Nghiên cứu các tính chất quang của hợp chất bán dẫn vùng cấm rộng

DAI HOC QUOC GIA HA NOI
TRITOING
DAI HOC KHOA HOC
TlT
NHIEN
DE TAI:
NGHIEN
ctru
CAC TINH CHAT QUANG CUA HOP CHA
BAN
DAN
VUNG CAM RONG
Ma so: QT- 05-08
Chi4 tri
de
rai
: TS. Pham Van Ben
Cdc cdn bg tham gia : ThS. Hoang
Chi
Hieu
CN.
Nguyen
Thanh Chuong
CN.
Nguyen
Anh Tuan
rJAi
HOC QUOC GIA HA
NOI
rpuMG
TAW THONG

TIN
THU
ViEN
or
I
b^^
HA NOI - 2005
BAO CAO TOM TAT
^•^
DETAI:
NGHIEN
CUtJ
CAC TINH CHAT QUANG CUA HOP CHAT
BAN DAN
VUNG
CAM
RONG
MA SO : QT- 05 - 08
CHU TRI DE TAI : TS. PHAM VAN BEN
CAC CAN
BO
THAM
GIA: TH.S HOANG CHI HIEU
CN.
NGUYfiN
THANH CHUONG
CN.
NGUYfiN
ANH TUAN
1.

Muc tieu va noi dung nghien curu:
+ Xay dung he kfch thich va thu pho huynh quang tren ca so may do
sdc each
tu kep GDM -
1000
va ky thuat lock-in.
+ Nghien cuu cac tfnh chat quang cua cac hop chat ban
dSn viing
cam
i
2.
Cac ket qua dat
dupe.
+ Tim hieu ly thuyet vl tfnh chat quang cua cac hgp chat ban
dSn vimg
cam rong.
+ Xay dung he kfch thfch va thu pho huynh quang tren ca so may dc
sdc each tir
kep GDM - 1000 va ky thuat lock- in.
+
Thu va nghien
ciJu
pho huynh quang cua cac hop chat ban
dSn vian
cam rong ZnSe, ZnS
\'a
ZnS
:
Mn
'^'

Kei qud dao tao: 03 sinh vien bac cu nhan
*
Cdc cong trinh cong bo: 02 bao cao khoa hoc tai Hoi nghi Vat
'.
toan quoc lan thu
\a.
Ha Noi
tir
23 - 25/11/2005.
3.
Tinh hinh sur
dung kinh
phi.
+ Tong kinh
phi
duoc cap
+ Tien dien,
nude
va
xSy
dung co
scf
vat chat
+
vat
tu van phong
+ Hoi nghi, in an bao cao
+ Cong tac
phi,
tau xe

+ Thue
mucfn
+ Chi
phi
nghiep vu chuyen mon
+ Ho tro dao tao nghien
ciiu
khoa hoc
20.000.000d
SOO.OOOd
SOO.OOOd
2.000.000d
: l.OOO.OOOd
S.OOO.OOOd
:
V.OOO.OOOd
: 400.000d
XAC NHAN CUA BCN KHOA VAT LY
PGS.TS.
Nguy
in The Binh
CHU TRI DE TAI
TS. Pham Van Ben
PHO
HlEl TRUOHG
GS.TS.'^i**^
^JC
BRIEF REPORT
TTTLE:
INVESTIGATION ON THE OPTICAL PROPERTIES OF

SEMOCONDUCTOR COMPOUNDS WITH THE WIDE BAND GAP
CODE: QT- 05-08
COORDIMATOR
:
PHAM VAN
BEN
KEY
IMPLEMENTS:
HOANG
CHI
HIEU
NGUYEN THANH CHUONG
NGUYEN
ANH
TUAN
1.
Objective and Matter of this study:
+ To construct the excitation system and obtain luminescence spectra using
the double grating spectrometer GDM 1000 and the
lock-in
amplification
technique.
+ To investigate the optical properties of semiconductor compounds with the
wide band gap.
2.
Main results:
We succeeded in:
+ Carrying out the theory of optical properties of
wide-band
gap

semiconductors.
+
Constructing excitation system and obtain luminescence spectra using the
double grating spectrometer GDM -1000 and the lock-in amplification
technique.
+ Investigating some optical properties of some wideband gap semiconductor
compounds such as
ZnSe,
ZnS and ZnS:Mn.
Education results: 3 bachelor theses
Publications: 2 papers on
Tlie
6^^
Vietnamese Confference on Physic, Hanoi
November 23-25, 2005.
MUC LUC
1,
Md
dau
H.
Noi dung
i. Cdc tinh
chdt
quang cua cdc
hgp
chat bdn ddn vung cdm
rpng
a. Cau tnic tinh the va cau tnic vung nang
lugng
b.

