RECOMBINATION ENHANCED MOBILITY OF DISLOCATIONS IN III-V COMPOUNDS

HAL Id: jpa-00223065

https://hal.archives-ouvertes.fr/jpa-00223065

Submitted on 1 Jan 1983

HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci- entific research documents, whether they are pub- lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.

L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

DISLOCATIONS IN III-V COMPOUNDS

K. Maeda, S. Takeuchi

To cite this version:

K. Maeda, S. Takeuchi. RECOMBINATION ENHANCED MOBILITY OF DISLOCATIONS IN III-V COMPOUNDS. Journal de Physique Colloques, 1983, 44 (C4), pp.C4-375-C4-385.

�10.1051/jphyscol:1983445�. �jpa-00223065�

JOURNAL DE PHYSIQUE

Colloque C4, suppl6rnent a u n09, Tome 44, septembre 1983 page C4-375

RECOMBINATION ENHANCED M O B I L I T Y OF DISLOCATIONS I N 111-V COMPOUNDS

K. Maeda and S. Takeuchi

I n s t i t u t e f o r S o l i d S t a t e P h y s i c s , U n i v e r s i t y o f Tokyo, Roppongi, Minato-ku, Tokyo 106, Japan

R6sum6 - On examise l e s c a r a c t e r i s t i q u e s q u a n t i t a t i v e s d ' e f f e t de renforcement p a r i r r a d i a t i o n aux e l e c t r o n s s u r l e g l i s s e m e n t des d i s l o c a t i o n s dans des composes 111-V (n-GaAs, n - I n P ) . Cet e f f e t e s t i n t e r p r c t e s u r l a base du mecanisme de P e i e r l s , p a r un a c c r o i s s e -

ment de l a m o b i l i t e des decrochements g r a c e a 1 'e n e r g i e relachQe p a r l e s r e c o m b i n a i s o n s non r a d i a t i v e s des p o r t e u r s i n j e c t & s u r l e s n i v e a u x

l o c a l i s @ s a s s o c i e s aux d i s l o c a t i o n s . A b s t r a c t -

beam i r r a d n - I n P ) a r e

Q u a n t i t a t i v e f e a t u r e s o f t h e enhancement e f f e c t by e l e c t r o n i a t i o n on t h e d i s l o c a t i o n g l i d e i n T I I - V compounds (n-6aks,

surveyed. The e f f e c t i s e x p l a i n e d i n terms o f t h e enhanced k i n k m i g r a t i o n i n t h e P e i e r l s mechanism w i t h an a s s i s t o f t h e energy r e l e a s e d by t h e n o n - r a d i a t i v e r e c o m b i n a t i o n of t h e i n j e c t e d c a r r i e r s a t t n e l o c a l i z e d l e v e l a s s o c i a t e d w i t h t h e d i s l o c a t i o n .

1 - INTRODUCTION

The remarkable i n f l u e n c e s o f e l e c t r o n i c e x c i t a t i o n , e.g. by 1 ig h t i l l u m i n a t i o n , on t h e p l a s t i c b e h a v i o r i n 11-VI compounds and a l k a l i h a l i d e s a r e known as t h e photo- p l a s t i c e f f e c t . As f o r elemental and 111-V compound semiconductors w i t h h i g h e r covalency, d i f f e r e n t t y p e s o f p h o t o p l a s t i c o r photomechanical e f f e c t had been r e p o r t e d e a r l i e r /I/, a l t h o u g h t h e i n t e r p r e t a t i o n o f t h e e f f e c t s has n o t been estab- l i s h e d . F o r t h e p a s t s e v e r a l y e a r s , an e l e c t r o n i c e x c i t a t i o n e f f e c t on d i s l o c a t j o n m o b i l i t y ( b o t h f o r c l i m b and g l i d e ) became r e c o g n i z e d i n some o p t o e l e c t r o n i c d e v i c e s

f a b r i c a t e d f r o m 111-V compounds /2,3/, though t h e q u a n t i t a t i v e f e a t u r e o f t h e e f f e c t was n o t c l a r i f i e d . The reason t o make t h e s t u d y d i f f i c u l t c o n s i s t s i n t h e coinplex

s t r u c t u r e o f d e v i c e s w h i c h i n t r o d u c e d f a t a l a m b i q u i t y i n e s t i m a t i n g t h e s t r e s s d r i v i n g i n d i v i d u a l d i s l o c a t i o n s . A c o u p l e o f y e a r s ago, t h e p r e s e n t a u t h o r s p e r - formed f o r t h e f i r s t t i m e q u a n t i t a t i v e measurements o f t h e e f f e c t o f electron?^

e x c i t a t i o n by e l e c t r o n beam i r r a d i a t i o n on t h e d i s l o c a t . i c n m o b i l i t y i n GaAs under w e l l - d e f i n e d c o n d i t i o n s / 4 / . The r e s u l t s showed a t y p i c a l f e a t u r e o f t h e recombina-

tion-enhanced d e f e c t m o t i o n .

The p r e s e n t paper aims t o s u r v e y t h e q u a n t i t a t i v e r e s u l t s o b t a i n e d so f a r by t h e p r e s e n t a u t h o r s f o r 111-V compounds, GaAs /4,5/ and I n P /ti/, i n comparison w i t h t h e r e s u l t s o f S i by KGsters and Alexander (KA) / 7 / f o r w h i c h a q u i t e s i m i l a r e f f e c t was r e p o r t e d under a l a s e r i l l u m i n a t i o n . " Based on t h e e x p e r i m e n t a l f j n d i n g s , d i s - c u s s i o n i s made o f t h e m i c r o s c o p i c processes i n v o l v e d i n t h e enhancement phenomenon.

2 - EXPERIMENTAL PROCEDURES

F o r measuring d i s l o c a t i o n v e l o c i t y , a r a t h e r n o v e l t e c h n i q u e u s i n g a scanning e l e c -

* _{I t} i s n o t p r i m a r i l y i m p o r t a n t whether a h i g h energy e l e c t r o n beam i s used o r a l i g h t i s used t o e x c i t e t h e specimen. I n f a c t , t h e d i s l o c a t i o n g l i d e enhancement was observed a l s o i n t h e n-GaAs specimen b e n t f o r 1 h r a t room t e m p e r a t u r e under

i l l u m i n a t i o n w i t h a l i g h t f r o m a 2.2 W A r i o n l a s e r (514 nm).

