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

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

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

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:

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 D U N G 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

+ 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)

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

PGS.TS.Nguyen The Binh PGS.TS.Ta Dinh Onh

Xac nhan ciia Trucmg DHKHTN

» M 6 HI?U TRl/ONG

o

l;^-: D A I I

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

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

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

n^^ e-'"' (1-1)

e ^ ^ + 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

e « e ' « i # s #

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:

V i £ ^ ^ 3 m^ (1.2)

2 4 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

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 e

^ # I • S # e

a 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^N J cxpi-^) (1.5)

2kgT

1.2.3 Ban dan loai n:

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)

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:

(1.8)

' kM^c^ylKia,) r)

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

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 CV-

Cd 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

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 thdy fihh dii

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:

- 1

a, =-a(l,-V3,0);a2 =-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:

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

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)

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

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"^,

J)1 / ?5 3

Co chi tin x^ chu yiu ndi chung diiu khiin sy djch chuyin cua di§n tiir trong ZnO livt kc ngin gpn nhu sau:

- ran X9 khdng tinh khiit ion hda do sy l?ch ciia cic h?it tai tg do do thi CoulombI tic dyng xa cua cic tim di^n tich cd nguyin nhan do cic sai hdng hofic sv pha tq)

- I in x^ phonon cd nguyin nhan bdi tuang tic gi&a di^n tich chuyin dOng \(n

di^n trudng giy bdi cic di?n tich phin eye liin quan tdi dao dgng m ^ g do cic ion

ty nhiin ciia cic liin kit trong bin din phan eye

- Tin X9 phonon im hgc vi bien d ^ g ham thi

- rin x^ ip di$n xult hiin do di?n trudng sinh ra do biln d ^ g cd liin quan tdi cic phonon trong tinh thi khdng cd tinh ddi ximg dio

- Niu m§t dg l?ch m ^ g vi sai hdng ty nhiin trong bin din cao, tin x^ l|ch m^ng

\ i tin x^ do sai hdng ciing cd the dugc xem xit nhu li mgt ca chi tin x^ cd the 1.5.2 Djch chuyin trong difn trirdng cao

Sy tinh toan \ ^ tdc kio theo cac di^n tir ddi vdi d$c diim ciia di#n trudng dugc vi irC'n hinh 1.12 cho trudng hgp ZnO wurtzite, khi ting di^n trudng, v ^ tdc kio theo ciia di^n tir ting idi eye d^i cd 3.10^cm/s Khi ting di^n trudng han ni^a, thi v§n tic niy

CKun

100 200 300 T.'mpenturc("C)

400 : v^r * ;

1.5.3 Tinh chit difn cda ZnO pha tf p

ZnO cd mOt tiim ning ung dyng rlt Idn đi vdi nhiiu thilt bj quang hgc vimg budc sdng ngin Dl thu dugc khi ning đ thi ci hai lôi ZnO din loai n vi din lôi p

la khdng the thilu dugc, tuy nhiin vi^c pha tap hat tii li rlt khd khin, die bi^t li dl thu

dugc vat lieu din loai p Vdi ZnO di thu dugc tinh din loai n la tuang đi di ding bfing each du Zn hoic pha tap Al, Ga, In Tuy nhiin đi vdi pha tap loai p, ZnO biiu Ig di|n trd suat dang ki đi vdi su hinh thinh cic muc acceptor ndng Su khd thu dugc pha tap ludng cue (loai n va p) trong vat lieu viing cam rpng khdng phii la hiim ZnSe

va GaN rat di pha tap loai n, trong khi khd pha tap loai p

1.5.3.1 ZnO pha tap loai n

ZnO vdi cau true wurtzite la mpt chat bin dan vdi tinh din loai n ty nhiin do su khdng hgp thirc vi su cd mit ciia cac sai hdng bin trong nhu cac niit khuyit O (VQ) va

Zn diin ke (Znj) ZnO khdng pha tap thi hien tinh din loai n vdi mat dp electron rlt cao khoang lỐcm''

0 50 100 150 200 250 300 360

EJectric Field (kV/cm)

Hinh 1.13 Van toe keo theo cua electron doi vai dien truang trong

truang hap ZnO wurtzitẹ

Trong pha tap loai n, cac nguyen td nhdm III nhu Al, Ga, In dugc su dyng di thaj' thi Zn, cac nguyen td nhdm VII nhu CI, I thay thi Ọ Pha tap diing cac nguyen td Al,

