NONLINEARITY AND SWITCHING BEHAVIOR OF THERMOOPTICAL SCHOTTKY SEED DEVICES

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NONLINEARITY AND SWITCHING BEHAVIOR OF THERMOOPTICAL SCHOTTKY SEED DEVICES

D. Jäger, F. Forsmann

To cite this version:

D. Jäger, F. Forsmann. NONLINEARITY AND SWITCHING BEHAVIOR OF THERMOOPTICAL SCHOTTKY SEED DEVICES. Journal de Physique Colloques, 1988, 49 (C2), pp.C2-101-C2-104.

�10.1051/jphyscol:1988222�. �jpa-00227639�

NONLINEARITY AND SWITCHING BEHAVIOR OF THERMOOPTICAL SCHOTTKY SEED DEVICES

D. JXGER and F . F O R S M A N N ( ~ )

I n s t i t u t fiir Angewandte Physik, U n i v e r s i t d t Miinster, 0-4400 Milnster, F.R.G.

Abstract

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W e discuss novel externally controlled operation characteris- t i c s of thermooptical SEED elements. Differential g a i n , memoryless s w i t c h i n g , and ON and O F F switching by optical s i g n a l s are observed.

1

-

INTRODUCTION

In r e c e n t y e a r s two k i n d s of SEEDS have been proposed based on different o r i g i n s of their nonlinearities. I n case of the GaAs/AlGaAs MQW pin d i o d e , the quantum confined Stark effect i s used to c o n t r o l the absorption 1 The second c l a s s a r e thermooptical SEED e l e m e n t s w h e r e the temperature i s changed by the opto- electronically generated Joule's heat /2/. Low power optical bi- and muliti- stability in materials such a s S i , I n P , G a A s and C d S have been observed at resonant and nonresonant w a v e l e n g t h s /2-6/.

I n this paper we present novel theoretical and experimental r e s u l t s o n thermooptical S i Schottky S E E D d e v i c e s /7/ w h e r e the external resistance a d d s a further nonlinearity. A s a r e s u l t , controllable differential g a i n , memoryless switching and ON and O F F switching by optical signal pulses can be a c h i e v e d , f o r example.

2 - T H E O R E T I C A L S E E D

In Fig. l(a; a sketch of the Schottky S E E D similar to those in /7/ i s shown. T h e electrical properties a r e that of a c o m m o n Schottky diode with a n ohmic contact at the front surface and a rectifying metal semiconductor contact a t the back where a depletion layer i s formed. Optically the device behaves a s a Fabry-Perot cavity operated in reflection.

' 0

TEMPERATURE. T

(a) (b)

Fig. 1 - (a) Sketch of the thermooptical S i Schottky S E E D biased in reverse direction. In this paper T o i s room t e m p e r a t u r e , d = 2 3 0 pm and Xo = 1.06 pm f r o m a Nd:YAG laser.

(b: Conventional graphical construction to s h o w optical bistability 8 . T h e solid line i s given by eq.(l), the dashed l i n e s represent eq.(2). C u r v e ( 1 : denotes the c o m m o n straight line f o r R = 0 , c u r v e (2) s h o w s the influence of R , s e e text

.

( l ) ~ u p p o r t e d by t h e Bundesrninister f u r Forschung und Technologie. F . R . G .

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1988222

C2-102 JOURNAL DE PHYSIQUE

T h e following theoretical treatment i s based upon two expressions which a r e commonly used to d e s c r i b e optical bistability (OB) by a graphical construction.

F i r s t , the absorption A = P a / P i n , i.e. the ratio of absorbed power to input p o w e r , i s given by the wellknown Airy formalism according to

H e r e R I and R2 a r e the reflectivities of the front and back s u r f a c e s , respec- tively. T h e transmission Tr = exp(-ad) and the phase @ = 2nnd/X0 a r e determined by the temperature dependent optical parameters, absorption coefficient a and index of refraction n. S e c o n d , the temperature r i s e T-To = Rh(Pa+Pe) i s assumed to be linearly dependent on the total power where P, = IoV i s the electrical power / 8 / . Assurfling now a negligible dark c u r r e n t and a photocurrent I p h = q P a , w e obtain

w h e r e R h i s the heat resistance and the photoconductivity of the photodiode.

C l e a r l y , the external resistance R i n t r o d u c e s a nonlinearity in eq.(2), the influence of which can be judged from F i g . l(b): C u r v e (1) represents the linear c a s e with R = 0 and c u r v e (2) s h o w s a curvature d u e to R # 0. Quantitative results of the influence of the external resistance on the fundamental behavior of the d e v i c e can be dravn from Fig. 2 w h e r e three special t y p e s of operation a r e demonstrated.

1.

2

E! 0.5

F A

^{I /}

T I

5:

m a

0

TEMPERATURE, T 1°C) TEMPERATURE, T (OC) TEMPERATURE. T I0C)

Fig. 2 - Graphical c o n s t r u c t i o n , absorption vs. temperature calculated from eq.(l) (solid lines) and eq.(2) (dashed lines). T h e parameters a r e R l = 0 . 3 1 5 , K 2 = 0 . 9 5 , Vo = 1 2 0 V , r) = 2 A/W and To = 17.4 " C . a ( T ) from Ref. / 9 / .

(a) R = 0 and P i n = 0.92 mW for ( 1 ) and R = 34.5 kR and P i n = 1.1 mW for (2).

(bi R = 2 5 k R and P i n = 0.1, 1 and 4 mW for c u r v e s (1) to (3).

(c) K = 4 5 k R and P i n = 0.5, 1 . 5 5 and 2 mW for c u r v e s (1) to (3).