Su thay doi do rong viing cam theo nhiet do
c. Su thay doi do rong vung cam theo nong do tap chat
d. Cac ca che hap thu trong ban
din
vung cam rong
e. Cac ccf che tai
hgp biic
xa trong ban
dSn
vung
c^m
rong
2,
Xdy dung he
kich
thich vd thu
phd
huynh
quang,
tdn xa Raman
tren ca sd mdy
dcm
sdc cdch tu kep GDM
-1000
diing ky thuat lock - in
a. Md dau
b.
He kfch thfch pho huynh quang va tan xa Raman
c. He thu pho huynh quang va tan xa Raman
d. Cac ket qua do pho huynh quang va tan xa Raman

e. Ket luan
3,
Nghien citu tinh chdt quang cua bdn ddn
viing
cdm rong ZnSe
a. Ma dau
b.
MSu nghien
ciJu
va thiet bi thuc nghiem
c. Cac ket qua va bien luan
^
Pho phat quang (huynh quang) ciia tinh the ZnSe
*
Su phu thuoc vi trf va cucmg do
ciia
dam phat quang
\aing
da cam-do a 606 nm vao mat do nang lugng kfch thfch
*
Su
t^t
nhiet phat quang cua tinh
the'
ZnSe
d. Ket luan
4, Pho huynh quang cua bdn ddn vung cdm rong ZnS
vd ZnS : Mn
5,
Kit ludn

6, Tdi lieu tham khao
7, Phu luc
- 02 bdi bdo tai hoi nghi vat ly toan qudc
Idn
thit 6 nam 2005
'
03 khod ludn tdt nghiep nam
20.04-2005
L MO DAU
Cac hgp chat ban din vung cam rong loai
A^B^ A^B^
v6i do rong vung
cam khoang mot vai electron von nhu: ZnSe, ZnS, CdTe, CdS, ZnO.vv. dugc
ling dung rong rai trong cac dung cu quang dien tu. Chiing dung de che tao
cac di ot phat quang, quang tra, nhung cua so trong suot trong viing kha kien
va hong ngoai gin
[1,
2, 3, 4]. Trong ph6 phat quang cua cac hgp chat ban
din
nay tii 4,2K den 300K, ngoai nhiing vach dac trung cho su tai hgp
biic
xa cua
cac exciton tu do, exciton lien ket tren cac donor, acceptor, cac electron tu do
tir viing
din xuong cac
miic
tap chat, con
xu^'t
hien cac dam rong dac trung
cho su tai hgp

biic
xa cua cac cap donor - acceptor [5, 6, 7, 8, 9].
Khi pha cac kim loai chuyen tiep nhu Mn, Fe, Ni, Co
vdi
vo dien
tir
3d
chua lap day vao cac hgp chat ban din
wng
c^'m
rong se tao thanh cac ban
din ban
tir.
Cac ion
ciia
cac kim loai tren (goi la cac ion
tijf)
se tao nen trong
viing cam ciia cac hgp chat ban din nay nhiing
miic
nang lugng xac dinh. Vl
the trong pho phat quang
ciia
cac hgp chat ban din vung cam rong con xuat
hien nhiing
\'ach
dac tnmg cho su tai hgp
biic
xa cua cac polaron tii lien ket,
cac dam phat quang dac tnmg cho cac ion tii va pho phat quang cua chiing

dugc chuydn sang viing hong ngoai gan [10, 11, 12, 13,
14].
Nhim lam sang to mot vai ca che tai hgp
biic
xa va kha nang
iing
dung
ciia
cac hgp chat ban din viing cam rong, chiing toi thuc hien de tai: Nghien
ciiu
cac tfnh chat quang cua hgp chat ban din
\aing
cam rong.
n.
NOI DUNG
1.
Cac
tinh
chat quang cua cac hgp chat ban
dSn
vung cam rong
a. Cau true tinh the va cau true viing nang
lixgng
* Cdu
trdc
tinh the
Cac tinh thd
A'B^ A^B'
dugc tao thanh
tii

cac kim tu nhom 2 hoac 3 (A)
va cac nguyen
tir
a kim nhom 6 hoac 5 (B) lien ket
vcd
nhau theo dang h6n
hgp ion va cong hoa tri
(vi
du nhu ZnS
:77%
la lien ket ion va 23% la lien ket
cong hoa tri). Trong hen ket ion cac nguyen tu kim loai A cho hai dien
tir
hoa
tri de tra thanh ion hoa tri duong hai
A^"^
co
c^'u
hinh
dien tii a
Icfp
ngoai ciing
3d^pM^°,
cac nguyen
tir
a kim B nhan hai dien
tir
tra thanh ion hoa tri am hai
B^'
CO

cau
hinh
ldp dien tu ngoai ciing
3s^p^.
Trong lien ket cong hoa tri m6i
nguyen
tir
A hay B deu dong gop vao lien ket chung 4 dien tii de tao thanh cau
hinh day dii ciia 16p vo dien tu. Nguyen tu
A
se tra thanh ion hoa tri am hai
A^'
CO
cau hinh dien tu ngoai cung
4s^p^
con nguyen
tir
B se tra thanh ion hoa tri
duong hai
B^""
vdi
cau
hinh Icfp
vo ngoai cung
3s^p^
Cac nguyen tii
A
va
B
lien ket v6i nhau theo mot cau tnic tuan hoan, tao

thanh tinh thd. Cd nhieu dang
hinh
thii khac nhau ciia tinh the ban din viing
cam rong, nhung deu xuat phat
tir
hai dang co ban: dd la cau tnic luc giac
(Wurtzite) va cau tnic lap phuang (Sphalerite hay Zincblende).
Vide
tinh thd
nhan cau tnic luc giac hoac lap phuang la tuy thuoc vao nhiet do va ban chat
ciia tiing hgp chat ban din. Vai tinh the ZnS thuoc nhdm
A-^B^
thi a nhiet do
nung nho han
950°C
tinh thd nay thudng cd cau tnic lap phuang a nhiet do tir
950*^
den
1020^C
thi cd khoang 70% ZnS a dang cau
true
luc giac va a nhiet
do tir
1020°C
den
1200°C,
ZnS hoan toan
o
dang cau tnic luc giac. Nhu vay cd
thd xem

