BO GIAO DUG VA OAO TAO
DAI HOC QUOC GIA HA N O I
TRLTCJNG DAI HOC KHOA HOC TlTNHIEN
-oOo-
Le Thi Thanh Birth
Che tao va nghien cihi mot so tinh chat cua cac mang
mong ban dSn dung dich ran A B
Chuyen nganh: Vat ly Dien tijf
J
LUAN AN PHO TIEN SI KHOA HOC TOAN - LY
NGUdl HU^6NG
DAN
KHOA HOC
l.GSPTSLeKhacBinh
2. PGS PTS Nguyen Ngoc Long
O C r O N ' - '-:••:)'• MAf.OI;
HA NOI -1996
MUC
1.3.2 Ha'p thu chuyin ddi thang
1.3.3 Ha'p thu chuyin ddi nghieng
1.4. Cac cach^'phat huynh quang trong ban dan
1.4.1
1.4.2
1.4.3
1.4.4
1.4.5
1.4.6
Khai niem chung
Mo hinh tpa dp cau hinh
Tai hop viing - viing
Tai hop buc xa qua cac trang thai exciton
Chuyin ddi vung - tap ch^t
Chuyin ddi done - axepto
1.5. Mdt s6 phuong phap ch^'tao tinh thi va mang dung dich thi
1.5.1 Cdc phuong phap klo dan tinh the
1.5.2 Cac phuong phap che tao mang dung dich ran
10
12
13
15
15
17
18
20
20
44
45
2.2. Ha bdc bay chan kh6ng
45
2.2.1 Bom chan khdng
2.2.2 Buong hoc bay
2.2.3 Ngudn bdc bay
2.2.4 D^bdc bay
45
45
47
47
2.3. H e do phd huynh quang va phd truyen qua
47
2.3.1 H e do phd huynh quang
2.3.2 H e do ph6 truyen qua
2.3.3 Cac phep do khac
47
50
51
3.4.2 Phuong phap hda dung dich mudi tap chat cung vao dung dich phun nen
63
3.5. Tao dien cue trong sudt Sn02 va l^m dien cue ohmic len mang Zn^^Cdi.^^S
66
3.6. Che'tao mau Zn^Cd^.^S bang phuong phap diing Id vi song
68
3.7. Ph6 nhilu xa tia X ciia mtlng Zn^Cdi.,S
70
3.8. Anh bfe mat cac mang Zn^Cd^^^S chup bang kinh hiln vi dien tu
73
3.9. K a luan
75
Chirang 4. TINH CHAT QUANG vA HUYNH QUANG CUA M A N G Zn.Cdi
KHONG PHA TAP
,S
4.2.7 Hien tupng quang hda ciia mang Zn^Cd,,^S
4.3. K^ luan
94
99
105
Chirang 5. HUYNH QUANG CUA CAC M A N G ZnxCd,.xS PHA TAP Cu VA Mn 106
5.1. Phd huynh quang ciia m ^ g Zn^Cdi^^S : Cu
5.1.1 Dang pho huynh quang. Anh hudng cua sir pha lap ddng len pho huynh quang
5.1.2 Ph6 huynh quang cua mang Zn^Cdj ^SiCu vdi cac thdng sd thanh phan x khac
nhau....=...
5.1.3 Ph6 huynh quang cua mang Zn^^Cdi.^S : Cu khi kich thfch lien tuc
vdi cac cudng dp khac nhau va a cac nhiel do khac nhau
5.1.4 Ca che' biic xa ciia dai sdng dai trong phd huynh quang cua mang
Zn^Cd,.^S:Cu
5.1.5 Tach ph6 huynh quang
5.2. Phd huynh quang ciia mang Zn^Cdi^^S : Mn
5.2.1 Dang phd huynh quang. Anh hudng ciia su pha tap len ph6 huynh quang
5.2.2 Pho huynh quang ciia mang Zn^Cdi.^S : Mn vdi cac thong sd thanh phan
x khac nhau
5.2.3 Sir phu ihupc cudng dp kich thfch va nhiet dp cua pho huynh quang ciia
mang Zn^Cdi.,S : Mn
5.2.4 Ca che'biic xa ciia dai song dai trong pho huynh quang cua mang
Zn^Cdi.^SrMn
106
106
109
111
- dai tu kich boat
- dai sdng dai
- nhiet dp de'
- nhiet dp do
- cudng dp kich thfch
- ban dp rpng dai pho
- xac sua't chuyen ddi biic xa cap D-A
MO
DAU
Hap chat ban dan A " B ^ la ddi tupng nghien cuti ciia rat nhieu cong trinh. Cac
hop chat A B
cd nhieu dac tinh ca ban dang quy nhu dp rpng viing cam Idn,
chuyen miic thing.
Dp rpng viing cam Idn ciia cac hop chat A B
cho phep md rpng gidi ban ufng
dung cua cac linh kien quang dien tuf sang mien nhin thay va cue tim gan.
