Chế tạo và nghiên cứu một số tính chất của các màng mỏng bán dẫn dung dịch rắn a2b6

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

LUC

Mord^u

1

Chirang 1. CAC HOP CHAT BAN DAN ZnS, CdS vA CAC DUNG DICH RAN
BAN DAN Zn,Cd,.,S
1.1. Cft'u true dnh thi cua ZnS va CdS

5
5

1.1.1 CS^u tnic mang lap phuong gia kem
1.1.2 C^u tnic mang luc gidc Wurtzite
1.1.3 Mang tinh the ZnS va CdS

5
6
8

1.2. Ca'u tnic vising nSng lupng cua ZnS va CdS

10

1.2.1 Ca'u tnic viing nang lupng ciia mang I^p phuong
1.2.2 Ca'u true virng nang lupng cua mang luc giac Wurtzite
1.2.3 Viing nang lupng cua ZnS va CdS
1.3. Tinh ch^t h^p thu ciia ban dSn
1.3.1 Khai niem chung

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

21
25
28
33
35
37
37
38

1.6. T6ng quan v^ dung dich ran Zn^^Cdi.j^S

39

1.7. K6t luan

41

Chirang 2. KY THUAT THl/C NGHIEM

43

2.1. He tao mang

43

2.1.1 L6
2.1.2 Bpgamau
2.1.3 He thdng vdi phun, khi nen

44

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

2.4. K ^ luan

Chuong3. CHE TAO VA NGHIEN

51
CLTU

CAU TRUC CUA M A N G Zn^Cd,.,S

53

3.1. Tao mang Zn^^Cdj.^S bang phuong phap phun dung dich len de'ndng

53

3.2. Anh hudng cua nhiet dd d^d^n ch^t lupng m^ng

55

3.3. Ch^d6 u mang

60

3.4. Che^dOphatap

61

3.4.1 Phuong phap nhiing mang vao dung dich mudi tapcha'trdi ii d nhiet dp cao

61

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

78

4.1. Tfnh cha't quang cua mang Zn^Cd].xS

78

4.1.1 Ph6 hSp thu cua mang Zn.Cdi.^S
4.1.2 X^c dinh d6 r6ng viing ca'm cua cac mang Zn^^Cdi.^S
4.2. Huynh quang ciia cdc mang Zn^Cdi.^S khdng pha tap

78
80
82

4.2.1 Dang phd huynh quang
4.2.2 Su phu thudc ciia dinh ph6 huynh quang theo thanh phan x
4.2.3 Pho huynh quang phan giai thai gian, su phu thupc ciia pho huynh quang
v^o cudng dd kich thich. Thdi gian sdng huynh quang
4.2.4 Anh hudng ciia che'dd li nhiet len huynh quang ciia mang Zn^Cdj.^S
4.2.5 Su phu thudc nhiet dd cua ph6 huynh quang cua cac mang Zn^Cdj.^S

83
86
87
91
92


4.2.6 Co che' biic xa cap dono - axepto trong phd huynh quang cua mang
Zn^Cdi.^S khdng pha tap

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

113
114
117
117
120
121
123

5.3. K ^ luan

124

Ket luan

126

Cac cong trinh khoa hoc lien quan den luan an

129

Danh muc tai lieu tham khao

131


DANH

SACH CAC K t HIEU StTDLNG TRONG LUAN AN

a

<7i

e
X
M
11
T

d
hv
k
m*^.
m*h
Hi
^
X

D-A
E.A
ED

E,,,
Eg
Ei
Ep

R
SA
SD
Td

1

J
'W

w^.

- he sd'ha'p thu
- tie't dien ha'p thu ciia tam i
- hang sd dien moi ciia cha't ban dSn
- budc sdng anh sang
- khdi lupng rat gpn ciia exciton
- ndng dp tap cha't
- thdi gian sdng huynh quang ciia mang
- dd day ciia mang
- nang lupng photon
- vecta sdng ciia dien tii
- khdi luomg hicu dun^ cua dien tix
- khdi lupng hieu dung ciia 16 trong
- mat dp trang thai i
- vecta sdng cua phonon
- thanh phan Zn trong mang
- dono - axepto
- nang lupng ion hda axepto
- nang lupng ion hda dono
- nang lupng dinh huynh quang
- nang lupng viing ca'm
- nang lupng dien tir d trang thai i
- nang lupng phonon
- he sd phan xa

