vao boat d6ng c6 hieu qua.
+ Che tao thanh cong cac loai bia ZnO va ZnO pha tap bang phuofng
phap gom truy6n thong.
-h Tim dugc che do cong nghe de che tao mang ZnO va mang ZnO pha
tap In tren de p-Si va de thuy tinh bang phucDmg phap phun xa r.f. magnetron
tren thiet bi Univex-450.
+ Che tao mang quang tra ZnO nhay a vung UV.
+ Che tao thanh cong pin mat trai n-ZnO: In-p-Si de lam cam bien nhay
quang.

I

I

f

f

+ iJng dung lap chuyen tiep p-n lam cam bien dong ma tu dgng den
duong.
+ Cong tac nghien curu:
1/ Preparation ofn-ZnOAn/p-Si heteroj unction by r.f magnetron
sputtering. Nguyen Viet Tuyen, Ta Dinh Canh, Pham Van Ben, Bach
Van Sy, Nguyen Xuan Nghia, Tran Thi Quynh Hoa and Nguyen Ngoc
Long Proceedings of the eleventh Vietnam-German seminar on Physics
and Egineering, Nha trang 2008 (In the press)
2/ Photoconductive UV detectors based on ZnOfdms prepared by RF
magnetron sputtering method, Nguyen Viet Tuyen, Ta Dinh Canh and
Nguyen Ngoc Long. Comm. In Physics, 2008 (in the press)
-h Cong tac dao tao :
* Da hudng dan 2 khoa luan tot nghiep
1/ Nguyen Si Hieu, ''Che tao va khao sat mang ZnO d6' thuy tinh
bang hoc bay nhiet kem axetat trong chan khong" Ha Ngi - 6/200L
2/ Nguyen Hong Viet, "Che tao va khao sat mang ZnO pha tap Al
tren de thuy tinh bang phuong phap phiin xa R. F magnetron", Ha
Ngi- 6/2002.
* Da hudng dan 1 luan van cao hoc:
r

1/ Bach Van Sy, ''Che tao va khao sat mang ZnO, ZnO pha tap lam
sensa nhay quang vung UVva VIS''' - Ha Noi, 12/2008.
* Dang hirdng dan 1 nghien curu sinh trong hu6ng nghien curu nay.
4. Tinh hinh su dung kinh phi:


Tong kinh phi thirc chi: 20.000.000 d6ng (mudi lam trieu dong chan),
Trong do cac khoan da chi:
Thanh loan dich vu cong c6ng : 600.000 d (tien dien)
Thue mu6n : 8.500.000 d
Chi phi nghiep vu chuyen mon : 10.300.000 d
Chi phi khac (QLCS): 600.000 d
Da thSng qua churng tijr tai phong tai vii.
Xac nhan ciia ban chii nhiem Khoa
(Ky va ghi ro ho ten)

PGS.TS.Nguyen The Binh
Xac nhan ciia Trucmg DHKHTN

» M 6 HI?U

o
l;^-: D A I I

TRl/ONG

Chii tri di tM
(Ky va ghi ro ho ttn)

PGS.TS.Ta Dinh Onh

Brief of the Report
1. The title of the project
Fabrication, investigation the properties of n-p heterojuction based
on ZnO thin films and their ability of applications.
The code number: QT - 08 - 16.
2. Main responsible person: assoc. prof. Dr Ta Dinh Canh.
3. Main implementation numbers:
Bachelor Nguyen Viet Tuyen
4. The objects.
The n-ZnO:In/p-Si heterojunction solar cells were made by
magnetron sputtering. The wavelength dependent properties of the
photoresponse for the heterojunction were investigated in detail by
studying the effect of light illumination on current - voltage (I-V)
characteristic, photocurrent spectra at room temperature. From the
photocurrent spectra, it was observed that the visible photons are
absorbed in the p-Si layer and under reverse bias conditions, while
ultraviolet (UV) photons are absorbed in the depleted n-ZnO:In under
reverse bias conditions. These resuhs indicated that ZnO:In films
prepared by the r.f. magnetron sputtering are good enough to be used
in photoelectrical devices.
5. The content of research.
The p-type Si (100) wafers (7-25 Qcm) were used as substrates for the
ZnO:In/Si heterojunction. Si (100) wafers were cut into pieces of lilcm.
Prior to the deposition, the wafers were dipped into buffered oxide etchant
(HF:H20 = 1:7) for 1 minute to remove native oxide. Then the samples were
ultrasonically cleaned with boiling acetone, ethanol, and de-ionized water for

10 min. ZnO:In films were deposited with an r.f magnetron sputtering
system using a ZnOiIn (2%) target with diameter of 7.5 cm and 0.5 cm thick.
The sputtering parameters were optimized at a substrate temperature of 150
''C, r.f. power of 250 W and sputtering Ar pressure of 5.8110'^ Torr. After the
ZnO:In film was deposited, for measuring the electrical properties, an hi
ohmic contact (0.5 mm diameter) was made onto the ZnO:In films being
used as a top electrode and an In-i-Al ohmic contact was made onto the p-Si
substrate being used as a bottom electrode.
The resistivity of the ZnO:In film was measured with a four-point
probe system. The dark current-voltage (LV) measurements were done
keeping the sample in the dark for several hours by using a Keithley
multimeter (Model 2400).
6. Results:
1/ Preparation ofn-ZnO:In/p-Si heterojunction by r.f magnetron
sputtering. Nguyen Viet Tuyen, Ta Dinh Canh, Pham Van Ben, Bach
Van Sy, Nguyen Xuan Nghia, Tran Thi Quynh Hoa and Nguyen Ngoc
Long Proceedings of the eleventh Vietnam-German seminar on Physics
and Egineering, Nha trang 2008 (In the press).
2/ Photoconductive UV detectors based on ZnOfdms prepared by RF
magnetron sputtering method. Nguyen Viet Tuyen, Ta Dinh Canh and
Nguyen Ngoc Long. Comm. In Physics, 2008 (in the press)
7.Conclusion
* Obtaining the aims of the project.
* Training 2 graduate students, 1 master student.