Ga, In da dugc nhieu nhdm nghien cim ap dung va thu dugc cac mang ZnO vdi tinh

dan loai n, chit lugng caọ Myong va cac cdng sy da nudi cay mang ZnO pha tap Al

19

bang phuong phap MOCVD vi di thu dugc mang tinh din cao vdi dien trd suit thap nhll la 6,2.10"*Qcm Cac nghiin cim cung cho thIy d^c tinh cua mang ZnO lo^i n phy thupc vao nhiet dp tao mang, ndng dp hat tai cua mang ZnO:Al ting dan di?u khi nhi^t

dp tao mang tang, diiu niy dugc giai thich li do su anh hudng ciia cic donor ngo^i lai (Al' ) len cac vj tri thay thi (Zn^') vdi dp bin nhi^t cao han Ngoai ra, sy ting ndng dp hat tai cung chi ra ring, chit pha tap Al thay thi tdt tai vj tri nguyen tu Zn trong tinh

thi ZnO Trong khi dd, dien trd suit cua mang ZnO:Al giim dan di^u khi nhi^t dO t^o

mang tang, do sy tang ndng do hat tai tai biin hat va cac hieu img ben trong Vi ching,

sy giam dien trd suat la hgp nhat vdi sy ting tinh kit tinh va sy dinh hudng ciia ciu triic tinh the cua mang (hinh ve 1.13)

Sy pha t^p ZnO loai n cho din nay da cd nhung tiin bg rat tdt

1.5.3.2 ZnO pha t^p loai p

Vi^c pha tap loai p trong cac chat bin din viing elm rgng rat khd thyc h i ^ di

dugc nhlc lai nhiiu lln, vi nhu ddi vdi GaN va ZnSe Khd khin dd xult hi?n trong rlt nhiiu nguyen nhan, chat pha t^p cd the bj bii trir bdi cic sai hdng ty nhiin ning lugng

thap, vi dy nhu Zn, va VQ boic t^p chat nin (H).Cac acceptor trong ZnO bao gim cic

nguyen td nhom I nhu Li, Na, K, Cu, Ag, l6 trdng Zn va cic nguyin td nhdm V nhu N,

P, As Tuy nhien phan nhiiu trong chung hinh thanh cic acceptor sau va khdng ddng gop nhieu vao tinh dan loai p Cac nguyin td pha tap cd nhiiu triin vgng ddi vdi ZnO loai p thupc nhom V mac dii ly thuyit dua ra gia thuyit vi nhOng khd khan trong vi$c

thu dugc cac mire acceptor ndng, trong do N la chat pha tap cd nhiiu hua h^n nhlt

Tinh dan cua mang ZnO loai p phu thupc vao nhiiu yiu td, trong dd cd ndng d$ chat pha tap, nhiet dp de Nghien ciru cua Jianguo Lu va cic ddng sy vi sy inh hudng cua ndng dp N (mdi trudng NH3-O2) ddi vdi mang ZnO loai p di cho thIy tit ci cic mang deu the hien tinh din loai p, bieu thj ring N da dugc dua vao ming ZnO, ddng

vai tro la mot acceptor (bang I) Tinh chat dien tdt hern, vi nhu mat dp h^t tii N =

7,3.l0''cm \ dien trd suat p = 31Qcm va dp linh dpng Hall ji = l,3cm^A/s di thu dugc

ndng dp NH3 ting, N dua vao ZnO se dugc tang cudng Nhu vay, mat dp hat tai mang ZnO loai p dugc cai thiin Tuy nhiin, neu ndng dp NH3 qua cao, se tdn tai trong tinh thi ZnO niit khuyit Oxy va Zn diin ke mat dp Idn do sy thiiu ciia Oxy trong mdi trudng ddng vai trd cua cac donor Do dd mat dp hat tai ciia mang ZnO loai p giam manh vi su tu bii trir cao Ddi vdi hau hit cic mang, tinh linh ddng thap cd thi la kit qua tir clu tnic theo hinh cot hoan toan xic dinh va khi nang Idn chd sai hdng mang ddng vai trd nhu la trung tam tan xa cua hat tai

Bang 1 Tinh chat dien ciia mang ZnO kieu p, pha tgp N nudi cay a cac nong do khac nhau