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1983445

t r o n microscope i n t h e cathodoluminescence mode (SEM-CL) was employed t o observe d i s l o c a t i o n s . The method i s based on t h e f a c t t h a t t h e r a d i a t i v e r e c o m b i n a t i o n o f excess c a r r i e r s e x c i t e d by an e l e c t r o n beam i s suppressed around d i s l o c a t i o n s and as a r e s u l t t h e p o s i t i o n s where t h e d i s l o c a t i o n s emerge f r o m beneath t h e specimen s u r f a c e can be observed as dark s p o t s i n t h e SEM-CL micrograph. One o f v a r i o u s advantages o f t h i s method o v e r t h e c o n v e n t i o n a l e t c h - p i t method i s t o enable us non- d e s t r u c t i v e o b s e r v a t i o n o f d i s l o c a t i o n s i n b u l k specimens f o r which a p p l i e d s t r e s s can be e s t i m a t e d w i t h accuracy. I n t h e p r e s e n t study, an apparatus f o r a p p l y i n g bending l o a d on specimens was i n s t a l l e d i n t h e specimen chamber t o a l l o w i n - s i t u measurements o f d i s l o c a t i o n motion. For t h e d e t a i l s o f t h e i n s t r u m e n t a l set-up, t h e r e a d e r i s r e f e r r e d t o /5/.

S i n g l e c r y s t a l s used were HB-grown, Si-doped n-GaAs ( n = 1.4 x 1018cm-3, p = 2200 cm2/

Vs) and LEC-grown, S-doped n-InP ( n = 5 x 1018cm-3, 1~ = 1200 cm2/Vs). plate-shaped specimens (13 x 2.6 x 0.25 mm3) f o r bending were c u t f n t o two o r i e n t a t i o n s ; one f o r v e l o c i t y measurements o f 6 0 " - d i s l o c a t i o n s ( t h e s u r f a c e i s ( I T ] ) , t h e l e n g t h w i s e d i - r e c t i o n [T23] and t h e bending a x i s [ S a l ] ) and the o t h e r f o r screw d i s l o c a t i o n s l t h e s u r f a c e i s ( 2 20 9), t h e l e n g t h w i s e d i r e c t i o n [20 2 9 1 and t h e bending a x i s [112]).

A p o l i s h e d specimen was p l a c e d on t h e f o u r - p o i n t bending j i g i n t h e SEM chamber and b e n t under a p r e s c r i b e d l o a d and a t v a r i o u s temperatures e i t h e r i n t h e dark o r under e l e c t r o n beam i r r a d i a t i o n r e a l i z e d by defocusing t h e 30 keV e l e c t r o n probe beam o f t h e SEM. The v e l o c i t y o f i n d i v i d u a l d i s l o c a t i o n s was e v a l u a t e d f r o m t h e d i s t a n c e t r a v e l e d b y t h e d i s l o c a t i o n d u r i n g t h e l o a d i n g . For GaAs, t h e measurements were repeated i n - s i t u f o r t h e same specimen v a r y i n g e x p e r i m e n t a l c o n d i t i o n s such as tem- p e r a t u r e , s t r e s s , i r r a d i a t i o n i n t e n s i t y , e t c . For InP, however, t h e SEM-CL c o n t r a s t o f d i s l o c a t i o n s was n o t enough t o l o c a t e t h e d i s l o c a t i o n p o s i t i o n s a c c u r a t e l y , so t h a t t h e d e t e r m i n a t i o n o f them were made p r a c t i c a l l y by t h e double e t c h i n g method w i t h t h e a s s i s t a n c e o f t h e SEM-CL image as a complementary guide.

The d i s l o c a t i o n t y p e was determined from a s i m p l e g e o m e t r i c a l c o n s i d e r a t i o n . The d i s t i n c t i o n between a- and B - d i s l o c a t i o n s was made a c c o r d i n g t o t h e moving d i r e c - t i o n s f r o m t h e d i s l o c a t i o n source which were o p p o s i t e t o each o t h e r .

3 - RESULTS

3.1. C a r r i e r Recombination a t D i s l o c a t i o n s

As mentioned i n t h e preceeding s e c t i o n , d i s l o c a t i o n s i n 111-V compounds a c t as e f f i c i e n t r e c o m b i n a t i o n c e n t e r s o f i n j e c t e d excess e l e c t r o n - h o l e p a i r s . E s p e c i a l l y i n GaAs and InP, i t i s known /8/ t h a t t h e d i s l o c a t i o n s suppress t h e r a d i a t i v e recom- b i n a t i o n ( 1 uminescence) w i t h few e x c e p t i o n a l cases. The p r e s e n t SEM-CL o b s e r v a t i o n s showed t h a t t h e g l i d i n g d i s l o c a t i o n s i n GaAs, t h a t s h o u l d be d o u b t l e s s l y f r e e o f d e c o r a t i o n i n t h e moving s t a t e a t l e a s t a t l o w e r temperatures, a c t as n o n - r a d i a t i v e r e c o m b i n a t i o n c e n t e r s . F i g u r e 1 shows a s e r i e s o f micrographs t a k e n f r o m a VTR t a p e t h a t r e c o r d e d SEM-CL TV scanning images o f a moving d i s l o c a t i o n g l i d i n g under an a p p l i e d l o a d . I n e v e r y frame t h e d i s l o c a t i o n i s observed as a dark s p o t i n d i c a t i n g t h e n o n - r a d i a t i v e n a t u r e o f r e c o m b i n a t i o n a t t h e d i s l o c a t i o n w i t h a f r e s h c o r e . From a c a r e f u l comparison o f SEM-CL c o n t r a s t s o f c l e a n m i s f i t d i s l o c a t i o n s i n Gal-xA1xAsl-vPv h e t e r o s t r u c t u r e s w i t h TEM micrographs o f t h e same d i s l o c a t i o n s , P e t r o f f e t a j . - / 9 / concluded t h a t t h e d i s l o c a t i o n s g i v i n g d a r k c o n t r a s t s i n t h e SEM- CL a r e a l l d i s s o c i a t e d i n t o Shockley p a r t i a l s . T h e r e f o r e t h e g l i d i n g d i s l o c a t i o n s observed i n t h e p r e s e n t SEM-CL t e s t s a r e c o n s i d e r e d t o be d i s s o c i a t e d i n t h e moving s t a t e .

3.2. G l i d e Behavior

As demonstrated i n F i g . 1, t h e m o t i o n o f d i s l o c a t i o n s i s smooth and u n i f o r m . A t t h e same s t r e s s and t h e same temperature, t h e v e l o c i t i e s o f t h e same t y p e o f d i s l o c a t i o n s d i d n o t d i f f e r much f r o m each o t h e r , which means t h a t a l a r g e number o f r a t e process- es a r e i n v o l v e d i n t h e d i s l o c a t i o n g l i d e i n t h e d i s t a n c e s c a l e o f t h e SEX observa- t i o n . I n o r d e r t o see t h e g l i d e f e a t u r e i n t h e s h o r t e r range motion, i n - s i t u obser- v a t i o n s o f d i s l o c a t i o n s were c a r r i e d o u t f o r GaAs u s i n g a TEM equipped w i t h a t e n s i l e stage. The v i s c o u s g l i d e b e h a v i o r observed i n TEM was much t h e same as t h a t observed i n t h e SEN-CL.

