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VIBRATIONAL EXCITATIONS IN a-Si : F AND a-Si : F : H ALLOYS
B. Agrawal
To cite this version:
B. Agrawal. VIBRATIONAL EXCITATIONS IN a-Si : F AND a-Si : F : H ALLOYS. Journal de
Physique Colloques, 1981, 42 (C6), pp.C6-93-C6-95. �10.1051/jphyscol:1981629�. �jpa-00221565�
JOURNAL DE PHYSIQUE
CoZZoque C6, suppZ6ment au n012, Tome 42, de'cembre 1981 page C6-93
V I B R A T I O N A L E X C I T A T I O N S I N a-Si: F AND a-Si: F:H ALLOYS*
B.K. Agrawal
Department of Physics, University of AZZahabad, AZZahabad, India
Abstract.- The v i b r a t i o n a l e x c i t a t i o n s both i n t h e S i bulk band mode region and above i t a t the impurity c e n t r e s i n t h e various c o n f i g u r a t i o n s f o r t h e a-Si :F and a-Si :F:H a l l o y s , have been obtained by u s i n g a c l u s t e r Bethe l a t t i c e method.
The p r e d i c t e d frequencies a r e i n e x c e l l e n t agreement with t h e a v a i l a b l e experimental data.
W e consider here only the nearest-neighbor c e n t r a l and non- c e n t r a l force constants. The f o r c e c o n s t a n t s chosen t o reproduce t h e experimental frequencies a r e shown i n Table I. Figs. 1 and 2 e x h i b i t t h e phonon d e n s i t y of s t a t e s a t one S i atom and a t one F atom i n t h e SiF, SiF2 and SiF configurations. A l l tb c a l c u l a t e d
3
l o o a l i s e d mode frequencies a r e i n e x c e l l e n t agreement with t h e d a t a of Shimada e t al. 1 . It should be noted t h a t a c e n t r a l f o r c e constant ohosen f o r each configuration g i v e s r i s e t o two l o c a l i s e d frequen- c i e s i n S i F and S i F c o n f i g u r a t i o n s i n agreement with t h e measured 2 3 f requenci e s .
W e then c a l c u l a t e d the phonon d e n s i t y f o r SiFH and SiF2H confi- g u r a t i o n s ( ~ i g s . 3 a and '3b) r e s p e c t i v e l y . The o e n t r a l and a n g u l a r
1 . 4
- Fia. 1 : Local phonon den-
Si Fl
1 . 2
- s i t y o f s t a t e s f o r S i F
configuration. The conti- nuous and dashed curves d e p i c t t h e d e n s i t i e s a t P and S i atoms, r e s e c t i v e l y f o r 4 ~ 4 . 4 3 10 S dyn/om,
B - 0.34 x 10f dyn/cm where t h e resonance mode appears a t 224 cm" . (The value of
B i s here d i f f e r e n t from
0 0 . 2
- t h a t of Table I i n t h e text).
The s m a l l dashed l i n e s a t
0 100 200
300 400 500 600 700
800S i atoms show the connection t o t h e Bethe l a t t i c e .
FREQUENCY (cm-')
* Work supported i n p a r t s by Saience Research Council, U.K. and by Uhiversity Grants Commission, New DelM .
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1981629
C6-94 JOURNAL DE PHYSIQUE
Table I - Assignment of t h e measured f r e q u e n c i e s a g a i n s t t h e v a r i o u s c o n f i g u r a t i o n s i n a-Si:F and a-Si:F:H a l l o y s . 4 and 0
d e n o t e t h e c e n t r a l and a n g u l a r f o r a e c o n s t a n t s , r e s p e c - t i v e l y .
Resonance and l o c a l i s e d f r e q u e n c i e s i- Bond ( 1 o5 dyn/am) (om-1)
g u r a t i on
B Measured
- - -
a - S i S i - S i 1.40 0.17 510 4 90
S i F Si-F 4.43 1.01 300 300b
830 850a, 828b, 830"
. . .
-b- - - -
SiF2 Si-F 5.40 1.01 300 300
330 325& ( t e n t a t i v e )
86 8 870 (827la
968 965, (920la, 930b, 950", 975'
. . .
SiF3 Si-F 5.71 1 .O1 300 300b
375 380b
5 20 51 5&. 51 ob
84 0 8 ~ 8 ~
101 6 101 5 a p d , 101ob*
- - - . - - - _ _ _ - _ _ _ _ _ _ _ - _ _ _ - _
SiFH Si-H 2.27 0.43 529 51 5&, 510b
Si-F 4.43 1.01 792 8 28b
877
902 890b, 900d
2000 1 985b, 2000d
. . .
SiF2H Si-H 2.48 0.43 300 - b - - -
300
Si-F 5.40 1 .O1 330 325a ( t e n t a t i v e )
385 380b
529 51 5&, 51 ob
8 20 8 ~ 8 ~
83 9 840b
908 890b, 900'
992 975a
20 90 2090b, 21 O o d
a : r e f e r e n c e ( 1 ) b : r e f e r e n c e ( 2 )
a : r e f e r e n c e (3) a : r e f e r e n c e ( 4 )
f o r o e c o n s t a n t s f o r t h e Si-H bond were f i r s t f i t t e d t o reproduce t h e experimental f r e q u e n o i e s i n SiH, SiH2 and S i c o n f i g u r a t i o n s i n p u r e hydrogenated 51 m a t e r i s l , i . e . , 690 om-3and 2000 om-' f o r SiH, and 850 cm-', 890 om-' and 2090 cm-' f o r SiH2. For t h e S i H j c o n f i - g u r a t i o n t h e c a l c u l a t e d f r e q u e n c i e s a r e 875 cm", 910 om-' m d 2140
- 1
om . For t h e Si-P bonds, t h e v a l u e s o f t h e f o r o e c o n s t a n t s were choeen s i m i l a r t o t h e p u r e - f l u o r i n a t e d S i m a t e r i a l s . A p e r u s a l o f Table I r e v e a l s t h a t almost all t h e p r e d i c t e d f r e q u e n c i e s have been s e e n i n t h e i n f r a r e d d a t a .
FREQUENCY (em-') FREOUENCY (cm-')