- 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

c d t h e d a t g a n 100% [15].
Ngay nay, tit cac hop chat A B , ngudi ta da che tao dupe cac bpt huynh quang
hieu suat cao, cac quang trd nhay trong viing nhin thay.
Trong cac hpp chat A B , ZnS cd dp rpng viing cam Idn ban ca (Eg = 3,7eV).
Cung vi the ma ZnS cd limg dung thuc te rpng rai. Bpt huynh quang ZnS dupe sii
dung trong cac tu dien huynh quang, cac man Rangen, man cua cac dng phdng dien
tu. Ngudi ta da che tao dupe nhieu loai photodiot tren ca sd chuyen tiep p - n cua
ZnS. Suat quang dien dpng (photo emf) <5 cua chuyen tiep p - n tren tinh the ZnS
thudng dat tdi 2,5 V [15]
Ben canh ZnS, CdS (Eg = 2,4 eV) cung la mot trong cac vat lieu quan trpng
nhat thudng dupe sir dung trong cac luxmeter va cac he thdng pin mat trdi. Ddi vdi
cac he thdng pin mat trdi, mang mong CdS thudng dupe dting lam vat lieu cUa sd
trong cac chuyen tiep di the vdi cac ban dSn boat quang nhu Cu^S [47], CdTe [36].
Khong chi cac hop chat A B , ma ca cac dung dich ran ban dfin tren ca sd cac
hap chat nay cung dupe nghien ciin mot each rpng rai va cd nhieu ling dung trong
thuc te.


Dp rpng viing cam cua dung dich ran A B

cd the thay ddi dupe tiiy theo thanh

phan cua hop chat trong dung dich ran. Dieu dd tao ra kha nang che tao nhiJng
ngudn phat quang va cac dau thu quang lam viec trong viing pho trai rpng tir viing
hong ngoai tdi viing kha kien.
Mang Zn^Cdi^S la mot trong cac mang dung dich ran A B

dupe quan tam

nghien cuti nhieu [13, 83, 74, 21, 47]. Dp rpng viing cam cua Zn^Cdi.^S cd the thay

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:

1- Che tao mang dung dich ran ban dan bang phuang phap phun dung dich
2- Pha tap vao mang
3- Nghien ciiru tinh chat quang va huynh quang ciia mang ZUxCd^.^S
4- Nghien ciiu tinh chat huynh quang cua mang Zn^Cdi.xS pha tap Cu va pha
tap Mn.
Phuang phap nghien ciiu cua luan an la phuang phap thuc nghiem:
1- Cac mang Zn^Cd^.^S dupe che tao tren he phun dung dich do chung tdi tu che
tao.
2- Cac phuang phap phan tich bang ky thuat Vi phan tich tia X, nhilu xa tia X,
kinh hien vi dien tuf da dupe su dung.
3- Cac pho truyen qua va huynh quang cua cac mang Zn^Cdi.^S dupe khao sat
vdi cac thanh phan x thay ddi, ndng dp tap chat thay ddi, trong mien nhiet dp 77K 300K. Mot sd pho dupe do tai 2K va 4K.
4- Cac pho phan giai thdi gian cua mang Zn^Cd^.^S dupe do d 77K va 300K.
Cac ket qua chinh cua luan an la:
1- Da xay dung va hoan thien cac he tao mau, lam dien cite va cac he do pho
truyen qua va huynh quang.


2- Bang phuang phap phun dung dich len de ndng da che tao dupe mang da tinh
the dung dich ran ZuxCdi.^S cd dp rpng viing cam thay ddi tiir 2,4 eV den 3,5 eV va
cd hang sd mang phu hop vdi hang so mang cua don tinh the hoac mang Zn^Cdi.^S
che tao bang cac phuong phap khac.
3- Lan dau tien nghien cuu mot each he thdng pho huynh quang ciia mang
Zn^Cdi.xS che tao bang phuang phap phun dung dich, khdng pha tap va cd pha tap
Cu, Mn. Tim ra quy luat phu thudc ciia nang lupng dinh huynh quang cac mang vao
thanh phan x, nhiet dp T va ndng dp tap chat t] trong mang.
4- Lan dau tien cac pho huynh quang phan giai thdi gian cua mang Zn^Cdi.^S
va su phu thupc cua pho huynh quang vao cudng dp kich thfch dupe nghien ciiti.
Cac ket qua thuc nghiem dupe giai thich thoa dang, neu gia thiet ca che phat huynh
quang cua mang la su tai hpp cua cap dono - axepto.

