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Submitted on 1 Jan 1981
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OPTICAL-MODE DEFORMATION POTENTIAL
R. Alig, S. Bloom, M. Inoue
To cite this version:
JOURNAL DE PHYSIQUE
CoZZoque
C6,supple'ment
aun o
12,Tome
4 2 ,de'cembre
1981page
C6-484OPTICAL-MODE DEFORMATION POTENTIAL
R.C. A l i g , S. Bloom and M. ~ n o u e *
RCA
Laboratories, Princeton,
U . S . A. *RCALaboratories,
Tokyo,Japan.
A b s t r a c t . - From measurements i n t h e l i t e r a t u r e of t h e average e n e r g i e s , E ,
r e q u i r e d t o c r e a t e e l e c t r o n - h o l e p a i r s w i t h i o n i z i n g r a d i a t i o n i n s e v e r a l semiconductors, a v a l u e of t h e optical-mode d e f o r m a t i o n - p o t e n t i a l c o n s t a n t , KDt, h a s been o b t a i n e d . A r e c e n t a n a l y s i s has been extended t o i n c l u d e s c a t t e r i n g by t h e polar-mode electron-phonon i n t e r a c t i o n a s w e l l a s by t h e optical-mode deformation p o t e n t i a l . Expressions f o r t h e s e s c a t t e r i n g r a t e s were developed i n t h e f r e e - p a r t i c l e approximation. The o n l y U
%
knowni n
t h e r a t i o of t h e s e r a t e s i s KDt. These v a l u e s a r e KD = 1.8 X 1 0 x G e ~ l c m , where p i s t h e semiconductor d e n s i t y i n gm/cm3.tWhen a high-energy p a r t i c l e e n t e r s a semiconductor, i t l o s e s energy by c r e a t - i n g e l e c t r o n - h o l e p a i r s and phonons. For a p a r t i c l e of energy Eo, t h e average number
n
of p a i r s can b e measured t o determine t h e a v e r a g e p a i r - c r e a t i o n energy E = E ~ / ~ . The v a l u e of n can a l s o b e c a l c u l a t e d , a s d e s c r i b e d in Ref. 1. The r a t e a t which a p a r t i c l e c r e a t e s o p t i c a l phonons, r e l a t i v e t o t h e r a t e a t which it c r e a t e s e l e c t r o n - h o l e p a i r s , w i l l have a marked e f f e c t on t h e v a l u e f o r E . I n Ref. 1, t h i s r e l a t i v e phonon s c a t t e r i n g r a t e i s determined e m p i r i c a l l y from t h e measured and c a l c u l a t e d v a l u e s f o r E . I n t h i s paper t h e optical-phonon s c a t t e r i n g r a t e due t o t h e d e f o r m a t i o n - p o t e n t i a l i n t e r a c t i o n i s i s o l a t e d from t h e r a t e due t o t h e polar-mode e l e c t r o s t a t i c i n t e r a c t i o n , and t h e s e r a t e s a r e determined empiri- c a l l y from t h e measured and c a l c u l a t e d v a l u e s f o r E i n t h e e l e m e n t a l and b i n a r y semiconductors. I n t h i s way t h e v a l u e of t h e optical-mode d e f o r m a t i o n - p o t e n t i a l c o n s t a n t , KDt, i s a s c e r t a i n e d .I n Ref. 1 o n l y t h e energy dependence of t h e d e f o r m a t i o n - p o t e n t i a l e l e c t r o n - phonon i n t e f a c t i o n was c o n s i d e r e d . Here t h e e x p l i c i t forms of b o t h t h e deforma- t i o n - p o t e n t i a l and polar-mode e l e c t r o s t a t i c electron-phonon i n t e r a c t i o n s a r e introduced. The s c a t t e r i n g r a t e s due t o t h e s e i n t e r a c t i o n s a r e 2
and
r;E (E) =
-
where E i s t h e p a r t i c l e k i n e t i c energy, W O i s t h e optical-mode phonon energy, E
*
i s t h e e f f e c t i v e d i e l e c t r i c c o n s t a n t , p i s t h e semiconductor d e n s i t y , and e and m a r e t h e f r e e e l e c t r o n c h a r g e and mass.