MUC LVC
Trang
MQ DAU

1

Chuang 1: TONG QUAN VE VAT LY BAN DAN

3

1.1 Co so phan loai vat lieu

3

1.2 Phan loai vat lieu ban dan

5

1.2.1 Ban dan thuan

5

1.2.2 Ban dan loai p

7

1.2.3 Ban din loai n

8

1.3 CSu true tinh thi ZnO

11

1.3.1 Cau true tinh the ZnO luc giac

11

1.3.2 cau true tinh thi ZnO don gian kidu NaCl

12

1.3.3 Cau true mang lap phuong gia kem (zine blend)

13

1.4 Cau tnic viing nang lugng cua ZnO

14

1.4.1 Cau tnic vung nang lugng cua ZnO dang luc giac

14

1.4.2 Cau true vung nang lugng cua ZnO dang gia kem

15

1.4.3 Cau tnic vung nang lugng cua ZnO dang lap phuong dan gian ki6u
NaCl

16

1.5 Tinh chat dien ciia ZnO

17

1.5.1 Dich chuyen trong dien trucmg thap

17

1.5.2 Dich chuyen trong dien trucmg cao

18

1.5.3 Tinh chat dien cua ZnO pha tap

19

1.5.3.1 Tinh chat dien ciia ZnO pha tap loai n

19

1.5.3.2 Tinh chat dien cua ZnO pha tap loai p

20

1.6 Tinh chat quang cua vat lieu ban dan

23

1.6.1 Cac dac trung quang

23

1.6.2 Cac CO chi hdp thu anh sdng

24

1.7 Tinh chat quang cua ZnO

27

1.7.1 Cac exciton tu do

27


1.7.2 Cac exciton lien ket

28

1.8 Cac tiep xiic trong ban din

30

1.8.1 Tilp xuc p-n dong thi

30

1.8.2 Tiep xuc p-n di the

31

1.8.3 Tiep xuc Ohmic

33

Chuang 2: CAC PHUONG PHAP THI/C NGHIEM

36

2.1 Cac ky thuat phun xa

36

2.1.1 Phiin xa nguon mot chieu

37

2.1.2 Phiin xa nguon xoay chieu

39

2.1.3 Phiin xa magnetron

40

2.2 Nghien curu cau tnic bang phuang phap nhilu xa tia X

41

2.3 Quan sat hinh thai be mat bang kinh hiln vi dien tu quet (SEM)

43

2.4 Do dien tra suat

43

Chuang 3: KET QUA,BIEN LUAN, VA iTNG DUNG

45

3.1 Che tao va khao sat lap chuyen tiep n-ZnO:In/p-Si

45

3.1.1 Khao sat cau tnic

45

3.1.2 Khao sat tinh chat quang

46

3.1.3 Khao sat tinh chSt dien

48

3.2 Sur dung lop chuyin tiep n-ZnO:In/p-Si lam thiet bi dong ngat tu dong he
thong chieu sang den duong

50

3.2.1 So ddkhdi

50

3.2.2 So d6 chi ti8t

51

KET LUAN

53

TAI LIEU THAM KHAO

54


MOfDAU
Trong cac hgp chat ban din, ZnO la chit ban din c6 dg rgng viing cam Ian
(-3,3eV d nhiet do phong), do ben vvhig va nhiet do nong chay cao, gia thanh re. ZnO
thuang dugc diing lam vat lieu cho cac linh kien quang dien tu. ZnO c6 hieu suat lugng
^

y

t

'

tu phat quang c6 the dat tai gan 100%, ma ra trien vgng trong viec che tao laser ZnO
nhiet do phong. Mang mong ZnO c6 do dan dien va do truyen qua quang hgc cao trong
mien anh sang nhin thay dugc ung dung lam dien cue trong suot cho pin mat trai chat
lugng cao va gia thanh ha. Cac mang ZnO dan dien trong suot con dugc su dung trong
cac man hinh tinh the long, cac cua so dien tu, cac thiet hi quang hgc uon dugc, cac
guang phan xa nhiet de phii va kho phu, tham chi bgt ZnO con c6 ung dung trong che
f

r

\

'

tao kem chong nang. Dac biet, trong nhumg nam gan day, cac nha khoa hgc tren the giai
dang tap trung nghien curu vat lieu ZnO cau tnic nano vai nhieu hy vgng trong viec che
tao mot the he linh kien mai c6 nhieu tinh chat uu viet so vai cac mau khoi.