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)

IIT^VI

O cau tnic nay mdi d nguyen to chiia 4 phan tu A B

vdi tpa dp cac nguyen

tula:
- 4 nguyen tii B,vi a vi tri |a , cd cac tpa dp:
(0, 0, 0), (0, 1/2, 1/2), (1/2, 0, 1/2), (1/2, 1/2, 0)
- 4 nguyen tir A d vi tri |c|, cd cac tpa dp:
(1/4, 1/4, 1/4), (1/4, 3/4, 3/4), (3/4, 1/4, 3/4), (3/4, 3/4, 1/4)
Khac vdi cau tnic lap phuang cua kim cuang do mot nguyen tuf tao nen, cau tnic


gia kem chiia hai loai nguyen tut khac nhau. Ddi xiing diem d cac vi tri |a| va |c|
tuong utng vdi 43m. Mot nguyen tut bat ky dupe bao bpc bdi 4 nguyen tu khac loai:
Mdi nguyen tu

A"(B^)

dupe bao quanh bdi 4 nguyen tu B (A ) nam d dinh ciia tii

dien tren khoang each — j — , vdi a la thdng sd cua mang lap phuang.
Mdi nguyen tut A (B ) con dupe bao bpc bdi 12 nguyen tu ciing loai, chiing la
lan can bac 2, nam tren khoang each

fl

. Sau nguyen tu trong sd dd nam d dinh

cua luc giac, tren ciing mot mat phang vdi nguyen tir ban dau. Sau nguyen tir con lai
tao thanh phan lang tru gdm 3 nguyen tut nam d mat phang cao ban va 3 nguyen tu
nam d mat phang thap ban mat phang luc giac ke tren.
Dac tinh quan trpng ciia cau tnic nay la khdng ton tai tam ddi xiing hay tam
dao. Cac Idp A " - B ^ dupe dinh hudng theo true [111]. Do dd tinh the A " B ^ ' lap
phuang gia kem cd tinh di hudng. Cac mat ddi xufng nhau (h k 1) va (h k 1 ), cac
hudng ngupc nhau [h k I] va [h k 1 ] cd the cd tinh chat vat ly khac nhau.

1.1.2 Cau true mang luc giac Wurtzite [6]
Nhdm ddi xiing khdng gian cua mang tinh the nay la C'^gy - Pdamc. Mdi d
nguyen to chiia hai phan tu A B . Trong dd hai nguyen tii A " nam d vi tri: 0, 0, 0
va 1/3, 2/3 , 1/3 va hai nguyen tu B ^ nam d vi tri : 0, 0, u va 1/3, 2/3, 1/3 + u. Vdi
u ^ 3/5.
Mdi nguyen tu A lien ket vdi 4 nguyen tut B , nam d lan can 4 dinh tii dien:
mot nguyen tut of khoang each uc, 3 nguyen tut khac d vi tri

[l/3a' + cVl/2)Y^'
Xung quanh mdi nguyen tuf cd 12 nguyen tii lan can bac hai:


Hinh 2. Ca'u true mang tinh the luc giac Wurtzite [6]
nguyen tut A°

@

nguyen tir BVI

- 6 nguyen tut d dinh luc giac, trong ciing mot mat phang vdi nguyen tuf ban dau
va each nguyen tut ban dau mot khoang a.
- 6 nguyen tii khac d dinh lang tru tam giac, each nguyen tuf ban dau mot

khoang [1/3 a^ + 1/4 c^]'^l Neu - =

a

2V2
V3

1,6330 va u = 3/8 thi cac nguyen tu lan

can bac mot nam chfnh xac d dinh tii dien va 12 nguyen tut lan can bac hai deu nam
each nguyen tut ban dau mot khoang bang nhau.
IlnVI

Tinh the A B

cau tnic luc giac khdng cd tam ddi xiing vi the trong mang ton

tai true phan cue song song vdi hudng [0 0 0 1].
Ddi vdi mot chat, giiia cau tnic luc giac va cau tnic lap phuong ton tai mot mdi
lien he chat che. Cac hang sd mang cua 6 nguyen to luc giac hen he vdi hang sd
mang d nguydn to lap phuang bang cong thiic sau
^h =
trong do:

2^K

Ch = 3-V3a,

a^ va c^ la hang sd mang luc giac.

a^ la hang sd mang lap phuang.
Vi tri tuang ddi cua nguyen tuf trong cac mang lap phuang va luc giac gan
gidng nhau. Su bao bpc cac nguyen tuf A (hay B ) bdi nhung nguyen tuf lan can
bac hai trong ca 2 loai mang cung nhu nhau. Su khac nhau ve tpa dp cac nguyen tuf
the hien d chd cau tnic luc giac dac tnmg bdi phan lang tru. De phat hien dupe su
khac nhau trong cac cau tnic nay can phai xet den cac nguyen tir lan can bac 3.