1020^C
la nhiet do chuydn pha tir cau tnic lap phuang sang cau tnic
luc giac.
V6i
cac tinh thd thuoc nhdm
A'B'
thi mang tinh thd
ciia
chiing
thudng cd cau tnic dang lap phuang.
Tuy nhien khong thd xac dinh dugc khoang nhiet do 6n dinh cho timg
dang
ca'u hinh
cua tinh the. Vdi CdTe, cau tnic dang luc giac chi quan sat thay
d mau mang cdn cau tnic dang lap phuang quan sat thay d miu rdn. Du d
dang cau tnic luc giac hay cau
true
lap phuong thi trong
lidn
kd't trat tu gan,
mdi nguyen
tir
A^
(hay
B^)
ddu nim d tam ciia hinh
tii
dien tao bdi bdn nguyen
tir
B^

(hay
A').
*
Cdu
trdc
dang
lap phucmg
(Sphalerite hay Zincblende)
Cau tnic dang lap phuang dugc xay dung trdn co sd xdp quy luat xep
ciu
ciia
hinh lap phuong vdi cac dinh la nguyen tir B (S) dugc ky hieu la
O.
Cac nguyen tir A (Zn) nam trong mot nira sd hdng bdn mat, cac hdng A (Zn)
dugc
kyfcidu
la dinh hudng song song vdi nhau (hinh
1
a)
Hinh
1:
Cau tnic cua ban din vung cam rong
a : Dang lap phuang ( Sphalerite hay Zincblende )
b : Dang luc giac ( hay Wurtzite )
Nguydn tir
A
dugcky hieu la :
^
Nguydn tir
B

dugc ky hieu la:
O
Nhdm ddi xiing khong gian cua Sphalerite la:
T"^
F43m.
6
cau tnic
Sphalerite, mdi
6
mang
ngu\en
td cd 4 phan tir
A^B^
(ZnS). Mdi nguyen tir
A
(Zn) dugc bao quanh bdi 4 nguydn tir B (S) dugc dat trdn cac dinh cua
tii
dien
d cung khoang
each
^/3
trong dd a la hing sd mang. Ngoai ra bat ky mot
8
nguyen td nao thuoc ciing mot loai cung dugc bao quanh bdi 12 nguyen tir
ciing loai dd d khoang
each
V2-,
trong dd 6 nguyen tir dat d dinh cua luc
giac nim trdn ciing mot mat phang, 6 nguyen tii cdn lai tao thanh mot phan
lang kfnh tam giac. Neu dat cac nguyen tir cua mot nguyen td B (S) d cac

niit
mang lap phuong, tam mang cd toa
dg-cau
la (0, 0, 0)
thi
cae
nguydn
tii cua
nguydn td kia tai cac mit mang ciia tinh the Sphalerite nay, nhung vdi
niit
mang dau cd toa do (1/4, 1/4, 1/4). Khi dd 4 nguyen tir
B
(S) d cac vi tri (0, 0,
0);
(1, 1/2, 1/2); (1/2, 0, 1/2); (1/2, 1/2, 0) va 4 nguydn tir A (Zn) d cac vi tri
(1/4,
1/4, 1/4); (1/4, 3/4, 3/4); (3/4, 1/4, 3/4); (3/4, 3/4, 1/4).
[s]
* Cdu
true
dang luc gidc (hay Wurtzite)
+ Cau tnic dang luc giac (hay Wurtzite) dugc xay dung dua tren co sd
quy luat xep cau theo hinh 6 canh cua cac nguydn tir B (S) dugc
kyOidu
la
trong dd mot nira sd hdng bdn mat chiia nguydn tir A dugc ky hieu
la #
dinh
hudng song song vdi nhau ( hinh lb).
Nhdm ddi xiing khong gian cua cau tnic luc giac la:

(^^^
-
P63wc
.
O cau tnic Wurtzite, mdi mang nguydn td ciing chiia 4 phan tir
A^B"^
(ZnS).
Toa do cua mdi nguydn tir A dugc bao quanh bdi 4 nguydn tir B (Z) dat tren
cac dinh
tii
dien d
ciing
khoang
each [aV3
+
c^(u
-
1/2)"]'^
, trong dd a la hing
sd mang, u la hing sd mang doc theo
true
Z. Ngoai ra bat ky mot nguydn td
nao thuoc ciing mot loai cung dugc bao quanh bdi 12 nguyen tir cung loai dd,
trong dd cd 6 nguyen tir d dinh
ciia
mot luc giac nim trong cimg mat phing
vdi nguydn tir dau va
each
nd mot khoang la a, 6 nguydn tir kia d dinh mat
lang tru cd day la mot tam dien d khoang

each
bang
[^^
+ —] ~
. Cac toa
J
4
do cua cac nguydn tir A (Zn) la (0, 0, 0); (1/3, 2/3, 1/2): va cac toa do
ciia
cac
nguyen
tuB(S)
la (0, 0, 4); (1/3. 2/3, 1/2
+
u). [3]
* cdu
trdc
viing ndng
lugng
Trong cac hgp chat ban din, do su tuong tac giiia cac nguydn tir dat gan
nhau, ma din de'n cac
miic
nang lugng cua cac nguyen tir bi dich chuyen, tach
miic,
va md rong tao thanh viing ggi la
viing
nang lugng. Cd hai loai
wng;
vung hda tri va vimg din. Viing choan toan bg cac electron va dugc tao ndn tir
cac

miic
nang lugng cua cac electron bdn trong cua cac nguyen tir tu do goi la
viing hda tri. Viing choan mot phan cac electron hoac tu do va dugc tao ndn
tir
cac
miic
nang lugng cua cac electron ben ngoai
ciia
cac nguyen tir
each
ly goi
la vung din. Giiia viing hda tri va vung din la viing cam. Khoang
each
nang
lugng
giiia
dinh viing hda tri va day vung din ggi la do rong viing cam Eg.
Vdi ban din viing cam rong thi Eg cd gia tri tir 1 ev de'n vai ev, ndn bing
chuyen dong nhiet, cac electron khong the chuyen tir
\aing
hda tri
Idn
viing
din. Nhung nhd cac kfch thfch ben ngoai nhu nhiet nang, quang nang cac
electron nhan them nang lugng chuyen tir vimg hda tri
Idn
viing din.
De xac dinh pho nang lugng ciia cac dld'ctron trong cac hgp chat ban
din ta phai giai phuang trinh Shrodinger:
Hy

= E(k)
\j;
(1)
Vide
tfnh toan ly thuyet nang lugng E(k) ngay ca ddi vdi cac tinh the
don gian ciing rat phiic tap.
Vdi dang cau tnic viing nang lugng don gian nhat khi
\aing
khong bi lap
day thap nhat cd cue tieu d tam viing va vdi trudng hgp khong suy bien
(k
=
0) thi d gin gia tri
cue
tidu, nang lugng cd thd phan tfch theo chudi
luy
thira sau:
E(k)
=
EQ
-h Ak'x
+
Bk-y
+
Ck'z +
cac sd hang bac cao (2)
Trong dd: kx. ky, kz la ba thanh phan cua vec ta sdng
I
A,
B, C la cac hing sd duong

10
+ Trudng hgp tinh thd cd ca'u tnic lap phuang thi A
=
B
=
C, nang lugng
tfnh cho day viing
nh^n
gia tri sau:
2
2
2m
e
2m
e
Trong dd
^*
la khdi lugng hieu dung cua electron
Tuong tu d gan gia tri nang lugng cue dai trong vimg k = 0 ta cd nang
lugng.
E(k)
=
E'o-Ak;
-Bk;
-Ck,?
(4)
Vdi tinh the cd ca'u tnic lap phuong A
=
B
=

C ta cd
2
2mi^
'^'""
Trong dd
m',
la khdi lugng hieu dung
ciia Id
trdng.
Dd thi cua E(k) theo k
iing
vdi viing hoa tri va
\aing
din deu cd dang parabol.
Khi
cue
tieu cua nang lugng
\aing
din va cue dai cua nang lugng
ciia
viing hoa tri deu nim d k
=
0 ta cd chuydn ddi dien tir thang (hinh 2a).
Khi cue tieu cua nang lugng vimg din
vh
cue dai cua nang lugng
ciia \amg
hoa
tri nim d k khac nhau ta cd chuyen
miic

dien tir nghieng (hinh 2b).
Khoang
each
ve mat nang lugng giua day vimg din va dinh vimg hoa tri
goi la do rong
\iing
cam.
E
=Eo-Eo'=E,-E,
(6)
11
E(k)
Efk)
Ec
Ev
•^
k
Hinh 2: Chuyen
miie
thang (a) va chuydn
miic
nghieng (b)
trong ban din viing cam rong
b.
Su
thay
ddi do rong vdng cdm theo nhiet do
Su phu thuoc cua do rong viing cam Eg cua ban din
\aing
cam rong vao

nhiet do dugc bidu didn bing cong thiic Varshini
[11]
(hinh 3).
Eg(T)
=
Eg(0) -
T
+
fi
(7)
Trong dd: Eg(0) la do rong
\aing
cam d
0
K.
0,a
la cac he sd dich chuydn nhiet cua do rong
\iing
cam
iing
vdi nhiet
do thap va cao.
12
E (cm"')
22500
22000 -
21500
21000
20500
^^