31 7,6.10'

Do linh dong (cmWs) 2,4 1,3 1,9

Mat do hat tai (cm-^) +4,6.10"

+7,3.10"

+2,4.10'"

• »

Kiiu hat tai

Sau khi u nhiet, tat ca cac mang diu the hien tinh din loai p va cd tinh chit dugc cai thien so vdi cac mau mdi nudi cay (bang 3) Diiu nay dugc giai thich la do sy tang kha nang hoat hda ciia cac acceptor thy ddng vi qua trinh xu ly nhiet

20

Bang 2 Cac tinh ehdt di^n cua mang ZnO mai moc mam pha tgp P, ngung kit tgi cdc nhiet do de khac nhau (Ts)

122 11,7

Do linh dgng Hall (cm^/Vs) 2,15 1,26 0,704 0,0623 0,211 0,0875

Nong dg hat tai (cm'^) 4,50.10"

Hinh 1.14 Anh huang cua nhi^t dq di ddi vai tinh ddn ndng dg hgt tdi,

dg linh dgng Hall vd dien trd sudt cua mang ZnO

Bang 3 Tinh chat dien ciio edc mang ZnO:P u nhiet tgi 550^C

Do linh dpng Hall (cm^A^s) 0,181 0,173

Nong dp hat tai (cm"') 4,54.10"

1,07.10"

Loai

P

P

121

88,4

0,223 1,01 0,154 0,173

1.6 Tinh chat quang cua vat lifu bin dan

1.6.1 Cac d^c trung quang

Khi cd mpt chiim anh sang don sac chiiu vao mpt vat, do sy phan xa trin bi mit

va su hap thy bin trong, cudng dp chiim inh sang giim

a Hf so phin xa R(X)

Xac djnh blng ty sd giira cudng dp anh sang phan xa IR(A,) va cudng dp inh sing

ban diu tdi bi mat tinh thi lo(^) H? sd phan xa la mpt dai lugng khdng thii nguyin,

thudng bieu diin dudi dang phan trim

R{X) = lA^)/l,(X) (1.15)

Hi sd phan xa phy thupc vio budc sdng inh sang, sy phu thupc dd gpi li phi

phan xa ciia mau

b H$ so truyen qua T(X)

Xac djnh blng ty so giiia cudng dp anh sang truyin qua mlu va cudng dp inh

sang tdi Hi sd truyin qua la mgt dai lugng khdng thu nguyin, thudng biiu diin dudi

dang phan trim

T(X) = I,(?.)/I,(X) (1.16)

Hi sd truyin qua phu thugc vao budc sdng anh sing, su phy thupc do gpi la pho

truyin qua cua mau

c Hf so hap thy a(X)

Xic dinh tir djnh luat hip thy inh sing Buger-Lamber:

I(x) = Io(l-R)exp(-ax)

X I(x)

23

Cd thi xem h§ sd hip thy a(X) nhu xic suit h ^ thy photon inh sing trin mOt don vj

bi diy cua mlu H§ s6 h ^ thy li d»i lugng d$c trung cho mdi tnrdng hip thy vi phy

thupc vao budc sdng inh sing H$ sd hip thy cd thu nguyin li nghjch dio dO dii, phy

thupc vao budc sdng inh sing, su phy thugc dd ggi la pho hip thy

d Cic hing so quang

n ' - k ' =e,(co)

(1.18)

2nk = = 62(0))

EQCO

Ta thIy, cic hlng sd quang n (chiet suit), k (chi sd hip thy hay h§ sd tit), cQng

nhu £,,£; (phin thyc vi phin io ciia do di^n thim) vi bin chit li hoin toin tuang

duong nhau, diu li cic thdng sd vT md d$c trung cho tuang tic cua sdng di^n tir vdi

mdi trudng hap thy

Di die trung cho su hap thy sdng di^n tir cua vat chat, ngudi ta diing dai lugng

a = 2 ^ = ^ (1.19)

c X

D^i lugng a chinh la h^ sd hap thu di ndi tren, vi gii trj nd bing nghjch dio d$

day ciia lap vat lieu ma sau khi di qua ning lugng sdng di^n tir giim di e lln

H^ sd phin xa R liin h^ vdi cic hlng sd quang n va k theo cdng thirc

^ ^ ( n - l ) ! ^ (1.20) (n + l ) ' + k ' ^ '