As f o r InP, w h i l e t h e v e l o c i t y o f 6 - d i s l o c a t i o n s was r e p r o d u c i b l e as i n GaAs, t h a t o f a - d i s l o c a t i o n s was q u i t e s c a t t e r e d . Due t o t h e p o o r r e p r o d u c i b i l i t y , t h e e f f e c t o f t h e e l e c t r o n i r r a d i a t i o n on t h e a- d i s l o c a t i o n s i n I n P was n o t s u c c e s s f u l l y i n v e s t i - gated.

0 Thus, t h e d i s l o c a t i o n s on w h i c h t h e e f f e c t o f e l e c - t r o n i r r a d i a t i o n was i n v e s t i g a t e d a r e t h o s e w h i c h e x h i b i t e d t h e v i s c o u s g l i d e presumably c o n t r o l l e d b y t h e P e i e r l s mechanism.

3.3. Enhanced G l i d e

3.3.1. Q u a l i t a t i v e Features - I n F i g . 2 t h e e f f e c t o f t h e 30 keV e l e c t r o n beam i r r a d i a t i o n on t h e t r a v e l i n g d i s t a n c e o f an i s o l a t e d d i s l o c a t i o n i s

shown as a f u n c t i o n o f t h e l o a d i n g t i m e . Upon 9 s commencement and c e s s a t i o n o f t h e i r r a d i a t i o n , t h e i d e n t i c a l d i s l o c a t i o n q u i c k l y changed i t s v e l o c i t y . What i s i m p o r t a n t i n t h i s f i g u r e i s t h a t t h e enhance, ment e f f e c t i s c o m p l e t e l y r e v e r s i b l e . Consequently . t h e enhancement e f f e c t i s d e f i n i t e l y n o t due t o any i r r e v e r s i b l e change such as s u r f a c e c o n t a m i n a t i o n , r a d i a t i o n damage and so f o r t h .

The e f f e c t o f e l e c t r o n beam i r r a d i a t i o n was a l s o r e c o g n i z e d i n t h e v i s c o u s d i s l o c a t i o n m o t i o n i n TEM.

The d i s l o c a t i o n g l i d e was enhanced s i g n i f i c a n t l y onl:18s a t l o w temperatures below 450 K, w h i c h i s c o n s i s t e n t w i t h t h e o b s e r v a t i o n i n t h e b u l k specimen d e s c r i b e d i n t h e n e x t s e c t i o n . T h i s f a c t s t r o n g l y suggests t h a t t h e enhancement t a k e s p l a c e i n t h e i n t r i n s i c P e i e r l s mechanism r a t h e r t h a n d e p i n n i n g o f d i s l o c a -

t i o n segments f r o m some p o i n t o b s t a c l e s . 50 um

3.3.2. Temperature Dependence - The t e m p e r a t u r e

dependence o f o f d i s l o c a t i o n v e l o c i t y v . under F i g . 1 - SEM-CL TV scanning e l e c t r o n i r r a d i a t i o n e x h i b i t s a q u i t e d j s t i n c t i v e

j/aieiag.a

f e a t u r e : A t h i g h temperatures above Tc t h e v e l o c i t y

n-GaAs

screw dislocation

%

0

I

F i g . 2 - E f f e c t o f e l e c t r o n beam i r r a d i a t i o n on t h e t r a v e l i n g d i s t a n c e o f an i s o l a t e d screw d i s ! o c a t i o n i n n-GaAs as a f u n c t i o n o f l o a d i n g t i m e .

'0 1000 2000 " ~ 0 0 0 5000

Loading Time ( s )

u . c o n i n c i d e s w i t h t h a t i n t h e dark vd. Below Tc i t d e v i a t e s f r o m t h e dependence i n t h e d a r k t o a h i g h e r v a l u e f o l l o w i n g a n o t h e r A r r h e n i u s f o r m u l a w i t h a l o w e r a c t i v a - t i o n energy t h a n t h a t i n t h e dark. F i g u r e 3a shows I n v - l / ~ p l o t s f o r t h r e e t y p e s o f d i s l o c a t i o n s i n t h e n-GaAs and F i g . 3b f o r 6- d i s l o c a t i o n s i n t h e n-InP.

The c h a r a c t e r i s t i c dependence i s common t o a1 1 cases, though t h e v e l o c i t y measure- ment was n o t a c t u a l l y made f o r t h e screw d i s l o c a t i o n s i n n-GaAs up t o h i g h temper- a t u r e s . I n t h i s r e s p e c t , a q u i t e s i m i l a r l n v - I/T r e l a t i o n was found i n S i / 7 / . The e f f e c t o f i r r a d i a t i o n i n t e n s i t y on t h e t e m p e r a t u r e dependence was i n v e s t i g a t e d f o r a - d i s l o c a t i o n s i n n-GaAs.

F i g u r e 4 demonstrates t h e two temperature dependences f o r two i n t e n s i t i e s . The magnitude o f t h e a c t i v a t i o n energy under i r r a d i a t i o n i s found t o b e c o n s t a n t independ- e n t o f t h e i r r a d i a t i o n i n t e n - s i t y . The i n c r e a s e i n i n t e n - s i t y s i m p l y s h i f t s up t h e I n vi - l / T r e l a t i o n i n para1 - 1 e l . I n o t h e r words i t i s t h e p r e e x p o n e n t i a1 f a c t o r t h a t i s a f f e c t e d by t h e i r r a d i a t i o n . I t i s n o t e d t h a t t h e p r e e x p o n e n t i a l f a c t o r v h v a l u a t e d b y e x t r a - p o l a t i n g 2 t h e I n vi - llr r e l a t i o n below i s o r d e r s o f magnitude s m a l l e r t h a n t h a t i n t h e d a r k . T h i s i s a r e m a r k a b l e d i f f e r e n c e f r o m t h e b e h a v i o r of t h e doping e f f e c t o f d i s l o c a t i o n m o b i l i - t y observed i n v a r i o u s semi- c o n d u c t o r s /10,11/, i n w h i c h t h e p r e e x p o n e n t i a l f a c t o r a r e n o t g r e a t e l y a f f e c t e d .

3.3.3. I n t e n s i t y Dependence -

The dependence o f t h e d i s l o - c a t i o n v e l o c i t y on t h e i r r a - d i a t i o n i n t e n s i t y was meas- u r e d a t a f i x e d t e m p e r a t u r e below Tc. F i g u r e 5 shows

T ( K )

800 700 600 500 LOO 350 300

I ' ' ^I I

F i g . 3a - Temperature dependences o f d i s l o c a t i o n v e l o c i t y f o r t h r e e t y p e s o f d i s l o c a t i o n s i n n-GaAs i n t h e d a r k and under e l e c t r o n beam i r r a d i a t i o n .

n-lnP

= 2 2 ~ ~ l m * dark irrad.

B

-

>.

2

-

C 0

.- 316'-

-

5

lo-"'-

'-<...