From Fig. 2(a), it i s o b v i o u s that (i) the optical switching power i s slightly i n c r e a s e d , (ii) the contrast ratio is clearly enlarged and (iii) the temperature shift and hence Lhe total dissipated power for switching between ON and O F F a r e decreased. Fig. 2(b) reveals a novel kind of OB w h e r e the tempera- ture s w i t c h e s from a high to a low value at P i n = 4 m W , additionally to the common bistability near P i n = 1 mW. Memoryless switching can be s e e n in Fig. 2(c) w h e r e c u r v e (2) nearly matches A(T) over a large region of tempera- tures.

N o t e , h o w e v e r , that the dark current Id has been omitted and that Id and can depend on V. T h e r e f o r e , for a more exact c a l c u l a t i o n , eq.(2) h a s to be reformulated

/ a / .

The measured c w characteristics of a Schottky S E E D device a r e plotted in Fig. 3.

Fig. 3 - Measured influence of the external resistance K on room temperature reflection characteristics of the S i Schottky SEED of Fig. 1 a t a voltage of Vo = 1 1 0 V. R = 0 , 7.85, 9 . 2 3 and 1 0 k R for (a) to (d), respectively.

I n Fig. 3(a) the results for R = 0 a r e shown for comparison. A t R = 7 . 8 5 k n (Fig. 3(b)), two different hysteresis l o o p s can be distinguished which exhibit a large contrast ratio. Increasing the resistance f u r t h e r , a situation o c c u r s where from a practical viewpoint a memoryless switching a p p e a r s , s e e Fig. 3(c), which i s changed to a behavior of differential gain in F i g . 3(d), i.e. the negative slope of the c u r v e can be changed continuously by choosing R > 9.23 kR.

4

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ON AND O F F SWITCHING

T h e nonlinearity d u e to the external resistance can be used to switch the d e v i c e ON and O F F by optical pulses superimposed on the holding power which i s in the region of bistability, s e e F i g . 4(a). E x p e r i m e n t a l l y , the holding power i s P i n =

5 mW. Assuming now a s t a t e of high reflection ("ON") an additional input pulse s w i t c h e s the d e v i c e to a low reflecting s t a t e ("OFF") which i s the usual case.

( a ;

TIME, t ^(rns)

Fig. 4

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Experimentally observed ON and O F F switching by using optical input s i g n a l s and a constant holding power. T h e experimental values a r e Vo = 148 V and R = 12.31 k f 2 . (a) P i n and P r e f l a s a function of t i m e ; (b) Pe and P r e f l VS.

optical input power P i n .

C2-104 JOURNAL DE PHYSIQUE

H o w e v e r , in the present c a s e the device can again be switched on by a second pulse of a b o u t twice the a m p l i t u d e a s before. T h e background of this behavior i s illustrated by the c u r v e s in Fig. 4(b). If the second pulse i s high enough ( %

llmW in t h i s case) the dissipated electrical power i s reduced when the pulse i s switched on which l e a d s to a relative c o o l i n g of the d e v i c e , cf. Fig 2(b). Note that here Pe determines T s i n c e Pe > > P i n . T h e temperature i s n o w below the s w i t c h o f f temperature of the first h y s t e r e s i s s o that after the optical pulse the device r e m a i n s in the s t a t e o f l o w temperature which n o w belongs to the O N s t a t e of the device.

5 - S U M M A R Y AND CONCLUSION

T h e o r e t i c a l and experimental r e s u l t s s h o w that the nonlinearity of thermooptical Schottky S E E D d e v i c e s can be controlled by the external r e s i s t a n c e , R. A s a r e s u l t , the total dissipated power f o r switching and hence the corresponding temperature shift c a n be reduced significantly by choosing a suitable value of R a s compared to the c a s e R = 0. S i m u l t a n e o u s l y , the contrast ratio i s increased and a new kind of bistability and memoryless switching i s o b s e r v e d ; A s the most important r e s u l t , h o w e v e r , i s i s shown for the first time that the additional nonlinearity can be used to switch the d e v i c e O N and O F F by optical pulses superimposed on a constant holding power. In c o n c l u s i o n , thermooptical e l e m e n t s a r e found to exhibit a lot of interesting features which can be of importance concerning technical a p p l i c a t i o n s in digital optical or optoelectronic data processing. T h e external c o n t r o l of the characteristics and the possibility of O N and O F F switching a r e the most striking results.

REFERENCES

1 M i l e D.A.B., C h e m l a , D.S., D a m e n , T.C., W o o d , T.H. B u r r u s , C.A., G o s s a r d , A.C. and W i e g m a n n , W., I E E E J . Quantum Electron. QE-21 (1985) 1462.

/2/ J a g e r , D., F o r s m a n n , F. and W e d d i n g , B., I E E E J . Quantum Electron. QE-21 (1985) 1453.

/3/ F o r s m a n n , F. and J a g e r , D., Opt. Commun.,

65

(1988) 57.

/4/ F o r s m a n n , F., J a g e r , D. and N i e s s e n , W., Opt. Commun.,

62

(1987) 193.

/5/ J a g e r , D . , N i e s s e n , W . , F o r s m a n n , F., T h i e n p o n t , H. and van G e e n , R., Appl.

O p t i c s , in press.

/6/ W e g e n e r , M., W i t t , A., K l i n g s h i r n , C., G n a s s , D. and Jager,D., Appl. Phys.

Lett.,

52

(1957) 342.

/7/ J a g e r , D. and F o r s m a n n , F., Solid-State E l e c t r o n . , 3 0 (1987) 67.

/8/ F o r s m a n n , F. and J S g e i , D., Appl. Phys. B

41

(1988)151.

/9/ L i e t o i l a , A. and G i b b o n s , J.F., J. Appl. Phys.,

53

(1982) 3207.