CHl/QNG 1 TdNG QUAN V£ VAT LI$U BAN DAN
L I Cor so* phan loai vat lifu:

Buc tranh ve cac vung nang lugng cua dien tu trong trudng tuin hoan cua tinh thi
cho phep ta xac djnh dugc chit rln la chit din dien hay la chit each di?n, can cur vao
viec cac dien tu khong lap dly hay c6 lip dly cac vung nang lugng. D I lam viec do
ngoai viec phai biet cac vung nang lugng ta con can nhac lai rang vi cac di?n tu tuan
theo thong ke Fermi - Dirac cho nen trong moi trang thai vat ly (dac trung bai ham
song va hinh chieu spin) ciia dien tu chi c6 thi hoac la khong c6 hat nao, hoac la c6
mot hat; khong the c6 hai dien tu ciing t6n tai d6ng thai trong mot trang thai vat ly. Khi
trong mot trang thai vat ly da c6 mgt dien tu roi thi ta noi trang thai do da bi chiem

hoac da day; neu con c6 cac dien tu khac thi cac di^n tu do phai chilm cac trang thai
khac ( nguyen ly loai trii Pauli). Khi c6 mot trang thai ma trong d6 khong ton t^i mgt
dien tu nao ca thi ta noi trang thai do la con trong; di?n tu tir mgt trang thai khac c6 the
nhay vao chiem trang thai con trong nay.
MHtIS

Conduction Band
Valtnce Band
Semiconductors
Conduction Band

Eg
Val*nct Band
Insutaton
Conduclon Band

Eg
^ I t n c t Band

Hinh 1.1: Cau true viing nang lu(mg cua kirn loai, ban dan va chat each di^n
Gia su chit rln c6 mgt vung nang lugng ma mgt phin dS dly, mgt phin con trdng.
C) nhiet do T == 0 cac trang thai vdi nang lugng duai muc Fermi Ep da dly hit, con cac
3


trang thai vai nSng lugng tren muc Fenni thi hoan toan trdng. Nhtog tr?ng thAi trong
sat muc Fenni c6 nSng iugrng khac rat it so vai nSng lugng c4c t r ^ g thii di dfiy d sit
muc nay. Do do chi can tmyen them cho h? di§n tu mgt rat be la cung c6 the Ikm cho
dif n tu chuyen doi tu trang thai dly sang trang thai trong, nghia 1^ lam thay doi ph&n
bo nang lugng. C) nhi^t do T # 0 c6 them di$n tir vcri ntog lugng tren muc Fermi vi

nhung trang thai chua dly vai nSng lugng dudi muc Fermi, s\r thay doi him ph&n b4
khi truyen nang lugng cho hf cang de dang han, du cho do la n&ig lugng rit b6. Khi ta
dat chat ran nay trong di?n trucmg, dien trudng tac dyng len cic di^n tu, truyen nftng
lugng cho cac di^n tu va lam cho dien tu chuyen tu cac trang thai day sang tr^ng thii
trong, lam thay doi ham phan bd va dan den s\r xuat hi^n dong di^n cho du di$n trudng
yeu.Chal tin nhu vay la chat dan dien.Vung nSng lugng trong chat dan di§n mi m^t
phan da day va mot phSn con trong ggi la viing din. Kim loai c6 clu tnic viing ndng
lugng va su phan bo dien tu trong vimg din nhu da trinh bay a tren, nen la chit din
dien.
Trai lai, neu pho nSng lugng ciia chAt rin c6 mgt vimg cim vai mpt be rgng A£
du lom, ma tat ca cac trang thai duai viing nay dSu da dAy, cac kich thich nhi?t se khong
the truyen du nang lugng cho dien tir d^ no chuyen tir mot trang thai duai viing elm len
mpt trang thai tren vimg cAm, do do khong iM lam thay d6i ham phan b6, nghia li
khong th6 lam xuk hien dong dien. Chit tin c6 clu tnic va su phan b6 di^n tu nhu v$y
la chat each di^n. Vimg nang lugng duai viing elm, gdm cac trang thai da dly, ggi li
\ung hoa tri. Cac dien tu lip dly viing hoa tri gpi la dien tu hoa trj. Viing elm cang
rpng thi tinh chat each dien cua chit rln cang t6t.
6 nhiet do T ?t 0 khong cin qua Ian, thi du nhu a nhiet dp phong, cac d ^ g
chuyen dong nhiet trong chit rln c6 thd truySn du ning lugng cho di^n tir dl kich thich
Chung tir viing hoa trj da day len vimg nSng lugng con trdng a phia tren viing elm, lim
cho \ iing n^ng lugng con trong nay c6 cac dien tu phan b6 gidng nhu a trong vimg din
cua chat dan di?n. Viing nang lugng con tr6ng do a phia ben ngay sat vimg elm cung
duac gpi la viing dan. Theo cong thirc phan b6 Femii, n6ng dp di^n tij trong viing din
CO dp Ion vao ca:


n^^
e-'"'
e^^ + 1

(1-1)

nh6 Hon nhigu so v6i ndng d$ d i ^ tur trong kim lo^i. Khi c5 nhfhig di$n ti^ chuy^
tir viing hoa trj len vung din, vugt qua vung elm c6 b£ rOng rlt b^, thi trong vung hoi
tri xult hi^n nhihig trang thai tr6ng. Vi trong viing hoi tri bay gid l^i c6 cic tr^ng thdi
trong vdi nSng lugng v6 ciing gin ning lugng cic t r ^ g thai dly cho nen dudi tic d\mg
cua mot dien truang khong can Ion llm cic di§n tii trong vung hoa tri ciing c6 thi thay
doi sir phan bo va do do cung tham gia vao s\r xult hi^n dong di^n. So cic trang thii
trdng nay trong viing hoa tri bing s6 di^n tu trong viing din. Nhi^t dO cang ting thi s6
nay cang tang.
Cac chat each dien ma viing cam c6 be rgng A£ rat be tra nen din dien 6 nhi$t dp
T #0 khong qua Ion va dugc gpi la chat ban din. Cic chat ban dan c6 nhihig tinh chit
rat dac bi^t, lam ca so khoa hpc cho s\r ung dyng cic chat do trong ky thuat.
1.2 Phan loai v|t lifu bin din
1.2.1 Bin dan thuan
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Hinh 1.2: Lien ket trong ban dan thuan
Nhutig chit ban din dan chit nhu Ge, Si hay hgp chit nhu GaAs, InSb,
CdS....thuln khiSt ve mat hoi hpc, khong Ian tap chit, khong lech hgp thuc, khong c6
cac sai hang clu tnic tich di^n, dugc gpi la cac chit ban din thuin, bin din rieng va
cung con gpi la ban dan loai I.
Vai loai vat lieu nay khi 6 nhi^t dp OK, vimg din hoan toan trong, khong c6 di^n
tir din. Khi nhiet dp tang len, dien tu a vimg hoi tri c6 thfi thu dugc mpt ning lugng