1.5 1.6 _1.7 1.8 1.9 2.0 2.1 2.2 llT(10-31C')

F i g . 3b - Temperature dependences o f d i s l o c a t i o n v e l o c i t y f o r 6 - d i s l o c a t i o n s i n n-InP i n t h e d a r k and under e l e c t r o n beam i r r a d i a t i o n .

The parameters i n eq. ( 1 ) e v a l u a t e d ¹ IT K')

f r o m F i g s . 3a, 3b and t h e d a t a f o r F i g . 4 - Temperature dependences o f a- S i / 7 / a r e summarized i n T a b l e 1. d i s l o c a t i o n v e l o c i t y i n n-GaAs f o r two Note t h a t ( 1 ) t h e v a l u e s o f i r r a d i a t i o n i n t e n s i t i e s .

p r e e x p o n e n t i a l f a c t o r v$ a r e

t y p i c a l 1 y an o r d e r o f 1 04-5m/s 1o6-

whereas t h e vz has much s m a l l - ^n-GaAs a-dislocation e r v a l u e s determined b y t h e ^ul r = 4 0 MNlm2

i r r a d i a t i o n i n t e n s i t y ; ( 2 )

-

^/"

f3- and screw d i s l o c a t i o n s i n

GaAs have v e r y c l o s e v a l u e s

.- .P

o f Ei as w e l l as Et. 8

f lo-'

4 - DISCUSSION _z ^{C 0}

4.1. Enhanced Component

-

ii

When d i s l o c a t i o n s i n t e t r a - 6 n e d r a l l y c o o r d i n a t e d c r y s t a l s

a r e d i s s o c i a t e d as supposed ^/!J

i n t h e p r e s e n t case, t h e 1 6 ~

m o b i l i t y o f t h e whole d i s l o - ¹ o - ~ 16" 1

Irradiation Intensity ( ~ l r n * ) c a t i o n p i s determined b y

t h o s e o f t h e p a r t i a l s p1 and F i g . 5 - I n t e n s i t y dependence o f a - d i s l o c a t i o n

p2 as v e l o c i t y i n n-GaAs.

l / = l / l + l / 2 . ( 2 ) t h e i n c r e m e n t o f v e l o c i t i e s f r o m t h e

v a l u e i n t h e d a r k as a f u n c t i o n o f ^T (K)

t h e number o f e l e c t r o n s i n c i d e n t p e r 600 500 I 400 I 300 I

Therefore, t h e measured m o b i l i t y i s determined d o m i n a n t l y b y t h e p a r t i a l w i t h a s m a l l e r m o b i l i t y .

u n i t t i m e on t h e specimen s u r f a c e o f u n i t area. The dependence i s almost l i n e a r , w h i c h i n d i c a t e s t h a t t h e p r e e x p o n e n t i a l f a c t o r i s p r o p o r t i o n a l

I n t h e z i n c b l ende c r y s t a l s , t h e r e a r e s i x t y p e s o f d i s l o c a t i o n s a s s o r t e d a c c o r d i n g t o t h e c o n s t i t u e n t p a r t i a l s by d i s t i n g u i s h i n g t h e o r d e r ( l e a d i n g o r t r a i l i n g ) as shown i n F i g . 6. The d i s l o c a t i o n s whose v e l o c i t i e s were measured i n t h e p r e s e n t

n-GaAs

\

t o t h e r a t e o f c a r r i e r i n j e c t i o n b y t h e i r r a d i a t i o n .

Thus, a u n i f i e d e x p r e s s i o n o f d i s l o -

-

c a t i o n v e l o c i t y i n c l u d i n g t h e e x c i t - 2

a t i o n i n t e n s i t y as a n o t h e r parameter 5 1 ~ 7 - i s _{v = V:} exp(-Et/kT) ^.-

-

1

y

+ 11 'I exp[- (E* - A E ) / ~ T ]

. ,

Here, E~ i s t h e a c t i v a t i o n energy i n ,O t h e d a r k (1=0) and E - A E = E ~ is t

-

t h e a p p a r e n t a c t i v a t i o n energy under 6 i r r a d i a t i o n below T

.

so t h a t no e f f e c t o f i r r a d i a t i o n i s observed. A t l o w temperatures under i r r a d i a t i o n t h e second t e r m predomi-

n a t e s . l d O

4 ^"4.

1=0.044Alm2

in the dark

I ,

1'5 2 .O 2.5 3.0 3.5

Table 1 - Parameters evaluated from t h e experiments. E i s t h e band gap energy

a t 300 K. 9

Ga As Ga As GaAs InP S i /7/

a B screw B 30°/900

v: (m/s) 9x1 o2 8x1 0' 9x105 7x1 05 3x1 0 4

v: (m/s) 4x1 0-4 3x1 0-' 3x1 Od2 5x1 0- 3x1 0 - I

g ( ~ n - ~ / s ) 5 ~ 1 0 ~ ~ 6x1 O2 4x102' 6x1 02 lx1O2'

~ : / ~ ( r n " ) 8 ~ 1 0 - ~ ~ 5 ~ 1 0 - ~ ~ 8 ~ 1 0 - ~ ~ 8 ~ 1 0 - ~ ~ 3x1 O-'

zt (ev) I .oo 1.7 1.72 1.60 1.82

E; ( e v ) 0.29 0.6 0.64 0.70 1.14

E~ (eV) 20.7

>I.]

Em (eV) 1.0> 20.7 1.7> 21.1 1.7> 21.1 1.6, 20.9 1.8> 20.7

Edk(eV) 50. 6 51 - 3 51.3 - 51.4 - 52.3 -

E~ (eV) 1.43 1.43 1.43 1.28 1 - 1 1

study a r e i n t e r p r e t e d as a ^-t 90°(a)/300(a), B + 30°(B)/900(B) and screw -t 30"(ct)/30°(~).

I f we n e g l e c t t h e o r d e r o f p a r t i a l s /12, 13/, the common component between a- and screw, and between 6- and screw d i s l o c a - t i o n s a r e 30°(ct) and 30°(fK) p a r t i a l s , r e s p e c t i v e l y . As seen i n Fig. 3a and noted p r e v i o u s l y , t h e a c t i v a t i o n energies Et o f t h e B- and screw d i s l o c a t i o n s a r e c l o s e t o each o t h e r . I n a d d i t i o n , both o f them e x h i b i t lower m o b i l i t y than t h e a - d i s l o c a t i o n . From these f a c t s i t may be deduced t h a t t h e 3O0(B) p a r t i a l posesses t h e lowest m o b i l i t y among a l l the p a r t i a l s and determines t h e m o b i l i t y

o f t h e B- and t h e screw d i s l o c a t i o n s i n ^x

the dark as concluded p r e v i o u s l y by 30(a)

Ninomiya /14/. Fig. 6 - S i x types-of d i s s o c i a t e d d i s -

l o c a t i o n s along <110> d i r e c t i o n s on As seen i n Table 1, E . i s a l s o c l o s e t o (111) s l i p plane.

