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ELECTRICAL EFFECTS OF DISLOCATIONS IN GALLIUM ARSENIDE
D. Gwinner, R. Labusch
To cite this version:
D. Gwinner, R. Labusch. ELECTRICAL EFFECTS OF DISLOCATIONS IN GALLIUM AR- SENIDE. Journal de Physique Colloques, 1979, 40 (C6), pp.C6-75-C6-79. �10.1051/jphyscol:1979616�.
�jpa-00219032�
JOURNAL DE PHYSIQUE CoZZoque C6, suppZC.nent au n06, tome 40, juin 1979, page C6-75
ELECTRICAL EFFECTS OF DISLOCATIONS I N GALLIUM ARSENIDE D. Gwinner and R. Labusch
Institut fiir Angewandte Physik der 1"U CZausthaZ clnd Sonderforschungsbereich 126, Gottingen-CZausthaZ, der Deutschen Forschungsgemeinschaft, F.R.G.
Resume.- Nous avons d@formi! de maniere dynamique des monocristaux de GaAs de type p e t n avec des densites de p o r t e u r s de charge aussi basses que p o s s i b l e . Pour r e c e v o i r des grandes d e n s i t e s de d i s - l o c a t i o n s , i l s e t a i e n t courbes plastiquement jusqu'ii des rayons de courbures de 1 'o r d r e de Z X ~ O - ~ m.
Pour mesurer 1 'e f f e t H a l l e t l a c o n d u c t i v i t e avant e t apres deformation p l a s t i q u e , 1 'i n f l u e n c e des d i s l o c a t i o n s s u r l e s p r o p r i e t e s e l e c t r i q u e s a e t e etudiee. D'autres e c h a n t i l l o n s non-deformes p a r l a chaleur, s e r v a i e n t a c o n t r b l e r l a contamination pendant l e processus de deformation. La d e n s i t e des p o r t e u r s de charge e t l e u r m o b i l i t e d l H a l l diminuaient pour l e s deux sens de courbure. Les r e s u l t a t s sont d i s c u t e s en termes d ' e t a t s de "dangling bonds" i n t r o d u i t s dans l a bande i n t e r d i t e .
Abstract.- p- and n-type GaAs s i n g l e c r y s t a l s w i t h as low as a v a i l a b l e i n i t i a l c a r v i e r concentra- t i o n s were dynamically deformed by p l a s t i c bending up t o h i g h d i s l o c a t i o n d e n s i t i e s . The r a d i i o f c u r v a t u r e were o f t h e order o f 2x10- m. Measuring t h e H a l l e f f e c t and c o n d u c t i v i t y before and a f t e r p l a s t i c deformation the i n f l u e n c e o f d i s l o c a t i o n s on t h e e l e c t r i c a l p r o p e r t i e s was i n v e s t i g a t e d . The contamination d u r i n g deformation was c o n t r o l l e d by specimens which remained undeformed w h i l e heated.
Both t h e c a r r i e r c o n c e n t r a t i o n and t h e i r H a l l m o b i l i t y decreased a f t e r deformation, independent o f t h e s i g n o f bending. The r e s u l t s are discussed i n terms o f "dangling bondo-states introduced i n t o t h e gap.
1. I n t r o d u c t i o n . - D i s l o c a t i o n s a r e under suspicion t o be r e s p o n s i b l e f o r t h e degradation o f GaAs l a s e r diodes /1,2/. Although, so far, no r a d i a t i v e recom- b i n a t i o n a t d i s l o c a t i o n s could be observed /3/, i t i s conceivable t h a t they can a c t as very e f f i c i e n t centers of n o n r a d i a t i v e recombination. Luminescence c o u l d a l s o be quenched through t h e presence o f i o n i - sed i m p u r i t i e s i n t h e v i c i n i t y o f charged d i s l o c a - t i o n s . Vhatever t h e mechanisms may be, i n o r d e r t o understand t h e e f f e c t s o f d i s l o c a t i o n s i t i s neces- sary t o i n v e s t i g a t e t h e i r energy l e v e l s i n t h e f o r - bidden band. This can be done by H a l l - e f f e c t and m o b i l i t y measurements. An a n a l y s i s o f these measu- rements w i t h t h e a i d o f a r a t h e r s t r a i g h t f o r w a r d theory y i e l d s t h e p o s i t i o n and c h a r a c t e r (donor -
o r acceptor l i k e ) o f t h e d i s l o c a t i o n s t a t e s and, depending on t h e f i l l i n g of these l e v e l s , t h e h e i g h t o f the p o t e n t i a l b a r r i e r around t h e charged d i s l o - c a t i o n core / 3 / .