\
,
^ \
-
\v
\.
\.
—1
1—1
1 1
+i^—1—
T(K)
0 50 100 150 200 250 300 350
Hinh
3 : Su phu thuoc do rong vung cam Eg
ciia
Cdi.^Mn Je
(
x=
0.73) theo nhiet do T
Bang 1 : Gia tri do rong vimg cam cua mot sd hgp chat ban din viing cam
rong [10].
Cac hop chat
ban
d^n
ZnSe
ZnS
ZnO
CdSe
ZnTe

CdS
GaP
GaAs
ZnP
Do rong vung cam Eg (v)
a
4.2
K
2.817
3.700
1.606
1.850
2.390
2.580
2.40
1.520
1.42
o 300
K
2.670
3.640
1.50
1.74
2.28
2.53
2.25
1.430
1.28
13
/*»

c.
Suthay
doi
cua
do rong vdng cdm theo nong do cua tap chdt,
Bing thuc nghiem, ngudi ta thay ring ddi vdi da sd cac hgp chat ban
din viing cam rong, khi tang ndng do ciia tap chat trong mot khoang nao dd
thi do rong
\amg
cam cua chiing tang (hinh 4).
Eg (eV)
2.6
2.4
2.2
2.0
1.8
0.2 0.3 0.4 0.5 0.6 0.8
Hinh 4 : Su phu thuoc do rong viing cam Eg cua tinh the
Cd,.,Mn ^Te
vao ndng do x cua Mn d nhiet do 300 K
Mot sd trudng hgp dac bidt: nhu ban din loai
A"B^
pha cac kim loai
chuydn tiep cd ldp vd 3d chua lap diy tao thanh ban din ban tir thi khi tang
ndng do tap chat thi do rong viing cam giam cham den mot gia tri nao dd, sau
dd Eg lai tang theo ndng do x cua tap chat. Nguydn nhan cua hien tugng nay
la do tuong tac trao ddi s - d
,
p - d cua cac dien tir 3d cua cac ion ttr vdi cac
dien tir din.

Cd 3
each
xac dinh do rong
\Tmg
cam bing phuang phap quang: do pho
hap thu d gin bd hap thu, pho phan xa, pho exciton. Trong dd phuong phap do
pho hap thu d bd vimg cam thudng dugc ap dung nhieu nhat va tuong ddi don
gian. Ddi vdi nhiing chuyen
miic
thing dugc phep he sd hap thu
ciia
hgp chat
ban din dugc xac dinh bing he thiic [13] :
a(v) =
A(hv-Ej'^^
(8)
14
Trong dd A la mot hing sd
X^y
dung dd thi hien didn su phu thuoc cua
a^
theo hv ta se dugc
dudng thing va keo doan thing dd ta cd diem cit true hv tai hv
=
Eg. Ddi vdi
cac chuyen
miic
thing khong the xay ra hap thu vdi hv < Eg.
a^
hv

Eg
Hinh 5 : Su phu thuoc
ciia
he sd hap thu d gan bd vimg
cam vao nang lugng hap thu cua ban din
\aing
cam rong
d, Cdc ca che hdp thu trong bdn ddn viing cdm rong
Khi chieu mot
biic
xa didn tir vdi tan sd v vao mot hgp chat ban din thi
xay ra su hap thu cac photon cua
biic
xa didn tir dd. He sd hap thu a cua hgp
chat ban din cd thd xem la xac suat hap thu photon. Neu trong hgp chat ban
din ton tai mot sd co
chd'hap
thu dgc lap nhau, dac trung bing cac xac suat
a
(v) thi xac suat tdng cong cua cac qua trinh hap thu la:
(9)
Qua trinh hap thu
biic
xa lidn quan den su chuydn doi nang lugng cua
photon sang dang nang lugng khac cua tinh the, ndn trong ban din
\iing
cam
rons
cd mot sd ca che hap thu sau: (hinh 6)
15

E(k)
Ec
Ev
l(la)
/\
1
/\
/\
3b
:>a
2a
J
3c
/\
Ec
Hinh 6 : Mdt sd co
chd'hap
thu trong ban din vimg cam rong
+ Hap thu
CO
ban (hay hap thu ridng) lidn quan den chuydn
miic ciia
cae
didn tir giira cac vimg nang lugng cho phep: tir viing hoa tri
Idn \iing
din
(chuyen
miic
1). Hap thu nay cd dac diem.
- Nang lugng hap thu hv >

Eg
- Phd hap thu ed mot viing ma he sd hap thu giam nhanh
iing
vdi bd hap
thi
-
Ddi
\'di
chuyen
miic
nghidng nhat thie't phai cd su tham gia cua
phonon.
+ Hap thu cua cac hat tir didn tu do lidn quan den chuydn
miic ciia
didn
tir e' hoac
Id
trdng h trong cac vimg nang lugng cho phep (didn tir trong
\amg
16
din hoac 16 trdng trong vung hoa tri) hoac giua cac xiing con cho phep. Hap
thu nay cd dang dudng cong don dieu, khong cd
cue
dai vi hap thu nay khong
cd
tinh Igc
lua (cac chuydn
miic
2 va 2 a). Vdi hap thu
iing