each o t h e r between th& 5- and t h e screw

d i s l o c a t i o n s . T h i s may be r e f l e c t i n g t h a t t h e m o b i l i t y o f t h e 30°(8) p a r t i a l i s enhanced by t h e i r r a d i a t i o n b u t s t i l l low enough t o c o n t r o l t h e whole d i s l o c a t i o n motion. Unfortunately, i t i s n o t known from t h e present r e s u l t alone which p a r t i a l

i s r e s p o n s i b l e f o r t h e enhancement o f the a - d i s l o c a t i o n . 4.2. Enhancement Mechanism

4.2.1. Heating o f L a t t i c e - As t h e most t r i v i a l cause o f t h e enhancement, one may suspect a h e a t i n g o f l a t t i c e by t h e e l e c t r o n i r r a d i a t i o n . This was checked by various t e s t s /4-6/. (1) A small thermocouple t h a t was touched d i r e c t l y on t h e specimen surface d i d n o t d e t e c t a s i g n i f i c a n t temperature r i s e , i n agreement w i t h a t h e o r e t i c a l estimate. (2) I f t h e enhancement was caused by h e a t i n g o f t h e l a t t i c e , the temperature r i s e should be almost p r o p o r t i o n a l t o t h e i r r a d i a t i o n i n t e n s i t y I, so t h a t t h e v e l o c i t y under i r r a d i a t i o n would depend on I q u i t e non-1 i n e a r l y . This i s i n c o n s i s t e n t w i t h t h e a c t u a l l i n e a r v . - I r e l a t i o n ( F i g . 5). ( 3 ) The same conclu- s i o n was drawn from another t e s t varyingzthe average e l e c t r o n dose r a t e by chopping the i r r a d i a t i o n o f a f i x e d i n t e n s i t y a t various d u t y cycles, which gave a l i n e a r r e l a t i o n between t h e d i s l o c a t i o n v e l o c i t y and t h e d u t y c y c l e o r t h e average power

i n p u t /4/. ( 4 ) Furthermore, i n e v e r y case, i f t h e h e a t i n g e f f e c t was t h e cause, one would e x p e c t t h e ]nui-1/T r e l a t i o n merged w i t h t h e ]nud-1/[P r e l a t i o n i n a g r a a u a l way f o l l o w i n g v; e x p [ - E ~ / ~ ( T + A T ) ] , where AT i s t h e t e m p e r a t u r e r i s e t h a t s h o u l d be p r o p o r t i o n a l t o t h e temperature T, w h i c h i s q u i t e u n l i k e l y . Thus, t h e e f f e c t o f l a t t i c e h e a t i n g b y i r r a d i a t i o n i s concluded t o be n e g l i g i b l e i n t h e p r e s e n t s t u d y .

4.2.2. Charge S t a t e E f f e c t - A l t h o u g h t h e mechanism o f t h e d o p i n g e f f e c t o r t h e charge s t a t e e f f e c t on d i s l o c a t i o n m o b i l i t y /10,11/ i s n o t y e t e s t a b l i s h e d , t h e p r e s e n t e f f e c t i s n o t e x p l a i n e d by t h e d o p i n g e f f e c t . I n GaAs, t h e m o b i l i t y o f t h e a - d i s l o c a t i o n i s known t o be i n s e n s i t i v e t o doping w h i l e t h a t o f t h e $ - d i s l o c a t i o n v e r y s e n s i t i v e /11/. I f t h e r o l e o f t h e e l e c t r o n i r r a d i a t i o n was t o change t h e quasi-Fermi l e v e l , t h e r e s u l t a n t e f f e c t s h o u l d be l e s s pronounced i n t h e a - d i s l o c a - t i o n t h a n t h e 6 - d i s l o c a t i o n , which i s c o n t r a d i c t o r y w i t h t h e p r e s e n t r e s u l t s .

Furthermore, w h i l e t h e d o p i n g e f f e c t m a n i f e s t s i t s e l f w i t h a change i n t h e a c t i v a t i o n energy o f t h e d i s l o c a t i o n v e l o c i t y , t h e a c t i v a t i o n energy i n t h e p r e s e n t case does n o t depend on t h e i r r a d i a t i o n i n t e n s i t y t h a t would change t h e quasi-Fermi l e v e l as t h e doping does. Thus t h e charge s t a t e e f f e c t i s u n l i k e l y t o be t h e cause o f t h e enhancement e f f e c t .

4.2.3. Recombination Enhanced D e f e c t M o t i o n - As shown i n 3.1, r e c o m b i n a t i o n s o f i n j e c t e d c a r r i e r s a t d i s l o c a t i o n s a r e n o n - r a d i a t i v e . A c t u a l l y , b a l l i s t i c phonon e m i s s i o n can be observed d u r i n g n o n - r a d i a t i v e r e c o m b i n a t i o n i n d i s l o c a t e d GaAs c r y s t a l s /15/. Weeks e t a l . /16/ c o n s i d e r e d t h a t t h e v i b r a t i o n a l energy disposed l o c a l l y a t a r e c o m b i n a t i o n c e n t e r b y a n o n - r a d i a t i v e t r a n s i t i o n i s d i r e c t l y u t i l i z e d b y t h e d e f e c t i t s e l f t o a s s i s t i t s own r e a c t i o n o r m o t i o n b e f o r e t h e energy d i s s i - pates i n t o t h e s u r r o u n d i n g medium. Based on a more g e n e r a l i z e d model, Sumi /17/

d e r i v e d e x p r e s s i o n s f o r t h e r e c o m b i n a t i o n enhanced r e a c t i o n r a t e t h a t v a r y depending on t h e r a l a t i v e magnitude o f E~ w i t h r e s p e c t t o E*, where E* i s t h e a c t i v a t i o n energy o f t h e r e a c t i o n a t t h e t h e r m a l e q u i l i b r i u m - ( i n t h e d a r k ) and E~ t h e energy r e l e a s e d upon t h e n o n - r a d i a t i v e r e c o m b i n a t i o n . A c c o r d i n g t o h i s t h e o r y , t h e enhance- ment r e a c t i o n r a t e i s g i v e n by

( nlR exP [-(Et - E,)/k~l 2

f o r E~ < y Et (3a

2 2

y ) k ~ l f o r y E~ < E~ < 2

( 3 b ) f o r E ~ / Y 2 < E~ , ( 3 c ) where R i s t h e r e c o m b i n a t i o n r a t e . The parameter y i s t h e d i r e c t i o n a l c o s i n e between

t h e r e a c t i o n c o o r d i n a t e and t h e a c c e p t i n g c o o r d i n a t e on which t h e c e n t e r c a p t u r e s t h e c a r r i e r . U s u a l l y t h e a c t u a l magnitude o f y (51 ) i s n o t known a p r i o r i

.

a g e n e r a l argument, l e t eqs. ( 3 a ) - ( 3 c ) be r e p l a c e d by a common e x p r e s s i o n

R~~ = ~ I ~ R exp [ - ( E ~ - E ~ * ) / ~ T ]

.