I n v e s t i g a t i o n s o f t h i s t y p e have been r a t h e r successful i n Ge and S i where one dimensional d i s - l o c a t i o n bands have been found t h a t a r e p a r t l y occu- p i e d w i t h e l e c t r o n s if t h e d i s l o c a t i o n s a r e edge type, so t h a t they can a c t as donors o r as acceptors, depending on doping and temperature. I n GaAs and o t h e r 111-V compounds t h e r e a r e two types o f edge d i s l o c a t i o n s , one w i t h a core o f Ga-atoms (Ga-dis- l o c a t i o n ) and one w i t h a core o f As-atoms (As-dis-
l o c a t i o n s ) . From elementary c o n s i d e r a t i o n s one would expect Ga- and A s - d i s l o c a t i o n s t o behave l i k e deep acceptors and donors r e s p e c t i v e l y / J / . I t should be mentioned a t t h i s p o i n t t h a t , i n c h a r a c t e r i ~ i ~ n g Ga- and A s - d i s l o c a t i o n s we have assumed t h a t both types a r e i n t h e " g l i d e - s e t " / 5 / and t h a t t h e two types swap c h a r a c t e r s i f they a r e both i n the
" s h u f f l e s e t " .
Attempts t o demonstrate t h e existence o f d i s - l c c a t i o n s t a t e s i n GaAs by H a l l e f f e c t measurements have f a i l e d so f a r because t h e i r e f f e c t on t h e c a r - r i e r d e n s i t y was t o o small compared w i t h t h e doping c o n c e n t r a t i o n o f t h e undeformed specimens /6,7,8/.
I n t h e p r e s e n t i n v e s t i g a t i o n we have t r i e d t o overcome t h i s d i f f i c u l t y t a k i n g b u l k m a t e r i a l o f t h e lowest doping c o n c e n t r a t i o n t h a t was a v a i l a b l e and, a t t h e same time, bending t h e specimens t o an e x t r e - mely small r a d i u s o f curvature i n o r d e r t o o b t a i n a m a j o r i t y o f e i t h e r Ga- o r A s - d i s l o c a t i o n s .
2. Experiments .- The i n i t i a l n-type m a t e r i a l was a bar o f n o m i n a l l y undoped GaAs provided by t h e Sie- mens research l a b o r a t o r y , Erlangen,West Germany.
The grown-in d i s l o c a t i o n d e n s i t y as obtained by e t c h i n g on (111)-planes f o l l o w i n g t h e r e c i p y o f S c h e l l /9/, t u r n e d o u t t o be o f t h e order o f 10Bm-2.
Rectangular bars w i t h the dimensions 1 8 x 7 . 5 x 4 . 5 ~ 1 0 - ~ m3 were prepared from t h i s m a t e r i a l . From H a l l - and
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1979616
C6-76 JWRNAL DE PHYSIQUE
mobi 1 i t y measurements we found between 9x10" and For t h e p-type m a t e r i a l t h e dopant was unknown.