Nhu vay mudn xac dinh cic hlng sd quang ta phii do h? sd hip thy ho|c h? s6

phan xa

1.6.2 Cac CO che hap thy inh sing

Khi chiiu mgt chiim anh sing don sic tin sd v (budc sdng A.), cd cudng dO Uv)

len bi mit tinh thi ban din thi mgt phin inh sing si phan xa trd lai mdi trudng IR(V),

mpt phan anh sang truyin qua chat bin din IT(V), phin con I^i hoic bj tin xa hojc bj

hap thu trong ban din Trong mpt viing phd cho trudc cIn phii tinh din cic CO chi h ^

thu chu yiu, co ddng gdp Idn nhlt vao phd hip thy Vi qui trinh hip thy inh sing

chinh li qui trinh chuyin ddi ning lugng cua photon sang cic dang ning lugng khic cua tinh thi nin cd thi phin chia thanh cic co chi hap thy nhu sau :

Hinh 1.15 Cac ca che hdp thu photon dnh sdng

' Hap thy co bin (hay hap thy riing) xiy ra khi di^n tu chuyen tir viing hda trj l£n

viing din (chuyin ddi 1 va 1 a trong hinh 1.15), hip thy co ban xiy ra khi hv > Eg

- Hap thy do cic difn tu ty do va Id trdng tu do liin quan din chuyen mdc ciia

diin tu hoac l6 trdng trong vimg nang lugng cho phip hay giiJa cic vimg eon cho phip

(chuyin ddi 2, 2a-d)

- Hap thy do tap chit liin quan din chuyin muc ciia diin tu hay lo trdng githi cic muc bin trong tam tap chit hoic giu'a cac viing nang lugng cho phip vi cic mdc nang lugng t^p chat trong viing cam (chuyin ddi 3, 3a-c, 4)

- Hap thy do chuyin muc gi&a cic tap chat liin quan din chuyin muc cua di§n td hay Id trdng giira cac mire tap chat trong vimg cam

- Hap thy exciton liin quan din sy hinh thanh hoac phan hiiy exciton (chuyin ddi

5, 5a)

- Hap thy plasma liin quan din viec hap thy nang lugng sdng inh sing cua

plasma diin tu - Id trdng dan din su chuyin plasma lin trang thai lirgng td cao han

- Hap thy phonon, liin quan din sy hap thy ning lugng ciia sdng anh sing bdi cic dao ddng mang tinh thi va tao thanh cic phonon mdi

25

Trong hip thy co ban, chuyin muc ciia diin tiir kh&ig kem theo sv thay doi dh vecto sdng if (chuyin muc 1 hinh 1.15a) dugc ggi li chuyin mtrc thing, chuyin mfe

thing chi cd thi xay ra khi diy viing din va dinh viing hda trj ciia bin din nim d cin%

mgt gia trj k trong khdng gian victo sdng Chuyin mire kim theo sy thay dii ding U cua vecta sdng T(chuyin muc la hinh 1.15a) dugc ggi la chuyin mure n g h i ^ Hip thu CO ban chuyin muc nghiing nhlt thiit phii cd sy tham gia cua phonon

/ / \ '

I

Hinh 1.16 Chuyin ddi thdng (a) vd chuyin dai nghiing (b)

trong qud trinh hdp thu cua bdn ddn

Quy tic Ipc lya cho cic chuyin muc thing vi dugc phip: k, s k^

Trong chuyin ddi thing dugc phep, h? sd hap thy a(v) xac djnh bdi:

1.7 Tinh chat quang cua ZnO

Cac tinh chat quang ciia mpt vat lieu ban din cd quan hf vdi ca cic hifu ung tir bin ngoai \ a ben trong chat ban dan Cac dich chuyin quang hpc bin trong gifta cic electron

trong vimg din va Id trdng trong vimg hda tri, bao gdm ca cic hieu ung exciton do tuang tic Coulomb, cac exciton dugc phan loai thanh cac exciton tu do va liin kit Cic tinh chat quang cd tic dgng tu bin ngoii liin quan din cac chat pha tap va sai hdng, thong thudng chiing tao ra cic trang thii diin tu giin doan trong viing cam, v i v i t h e inh hudng din ca cac qua trinh hip thy va hue xa quang Cic trang thai diin tu trong Uin kit exciton phy thugc manh vao vat lieu bin din, die biet la cau tnic viing Theo ly thuyit, exciton cd thi liin kit vdi cic donor, acceptor trung hda va mang difn Ddi vdi liin kit donor - exciton trung hda ndng, vi dy, hai electron trong liin kit exciton da dugc gii thiit la lien kit thanh trang thii ddi electron vdi spin blng khdng Tuang ty, ddi vdi liin kit acceptor - exciton trung hda ndng ciing dugc hy vgng c6 trang thii cip l6 trdng nh$n dugc tir dinh viing hda tri va mpt electron tuang tac