cIn thiSt de vugt qua viing cam va nhiy len viing din, dfi l^i a viing hoa tri "iP^ ™ ^
khuy^t dien tu. K6t qua la a vimg din xult hi$n cic di§n tu din va viing hoa tri xufit
hien mire trdng vai ndng dO nhu nhau. Cic di§n tu d viing din va cac 16 trdng d viing

hoa trj d6u c6 th6 tham gia vao qui trinh dan difn. Trong cac ban din lo^i nay, muc
Fermi dugc xac dinh bdi cong thuc:
Vi£^^3
2

4

m^

(1.2)

m,

6 nhiet dp cao han, trir mpt sd truang hgp khi c6 s\r chenh l#ch I6n ve khoi lugng
hieu dung nhu a InSb, su chuyin dich cua muc Fermi theo nhi^t dp li khdng ding kc.
Do do, ndng dp hat tai rieng cua ban din thuIn c6 thi dugc bilu diln bdi bieu thirc:
n =n^=iN,N,ycxp(-^)

(1.3)

Nhu vay trong ban dan thuIn, ndng dp hat tai dugc xac djnh bdi dp rOng viing
cam Hg va nhiet dp T ciia mlu. Neu ta dit dien trudng vao mlu sS xuat hi^n dong di§n.
1)6 la sy chuyen ddi c6 hudng cua dong thdi cac di^n tix d viing din va cac Id trSng d
\ iing hoa tri. Dp dan trong ban dan thuan dugc xac djnh bdi bieu thuc.
a = q(nn^ + pjip)

(1.4)

Trong do n, jin tuang img la ndng dp va dp linh dpng cua di?n tir; p, fip tuang iimg
la nong dp va dp linh dpng cua Id trdng, q = e la di?n tich nguyen td. Nhu vay djc dilm

dan dien rat quan trong cua chat ban dan thuan la su tham gia ddng thdi vdi sd lugng
nhu nhau ciia ca di^n tir tren viing din lln l6 trdng trong viing hoa trj. D$c diem thu hai
la ndng dp cua chung phu thupc rat m^mh vao nhi^t dp.
Trong linh vuc chi tao vat li^u bin din, dilu ki^n cdng ngh? th^rc tl khdng cho
phep che tao dugc cac chat ban din hoin toan tinh khilt mi khdng bj Ian it nhilu t?ip
chat. Mat khac, nhu da noi 6 tren, ban din thuIn khifit cd nhilu d$c tinh han chi khi
nang img dyng thyc tiln. Vi vay ngudi ta chu dpng pha th6m m$t lugng nguyfin t6
khac lo^i vao chat bin din tinh khilt di d^t dugc cic tinh chit mong mu6n. Trong m^t
v^t li?u nhu v$y, tinh din di^n xult h i ^ chu ylu do mOt lo^i h^t tii mi lo^ h ^ tii niy


dugc^quy djnh bdi t ^ chit pha vio, ngudi ta ggi cic vat li^u nhu v^y li cic bin din
t9p chit.
Tuy thugc ban chit cua vat li^u pha tap vao vat lifu bin din tinh khiet mi ngudi
ta CO the tao ra dugc hoic bin dan tap chat loai n hoic la ban dan tap chat loai p.
1.2.2 Bindlnlo^ip:
e

e

^# I •

a

e

S# e

e

a

Hinh 1.3: Lien ket trong ban dan iogip
Gia sir ring c6 nguyen tir C vdi n-1 di^n tu vanh ngoai (hoi tri n-1) mi ham song
gidng nhu ham song cua n-1 trong sd n dif n tu vanh ngoai ciia nguyen tu chit A. Neu
ta thay mpt nguyen tu A bang mpt nguyen tu C thi n-1 dien tu vanh ngoai cua C chua
du dk thay tat ca n di^n tu vanh ngoai cua A vi con thieu mat mpt di^n tu, do dd trong
viing hoa tri c6 mpt trang thai trdng ngay ca khi T = 0. Neu ta pha tap chat C vao chit
ban din de cac nguyen tu C thay the mpt sd nguyen tu A, thi trong viing hoi tri xult
hien cac trang thai trdng, nghia la s0 cd cac l6 trdng, ngay ca d nhiet dp T = 0. Khi ta
tang nhiet dp T thi lai cd them mpt sd dien tu bi kich thich tir viing hoi trj len vimg
din, lam cho trong viing din cd cac dien tii, trong viing hoa trj cd them Id trdng. Hi^u
sd ndng dp Id trdng va ndng dp dien tii la mpt lugng khdng ddi va blng ndng dp tap
chat.Cac l6 trdng la cac hat tai dien chinh. Chit ban din nay gpi la chat ban din loai p
(positive). Ndng dp l6 trdng trong ban din loai p:

p = (N^NJ cxpi-^)
2kgT

(1.5)