vdi chuydn
miic
giiia
cac viing con cho phep trong vimg nang lugng cho phep thi cd cue dai,
cue
tidu xen ke vi hap thu nay cd tfnh
Igc
lua (cac chuyen
miic
2b, 2c, 2d).
+ Hap thu ling vdi chuyen
miic ciia
cac hat tai didn lam cho nguyen tir
tap chat tir trung hda chuydn sang idn (chuydn
miic
3 va 3a). Chuyen
miic
nay
nim trong viing hdng ngoai xa.
+
Hip thu ling vdi chuyen
miic
cua cac hat tai didn lam cho nguydn tir
tap chat tii idn chuyen sang trung hda nim trong viing gin bd hap thu co ban
(chuyen
miic
3b, 3c). Ne'u cac tam dd la cac tam sau thi pho dich ve phia sdng
dai.
+
Hap thu ling vdi chuyen

miic giiJa
cac
miic
tap chat (chuyen
miic
4)
cung nim gan bd hap thu. Nd'u cac tap chat dd la cac tam sau thi pho hap thu
ciing dich chuyen vd
phia
sdng dai.
+ Hap thu exciton lien quan
dd'n
su hinh thanh cua cap didn tir
e"
va
Id
trdng h cd tuang tac culong (chuyen
miic 5).Pho
nang lugng hap thu exciton
nim d gan bd hap thu.
-I-
Hap thu phonon lidn quan de'n
vide
chuydn nang lugng anh sang
thanh nang lugng dao dgng mang d
\amg
hdng ngoai xa.
+ Hap thu plasma xay ra trong didu kien ndng do hat tai didn tu do du
cao
xa

thudng mang tfnh cong hudng: cong hudng plasma. He sd hap thu xiing
nay rat cao. Ngudi ta thudng nghidn
ciiu
phd phan xa cua miu. Cue dai
eiia
phd phan xa plasma thudng nim d
\iing
hdng ngoai xa.
+ Hap thu xay ra trong mot tam tap: Khi pha cac kim loai chuyen tid'p
nhu Mn, Fe, Ni, Co vdi ldp
\'d
3d chua lap day vao cac hgp chat ban din viing
cam rong, thi cac idn cua cac kim loai trdn se tao ndn trong vimg cam nhiing
miic
nang lugng xac dinh. Dudi tac dung
ciia
trudng tinh thd cac
miic
nang
lugng nay dugc tach thanh cac
miic
con. Khi chieu
biic
xa vao hop chat
han
17
OAI HOC QUOC GIA HA NOI
TRUNG TAM THONG
m\
THU

VIEN
DT
/52>6
din ludn xay ra su hap thu lien quan de'n chuyen ddi giira cac phan
miic
nhd
ciia
cac nguyen tir va idn ciia cac kim loai chuyen tid'p. Ke't qua ta thu dugc
mot dam hap thu tuong ddi rdng [11] (hinh 7).
Loai hap thu nay cung xay ra
giiia
cac
miic
nang lugng dac trung cho
ldp vd chua
lap
diy 4f
ciia
cac
idn
r-at
hid'm khi chiing
dugc
pha-
tap vao hgp
chat ban din xiing cam rong. Nhung pho hap thu dac trung cho cac idn da't
hid'm nay thudng la phd vach, vi ldp vd khong chiia day 4f nim sau bdn trong
ciia
vd nguyen tu nen ft bi anh hudng cua trudng tinh thd.
7000

OUOU
5000
4000
3000
2000
1000
E(cm'')
18000 19000
20000
21000
22000
Hinh 7 : Pho hap thu dac trung cho cac ion
Mn"""
trong
tinh the
Cd,.,Mn,Te
(
x=0.7)
d nhiet do
T=
5 K
e,
Cdc ca che tdi hop
bite
xq trong bdn ddn vung cdm rong
Khi hap thu nang lugng kfch thfch, trong cac ban din vimg cam rong,
cd the xay ra cac co che tai hgp
biic
xa chu yeu sau (hinh 8).
18

i—i
i
D
^
D
e
Ev
Hinh 8: mdt sd loai chuyen ddi
biic
xa trong ban din xiing cam rong
-i-Tai
hgp
ciia
cac didn tir va
Id
trdng tu
do:
tai hgp
biic
xa
xoing
-viing
(dudng 1),
H-
Tai hgp
biic
xa cua exciton tu do va exciton lidn ket (dudng 2).
+ Tai hgp
biic
xa cua cac hat didn tu do vdi cac hat tai didn dinh

xii
tren
cac tam tap chat: tai hgp vimg - tap chat (dudng 3).
-I-
Tai hgp
biic
xa cua cac hat tai didn dinh
xii
trdn cac tam tap chat:
tai
hgp
biic
xa
ciia
cap donor - acceptor (dudng 4).
+ Tai hgp
biic
xa ndi trong mot tam tap
*
Tdi hgp
bite
xq vung - viing.
Xet mot ban
din
xiing cam thing
bi
kfch thich bdi
biic
xa
(anh sang).