1.1.3 Mang tinh the ZnS va CdS [6]
1.1.3.1 ZnS
Tinh the ZnS thudng cd cau tnic lap phuong gia kem va luc giac Wurtzite. Cau
tnic luc giac cua ZnS on dinh d nhiet dp cao. Su chuyen pha tijf luc giac sang lap
phuang chi xay ra d nhiet dp 1020*^C - 1150*^C. Cac hang sd mang cua ZnS phu
thupc vao dp hoan thien ciia mang tinh the. Su ton tai ciia tap chat ciing gay nen sai
khac ve hang sd mang so vdi tinh toan ly thuyet. Oxy thudng la tap chat trong ZnS
tinh the luc giac. Nhung sai hong trong tinh the luc giac ZnS cd the tao ra mot viing
nhd cd cau tnic lap phuang nam trong tinh the luc giac.
Tinh the ZnS ket tinh trong cac dieu kien khac nhau cd the tao ra cac dang cau
tnic khac nhau. Dd la cac bien the ciia cau tnic lap phuang va cau tnic luc giac.
1.1.3.2 CdS
Tinh the CdS ciing ton tai d cau tnic lap phuang gia kem va luc giac Wurtzite.
Hang sd mang cua cac tinh thi thuc te phii hpp tot vdi cac tinh toan ly thuyet. Tuy
thupc vao dieu kien cong nghe, cd the nhan dupe cac tinh the CdS lap phuang va
luc giac mau do hoac mau vang. Cac thdng sd mang cua CdS va ZnS vdi cac cau
true lap phuong va luc giac dupe thdng bao trong bang 1.


Hang so mang
Hop chat

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

ddi nay thudng xay ra trong mot khoang thanh phan nao dd. Gidi ban cua khoang
nay dupe xac dinh bang phuang phap tao tinh the va phu thupc vao ndng dp tap
chat.
Trong mien chuyen tiep tii mang nay sang mang khac thi mang tinh the dung
dich ran cd the d dang hdn hop hai pha hoac cau tnic hdn don vdi cac gia tri sai
hong Idn.
Tac gia [14] nghien cuti su chuyin pha trong he Zn^Cd^.^S da chi ra rang str
chuyen pha trong mang tinh the lap phuang gia kem sang Wurtzite luc giac cd the
xay ra theo trinh tu 3C - lOH - 6H - 4H - 2H ddi vdi nhung thanh phan 0 < x <
0,062.


1.2. Cau true vung nang luong cua ZnS va CdS [6]
1.2.1 Cau true vung nang lupng cua mang lap phuong
Mang tinh the lap phuang gia kem cd ddi xutig tinh tien cua mang lap phuang
tam mat. Cac vecta tinh tien ciia mang la:
^1 = ^ a(l 1 0)

^2 = | a ( 1 0 1)

t 3 = | a ( 0 11)
trong do: a la canh ciia mang lap phuOng.
Mang dao la mang lap phuang tam khdi, cd cac vecta ca sd la:
Xi=27ia-\l,l,-l)
X2-27ra-Vl,-l, 1)

Xj = 2na\-l,

1, 1)

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]

Do mang lap phuang gia kem khdng cd ddi xiing dao nen cue dai cua viing hda
tri hai lech khdi vi tri k = 0 va lam mat di su suy bien viing cac Id trong nang Vj va
16 trong nhe V2.