Here Er* i s i n general a f r a c t i o n o f Er and s a t i s f i e s t h e r e s t r i c t i o n s Er* 5 Er and 0 - Ep* 2 E,. I n any case, t h e k i n e t i c s o f t h e r e c o m b i n a t i o n enhanced d e f e c t m o t i o n (REDM) i s c h a r a c t e r i z e d b y t h e r e d u c t i o n o f t h e a p p a r e n t a c t i v a t i o n energy and t h e p r e e x p o n e n t i a l f a c t o r t h a t v a r i e s i n p r o p o r t i o n t o t h e r e c o m b i n a t i o n r a t e R.

T h i s model a c h i e v e d a g r e a t success i n e x p l a i n i n g t h e enhanced a n n e a l i n g o f r a d i a - t i o n - p r o d u c e d p o i n t d e f e c t s i n GaAs, Gap and S i upon m i n o r i t y c a r r i e r i n j e c t i o n /18/.

The k i n e t i c s o f t h e enhanced g l i d e i s s u r p r i s i n g l y s i m i l a r t o t h a t o b t a i n e d i n t h e enhanced a n n e a l i n g , which s t r o n g l y suggests t h a t t h e p r e s e n t e f f e c t i s a l s o e x p l a i n - e d i n terms o f t h e REDM mechanism.

The r e c o m b i n a t i o n r a t e R i n eq. ( 4 ) i s r e l a t e d t o t h e c a r r i e r i n j e c t i o n r a t e o r t h e e l e c t r o n - h o l e p a i r g e n e r a t i o n r a t e g p e r u n i t volume. For t h e e l e c t r o n beam i n j e c - t i o n , g may be e v a l u a t e d as

g % v a l l ( E ~ ~ ~ s I (5) where v i s t h e a c c e l e r a t i n g v o l t a g e o f i n c i d e n t electrons, E. (s5eV) t h e i o n i z a - t i o n engrgy t o c r e a t e an e l e c t r o n - h o l e p a i r and 5 (cZvm) t h e "Onpenetration distance.

As R i s t o be p r o p o r t i o n a l t o g a t low i n j e c t i o n l e v e l s , we can r e w r i t e eq. ( 4 ) as

R,, = n i f I exp [-(st - ~ ~ * f l k l ]

.

The above formula q u a l i t a t i v e l y agrees w e l l w i t h t h e second term i n eq. (1 ) . For l a r g e r i n j e c t i o n ,

where P i s t h e power i n p u t per u n i t area and 6 t h e a b s o r p t i o n l e n g t h o f t h e l i g h t w i t h a photon energy o f hv. The c a l c u l a t e d values o f g i n t h e experiments a r e l i s t e d i n Table 1. I t i s noted t h a t the r a t i o s o f v? t o g a r e s i m i l a r t o each o t h e r among various d i s l o c a t i o n types and c r y s t a l s , suggesting a common mechanism being o p e r a t i n g i n the enhancement.

The e l e g a n t success i n e x p l a i n i n g t h e p o i n t d e f e c t annealing i n terms o f t h e REDM mechanism i s due t o t h e s i t u a t i o n t h a t t h e energy E released upon t h e n o n - r a d i a t i v e recombination a t t h e defects can be evaluated from f h e knowledge o f t h e e l e c t r o n i c energy l e v e l s associated w i t h t h e p o i n t d e f e c t s and hence t h e theory can be checked by comparing t h e E, d i r e c t l y w i t h t h e e x p e r i m e n t a l l y obtained r e d u c t i o n o f t h e a c t i v a t i o n energy 1181. I n t h e case o f d i s l o c a t i o n s , however, t h e knowledge o f t h e energy l e v e l s associated w i t h t h e d i s l o c a t i o n i s g e n e r a l l y s t i l l l i m i t e d . Even i n the cases o f Si and Ge f o r which t h e p o s i t i o n s o f t h e d i s l o c a t i o n l e v e l s a r e r e l a - t i v e l y well-documented 1191, the a c t u a l r a t e - c o n t r o l l i n g process o f t h e d i s l o c a t i o n g l i d e i n those c r y s t a l s i s l e s s founded i n comparison w i t h t h e case o f p o i n t d e f e c t s . 4.3. R a t e - c o n t r o l l i n g Process o f D i s l o c a t i o n G l i d e

Experimentally t h e d i s l o c a t i o n v e l o c i t y i n semiconductors i s w e l l expressed by a formula

v = A

-ern

where T i s t h e a p p l i e d s t r e s s . The d i f f i c u l t y w i t h t h e d i s l o c a t i o n m o b i l i t y problem i s t o e x p l a i n t h e s t r e s s e x p o n e n t m = l . O ' ~ 1 . 5 and t h e r e l a t i v e l y small magnitude o f t h e preexponential f a c t o r A . T ~ ( t y p i c a l l y %105"6m/s).

A comprehensive e x p l a n a t i o n invokes a viscous motion o f k i n k s due t o t h e s i g n i f i c a n t P e i e r l s p o t e n t i a l o f t h e second k i n d . The s t r e s s exponent near u n i t y i s explained by t h e d i f f u s i o n a l motion o f abrupt k i n k s i n t h e course o f t h e double k i n k nuclea- t i o n as i l l u s t r a t e d i n Fig. 7 and t h e small preexponential f a c t o r i s a r e s u l t o f k i n k

f

--A

L \L

F--;

---:--

I I

I I I I

I I

I / l I I d i f f u s i o n and the l a t e r a l migra-

, , I , , I

1

'Z, Dk

c o l l i s i o n s which e f f e c t i v e l y shorten t h e l e n g t h o f t h e d i s l o c a t i o n segment. The double k i n k formation r a t e per u j i t time per u n i t length, when t h e d i f f u s i o n a l m i g r a t i o n of k i n k s i s considered, i s w r i t t e n as 1201

K = ( ~ ~ r b h l a 2 k l ) exp ( - E d k / k ~ )

= (vkrbh/kp) exp [- (E, + E ~ ~ ) / ~ T ]

-

Here Dk i s the d i f f u s i o n constant o f k i n k s given by vkaL exp (-E,/~T), vk t h e v i b r a - t i o n a l frequency o f t h e k i n k ( t h e o r d e r o f t h e Debye frequency), b t h e s t r e n g t h of o f t h e Burgers vector, a the p e r i o d along t h e d i s l o c a t i o n , h t h e p e r i o d o f t h e

P e i e r l s p o t e n t i a l v a l l e y , E~ t h e k i n k m i g r a t i o n energy and E~~ t h e f r e e energy o f t h e double k i n k . The v e l o c i t y o f t h e d i s l o c a t i o n normal t o i t s e l f i s

v = 2hZK , (1 0)

where Z i s t h e mean d i s t a n c e swept by a k i n k along t h e d i s l o c a t i o n segment u n t i l i t reaches t h e end o f t h e whole segment o r i s a n n i h i l a t e d w i t h a k i n k o f opposite s i g n generated on the same segment. When Z i s determined by t h e mutual k i n k c o l l i - sions ( k i n k - c o l l i s i o n case),

2 = Zk = (vk/K) 112

= a exp (Edk/2kT) , (11)

where vk i s t h e d r i f t v e l o c i t y o f a k i n k given by ~ ~ ~ b h / k ~ . The i n s e r t i o n o f eqs.