Viing cam ciia cac hop chat A B
deu la thang, ddng thdi cac chuyen miic phat
quang gay ra bdi cac tam sau cd xac suat Idn, nen cd the by vpng cac chuyin ddi
dien tu vdi hieu suat lupng tu cao. Vi du ddi vdi ZnS, hieu suat lupng tu phat quang
doi lien tuc th 2,4 eV den 3,7 eV. Mang Zn^Cdi.^S hiia hen nhieu trien vpng suf
dung trong cong nghiep che tao cac linh kien quang dien tir nhu cac pin mat trdi,
cac diot phat quang, cac quang trd.
Nghien cufu cac tinh chsft quang va huynh quang cua mang Zn^Cdi.xS cho den
nay vin la de tai hap dan cac nha vat ly ban dan. Cac ket qua nghien ciiti nay cd the
cung cap nhuHg thdng tin ve ban chat cua nhiitig tam tap chat hoac ve cau tnic vi
md cua cac tam huynh quang, ca che biic xa huynh quang.
De nghien ciiru cac tinh chat quang va huynh quang cua ban dan, ngudi ta
thudng sir dung cac phuong phap pho hap thu va pho huynh quang. Viec su dung
cac phuang phap huynh quang cho phep don gian hda va lam giam gia thanh he
thdng do ludng kiem tra trong san xuat, bdi vi viec kiem tra cac dac tnmg huynh
quang cd the thay the viec do dac hang loat cac dac tnmg dien, quang dien cua vat
lieu. Trong sd cac phuong phap pho huynh quang thi quang huynh quang la phuong
phap dupe pho bien rpng rai nhat. Dd la phuong phap nghien culi nhay nhat ddi vdi
nhutig vat lieu cd ndng dp tam tap thap. Phuang phap nay con cd iru diem la khdng
can tao dien ctrc len ban dan, phep do cd the thuc hien nhanh, dan gian va chfnh xac
ma khdng ddi hoi cac thiet bi phiic tap [31].
Mac dii tinh chat quang va huynh quang cua mang Zn^Cdi^S da dupe mot sd
tac gia nghien ciiti, nhung ban chat cua cac dai pho, ca che phat huynh quang cua
cac tam vSn con la nhihig van de chua dupe lam sang to.
Tinh chat quang va huynh quang cua mang Zn^Cdi.xS che tao bang phuang
phap phun dung dich len de ndng Ian dau tien dupe nghien ciiti va cong bd trong
luan an nay.
Luan an dupe hoan thanh trong 5 nam (1992-1996) tai phdng thi nghiem cua bp
mon Vat ly Dai cuang, trudng Dai hpc Khoa hoc Tu nhien. Luan an dupe mang ten
"Che tao va nghien ciiti mot sd tinh chat cua cac mang mong ban din dung dich ran
A"B^".
Muc dich cua luan an nham:
Ngoai phan md dau, ket luan va danh muc tai lieu tham khao, luan an dupe
trinh bay trong 5 chuong:
- Chuang 1: Cac hop chat ban dan ZnS, CdS va dung dich ran ban dan
Zn^Cd^.^S.
- Chuang 2: Ky thuat thirc nghiem
- Chuang 3: Che tao va nghien ciiu cau tnic cua mang Zn^Cdi.^S
- Chuang 4: Tinh chat quang va huynh quang cua mang Zn^Cdi.^S khdng pha
tap
- Chuang 5: Huynh quang cua mang Zn^Cdi.^S pha tap Cu va Mn
Chuang 1.
CAC HOP CHAT BAN DAN ZnS, CdS
VA CAC DUNG DICH RAN BAN D A N ZoxCdi XS
1.1, Cau true tinh the cua Z n S va C d S
1.1.1 Cau true mang lap phirong gia Rem [6]
,
Nhom ddi xihig khong gian cua tinh the^ A. HT^VI
B ling
vdi mang tinh the nay la
Ti-F43m(hinhl)
Hinh 1. Cau true mang tinh the lap phuang gia kem [80]
.VI
nguyen tu B
(S), w^ nguyen tu A (Zn)
Lap phuong
gid kem a (A )
ZnS
ZnS
CdS
CdS
5,4145
5,832
Luc giac Wurtzite
a(A°)
c(A°)
3,8230
6,2565
4,1348
6,7490
Bang I. Cac thong sd mang cua ZnS va CdS [10]
1.1.3,3
ZnjCdi_j^
Trong dung dich ran, su xuat hien sai hong mang cd the la do sir thay the mot
loai nguyen tu nay bang mot loai nguyen tuf khac. Neu hai chat ban dau cd cau tnic
khac nhau thi cd su chuyen cau tnic tiif trang thai nay sang trang thai khac. Su bien
Vung Brillouin ddi vdi mang dao nay la 1 khdi bat dien dupe md ta tren hinh 3.