Sau qua trinh hap thu photon, cac hat tai didn tir do (e", h) se bi tan xa, sau mot
thdi gian hoi phuc, dien tir se chiem vi
trf
day viing din, cdn
Id
trdng se chiem
vi tri dinh
xoing
hoa tri. Trang thai nay dugc hinh thanh trong khoang tir
lO'^*^-
lO'^'s.
Cudng do
ciia
dam
biic
xa dac tnmg cho tai hgp viing
-
xiing dugc xac
dinh
bins
cons thirc (10)
[13]:
I = B(hv-EJexp(-^^^)
(10)
19
Trong dd: B : la mdt hing sd
Eg :
la
do rdng vung cam
K : la hing sd Bolztman

T : la nhiet do tuyet ddi
Vdi ban din cd vung cam khdng thing, thi tai hgp
biic
xa vimg -
viir ;
cua dien tir se cd thd xay ra kem theo su
biic
xa va hap thu phonon. Su tha:n
gia cua phonon la dam bao cho xung lugng dugc bao toan .
Ne'u chuyen
miic
kem theo
biic
xa phonon thi nang lugng
biic
xa
nh')
hon do rdng xiing cam :
hv_
=
E,-Ep
(11)
Nd'u chuyen
miic
kem theo hip thu phonon thi nang lugng
biic
xa
k
a
hon do rdng viing cam :

hv=E^
+ Ep
(12)
Trong dd:
Ep
la nang lugng cua phonon.
Lugng tir sang nay dd bi hgp chat ban din hap thu lai ndn khdng phat ra
dugc.
Cudng do cua dam
biic
xa dac tnmg cho tai hgp xoing - xiing
x^di
chuyen
miic
nghidng dugc xac dinh bing cong thiic:
I
= Io(hv
- Eg +
Ep)^
exp (-
f^^'-^g^EP
)
(13.
KT
*
Tdi hgp
bite
xq exciton tu do
Exciton la trang thai lien ket
ciia

cap didn tir
Id
trdng
(e"
-
h) trong
tinh thd ban din. Lien ket cua cap hat tai didn tir nay tdn tai la do tuong
tic
culong giiia didn tir va
Id
trdng. Cd hai loai exciton: Exciton
Fren!
J1
va
Exciton Wannier- Mott. Exciton Frenkel dd la exciton cd ban kfnh nhd, trong
dd didn tir va
Id
trdng tuong tac \'di nhau bdi luc culong, chiing ludn
lud \
dinh
xii
trong mot
niit
mang. Nang lugng hv <
E,
ma tinh the ban din hap thu dimg
de tao ra cap
e-
h" dd.
20

Exciton Wannier - Mott dd
la
exciton cd ban kfnh
Idn:
Khoang each
trung binh giira e va h
Idn
hon hing sd mang a cua tinh thd mot vai lin. Nhidu
exciton tu do lien ket vdi nhau tao thanh to hgp exciton tu do.
Theo md hinh Wannier-Mott, exciton tu do cd cau tnic tuong tu nhu
nguyen tir hidrd : gdm mot
Id
trdng cd didn tfch duong e va mot didn tir cd
777
777
dien
tich
- e. Nd cd khdi luong hieu dung
// =
—-—— coi nhu tap trung tai
trgng tam G va chuyen dgng tinh tid'n tu do trong tinh the. Nang lugng toan
phin cua exciton tu do gdm cd :
- Nang lugng tuong tac cua dien tir
Id
trdng trong exciton dugc xac dinh
bing he thiic :
2s tl
"' '^
Trong dd
S:

la hing sd didn mdi
ciia
tinh the
n=:
1,2,3,
4
E'
=
-^
(15)
2s tl
Dgng nang chuydn ddng tu do
ciia
exciton trong tinh thd
Ed=^
(16)
2//
Trons
dd : P
= hk
la xung lugng chuydn dgng khdi tam
ciia
exciton
Nd'u chgn gdc nang lugng la dinh
xomg
hoa tri thi ta cd nang lugng toan
phin cua exciton la :
£>^g-^
+ ^
(17)

n
"^
21
Exciton khdng ton tai d nang lugng cao, chiing se bi phan huy
thanJi
electron va
Id
trdng tu do,
xi
the'
^]^
co the coi nhu nang lugng idn hoa hay
nang lugng lien ket cua exciton .
Vdi chuyen
miic
thing nang lugng cua exciton tu do
tinh
tir dinh
xxing
hoa tri dugc xac dinh bing cdng thiic :
^:=Eg-^
(18)
n
Tit bieu
thuc(18)
ta thay ring pho hap thu va
biic
xa cua exciton gdm
nhiing vach hep
iing

vdi
n=
1, 2, 3 Cac
x^ach
nay se xit lai va lin
x^ao
xiing
pho hap thu bidn cua hgp chat ban din.Thudng ta chi quan sat dugc nhung
vach ling vdi n
=1,
2 vi cac vach tiep theo cd cudng do giam rat nhanh.
Trong chuyen
miic
thing
ciia
exciton tu do ciing cd the cd su tham gia
cua phonon. Khi dd, trong pho
biic
xa ta quan sat thay vach exciton tu do va
nhirng vach lap lai phonon cua nd dich ve phfa sdng dai.
*
Tai hgp
biic
xa cua exciton hdn kd't: Exciton lidn ke't la cap didn tir
-16
trdng dugc lidn ke't vdi nhau va lidn kd't trdn mot tam tap nao dd. Tam tap cd
the
la
donor, acceptor trung hoa hoac donor, acceptor da bi ion hda. Nhu
vky

