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INTERNAL FEEDBACK MECHANISMS OF OPTOELECTRONIC BISTABILITY IN CADMIUM
SULFIDE
S. Bogdanov, V. Lyssenko
To cite this version:
S. Bogdanov, V. Lyssenko. INTERNAL FEEDBACK MECHANISMS OF OPTOELECTRONIC BISTABILITY IN CADMIUM SULFIDE. Journal de Physique Colloques, 1988, 49 (C2), pp.C2-145- C2-147. �10.1051/jphyscol:1988234�. �jpa-00227651�
JOURNAL DE PHYSIQUE
Colloque C2, Supplement au n06, Tome 49, j u i n 1988
INTERNAL FEEDBACK MECHANISMS OF OPTOELECTRONIC BISTABILITY IN CADMIUM SULFIDE
S.V. BOGDANOV and V.G. LYSSENKO
I n s t i t u t e o f Problems o f Microelectronics Technology and Superpure M a t e r i a l s , USSR Academy o f Sciences, Chernogolovka 142432. Moscow D i s t r i c t . USSR
A b s t r a c t
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Two mechanisms of i n t e r n a l feedback in cadmium s u l f i d e i n e l e c t r i c f i e l d have been s t u d i e d , namely, thermal s h i f t of a b s o r p t i o n l i n e s and e l e c t r o n s t a t e t r a n s f o r m a t i o n due t o m u l t i p a r t i c l e i n t e r a c t i o n i n t h e h i g h c a r r i e r c o n c e n t r a t i o n system.O p t i c a l b i s t a b i l i t y caused by thermal h e a t i n g i s observed when t h e CdS c r y s t a l i s e x c i t e d n e a r t h e I bound e x c i t o n a b s o r p t i o n l i n e / I / . Impact i o n i z a t i o n of f r e e and bound e x c i t o g s o c c u r s in t h e c r y s t a l upon i t s i l l u m i n a t i o n i n e l e c t - r i c f i e l d . The impact i o n i z a t i o n c u r r e n t depends i n a t h r e s h o l d way on e x c i t o x and f r e e c a r r i e r c o n c e n t r a t i o n . A t a c e r t a i n f i e l d dependent c a r r i e r concentra- t i o n avalanche occurs, t h e e l e c t r i c c u r r e n t t h e r e w i t h i n c r e a s e s t h e c r y s t a l temperature by 5-20 K / 2 / , which i s followed by a r e d I s h i f t without e x c i t o n l i n e broadening. The s h i f t l e a d s t o a n i n c r e a s e in absogption on t h e e x c i t a t i o n wavelength, i n c a r r i e r d e n s i t y and c u r r e n t . Therefore, feedback r e s u l t s from enpact i o n i s a t i o n c u r r e n t h e a t i n g of t h e c r y s t a l (Fig.?). A s f i e l d i n t e n s i t y i n c r e a s e s , t h e h y s t e r e s i s l o o p i s broadened and switch-on and switch-off c r i - t i c a l power decreases.
I n t e n s i v e i r r a d i a t i o n of t h e CdS c r y s t a l with photon energy c l o s e t o A-exciton g i v e s r i s e t o o p t i c a l b i s t a b i l i t y governed by m u l t i p a r t i c l e i n t e r a c t i o n s i n t h e h i g h c a r r i e r c o n c e n t r a t i o n system /3/. When a p p l i e d t o t h e c r y s t a l , e l e c t r i c
f i e l d produces a r e d s h i f t and broadening of t h e e x c i t o n a b s o r p t i o n l i n e /4/
a s well a s l i n e broadening owing t o c a r r i e r impact i o n i z a t i o n /2/. The f i e l d induced a b s o r p t i o n n e a r A-exciton energy may exceed two-photon and Urbah ab- s o r p t i o n and determine photogenerated c a r r i e r c o n c e n t r a t i o n , a f f e c t i n g i n such a way c r i t i c a l switch-off i n t e n s i t y (Fig.2). The absence of an e x c i t o n l i n e s h i f t i n t h e t r a n s m i s s i o n spectrum (Fig.3) s u g g e s t s t h a t t h e l a t t i c e tempera- t u r e i s unaffected. The b e s t agreement between t h e experimental and computed curves i s obtained under t h e assumption t h a t t h e e x c i t e d a r e a i s s p l i t i n t o two p a r t s , namely, t h e r e g i o n , where e l e c t r o n - h o l e plasma i s found, h a s t h e l g e f l e
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t i v i t y c o e f f i c i e n t of 0.23 and t h e t r a n s m i s s i o n spectrum w i t h n p = 3-10 cm- /5/, and r e g i o n w i t h lower d e n s i t y e x c i t o n gas. A good agreement between t h e
4
experimental and computed d a t a i s obtained by changing t h e only parameter, na- mely, p e r c e n t r a g e d of t h e s u r f a c e e x h i b i t i n g ffplasmonic" p r o p e r t i e s .
i n c r e a s e s w i t h i n c r e a s i n g e l e c t r i c f i e l d . No single-phase model ( i n c l u d i n g t h e P
"dead l a y e r " model) provides an agreement a t a h i g h e x c i t a t i o n i n t e n s i t y . I n t h i s c a s e feedback r e s u l t s from t r a n s f o r m a t i o n of t h e a b s o r p t i o n spectrum w i t h i n c r e a s i n g nonequilibrium c a r r i e r d e n s i t y . The c a r r i e r d e n s i t y b e f o r e switch- o f f and, hence, c r i t i c a l switch-off power a r e determined by e l e c t r i c f i e l d i n - t e n s i t y .
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1988234
JOURNAL DE PHYSIQUE
Fig. 1
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Transmission T versus excitation power in electric field: 1-
2.5kV/cm; 2
-
2.6 kV/cm; 3-
2.7 kV/cm.Aex
= 487 nm.Fig. 2
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Transmission T versus excitation power in electric field: 1-
0 V/cm;2
-
1.2 kV/cm; 3-
1 - 5 kV/cm,a,,
= 487 nm.Fig. 3
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Transmission T (EIIC) in electric field: 1-
0 V/cm; 2-
1.5 kV/cm;3
-
1.7 kV/cm; 4-
2.0 kV/cm.A e x
= 487 nm, Ee, 1 C.REFERENCES
/1/ Degenais M., P h i l . Trans. R. Soc. Lond. 1 (1984) 265.
/2/ lebedev I . V . , Lyssenko V.G., Sov. Phys. 9 z . Tverd. Tels 2 4 (1982) 3040.
/3/ Majumder F.A., Swoboda H.-E., Kempf K . , Klingshirn C . , ~ h ~ s y ~ e v . &B (1985) 5581
--- . -
/4/ Dow J.D., Redfield D . , Phys. Rev. B1 (1970) 3358.
/5/ Bohnert K., Schmieder G . , ~ l i n ~ a h i z C . , Phys. S t e t . S o l . , (1982) 175.