1.2.3 Ban dan loai n:
e

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Hinh 1.4: lien kit trong ban dan logi n
Xet mpt chit ban din cd chua cac nguyen tu ciia mpt chat A nio dd. Gii sd m8i
nguyen tir /4 c6 n dien tir vanh ngoai ( hoi tri n ) la nhihig di?n td trd thanh m5i nguyin
tir luu dpng trong chit rln. Tit ca cac difn tu nay lap dly vung hoi trj khi T = 0 vi
cung chi vira du de lap day viing hoa trj. Ta hay thay the mpt nguyen tu A trong tinh
th^ bang mpt nguyen tu 5 c6 n +1 di?n tu vanh ngoai (hoi tri n +1) ma neu lly di mOt
di^n tir vanh ngoai thi ion duong fl* con lai cd cau tnic di^n tu gidng nhu nguySn tdi^.

Khi do n dien tir vanh ngoai cua ion B^ thay the n di$n tu vanh ngoii cua nguygn txxA
bj lay di va ciing vdi cac di^n tir vanh ngoai cua tat ci nguyen tu A khic lip dly viing
hoa trj khi 7 = 0 .
Con mpt dien tu vanh ngoai nua bj thira ra cua nguyen tu B thi sao? Vi trong viing
hoa trj khdng con trang thai trdng nao nQa cho nen di?n tu nay chi cd the chilm m^t
trang thai trong viing dan va trd thanh dien tir dan. Do dd nlu ta pha t^p chit B vio
chat ban dan A de cac nguyen tu B thay the mpt sd nguyen tu A, thi trong vung din s€

CO cac dien tir dan ngay ca d nhiet dp r = 0, chat bin din trd thanh din di^n mi cic h^t

tai di^n chinh la cac di^n tir. 6 nhiet dp F 9^ 0 vi cd them cic di^n tir bj kich thich tir
vimg hoa tri len viing din cho nen ndng dp di?n tu trong viing din ting len, ngoii ra l^i

CO them cac Id trdng. Hieu so ndng di?n ni va ndng dp I6 trdng la mgt lugng khdng dli
va bang ndng dp t^p chat. Chat ban dan nay gpi la bin din lo^i n (negative).
Rd rang la d viing nhi?t dp thip, khi ma kBT«ED ho$c kBT«E», qui trinh
chuyen ddi h^t tii tir viing hoa tq len viing din li khdng ding kl. H^t tii d i ^ dugc t90
8


thanh chu ylu li do kit qui cua qui trinh ion hoi cac nguyen tu tap chit. Do v$y, ndng
do can blng cua h^t tii trong trudng hgp nay phu thugc vao ndng dg t^p chit Nd, N..
Cu thi la:
Ndng do di^n td trong ban din loai n:
/i = (A^,A^^)^exp(--f^)

(1.6)

Do cic mire ning lugng tap chat nhd han nhieu so vdi ning lugng vung cam nen

su phu thugc ciia ndng dg hat tai vao nhiet do trong ban din tap chat yeu han nhilu so
vdi trudng hgp ban din rieng.
Theo chieu tang ciia nhiet dg, sd lugng nguyen tu tap chat bj idn hoa ting din. Do
lugng tap chat pha vao ban dan la hihi han nen se den liic toan bg cac nguyen tiir t^p
chat bi idn hoa het. Trong trudng hgp nay, ndng dg hat tai blng ndng dg nguyen td t^p
chat va trd nen khdng thay ddi theo nhiet dg, tire la:
n = Nd va p = Na
Nhiet dp Ts, ma tai do xay ra hi?n tugng nay, ph\i thugc vao muc ning lugng t^p
chat va ndng dp tap chat. Cy the la :
Ts =

^''{j,

(1.7)

Khi nhi?t dp tilp tuc tang, ndng dp hat tai dugc tao thanh bdi qua trinh chuyen
ddi dien tu viing hoa trj len vimg din cung tang len trong khi toan bd cic nguyen tu t^p
chit da bj idn hoa het. Ban dan tap chat chuyen thanh ban dan thuan vdi ndng dp hat tai
la n, va p . Nhiet dp chuyen tiep Tj cd thi xac dinh bdi bieu thirc:

'

kM^c^ylKia,)
r)

(1.8)

Thong thudng nguyen tir tap chat dugc lua chpn sao cho d nhiet dp lam viec,
nang lugng nhiet tai nhiet dp dd du Idn de ion hoa hau nhu hoan toan cac nguyen tu
donor hoac acceptor trong chat ban dan. Nhu vay, dong di^n trong cac ban din tap chit

it bj thay ddi theo nhiet dp nhu trong trudng hgp cac chat ban din thuan khiet.


