INTERNAL FRICTION INVESTIGATION ON THE MOBILITY OF DISLOCATIONS IN III-V COMPOUNDS

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INTERNAL FRICTION INVESTIGATION ON THE MOBILITY OF DISLOCATIONS IN III-V

COMPOUNDS

D. Quélard, P. Astié, J. Gauffier

To cite this version:

D. Quélard, P. Astié, J. Gauffier. INTERNAL FRICTION INVESTIGATION ON THE MOBILITY

OF DISLOCATIONS IN III-V COMPOUNDS. Journal de Physique Colloques, 1987, 48 (C8), pp.C8-

173-C8-178. �10.1051/jphyscol:1987823�. �jpa-00227127�

INTERNAL FRICTION INVESTIGATION ON THE MOBILITY OF DISLOCATIONS IN 111-V COMPOUNDS

D.

QUELARD,

P. ASTIG and J.L. GAUFFIER

Laboratoire de Physique des S o l i d e s , a s s o c i e au C N R S . INSA, Avenue de Rangueil, F-31077 Toulouse Cedex, France

RESUME

La mobilitk des diffkrents types d e dislocations contrdlant l a deformation des compos6s 111-V a i t 6 Ctudide par des expkriences d e f r o t t e m e n t intgrieur e n t r e 0,l et 0,98 Tm sur des monocristaux d'InSb non dop6s. '

Les rksultats originaux o n t

6t6

obtenus

A

partir d e deux sous-structures d e dislocations distinctes rksultant d e l a dkformation plastique e n glissement simple deux tempkratures diff6rentes :

A

403 K o b l'on observe une population

A

c a r a c t k r e vis prgdominant ; 495 K o b I' on observe l a fois des dislocations vis, 60" et des dipdles coins. On a ainsi mis e n kvidence un pic d e relaxation dQ aux dislocations vis dont I'inergie d'activation 1,15 eV e s t t r & s proche d e celle attribuck aux mouvements des dislocations vis 5 partir d'autres techniques et d e l a ddformation plastique notamment.

ABSTRACT

The mobility of t h e different types of dislocations involved in t h e deformation of 111-V compounds h a s been studied with internal friction experiments from 0.1 t o 0.98 Tm in undoped InSb single crystals.

Original results have been achieved with two distinct dislocations substructures established by single glide plastic deformation a t t w o different temperatures : 403 K, which leads t o a screw dislocation predominance ; 495 K, which leads t o a mixed 60°, screw, and e d g e dipoles substructure. We have got a relaxation peak due t o screw dislocations, with a n activation energy 1.15 eV, very close t o t h a t ascribed t o screw dislocations movement by other techniques (plastic deformation).

INTRODUCTION

The reduction of t h e initial dislocation density in t h e wafers of 111-V compounds semiconductors a s GaAs or InP used a s substrates in optoelectronics devices is one chief problem of semiconductor industry.

For t h e purpose of solving such problems, i t seems necessary t o answer t w o questions :

i) Which mechanisms a r e involved in dislocation nucleation during t h e crystal growth, generally assumed by t h e LEC technique ( 1 ) ?

ii) In which way d o t h e dislocations move under t h e strong thermal stresses involved during t h e growth ?

Therefore, t h e study of t h e dislocation mobility in covalent crystals constitutes a n important point f o r t h e technology of semiconductors. I t c a n b e also full of interest from a fundamental point of view in t h e c a s e of 111-V compounds.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1987823

C8-174 JOURNAL DE PHYSIQUE

The second point has been studied extensively with local techniques a s individual dislocation velocities e s t i m a t e d by double etching, o r with global techniques a s plastic deformation a t a constant strain r a t e [2].

More recently, t h e use of different local techniques a s "in situ"

TEM

[3, 41, and SEM observations [5], or X-ray topography [6] has brought o u t interesting informations about t w o points which a r e still r a t h e r obscure:

-

t h e differences of mobilities between screw, 60' type, and 60° type dislocations

-

t h e role of t h e 2nd kind Peierls potential in t h e dislocation displacement : this potential seems t o be important in a l l covalent crystals [7].

With t h e study of t h e internal friction versus temperature of such deformed materials, w e should be able t o realize a n energy spectroscopy of t h e movement of t h e different types of dislocations and t o distinguish between t h e two mechanisms : double kink nucleation and geometrical kink migration [8]. In f a c t , in covalent crystals t h e activation energies of both mechanisms s e e m t o be very close [9]. Then, such a technique may b e a very promising way t o study in detail t h e dislocation mobility in 111-V compounds.