2x1OZ2 shallow donors p e r m3, depending on temperatu- re, and m o b i l i t i e s around 0.5 m2/Vs. Examples a r e given i n f i g u r e s 1,2 (curves 1 ) . The samples were then c u t along t h e i r l o n g axes t o o b t a i n two halves of 1 8 x 7 . 5 x 1 . 8 ~ 1 0 - ~ m3 w i t h almost i d e n t i c a l proper- t i e s f o r bending i n o p p o s i t e d i r e c t i o n s .
n II
radius of curvature r = 2.Lmm
F i g . l a : E l e c t r o n c o n c e n t r a t i o n o f an As-bent sam- p7e versus r e c i p r o c a l temperature, 2 : dc-method, 2 : ac-method.
y - - . mdeformed 1
F i g . same
,- 7
7 U 5
C
l b : H a l l m o b i l i t y versus temperature f o r t h e sample .
-
3 control
The i n i t i a l d i s l o c a t i o n d e n s i t y was comparable t o t h a t of the n-type m a t e r i a l . H a l l e f f e c t and m o b i l i t y measurements were c a r r i e d o u t on samples w i t h dimen- sions : 1 8 x 7 x 3 . 9 ~ 1 0 - ~ m3 . The d e n s i t y o f shallow acceptors v a r i e d from 2x1OZ2 t o 4 ~ 1 0 ~ ~ per m3 w i t h temperature and t h e mobi 1 i t i e s between 0.06 and 0.01 m2/Vs. T y p i c a l data can be seen i n f i g u r e s 3, 4 (curves 1 ) . A f t e r c u t t i n g and p o l i s h i n g two h a l - ves o f 1 8 ~ 7 x l x 1 9 - ~ m3 remained.
t
The c r y s t a l l o g r a p h i c o r i e n t a t i o n had been cho- sen so t h a t the long a x i s was perpendicular t o (512) and t h e f l a t and t h e narrow s i d e faces p a r a l l e l t o
(021) and (112), r e s p e c t i v e l y . I n p r e l i m i n a r y t e s t s t h i s o r i e n t a t i o n w i t h <112> as t h e bending a x i s had turned o u t t o be best s u i t e d f o r s t r o n g bending w i t h o u t breaking t h e specimens.
Experimentally t h e type o f bending was revealed by c u t t i n g t h e samples along t h e main g l i d e planes, where t h e p o l a r i t y i s most pronounced. Chemical e t c h i n g then r e v e a l s t h e k i n d o f atoms on t h e two opposite faces ( a f t e r H. Steinhardt, D i s s e r t a t i o n , Gottingen 1972).
P l a s t i c deformation was c a r r i e d o u t i n two steps. F i r s t each specimen was deformed t o a r a d i u s o f c u r v a t u r e r = 5 ~ 1 0 - ~ m i n a t h r e e p o i n t bending apparatus w i t h k n i f e edges made o f q u a r t z . Then i t was placed v e r t i c a l l y between f l a t quartz stamps and squeezed u n t i 1 i t was almost U-shaped w i t h r = 2 x l 0 - ~ m as a minimum r a d i u s o f c u r v a t u r e i n t h e c e n t r a l p a r t . A l l p l a s t i c deformation was done under dynamic c o n d i t i o n s w i t h an I n s t r o n machine. The temperature was 873 K and t h e specimens were p r o t e c t e d by a f o r - n i n g gas atmosphere o f s p e c i a l p u r i t y i n a quartz tube furnace. I n t h e c e n t r a l p a r t w i t h the h i g h e s t degree o f p l a s t i c deformation t h e e t c h p i t d e n s i t y on t h e (111)-face which i n c l u d e d t h e s m a l l e s t angle w i t h t h e < l l 2 > - d i r e c t i o n was 8 . 5 ~ 1 0 " K 2 . This num- ber must be regarded as a lower l i m i t t o t h e t r u e d i s l o c a t i o n d e n s i t y because i t i s c l o s e t o t h e l i m i t of r e s o l u t i o n o f our microscopic observation.
Specimens w i t h cross s e c t i o n s o f about
2 x 0 . 5 ~ 1 0 - ~ m2 were then c u t from t h e c e n t r a l p o r t i o n w i t h t h e i r l o n g axes p a r a l l e l t o the bending a x i s . The specimen ends which remained p r a c t i c a l l y unde- formed under t h r e e p o i n t bending, had been c u t o f f . One o f them was placed near the deformed sample du- r i n g t h e second deformation, s e r v i n g as a c o n t r o l specimen f o r contamination.