D$c dilm din difn chu ylu blng m$t lo^i h9t tii 19! ft bj phy thu^c vio nhi^ t
lam cho cic ban din t^p chit trd thinh mpt vit li^u qu^^ trong lihh v\rc chi t^o ciclin
kien dien tu nhu diode, transistor hoic cic m^ch t6 hgp...Dd chinh li co sd cho mi
cudc each mang trong ITnh vuc ky thuat vacdng ngh§ di^n tiir cung nhu cdng ngh
thdng tin.
Khi nghien cuu clu tnic dien tu ciia cac chat din di^n va cic chat cich di$
chung ta da thiy ring trong chit bin din, la chit cich di^n ma viing elm cd bl rOng A
rlt be, d nhiet dp Ti^O mpt sd dien tu bi kich thich tir viing hoi trj len vung din va tr
thanh dien tu dan, de lai trong viing hoa tri nhumg I6 trdng ciing li cic h^t tii di^
Ndng dp cac hat tai phy thugc nhi^t dg T theo cdng thuc . Cic chat bin dan dd dug
gpi la cac chat ban din thuan, cd tinh chat cich di^n khi dugc giO" d nhi^t dp r = 0.
Tom lai, neu ta pha tap dl thay mgt sd nguyen tu mgt lo^i nio dd ciia chit bi
dan bang nhOmg nguyen tiir cd cau t^o tuang ty nhung vanh ngoii cd thfim m^t di^n ti
thi ta sS dugc mgt chat ban din loai n mi di?n tir la h^t tii chinh, ndng dg di§n td W
han ndng dp Id trdng. Tap chat lo?ii nay gpi la chat hifin di^n tu (donor). M$t khic, n^
ta pha tap de thay mpt sd nguyen tir mpt loai nio dd ciia chat ban din blng nhthi
nguyen tu c6 cau tao tuang ty nhung vanh ngoai cd bdt di mpt di^n tu, thi ta s€ du^
mpt chat ban dan loai p ma Id trdng lai la h^t tai chinh , ndng dp Id trdng Idn hem nil
do dien tir. Tap chat loai nay gpi la tap chat nhan di?n tu (acceptor).
Chu y ring khi ta pha tap nguyen tu B vao chit bin dan de thay thi cho nguyin ti
A thi mpt dien tir vanh ngoai cua B bj du ra va trd thanh di?n tu din, cho nen thyc SU
chi CO ion duong B* thay the nguyen ta A mi thdi. Tai nut chua nguyen tu B bay gid cc
them mpt dien tich +e so vdi khi chua thay.Trong trudng coulomb ciia di^n tich duan|
nay cac dien lir dan c6 cac trang thai lien kiet gidng nhu nguyen tu hydro, vdi ninj
lugng am so vdi nang lugng tdi thieu cua dien tir ty do trong viing din. Mire nan|
lugng gian doan nay nam trong voing cam va gpi la muc ciia tap chit hiln di^n tii (min
donor ). Ngugc lai, so vdi nguyen ni A thi nguyen tu C con thilu mpt di?n tu, cho nft

khi C thay vao cho ciia A thi nguyen tir C con bit them mpt di?n tir vimg hoa trj vi tri
thanh mot ion am C thay the A. Tai nut chira C bay gid cd them mpt difn tich -c «
10


vdi khi chua thay. Trong trudng Coulomb cua di^n tich -e niy cic Id trdng mang d i ^
duong cQng cd cic trsmg thii lien kit, vdi ning lugng am so vdi ning lugng tdi thilu
cua Id trdng t\r do.Vi ning lugng cua Id trdng cd diu ngugc lai so vdi ning lugng cua
trang thai trdng, tinh tir mure Fermi nim trong vung cam, cho nen neu quy vi trang thii
trdng ciia di^n tu thi nguyen tu C tao ra them cac muc ning lugng gian doan cd gii tri
duong so vdi cue dai viing hoa tri, nghTa la cung nlm trong viing cam. Cac muc niy
gpi la cic muc ciia tap chat nhan dien tu (muc acceptor).
1.3 Cau true tinh the ZnO.
Ve mat ly thuyet, ZnO khdng phii la mpt vat li?u mdi dugc khim phi. Cic nghiin
cim tren ZnO da dugc thyc hi?n lien tyc trong nhieu thap ky, ve mit tinh chat cua nd, di
cd cac bai bio tir nam 1935, tham chi sdm han. Vi dy, hang sd mang ciia ZnO dS dugc
khao sat tir nhieu nam trudc. Nhung nghien cuu da chi ra ring ZnO tdn tai trong ba loai
cau tnic ca ban: cau tnic lap phuang gia kSm kieu sphalerite (B2), cau tnic lye giic kieu
wurtzite (B4) va cau tnic lap phuang don gian kieu NaCl (Bi). Tinh the ZnO la chat diin
mdi, d dieu kien binh thudng bin vihig vdi cau tnic luc giic wurtzite. Khi ip suit thuy
tTnh cao ZnO cd cau tnic lap phuang dan giin kiiu NaCl va d nhi^t dp cao ZnO cd clu
tnic gia kem khi nudi cly tren de clu tnic lap phuang.
1.3.1. Cau true mang lye giac wurtzite.
Cau tnic luc giac wurtzite la cau tnic dn dinh va ben vimg ciia ZnO d dieu ki^n
nhiet dp phong va ip suat khi quyin va thupc ve nhdm khdng gian P63mc hoic CVCd thi hinh dung mang wurtzite gdm hai phan mang lye giac xep chat (hpc) Idng vao
nhau va dugc djch di mpt khoang bang u = 3/8 chiiu cao (trudng hgp cau tnic ly
tudng), mdi phan mang nay gdm 4 nguyin tii cung loai trong mpt d mang dan vi. Mpi
nguyen tir nhdm II dugc bao quanh bdi 4 nguyin tu nhdm VI hoac ngugc lai. Trong
thyc ti, hai phan mang nay Idng vdi nhau khdng diing vdi gia trj 3/8 chiiu cao ma tiiy
theo timg loai cation, gia tri djch chuyin nay se khac nhau. Mpt trong nhung tinh chit

dac trung cua phan mang luc giac xip chat la gia tri ty sd giira cac hang sd mang c va a.
Trudng hgp ly tudng thi ty sd c/a = >/3/8 = 1,633. Tren thyc te, cac gia trj cua ty sd
II


c/a ciia hgp chat A"B^' diu nhd han 1,633. Diiu niy churng td cic m$t khdng hoin
toan xip chat.
Tinh thi luc giic ZnO khdng cd tam ddi xiing, do dd trong m^g ton t^i tryc phin
cue song song vdi hudng [0001]. Liin kit ciia m^g ZnO vira li liin kit ion vvra li liin
kit cdng hoa tri, li loai liin kit pha trpn bao gdm 67% liin kit ion va 33% liin kit
cdng hoa tri. Dac diim quan trpng ciia liin kit cpng hoa trj li tinh dj hudng vi tinh bio
hoa vi mdi nguyin tu chi cd the cd nhiiu nhat mpt sd lien kit cOng hda trj nio dd.
O