( 9 ) and (11) i n t o eq. (10) gives t h e d i s l o c a t i o n v e l o c i t y i n t h e dark as vd = 2h(vkK) 112

= 2(vkabh /kT)-r exp [ - ( E ~ 2 +Emc/2)/kT]

.

Et = Em + E

-

The viscous k i n k motion i m p l i e s t h a t the elementary a c t i v a t i o n process i s t h e k i n k m i g r a t i o n even i n the double k i n k formation. This view r e q u i r e s t h a t t h e k i n k m i g r a t i o n i s t h e process i n which t h e enhancement takes place, because t h e double k i n k w i t h t h e c r i t i c a l w i d t h (several a ) i s n o t reached by a s i n g l e a c t i v a t i o n . I f we adopt t h i s view-point, an energy E ~ * , a f r a c t i o n o f t h e recombination energy EF released a t t h e kinks, i s s u b t r a c t e d i r o m t h e k i n k m i g r a t i o n energy Em i n eq. _... (9):

Thus t h e k i n k d i f f u s i o n constant under i r r a d i a t i o n i s expressed by

D~~ = nia 2 R exp [ - ( E ~ - E ~ * ) / ~ T ]

.

I f we suppose t h a t a l l o f t h e generated c a r r i e r s w i t h i n t h e m i n o r i t y c a r r i e r d i f f u - s i o n l e n g t h X (several pm) from t h e recombination c e n t e r recombinelat t h e center, t h e recombination r a t e ( % ( 4 n / 3 ) ~ ~ ~ ) i s estimated t o be ~ 1 0 " " ~ ~ s , which i s much h i g h e r than the thermal d i f f u s i o n r a t e o f a k i n k vkexp (-Em/kT). Hence t h e recombi- n a t i o n can take p l a c e i n every step o f t h e k i n k jump and t h e r e f o r e t h e Boltzmann f a c t o r o f t h e double k i n k f o r m a t i o n r a t e under i r r a d i a t i o n becomes exp[-(Em-Er*

+ E & ) / ~ T I .

Since t h e primary enhancement i s r e s t r i c t e d i n t h e e x c i t e d depth 5 (severaf pm i n t h e 111-V compounds and ~ 5 0 u m i n t h e S i case), the k i n k mean f r e e path 2 under i r r a d i a t i o n i s determined by t h e s m a l l e r value between 5 and Z P . The value of Zk (eq. (11 ) ) i s determined by E~~ alone and n o t a f f e c t e d by t h e r e d u c t i o n o f Em by t h e i r r a d i a t i o n . If we assume-that t h e value o f E~ i s SO small t h a t Zk< g (as discussed l a t e r , t h i s seems t o be v a l i d i n the I I I ~ V compounds and even i n t h e S i ) , the k i n k - c o l 1 is i o n case s t i l l holds under i r r a d i a t i o n too and hence the apparent a c t i v a t i o n energy i s w r i t t e n as

E. = E + E /2-E,*.

z m dk (15)

Therefore t h e r e d u c t i o n o f t h e a c t i v a t i o n energy AE i s given by E ~ * . Although a separate e v a l u a t i o n o f E~ and E~~ i s n o t p o s s i b l e from t h e present experiment o n l y , p e r m i t t e d ranges can be imposed on these values from a l o g i c a l c o n s i d e r a t i o n . From eqs. (1 3 ) , (15) and t h e r e s t r i c t i o n 0 5 ^E?* 5 ^{E ~ ,} i n e q u a l i t y r e l a t i o n s

%

i n Table 1

The v a l i d i t y o f t h e above assumption Zk < 6 i s s a t i s f i e d d o u b t l e s s l y i n the a - d i s l o - c a t i o n i n GaAs. I f we suppose Zk > 5, t h e k i n k mean f r e e path i s determined by 5

and hence the a c t i v a t i o n energy t o be observed under i r r a d i a t i o n E. and AE becomes Em + Edk - Er* and Er* - Edk/2, r e s p e c t i v e l y . From t h e same l o g i c a l c o h s i d e r a t i o n as

.. .

ma-de above, the r e l a t i o n s Edk $E; and dt > E > E - d;/2 a r e obtained. I f one evalu- m = ^t;

ates these i n e q u a l i t i e s , i t i s r e a l i z e d t h a t t h e values o f Ei o r t h e upper l i m i t s f o r E~~ a r e too small f o r t h e assumption Zk > 5 t o hold. Therefore t h e k i n k - c o l l i s i o n i s considered t o be t h e case w i t h a l l the i n v e s t i g a t e d d i s l o c a t i o n s . 4.4. D i s l o c a t i o n Levels

The evaluated recombination energies Er o r i t s lower 1 i m i t s Ep* a r e reason- a b l l y l e s s than t h e band- gap energy E o f t h e r e s p e c t i v e c r y s t a l s . A1 thoughg the d i s l o c a t i o n l e v e l s i n GaAs a r e f a r from established, some qua1 i t a t i v e discussion may be worthwhile.

The remarkable f a c t i s t h a t t h e mobi- l i t y o f @ - d i s l o c a t i o n i n GaAs i s s e n s i t i v e t o doping w h i l e t h a t o f a- d i s l o c a t i o n i n s e n s i t i v e /11/. The asymmetric r e s u l t o f t h e p o l a r bend- i n g suggested t h a t t h e a - d i s l o c a t i o n acts as a s t r o n g e r acceptor than t h e 8 - d i s l o c a t i o n /21/. These observa- t i o n s may l e a d us t o t h e p i c t u r e t h a t the acceptor l e v e l associated w i t h the @ - d i s l o c a t i o n i s l o c a t e d near the m i d d l e o f t h e energy gap w h i l e

t h a t o f t h e a - d i s l o c a t i o n near t h e F i g . 8 - Possible c o n f i g u r a t i o n coordinate valence band. This p i c t u r e i s diagrams r e l a t e d t o t h e n o n - r a d i a t i v e supported a l s o by a t h e o r e t i c a l c a r r i e r recombination event t o enhance t h e c a l c u l a t i o n by Jones e t a l . /22/ i f k i n k m i g r a t i o n . The k i n k m i g r a t i o n path the d i s l o c a t i o n core s t r u c t u r e i s along t h e r e a c t i o n coordinate Qp i s shown t h e g l i d e s e t ( t h e t e r m i n a t i n g atom by a d o t t e d curve.

o f t h e e x t r a - h a l f plane i s a r s e n i c f o r a - d i s l o c a t i o n and g a l l i u m f o r 8-di s l o c a t i o n )

.