Di lam ra cac thiit bj quang diin tu hieu suat cao, can thiit phii khao sit cic tinh chat va cac qua trinh chuyin trang thai quang hpc trong ZnO Cd rlt nhiiu cic ky thu$t thuc nghiim dung di nghiin cuu cic qua trinh chuyin ddi quang trong ZnO nhu h ^ thy, truyin qua, phan xa, huynh quang Trong phan nay, dau tiin chiing ta xem xit cic tinh chat ciia cac exciton bin trong, sau dd si tim hiiu cac liin kit ciia donor vi acceptor vdi exciton

1.7.1 Cic exciton tu do

Viing dan cua ZnO vdi cau tnic tinh thi wurtzite dugc xay dung tir cic tr^ng thii

s vdi hinh dang ddi xung Vung hda tri d trang thai p N6 bi tich thanh ba viing do trudng tinh the va tuang tic spin ~ quy dao Trudng tinh thi va tuang tie spin - quy dao nay chi phdi quang phd hap thy va phat xa d gan viing cam Cac dich chuyin exciton tu do bao gdm mpt electron tir vimg dan va mpt Id trdng tir ba viing hda trj dd

cd ten lln lugt la A (dugc cho la Id trdng ning), B (dugc cho la lo trdng nh?) vi C (tuang duong vdi tach vimg trudng tinh thi)

27

Ning lugng chuyin ddi ciia cic exciton ndi tai dugc tinh toin vdi nhieu ky thu|l khic nhau nhu quang phd hip thy nhif t do thIp, quang phd phan xa, quang pho huynh quang.Nghiin ciru phd huynh quang li mgt phuang phip hif u qua di khio sit clu tflk

Hinh 1.17 Viing exciton tu do trong quang phd PL cua ZnO a 15K

exciton Hinh 1.17 cho thIy mpt quang phd huynh quang tiiu biiu trong vimg excitonic

CO ban d 15K, vach phat xa tai 3,378eV dugc nghl din nhu li cic exciton A tg do v4

trang thii dich chuyin kich thich diu tiin ciia chiing

1.7.2 Cic exciton lien ket

Cac muc ning lugng electron rdi rac trong viing cam cua ZnO dugc sinh ra do cic tap chit hoac sai hdng trong vat lieu ban din, nd anh hudng din cic qui trinh hip thy

va phat xa quang hpc Kiiu vi cau tnic vimg cua vat lieu bin din inh hudng tdi cic trang thii electron cua liin kit exciton Cac donor va acceptor trung hda ho$c tich difn

cd thi lien kit vdi exciton

Cac lien kit donor - exciton (DBE) trung hda, ndng ndi chung chiim uu thi trong quang phd PL nhiet dp thap cua mang ZnO chat lugng cao do su cd mit cua cic nguln

donor duac dem den khdng chii y tir cac lap chat hoac cac sai hdng d mure ndng Cic

liin kit acceptor - exciton (ABE) thinh thoang cung quan sit thIy d mpt vii mang ZnO

cd ndng dp acceptor dang ki Cic vach sic net trong quang phd PL sinh ra do sy kit hgp cua cic exciton liin kit li diu hif u diing di nhan ra cic sai hdng hoic cic nguon tap chat khic nhau Mpi vach liin kit donor - exciton va acceptor - exciton diu quan sat dugc trong dai tii 3,348 - 3,374eV Hinh ve 1.18 thi hifn quang phd PL cua mlu khdi ZnO, cic vach phd ndi bat do liin kit exciton A vi cic donor trung hda quan sit thIy d 3,3598 ( D X ) ; 3,3605 (D^XJ; 3,3618 (D?XJ; 3,3650 ( D X ) va 3,3664eV (DjX^ ) Vach phd manh khac quan sit thay tai 3,3724eV (D^Xg) la do liin kit exciton