11


1.2.2 Cau true viing nang lupng cua mang luc giac Wurtzite
Mang tinh the Wurtzite cau tao tii hai mang luc giac long vao nhau. Mot mang
chiia anion, mang con lai chiia cation.
Cac vecta tinh tien ca sd ddi vdi mang Wurtzite la:
ti = |a(l,-V3,0)

^2-^a(l,V3,0)
?3 = c ( 0 , 0 , 1)
Mang dao cung cd cau tnic luc giac vdi cac vecta tinh tien ca sd la:

2=27ia-Vl,-V3,0)
X2 = 2 ^ - ^ 1 , 7 3 , 0 )
X3 = 27ic"V0,0, 1)
Viing Brillouin la mot khdi bat dien bieu diln tren hinh 5.
Do cau tnic tinh thi ciia mang lap phuang va mang luc giac cd khac nhau nen
the nang tac dung len dien tir trong hai loai tinh the khac nhau. Tuy nhien ddi vdi
cung mot chat, khoang each giua cac nguyen tit trong hai loai mang tinh the bang
nhau. Lien ket hda hpc ciia cac nguyen tut trong hai loai mang tinh the cung nhu
nhau. Chi cd su khac nhau cua trudng tinh the va vhng Brillouin gay ra su khac biet
trong the nang tac dung len dien tu. Bang phuang phap nhilu loan dien tu cd the
tinh dupe vung nang lupng cua mang luc giac tuf viing nang lupng cua mang lap
phuang. Sa do vung dfin va viing hda tri cua A B

vdi mang tinh the luc giac dupe

dan tren hinh 6.
So vdi sa dd viing cua mang lap phuang, ta thay rang do anh hudng cua nhilu

12


loan trudng tinh the ma miic Fg (J = 3/2) va F7 (J = 1/2) cua viing hda tri mang lap
phuang bi tach lam 3 md'c F9(A), F7(B) va F7(C) trong mang luc giac.

K

H
Hinh 5. Vung Brillouin ddi vdi mang tinh the Wurtzite [6]

Hinh 6. Cau true vung nang lupng ciia mang Wurtzite tai lan can k = 0 [6]

1,2.3 Vung nang lupng ciia ZnS va CdS
Tinh the ZnS va CdS cd the ton tai dudi dang lap phuong gia kem, luc giac
Wurtzite hoac bien the cua hai dang nay. Tiiy vao dang cu the cua mang tinh the ma
cau tnic viing cua ZnS va CdS cd tinh ddi xiing khac nhau. Tuy nhien, tat ca cac

13


dang tinh the ZnS va CdS deu cd dac diem chung la cd cau tnic viing thang: cue dai
tuyet ddi cua viing hda tri va cue tieu tuyet ddi cua viing dan cung nam tai gia tri
k = 0, tiic la d tam ciia viing Brillouin.
ZnS

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

^;

\

4

n
2

AEo

^1

^%

L3

0

^75"\^^^
-2

X

Lj

L

^ 1 5

A

T

A

3

r

Hinh 8. Sa dd vung nang lupng cua tinh the lap phuang CdS [14]
Tren hinh 7 va hinh 8 la sa dd viing nang lupng cua ZnS va CdS dudi dang tinh
the lap phuang. Khe nang lupng giua cac diem ddi xiing trong viing nang lupng ciia

14


ZnS va CdS cd the tham khao trong [14]. Khdi lupng hieu dung cua dien tu d Ian
can day viing din va cua Id trong d lan can dinh vung hda tri ciia tinh thi ZnS va
CdS theo tinh toan ly thuyet va thuc nghiem cd the tham khao trong [6].

1.3. Tinh chat hap thu ciia ban d i n
U . l Khai niem chung [24,17]
Neu chieu mot chum sang len mot ban mong ban din thi mot phan anh sang bi
phan xa lai tren be mat ban dSn, mot phan anh sang se di xuyen qua ban dSn, phan
con lai hoac bi tan xa, hoac bi hap thu trong ban dan. Nang lupng hap thu dupe
chuyen thanh cac dang nang lupng khac: npi nang, quang nang (huynh quang), dien
nang V.V.. Tuang tac cua anh sang vdi ban dSn dupe xac dinh bdi hai yeu to:
- Tinh chat cua anh sang: thanh phan pho, su phan cue, cudng dp, hudng truyen.
- Tinh chat cua ban dan: cau tnic viing, cau tnic tinh the v.v..
Ngoai ra, cac dieu kien ben ngoai nhiT: nhiet dp, ap suat, dien tnrdng, tii
trudng... ciing anh hudng Idn den qua trinh hap thu ciia ban din.
Trong qua trinh hap thu, photon vdi mot nang lupng xac dinh, se kich thich dien
tur tiit trang thai nang lupng thap ban len trang thai nang lupng cao han.

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

Q: - tiet dien ha'n thu cua tam i

Tiiy thupc vao ban chat ciia cac qua trinh hip thu, ngudi ta phan loai nhung
dang h i " thu chfnh nhu sau:
1- Hip thu CO ban (rieng) iam chuyen dien tii tir viing hda tri len viing din. Hip
thu ca ban xay ra khi hv > 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:

(4)

A - he sd ty le
Z - lay tdng theo tat ca cac chuyin ddi dupe phep.