Ak
Hinh 3. Vung Brillouin ddi vdi mang tinh the lap phuang gia kem [6]
10
Bang mot sd phuang phap nhu phuang phap gia the, phuang phap sdng phang
true giao, ngudi ta da tinh toan dupe cac viing nang lupng cua cac hop chat A B
Tat ca cac hpp chat A B
hpp chat A B
.
deu cd viing cam thang. Dp rpng viing cam cua cac
giam khi nguyen tuf lupng tang. Ddi vdi mang kim cuang trong
khdng gian vecta sdng, tai k = 0, trang thai nang lupng cao nhat cua viing hda tri
ling vdi r25 suy bien bac 3.
Ddi vdi mang lap phuang gia kem, trang thai cua r25- chuyen thanh Ti^y. Neu
tinh den tuang tac spin quy dao thi trang thai ri5v tai k = 0 se suy bien bac 6 thanh
trang thai Tg suy bien bac 4 va trang thai Fy suy bien bac 2. Su suy bien tai k = 0
duac bieu dien tren hinh 4.
(0,0,0)
Hinh 4. Sa do vung nang lupng cua mang tinh the lap phuang gia kem
tai lan can^ = 0 [6]
E,eV
Hinh 7. Sa do viing nang lupng ciia tinh the lap phuang ZnS [14]
CdS
E,eV
h^
8
v^
J
^
'^ns
.^4
^s
6
-Ll
^;
\
He sd dac trung cho qua trinh hap thu la he sd hap thu a. Neu anh sang cudng
dp IQ, fan sd VQ chieu den ban mong ban dSn cd chieu day d, thi anh sang sau khi ra
khdi mlu se cd cudng dp I tuan theo dinh luat Bouguer - Lambert:
I(Vo) = Io(Vo)exp(-ad)
(1)
trong dd a la he sd hap thu cua ban dSn d tan sd VQ cd thii nguyen c m ' \ Nd cho
biet dp day tuong ling cua chat ban din ma khi anh sang truyen qua cudng dp se bi
giam di e Fan.
15
a la ham sd ciia fan sd anh sang va phu thudc vao ban chat cua chat ban din. He
so hap Ihu (y l^ vdi: mai dp cac iam ha'p Ihu va (iel ditn han ihu ciia chung:
a = crN
(2)
Tiet dien hap thu ciia tam phu thupc vao nang lupng photon va ban chat ciia tam
hap thu. N^'u trong cha't ban din cd i loai tam. ha'p thu vdi cac ban cha't khac nhau
thi:
a = Xcc, =E^.:(hv)N,
trong ao:
(3)
a^ - ne sd nap tnu cua tam i
Nj- ndng dp tam i
Eg.
2 - Hip thu tap chit xiy ra do hien tupng ion hda cac nguy6n tir tap chit. Trong
qua trinh nay dien tir tiit miic nang lupng tap chit dupe chuyin ddn viing din hoac
dien tu tir viing hda tri dupe chuyen len miic nang lupng tap chat.
3 - Hip thu bdi cac hat tai dien tu do xay ra khi cac hat tai nay chuyen dpng
dudi tac dung ciia dien trudng sdng anh sang.
4- Hip thu bdi dao dpng mang xiy ra khi anh sang tuang tac vdi dao dpng
mang lam thay ddi sd phonon quang hpc.
5 - Hip thu exciton xay ra ddng thai vdi su hinh thanh cap dien tu - Id trong Hen
ket (exciton).
16
I
I
6 - Hap thu plasma do tap hop cac dien tu va Id trong tu do gay ra.
He sd hap thu dac tnmg cho kha nang hap thu photon cd nang lupng hv cua he
dien tu cd mat dp trang thai ban dau U; de chuyen tdi trang thai cao ban cd mat dp
trang thai nf. Neu xac suit chuyin rdi tuf trang thai i sang f la pif thi he so hap thu se
la:
a( hv) = ASP.jn.nj
trong do:
(7) chinh la dieu kien Ipc Ipa cho cac chuyen mufc thing. Trong trudng hpp nay
he sd hap thu :
Hinh 9. Chuyen ddi thang trong qua trinh hap thu cua ban din [30]
Chuyen ddi thang cd the xay ra khi day viing din va dinh viing hda tri cua ban
din nam d cung mot gii tri k trong khdng gian vecta sdng. Hinh 9 la sa do chuyen
ddi thing trong hap thu ciia ban dan.
1.3.3 Hap thu chuyen ddi nghieng [27]
Ddi vdi nhiing ban din cd viing cam khdng thing, trong qua trinh chuyen ddi,
nang lupng va vecta sdng ciia dien tut deu bi thay ddi. Chuyin ddi nay phii thuc
hien theo hai budc va cd su tham gia cua phonon. Mac dii trong tinh the ton tai rat
nhieu phonon khic nhau, nhung cac phonon khac tham gia trong cac chuyen miic
quang hpc chi gdm cac phonon dap ling cac dieu kien:
k. + q = kf
Trong qua trinh dd, nang lupng se dupe bio toan:
18
(9)
voi:
hVa = Ef - Ej - Ep
(10)
- Huynh quang catot (cathode) xuat hien khi chieu chiim tia dien tut cd nang
Itfpng cao.
20
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