The s c a t t e r i n g r a t e f o r i o n i z a t i o n , i . e . , t h e c r e a t i o n of e l e c t r o n - h o l e p a i r s , is 1
where C i s p r o p o r t i o n a l t o t h e m a t r i x element of t h e Coulomb i n t e r a c t i o n , E
2
E g' and E is t h e semiconductor bandgap.g
3
A s in Ref. 1, t h e r a t i o of Eqs. (1) and (3) was s e t t o a c o n s t a n t
,
times t h e r a t i o of t h e f a c t o r s
i n
t h e s q u a r e b r a c k e t s . I n Ref. l,, A' was assumed independent of t h e p a r t i c l e energy and i n v a r i a n t f o r e l e c t r o n s and h o l e s and f o r d i f f e r e n t m a t e r i a l s . From measurements of E i n S i , t h i s c o n s t a n t4
was determined e m p i r i c a l l y i n Ref. 1 t o be A' = 0.33eV
.
Here, t h e r a t i o of Eqs. (2) and (3) i s s e t , in t h e same way, t o a n o t h e r c o n s t a n t ,
times t h e r a t i o of t h e f a c t o r s in t h e s q u a r e b r a c k e t s . A s w i t h A ' , B ' i s assumed independent of t h e p a r t i c l e energy and i n v a r i a n t f o r e l e c t r o n s and h o l e s and f o r d i f f e r e n t m a t e r i a l s . From measurements of E i n CdS, and u s i n g
A' t o account f o r t h e d e f o r m a t i o n - p o t e n t i a l s c a t t e r i n g , B ' was determined 3
e m p i r i c a l l y t o b e B ' = 5300eV
.
The v a l u e s of E c a l c u l a t e d w i t h A' and B ' were i n good accord w i t h t h e measured v a l u e s in 1 3 o t h e r semiconductors. The a d d i t i o n of t h e polar-mode e l e c t r o s t a t i c i n t e r a c t i o n had o n l y a s m a l l e f f e c t on most of t h e c a l c u l a t e d v a l u e s of E given i n Ref.1.
3 4
Using B' = 5300eV i n Eq. ( 5 ) , t h e v a l u e of
l
cl2
i s 1.05 x 1012 e ~ - ~ / ~ s e c - l4
Using t h i s v a l u e of
l
cl2
and A' = 0.33eV i n Eq. (4) g i v e s3
where p i s t h e numerical v a l u e of t h e semiconductor d e n s i t y i n gm/cm
.
S i n c e t h e r e i s no i o n i z a t i o n s c a t t e r i n g f o r E < E and s i n c e r ( E ) dominates b o t hg'
rip
((E and r;E (E) f o r E>
-
5E t h i s v a l u e of KDt i s v a l i d f o r k i n e t i c e n e r g i e s g'C6-486 JOURNAL DE PHYSIQUE
Measuranents of KD have been r e p o r t e d f o r germanium and s i l i c o n . A l a r g e t
5 8
number of v a l u e s have been g i v e n f o r Ge
,
r a n g i n g from 4 t o 1 2 X 1 0 eV/cm. There a r e fewer measurements f o r S i b e c a u s e t h e z e r o - o r d e r v a l u e of KD f o r t h e6 8
c o n d u c t i o n band is z e r o by symmetry
.
The v a l u e 7 i n f i r s t o r d e r i s 9x
1 0 eV/cm. R e f e r e n c e s1. R. C. A l i g , S. Bloom, and C. W. S t r u c k , Phys. Rev.
m,
5565 (198G). 2 . E. M. Conwell, High F i e l d T r a n s p o r t i n Semiconductors, (Academic P r e s s ,NY,
1967).3. The c o n s t a n t A of Ref. l i s r e l a t e d t o A' by A' = h. A. 2
4. Although t h i s v a l u e of [ C ( i s a n o r d e r of magnitude s m a l l e r than t h e v a l u e found by f i t t i n g Eq. ( 3 ) t o F i g . 1 of E. 0 . Kane, Phys. Rev.
159,
624 (1967) f o r S i , d i f f e r e n c e s of t h i s s i z e may a r i s e when band s t r u c t u r e i s i n t r o d u c e d . 5. A. L. Smirl, in P h y s i c sof
Nonlinear T r a n s p o r t,&
Semiconductors, ( e d i t e dby D. K. F e r r y , J. R. B a r k e r , and C. J a c o b o n i , Plenum,