ly do B va cic donor Khoang ning lugng giira peak dd va peak chinh tai 3,3605 (D^X^) vio khoang I2meV phii hgp vdi ning lugng phan tich ciia cic vach exciton ty

do A va B 6 viing nang lugng thap ciia quang phd cic vach ABE ciing quan sit thIy tai 3,3564 (A?X^); 3,3530 ( A X ) v a 3 , 3 4 8 I e V ( A X ) T r o n g viing ABE, peak chinh tai 3,3564 (A^X^) ndi chung ludn quan sat thay theo thdng bio cua cic nhdm nghiin curu khic nhau va cd thi cd liin quan din cic acceptor Na hoic Li Hai peak yiu hon

cd thi chi ra su cd mat ciia cic trang thii acceptor sau hon

I

a

3.350 3.360 3.370

Photon Energy (eV)

Hinh 1.18 Viing exciton lien ket trong quang phd PL cua ZnO tgi lOK

29

1.8 Cac tiep xuc trong bin dan:

1.8.1 Tilp xic p-n ding the

Cac tilp xiic ddng vai trd quyit djnh tdi nhiiu ung dyng cua cic chat bin din

Phuang phap cd diin nhlt di tao tiip xiic p-n la bing khuyich tan

Chung ta xem xet tilp xiic p-n khi khdng cd thi hif u djch, khi do nd chi cin bing theo diiu kien can bing nhiet dgng Diiu nay cd nghia li, thi hoa hgc^ bing hing si trong viing tiip xuc Vi ^ la gin ria viing hoa tq ddi vdi bin din lo^i n, cic vimg ning

lugng bi be cong khi di qua tiip xiic nhu hinh vi

Hinh 1.19: Su udn cong viing ndng lugng khi cd tiip xiic

Khi ning lugng bi bi cong, ^ si d gan giua cua viing va vi vay ma n < n©, p < Trong dd no, Po: la ndng do sau ben trong ciia loai n vi p, viing niy dugc ggi 14 viing ngheo

Po-Gia thiet tiip xuc la rd net, Na va Nd thay ddi dgt nggt tai vimg tilp xuc, vi gii thiit Nd - Na, Po = Na-

Khi dd, trong vung ngheo p < N^ d bien trai va n < Nj phia bin phai Trong dd N

\ a Nj la mat dp idn hoa cua acceptor va donor Khi dd, cd mpt mang ludi cic difn idn

am ben phia ban dan loai p ciia tiep xiic va mpt hf thdng difn duong bin phia bin din

loai n Hai loai difn tich khac nhau nay tao ra mpt difn trudng, chinh li nguyin nhan din din viing ning lugng bj udn cong

Hinh 1.20 Tinh chat vung ngheo hgt tdi

1.8.2 Tiep xiic p-n dj the:

Niu mpt chit ban dan, cd vimg ning lugng hep thupc loai p va mpt chat ban din

cd viing nang lugng rpng han Ihudc loai n tiip xiic vdi nhau Muc Fermi cua chiing si

31

thang hing khi trang thii can blng dugc thiit lap, vi v^y vimg ning lugng cua chm

cung bi be cong Mdi trudng difn tu ngi ciing dugc thiit l^p gi&a hai viing tiep xi

gidng nhu md hinh ciia tiip xiic ddng thi

Khi dd, viing difn tich khdng gian ciia tiip xiic p-n dj thi:

1

'^ J (1^2)

N, va Nd Ian lugt la mat dp ion hoa mang cua bin dan loai p vi n Theo djnh ^

Gauss, truang dien tir se la:

^ i?//j(x-xy) 0 <x <XM

(1.23)

Vdi Ep va En la hing so di?n moi cua ban dan loai p va n

Vi vecto cam ung phap tuyen D = e.E phai lien tuc tai x = 0, nen NaXp = NpXn

DQ doc cua the tinh di^n dugrc xac djnh khi biet gia trj am ciia di^n tnrdng, vi di^

trucmg bang gradient ciia the tinh di?n, va mang dau am

Neu chon the ning bJng 0 khi x < Xp ta co:

Thi tiip xLic dugc tinh loan blng each su dyng cac gia tri trong khdng gian bl

chieu ciia cac mire Fermi Fn, Fp cac gia trj do dugc d ria viing hoi tri va viing din E^

Ecn trudc lien kit:

(1.25)