Internal friction experiments have previously been performed on Si [ l o ] , G e [9, 111 and InSb [111, by different authors essentially at high frequencies (KHz, MHz), o r a t low frequencies (Hz) and low temperatures (77 K

-

300 K) ; w e have investigated a t I H z a larger t e m p e r a t u r e range 177 K

-

1000 K]. We present in this paper t h e f i r s t results obtained on undoped lnSb deformed in single slip a t t w o different temperatures.

EXPERIMENTAL METHOD

The characteristics of t h e undoped InSb single crystals used in this work a r e shown in Table I.

Table I

The samples used f o r compression experiments were parallelepipedic (dimensions 20 x 6 x 6 mm 3 ). The compression axis was parallel t o <123> with lateral faces (11 1) aria (541) in order t o favour a single slip with activation of t h e (111) [ l ~ i ] primary slip system. We have proceeded t o t h e preferential abrasion of a lateral f a c e (541) for t h e purpose of favouring t h e activation of 60° type dislocation sources (soft mode) [14].

Resistivity CR.cm)

Carrier Conductivity concentration type

( ~ m - ~ )

5.9 t o 4.6.10 l 3 n

1.5 10 14 n 1st crystal

high

T

strained

2nd crystal low T strained

L

0.2

-

0.143

0.065

Deformation mode

single deformation

double deformation

Deformation temperature

(K)

495

523 + 403

Axial plastic strain

(96) 0.3 2 5

0.5 0.4

t o generate distinct dislocation substructures for t h e internal friction experiments.

All t h e samples have been strained under controlled a t m o s here (helium gas) by

P

^I

uniaxial compression, a t a constant strain r a t e & =1.6 10- s-

.

The compression apparatus h a s been described elsewhere [ 133

.

A f t e r plastic deformation, t h e samples were c u t in slices by a wire saw ; t h e internal friction samples (dimensions rV 20 x 2 x 0.8 mm3) with long axis parallel t o (123) (large l a t e r a l f a c e s

//

(54l)), were then gained by mechanical polishing, a subsequent chemical polishing allows to remove t h e s u r f a c e damaged by mechanical polishing.

The internal friction and elastic modulus measurements have been performed on a torsional pendulum working in f r e e decay a t 1 Hz, from 77 K t o 790 K, t h e temperature rise being assumed a t a constant r a t e of 2 K/mn. The measurement amplitudes ( i s maximum shear strain) ranged from 2 t o 6.5 lom6 [15].

Moreover, w e have controlled systematically by TEM observations t h e dislocation substructures a f t e r plastic deformation and their evolution a f t e r internal friction experiments.

EXPERIMENTAL RESULTS

Fig. 1 and fig. 2 show t h e typical shape of internal friction s p e c t r a carried o u t during t h e f i r s t temperature rise from 77 K t o 790 K for t h e t w o kinds of deformation ("high" and "low" temperature deformations).

In comparison, t h e internal friction spectrum typical of a n undeformed sample of t h e s a m e orientation has been reported under these curves. The values of Q-I measured a t low temperatures a r e r a t h e r low ( z 4 10 -4 ) and constant (this part is not reported on t h e curves); then i t increases from 500 K in t h e deformed samples, t o give rise t o a broad peak (fig. 1) or t o two peaks ffig. 2) superimposed in both cases o n t h e high temperature background of t h e type Q; = A exp ( - H ~ / ~ T ) [16].

Fig. 3 a and 4 a represent t h e variation of t h e internal friction versus T-I a f t e r substraction of t h e background. For t h e "high temperature" deformed samples, fig. 3 a shows t h e evolution versus strain of a broad peak (60 t o 80.10-~) with two components : one at low temperature (& 640 K) and t h e other a t high temperature (& 725 K). The low temperature component, preponderant in t h e c a s e of microplastic deformation (before LYP), is reduced in t h e case of macroplastic deformation, t o give way t o a n enlarged peak centered a t 690 K.

Fig. 4 a , relative t o "low temperature" deformed InSb, presents a rather different shape : t w o well $fined peaks appear, clearly separated, a t 570 K and 725 K , of lower amplitude (25 10 and 1 5 respectively) than t h e broad peak observed in "high temperature" deformed InSb.

Fig. 3 b and 4 b show t h e variation of t h e differentiated modulus versus T-I. On fig. 3 b, t w o minima appear a t t h e s a m e temperatures a s t h e t w o components of Q-I already invoked. These minima become less definite in macro l a s t i c range. Fig. 4 b

- P

c a r r i e s out t h e t w o minima corresponding t o t h e observed Q peaks with a n e x t r a minimum a t 650 K probably related t o a dislocation-point-defect interaction [17].