Hinh 1.5 Cau true mang tinh the luc giac kieu wurtzite cua ZnO.
1.3.2. Ciu triic m^ng lap phuong don giin kieu NaCl
Nhom ddi ximg khdng gian cua cau tnic nay la Fm3m. 6 m^g co sd ciia clu true
lap phuang dan giin kieu NaCl co the dugc xem nhu gdm hai phin m^g % phuong tim
m^t cua cation (Zn) va anion (O) Idng vao nhau, Uong dd phin m^ng anion (O) djch di
mpt doan blng a/2, vdi a la canh hinh l^p phuang. Moi d ca sd gom bdn phin tu ZnO
(hinh 1.6). Sd Ian can gan nhat cua cation va anion diu blng 6.
^Zn

Hinh 1.6 Cdu true mang tinh thi Igpphuang dm gidn kiiu NaCl ciia ZnO.

12


COng gidng nhu m$t sd chit bin din A°B^, ZnO clu true kiiu wurtzite cd thi biln
ddi sang hinh thii clu true gii bin 1|^ phuang don giin kiiu NaCl d ip suit thdyfihhdii

cao vi ngugc l^i tiiy theo nhi^ dg vi ip suit. Diiu niy li do sy giim kich thudc m^ng tinh
thi gay nin tuang tic Coulomb gii^a cic ion. Sy can blng pha dugc thiit l|p d ip suit
khoang lOGpa. Theo tinh toan, su thay ddi thi tich ciia hai trang thii nay vao cd 17%
va hlng sd mang trong cau tnic nay a = 4,27A. Gin day, cac nghiin curu churng minh
sy chuyin pha clu tnic da quan sat thIy ZnO clu tnic lye giic wurtzite trii qua mOt sy
bien ddi cau tnic vdi ip suit chuyin pha p = lOGPa va hoan thinh d khoing 15GPa.
1.3.3. Cau true mang lap phvorng gia kem
Day cung la mpt trang thai cau tnic gia bin cua ZnO nhung xuat hien d nhiet dp cao.
Nhdm ddi xumg khdng gian ciia cau tnic nay la T^ - F? 3m va gdm hai phan mang lap
phuang tam dien (fee) xuyin vao nhau 1/4 dudng cheo cua d mang. Mdi d co sd (hinh 1.3)
chira bdn phan tu ZnO vdi cac tpa dp ciia 4 nguyin tu Zn la: (0,0,0), (0, 1/2, 1/2), (1/2,0,
1/2), (1/2, 1/2, 0) va tpa dp ciia 4 nguyin tu O la: (1/4, 1/4, 1/4), (1/4, 3/4, 3/4), (3/4, 1/4,
3/4), (3/4,3/4, 1/4). Trong cau tnic nay, mpt nguyin td bit ky dugc bao bdi bdn nguyin tu
khac loai. Mdi nguyen tu O dugc bao quanh bdi bdn nguyin tu Zn nim d dinh ciia tu di?n
cd khoang each a >^ /2, vdi a la thdng sd ciia mang lap phuang. Mdi nguyin tu Zn (O) con
dugc bao bdi 12 nguyin tu ciing loai, chiing la Ian can bac hai, nlm tai khoang cich af-Jl.
Do su phdi vj theo kiiu tir dien ciia cau tnic wurtzite va lap phuang gia kem, 4 Ian can gin
nhit va 12 Ian can bac hai cd ciing mpt khoing each liin kit trong hai trudng hgp.

Hinh 1.7. Cdu true mong lap phuang gid kem cua tinh the ZnO.
13


1.4. Cau triic viing ning Ivgng cua ZnO
1.4.1. Cau true viing ning Ivgng ciia ZnO dang lye giic wurtzite
Tat ca cac hgp chat A " B ^ diu cd vimg cam thing vi dp rgng vimg elm giim khi
nguyen tu lugng ting. Mang tinh thi ZnO dang wurtzite clu t^o tir hai m^ng lyc giic ling
vao nhau, mgt mang chua anion va mang con lai chira cation. Cic victo tjnh tiln co sd ddi
vdi mang luc giac wurtzite la:
- =-a(l,-V3,0);a2

1
a,
=-a(l,V3,0); a, =c(0,0,l)

(1.9)

la biet mdi lien h? giua vecto tjnh tiin co sd cua m ^ g thyc vi m?mgdio:
ajCa^xaj)

a2(a3xa,)

a^{a^xa^)

(1.10)

Vi vay mang dao ciing cd cau tnic lyc giic vdi cac victo tjnh tiin co sd li:
b; = 2na''(l,-V3,0); b^ = 27ia-'(l,V3,0); b^ = 27ic-'(0,0,1)

(1.11)

Cau tnic luc giac ciia ZnO thugc nhdm ddi xung khdng gian CV (P63mc). Vimg
Brillouin thir nhat la mpt khdi bat di?n dugc biiu dien trin hinh 1.8.