The e f f i c i e n t n o n - r a d i a t i v e recombination a t t h e d i s l o c a t i o n s suggests a s t r o n g e l e c t r o n - l a t t i c e coup1 i n g a t t h e d i s l o c a t i o n l e v e l . F i g u r e 8 shows t h e c o n f i g u r a t i o n coordinate diagrams ( e l e c t r o n i c energy + e l a s t i c energy u vs c o n f i g u r a t i o n coordinate Q) r e l a t e d t o t h e paths t o be f o l l o w e d upon t h e c a r r i e r recombination and t h e a c t i - v a t i o n b a r r i e r along t h e r e a c t i o n c o o r d i n a t e . I n n-type c r y s t a l s t h e c a r r i e r recom- b i n a t i o n s t a r t s w i t h a capture o f an i n j e c t e d h o l e by t h e recombination c e n t e r occupied by an e l e c t r o n . Then the l a t t i c e i s r e l a x e d t o a d i f f e r e n t c o n f i g u r a t i o n t o achieve t h e minimal i n t e r n a l energy U through the multiphonon emission process.

As discussed above, t h e depth from t h e valence band t o t h e d i s l o c a t i o n l e v e l accept- i n g an e l e c t r o n ( i n d i c a t e d by E- i n F i g . 8 ) i s s m a l l e r i n t h e a - d i s l o c a t i o n than i n the @ - d i s l o c a t i o n , t h e n e t *energy E~ released upon t h e h o l e capture a c c o r d i n g l y tends t o be s m a l l e r i n t h e former than i n the l a t t e r . This agrees w e l l w i t h t h e t r e n d seen i n Table 1.

The recombination i s completed by t h e subsequent capture o f an e l e c t r o n over t h e b a r r i e r Bee. The a c t u a l values o f E~~ are considered t o be so small (suggested t o be ~ l r O eV for a - d i s l o c a t i o n , 0.04 eV for @ - d i s l o c a t i o n i n GaAs / 5 / ) t h a t t h e i n i t i a l charge s t a t e i s q u i c k l y r e s t o r e d t o be ready f o r f u r t h e r recombinations. This s i t u -

a t i o n t o g e t h e r w i t h t h e h i g h i n j e c t i o n l e v e l used i n t h e p r e s e n t experiments ensures successive recombinations a t t h e k i n k s i t e i n t h e course o f the double k i n k f o r m a t i o n 5 - CONCLUDING REMARKS

Since t h e f i r s t o b s e r v a t i o n o f the photomechanical e f f e c t i n germanium, t h e c o n f i r - m a t i o n o f t h e phenomenon was t r i e d by s e v e r a l i n v e s t i g a t o r s . However, some o f them d i d n o t reproduce t h e r e p o r t e d e f f e c t . I t s h o u l d be noted t h a t t h e t e s t s t h a t c a s t e d a doubt on t h e photomechanical e f f e c t were performed under r e l a t i v e l y l o w i l l u m i n a t i o n i n t e n s i t i e s o r a t h i g h temperatures, b o t h o f which may n o t have s a t i s - f i e d t h e c o n d i t i o n s t o observe t h e enhancement caused b y t h e REDM mechanism. I n an n-Gap s i n g l e c r y s t a l , a n o t h e r 111-V compound, i t was e v e r observed t h a t t h e growth r a t e o f d i s l o c a t i o n r o s e t t e s around an i n d e n t a t i o n was enhanced by an i n t e n s e l i g h t i l l u m i n a t i o n a t l o w temperatures /23/, which c o u l d n o t be e x p l a i n e d by a h e a t i n g e f f e c t . I n view o f these f a c t s , f u r t h e r s t u d i e s a r e necessary t o reexamine t h e enhancement e f f e c t o f d i s l o c a t i o n g l i d e i n semiconductors o t h e r t h a n the p r e s e n t m a t e r i a l s .

REFERENCES

E.g., KUCZYNSKI G.C., IYER K.R. and ALLEN C.W., J . Appl. Phys. 43 (1972) 1337 PETROFF P. and HARTMAN R.L., J . Appl. Phys.

5

YONEZU H., SAKUMA I., KAMEJIMA T., UENO M., NISHlDA N., NANNICHI Y . and HAYASHI I., Appl. Phys. L e t t . 24 (1974) 18.

MAEDA K. and TAKEUCHI S., Jpn. J . Appl. Phys.

3

MAEDA K., SAT0 M.. KUBO A. and TAKEUCHI S., J. Appl. Phys. 54 (1983) 161.

MAEDA K. and TAKEUCHI S., Appl

.

42

KUSTERS K.H. and ALEXANDER H., Proc. 1 2 t h I n t . Conf. on Defects i n Semicon- d u c o t r s (Amsterdam 1982), Physica B, t o be pub1 ished.

BOHM K. and FISCHER B., J. Appl. Phys. 50 (1979) 5453.

PETROFF P.M., LOGAN R.A. and SAVAGE A., Phys. Rev. L e t t .

44

PATEL J.R. and CHAUDHURI A.R., Phys. Rev.

143

CHOI S.K., MIHARA M. and NINOMIYA T., Jpn. J. Appl. Phys.

3

WESSEL K. and ALEXANDER H., P h i l o s . Mag. 35 (1977) 1523.

IMAI M. and SUMINO K., P h i l o s . Mag. A

47

40

NARAYANAMURTI V., LOGAN R.A. and CHIN M.A., Phys. Rev. L e t t .

9

WEEKS J.D., TULLY J.C. and KIMERLING L.C.. Phys. Rev.

B E

SUM1 H., Proc. 1 6 t h I n t . Conf. on Physics o f Semiconductors ( M o n t p e l l i e r , 1982), Physica B, t o be p u b l i s h e d .

/18/ LANG D.V. and KIMERLING L.C., Phys. Rev. L e t t . 2 (1974) 489; f o r a r e v i e w see DEAN P.J. and CHOYKE W. J., Adv. Phys. 26 (1977) 1 .

I 1 9 1 E.g., KVEDER V.V., OSIPYAN YU. A., SCHROTER W. and ZOTH G., Phys. S t a t u s S o l i d i ( a ) 72 (1982) 701; f o r a r e v i e w see LABUSCH R. and SCHROTER W, D i s l o c a t i o n s i n S o l i d s , e d i t e d by Nabarro F.R.N. (North-Holland, Amsterdam), 1980, Vo1. 5, p. 127.

/20/ HIRTH J.P. and LOTHE J., Theory o f D i s l o c a t i o n s (McGraw-Hill

.

1211 GWINNER D. and LABUSCH J., J . Physique, suppl

. ⁹

/22/ JONES R., OBERG S. and MARKLUND S., P h i l o s . Mag. B s (1981) 839.

1231 MAEDA K., UEDA O., MURAYAMA Y . and SAKAMOTO K., J. Phys. Chem. S o l i d s 38 (1977) 1173.