exciton lien kd't khong chuyen dong tu do trong tinh the ban din. Pho
biic
xa
cua exciton lien kd't gdm nhung vach hep vdi nang lugng nhd han nang lugng
tai hgp cua exciton tu do
\1
no khdng chuyen dong dugc trong tinh the.
Nang lugng cua cac vach dac trung cho su
biic
xa cua exciton hen ket
dugc xac dinh bing he thiic: hv
:= E„ ~
Ei^^
/^g 1
Trong dd:
E]^.
la nang luong cua exciton lien ket.
E;;,
thoa man dieu kien:
0.055Ei
<
E„
< 0.33 E, (20)
6
day
E,
la nang luong idn hda tap chat.
Trong cac ban din cd
x^ng
ca'm

khdng thang, cd chiia tap chat,
d^
bao
toan xung lugng, exciton khdng nhirng cd the trao doi xung lugng vdi phonon
ciia
mang tinh the ma cdn cd the truyen xung lugng cho nguydn tir tap chat.
*
Tdi hgp
bite
xq vdi chuyen mdc giita vung vd
mite
tap chdt,
+ Chuyen
miic
ndng: Trong cac hgp chat ban din tdn tai cac
miic
tap
chat bi ion hda donor hoac acceptor, cd the xay ra cac chuyen
miic
cua cac hat
tai didn de'n cac
miic
dd nhu sau:
- Dien ttr
tur
vung din chuyen xudng
miic
donor.
- Ld trdng lii vimg hda tri bi bit len
miic

acceptor. Nhiing chuyen
miic
tren cd the la cac chuyen
miic
kem theo
biic
xa photon, nhung vdi xac xuit
nhd hon
biic
xa phonon vi tiet didn bit hat tai didn trong trudng hgp
biic
xa
phonon
Idn
hon nhieu tiet didn bit cac hat tai dien trong trudng hgp
biic
xa
photdn (khoang
10"^
lan). Vi nang lugng idn hda Ei nhd, ndn budc sdng cua
photon phat ra la Idn, roi vao viing hdng ngoai.
-f-
Chuydn
miic
sau: Cac chuyen
miic ciia
cac dien tir tir
miic
donor
xudng xoing hda tri

va lis xomg
din xudng
miic
acceptor ggi la cac chuyen
miic
sau.
Ne'u chuyen muc la thing thi : hv
=
E^
-
Ej
Nd'u chuyen
miic
la nghidng
thi:
hv
= Eg - Ej
-
Ep
Trong dd:
Ej
la nang lugng ion hda donor hoac acceptor tuong
iing.
Ep
la nang lugng cua phonon tham gia vao tai hgp. Thuc nghiem cho
thay cac chuyen
miic
sau chi xay ra dd'i vdi cac ban din pha tap ft. Khi tang
ndng do tap chat, cd thd hinh thanh viing tap chat lam nhde ranh gidi cac
x^iing

ca ban.
Ddi x'di ban din xiing cam thang
j]^
<
jjj
ndn nang luong idn hda
donor
E^
nhd hon nang lugng idn hda acceptor
E.v
Khi dd dd dang phan bidt
duoc hai loai chuydn
miic
sau.
23
- Chuyen
miic
cua cac dien tir til vung din xudng
miic
acceptor,
biic
xa
ra cae photdn vdi nang lugng:
hvi
= Eg -
E^
- Chuydn
miic
cua cac didn tir
miic

donor xudng xoing hda tri,
biic
xa
cac photon vdi nang lugng:
hv2 =
Eg -
E^
Ddi vdi ban din cd
E^
=
E^,
mudn xac dinh ban chat cua cac chuyen
miic
phai xet su thay doi cua cudng do
biic
xa theo ndng do tam tap.
Nd'u ban din cd viing cam khdng thing thi chuyen
miic
donor - vimg
hda tri va chuydn
miic
viing din -
miic
acceptor can cd su tham gia cua
phondn.
* Tdi hgp bite xq cap donor -
acceptor.
+
Trong cac ban din tap chat, cac nguyen tir tap chat thay thd' cac
nguyen tir

ciia
mang tinh thd, khi bi idn hda lam xua't hien cac
miic
nang lugng
trong
\amg
cam cua ban din. Cd hai loai tap chat donor va acceptor. Trong
mot sd chit ban din chi tdn tai tap donor hoac acceptor, nhung cd nhieu chat
ban din ddng thdi cd ca tap donor va acceptor. Khi dd trong ban din nay tao
thanh cap donor - acceptor vdi nang lugng tuong tac cu long
2
A£ = -^
(21)
6 r
Trong dd:
r : la khoang each giiia donor va acceptor
£:
la hing sd dien mdi cua mdi trudng
Nang lugng lidn kd't cua cap donor - acceptor la:
E
-
ED
+
E_^
(22)
Tuong tac culong giua donor
\'a
acceptor lam giam nang lugng lidn ket di
AE,
vi the khi tai hgp D - A, photon phat ra cd nang lugng:

2
hv =
Eg-(E-AE)
=
E (ED
+
E,)+-^
(23)
s r
24