Hinh 1.8 Vimg Brillouin ddi vai mgng tinh thi wurtzite.

14


Hinh 1.9 Cdu true vung ndng lir^mg cm mgng tinh the wurtzite.
Bang phuang phap nhiiu loan cd thi tinh dugc viing nang lugng cua mang lyc

giic tir viing ning lugng ciia mang lap phuang. So dd viing din (CB) va viing hda trj
(VB) ciia hgp chat nhdm A"B^' vdi m ^ g tinh the lyc giic dugc cho trin huih 1.5. So
vdi so dd viing ciia mang lap phuang ta thay ring, muc Fg (J = 3/2) vi F? (J = 1/2) ciia
viing hda trj do inh hudng ciia nhieu l o ^ trudng tinh thi, hi tich thinh 3 phan vung
r9(A), r7(B) va r7(C) trong mang lyc giac.
1.4.2. Cau true viing ning Ivgng cua ZnO dang l^p phvong gii kim (zinc blende)

Hinh 1.10. Vung Brillouin cua mgng tinh the lap phuang gid kem

15


Mang lap phuang gia kim cd cau tnic ddi xixng tjnh tiin cua m^ng 1 ^ phudj
tam mat vdi cac vecto tinh tiin co sd li:
a, =^a(U,0); a, =^a(l,0,l); a, =^a(0,U)
d.

^

(1.13

^

Mang dao dang lap phuang tam khdi cd cic vecto tinh tiin ca sd la:
-I

b, =2Ka-'(l,l,-l); b, =27ia-'(l,-l,l); bj =2nc-(-1,1,1)

(1.13

Vimg Brillouin la mpt khdi bat di?n cyt.
1.4.3. Cau true viing nang lugng cua ZnO d^ng lap phu-ong dom giin kiiu NaCl

Cac vecto tinh tiin co sd ciia mang lap phuang don giin kiiu NaCl giong nh
trong mang lap phuang gia kim.
a, =ia(l,l,0);a2 =^a(l,0,l);a3 =ia(0,l,l)

(l.H

Vi ly do do viing Brillouin cua lo^i mang nay h^t nhu trudng hgp m ^ g l|p phuang gi
kim.

So dd viing nang lugng ciia ZnO vdi cau tnic tinh thi d^ng lyc giic kiiu wurtziti

lap phuang gia kim (zinc blende) va lap phuong don giin d ^ g NaCl dugc cho ti<
hinh 1.11.
15

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Hinh l.lLSado

vi^ng ndng luang ciia tinh thi ZnO

16

1.5. Tinh chit difn cila ZnO
Li mgt \^X li^u vung elm thing rgng, ZnO thu hut dugc nhieu sy chii y ddi vdi cic
img dung di^n tiir vi quang di^n tu. Nhung thuan Igi liin quan din vimg elm thing bao
gdm: hi#u di^n thi dinh thiing Idn, khi ning duy tri trudng dien cao.... Sy djch chuyin
electron trong vat lieu bin din cd thi dugc khao sit ddi vdi cic trudng d i ^ thap vi cao.
- Ddi vdi trudng dien du thap, ning lugng cua cac electron thu dugc tir trudng
ngoai la nhd khi so sinh vdi ning lugng nhi^t cua chiing, vi vi thi phd ning lugng
ciia cac electron khdng bj thay doi bdi trudng ngoai nhd do. Khi dd tdc dp tin x^
xac dinh cua cac electron linh dpng phy thupc vao ham phan bd ciia cac electron,
dp linh dpng ciia electron ddc lap vdi trudng ngoai va dinh luat Ohm dugc quan
sat thay.
- Khi trudng ngoii ting tdi diim ma ning lugng cic electron thu dugc tir trudng
ngoai khdng con la khdng dang ki so vdi nang lugng nhi^t ciia chiing nC^a, ham
phan bd electron thay doi dang ke tir cac gii tri can blng ciia chiing. Cic difn tu
trd thanh difn tu ndng, dugc die trung bdi mpt nhiet dp Idn han nhi^t dp mang.
Khi dd van tdc keo theo ciia cac dien tu Idn han cic gii tri d trang thii dn dinh ciia
nd.
1.5.1. Djch chuyen trong di^n trvdng thap
Hieu irng Hall la ky thuat dugc su dung rpng rai di do cac tinh chat dich chuyen va
danh gia chat lugng ciia cac Idp epitaxy. Ddi vdi vat lieu ban dan, nd tiet Id ndng dp hat
tai, loai hat tai va dp linh dpng ciia chiing. Cy thi han, sd li^u thyc nghi^m cua cic phip
do Hall trong dai nhiet dp Idn tir 4,2 - 300K cung d p nhung thdng tin dinh lugng vi dg
tinh khiit, cac sai hong mang, tinh ddng diu cua vat lieu, co chi tan xa... Hi sd Hall vi
dien trd suit p dugc xic dinh bing thyc nghiim va sau dd liin hi vdi cac tham sd dien
qua (ddi vdi tinh dan loai n) RH = rn/ne va JIH = ^H^P trong do n la ndng dp di?n tu ty
do, |iH li dp linh ddng Hall, rH li hi sd tin xa Hall ddc lap vdi cac ca chi tin xa ndi
riing. Khi cac hat tai chuyin dpng qua chat ban din, chung bat gap nhiiu co chi tin xa
diiu khiin dp linh ddng hat tai trong hi dien tu khac nhau.

17

OAi HOC QL"^,

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