DISCUSSION

In order t o analyse the experimental results, we will t a k e into account t h e dislocation substructure observed by TEM.

C8-176 JOURNAL DE PHYSIQUE

The first deformation, realized a t 495 K, i.e. above t h e athermal temperature Ta f 430 K f o r InSb [14]) gives rise t o a heterogeneous substructure with high density a r e a s with a l o t of e d g e dipoles and low density a r e a s with straight 60° and screw dislocations.

When getting from microplastic t o macroplastic range, t h e substructure becomes more homogeneous, t h e proportion of e d g e dipoles regularly rising, t h e amount of debris and loops increasing too.

This is in good agreement with t h e observed decrease of 60° type dislocation density, which c a n recombine t o form edge dipoles.

These points had previously been observed on undoped GaAs deformed in similar conditions [ 131.

The 2nd deformation at 403 K, i.e. below Ta, gives rise t o a much more simple substructure, with essentially straight screw dislocations (90 %) and some 60' dislocations (10 1).

From these observations, i t is allowed t o advance t h e following exploration scheme f o r t h e observed peaks [ 191 :

-

The 570 K peak (fig.3 b), only observed a f t e r low t e m p e r a t u r e deformation, c a n be referred t o s e w dislocations. The activation energy, estimated from t h e peak position (with TeCIO-fr s, which seems reasonable, taken into account t h e observed dislocations f r e e lengths), is about 1,15 eV. This value is very close t o t h a t estimated with plastic deformation results f141. So i t seems reasonable t o propose t h e s a m e mechanism of double kink nucleation o n screw dislocations, proposed by Karmouda [ I @ ] .

-

The low temperature component ^(C'/ 640 K) observed a f t e r 'high temperature'' deformation, c a n be due t o 60° dislocations. As a m a t t e r of f a c t , t h e peak amplitude decreases a s t h e 60° dislocations amount when t h e strain is increased. The activation energy estimated in t h e s a m e way a s before, is about 1.3 eV. This is close t o t h e value 1.2 eV previously measured from 600 6-type dislocation velocities by double etching ( 1 8 j ; w e may then ascribe this component t o 6 0 ~ k - t ~ ~ e dislocations.

-

The high temperature component ( h ' 7 2 5 K), observed in all t h e deformation temperatures and strains, wouidnvt be related t o t h e dislocation type. I t could be ascribed t o a climb process connected with t h e intrinsic d e f e c t migration which takes place in t h e crystal at such high temperatures.

Finally, t h e discussed minima of t h e differentiated modulus which correspond t o t h e observed internal friction peaks, seem t o suggest t h e relaxation origin of these peaks.

CONCLUSION

The f i r s t results of low frequency internal friction achieved from 0.1 t o 0.98 Tm on undoped InSb single crystals, strained at 0.5 Tm (below t h e a t h e r m a l temperature), give rise t o a peak related to screw dislocations, The maximum t e m p e r a t u r e of 0.7 Tm would g i ~ e a n activation energy of 1.15 eV, very close t o t h e value estimated from plastic deformation results by other authors. Further experiments a r e required t o identify t h e different components of t h e enlarged peak observed a f t e r deformation at 0.6 T, (above t h e athermal temperature), which gives use t o a much m o r e complex dislocation substructure.

ACKNOWLEDGMENTS

The authors would like t o thank J.J. Couderc and P. Chomel, Laboratoire d e Physique des Solides d e Toulouse, for TEM observations and constructive discussions.

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JOURNAL D E PHYSIQUE

Fig. I Fig. 2

- - -

U n d e f o r m e d lnSb

- -

-Undeformed lnSb InSb d e f o r m e d a t 4 9 5 K InSb d e f o r m e d

-

^{& = 0.3 %}

^-

^{0.5 % at 523 K + 0.4 % at 403 K}

- - - - -

& 2 2 %

-

& = 5 %

I ( < ) T ( K 1

R::? 7C.: :,::, * z i I ! ; M, :YX, 600 5Cfi

.01

Fig. 3 a (top) Fig. 3 b (top)

4

Q-' = Q-l

-

Q-l (background) 1 1 1

F ^{Q- = Q-}

-

Q-, (background)

v e r s u s T-I. Versus T- ^I

Fig. 4 b ( b o t t o m ) Fig. 4 a (bottom)

D i f f e r e n t i a t e d modulus Versus T-l

S a m e symbols.

D i f f e r e n t i a t e d modulus Versus T- ^I

S a m e symbols.