Khi tinh toan ngudi ta thudng gia thiet rang tat ca cac trang thai nang lupng thap
deu dupe lap day cac dien tu, con cac trang thai nang lupng cao deu trong. Thuc te
dieu kien nay thda man ddi vdi ban din khdng pha tap d nhiet dp rit thap (gan 0 K).

1.3.2 Hap thu chuyen doi thang [30]
Su chuyen ddi dien tuf giua cac trang thai tuan theo dinh luat bao toan xung
lupng va dinh luat bao toan nang lupng:
ki + k = kf

(5)

Ei + hv = E,

(6)

trong do: k^, kf - vecta sdng ciia dien tut d trang thai i, f
hk - xung lupng photon
Ej, Ef - nang lupng ciia dien tii d trang thai i, f
hv - nang lupng ciia photon
Vi ki, k f » k nen dieu kien (5) trd thanh
k.-kf

(7)

17

(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)

hVe = Ef - E, + Ep

(11)

Ep - nang lupng phonon
hva - nang lupng photon ling vdi trudng hop hap thu phonon
hVe - nang lupng photon ling vdi trudng hop biic xa phonon

Hinh 10 bieu diln sa do chuyen miic nghieng trong qui trinh hap thu. Ei(ki) va
Ef{kf) tuang ling la trang thai dau va trang thai cudi cua dien tuf trong chuyen ddi.
Chuyen ddi tii trang thai i sang trang thai f cd the xay ra theo hai budc, qua hai trang

7
>

k

Hinh 10. Chuyen ddi nghieng trong qua trinh hip thu cua ban din [27]
thai trung gian m hoac m'. Xet trudng hpp chuyen ddi qua trang thai trung gian m
nam trong viing dan. Dau tien, dien tuf chuyen miic thing Ei(ki) den Ejj^(k,) bao toan
vecta sdng k,. Sau dd d budc thu" hai, dien tut tuong tie vdi phonon cd vecta sdng
-^

^

^

,

-^

q = kf - kj va liic nay dien tii chuyen den trang thai Ef(kf). Tuang tu nhu vay, dien tut
cd the chuyin ddi thdng qua trang thai trung gian m' trong vung hda tri. Budc 1
dien tuf tuang tic vdi phonon cd vecta sdng q^va ddi den trang thai Ej^ (kf). Budc hai

19


dien tut chuyen miic thing len Ef(kf) trong viing din, bio toan vecta sdng kf.

1.4. Cac ca che phat huynh quang trong ban dkn
1.4.1 Khai niem chung [30],[6]
Khi hap thu nang lupng, chat ban din se d vao trang thai kich thfch. Cac cap hat
tai dien - dien tuf va Id trong - dupe hinh thanh. Qua trinh tai hop trong bin din cd
bin chat ngupc vdi qua trinh hap thu. Qua trinh tii hpp lam bien mat cac hat tai dien
trong ban din. Qua trinh nay cd the xay ra kem theo biic xa hay khdng biic xa
photon. Trong tnrdng hop tai hop khong kem theo biic xa , tat ca nang lupng dupe
giai phdng ra dupe truyen cho dao dpng mang (phonon) truyen cho hat tai dien tu
do thii ba (tai hpp Auger) hoac dupe diing de kich thich cac dao ddng plasma trong
chit ban din (tai hop plasma).
Trong trudng hop tai hpp biic xa, tit ca hoac mot phan nang lupng dupe giii
phdng dupe phit ra dudi dang lupng tuf anh sang. Qui trinh tii hop biic xa anh sang
dupe gpi la huynh quang.
Dieu kien chu yeu de xuat hien huynh quang la ban din phii d trang thii khong
can bang. Tiiy thupc vao phuong phap kich thich chat ban din, ngudi ta nhan dupe
cac dang huynh quang khac nhau nhu:
- Quang huynh quang xuat hien khi chieu vao chat bin dan anh sang cd budc
sdng thich hop.
- Dien huynh quang xuat hien khi kich thich ban dan bang dien trudng hoac
ddng dien qua cac Idp tiep xiic di thi hay chuyen tiep p - n.

- Huynh quang catot (cathode) xuat hien khi chieu chiim tia dien tut cd nang
Itfpng cao.

20