E l e c t r i c a l c o n t a c t s on n-type specimens were
D. Gwinner and R . L a b u s c h C6-7 7
made by a l l o y i n g t i n y spheres o f t i n onto t h e s u r f a - ce under an atmosphere o f HC1 gas a t 693 K. The con- t a c t s f o r p-type m a t e r i a l were t h i n p l a t i n u m wires, attached t o t h e sample w i t h a conducting epoxy glue.
H a l l e f f e c t and c o n d u c t i v i t y measurements were done w i t h a c u r r e n t source t h a t provided e i t h e r a constant dc- o r ac c u r r e n t o f constant amplitude and the v o l t a g e drop across t h e c o n t a c t s was measu- r e d w i t h a DVM and a l o c k - i n a m p l i f i e r , r e s p e c t i v e l y . The s t r e n g t h o f the magnetic f i e l d was 1.2 t e s l a , measured w i t h a H a l l probe t h a t had been gauged by NMR. Both methods gave e s s e n t i a l l y the same r e s u l t s . F o r the deformed p-type samples an a d d i t i o n a l arran- gement was used where t h e sample r o t a t e d a t constant frequency i n a constant magnetic f i e l d o f 1 t e s l a , w h i l e an ac c u r r e n t passed through i t . The phase s e n t i t i v e detected s i g n a l then d e l i v e r e d t h e pure H a l l voltage. The temperature ranged from 80 K t o 420 K, whereas f o r deformed n-type samples i t was l i m i t e d because o f t h e s t r o n g m o b i l i t y r e d u c t i o n a t low temperatures.
3. Results.- Pronounced d i s l o c a t i o n e f f e c t s on car- r i e r d e n s i t y and H a l l m o b i l i t y o f the n-type samples r e s u l t e d from deformation as shown i n f i g u r e s 1, 2 .
I n f i g u r e s l a , l b t h e temperature dependences o f t h e e l e c t r o n d e n s i t y and t h e m o b i l i t y f o r an As-bent sample are shown. The e l e c t r o n c o n c e n t r a t i o n o f the deformed sample i s reduced by a f a c t o r o f 100 a t low temperatures (curves 2, 2 ' ) , whereas t h e acceptor a c t i o n o f the contamination i s much weaker (cirrve 3 ) . The m o b i l i t y i s lower than t h e i n i t i a l value by a f a c t o r o f up t o 1000. Below 180 K no measurements were p o s s i b l e because o f t h e h i g h specimen r e s i s t a n - ce. I n f i g u r e s 2a, 2b the e l e c t r o n c o n c e n t r a t i o n and m o b i l i t y versus temperature f o r a Ga-bent sample are shown. Again a decrease o f b o t h values by f a c t o r s up t o 100 were measured (curves 2 ) , w h i l e t h e i n f l u e n c e o f contamination was n e g l i g i b l e (curves 3 ) . Experi- ments could n o t be continued below 200 K f o r t h e reasons given above.
I n both n-type samples the temperature depen- dence o f e l e c t r o n concentrations has s i g n i f i c a n t l y changed a f t e r p l a s t i c deformation. E v i d e n t l y the d i s l o c a t i o n s a c t as acceptors f o r f r e e e l e c t r o n s i n n-GaAs f o r b o t h d i r e c t i o n s o f bending. I n t h e case of Ga-bending t h e acceptor a c t i o n i s s t r o n g e r .
rod~us of curvature r = 2Amm
a
conhd %
F i g . 2a : E l e c t r o n c o n c e n t r a t i o n of a Ga-bent sample F i g . 2b : H a l l m o b i l i t y versus temperature f ~ r the versus r e c i p r o c a l temperature (n-GaAs). same sample.
JOURNAL DE PHYSIQUE
The d i s l o c a t i o n e f f e c t s i n p-type m a t e r i a l are n o t so pronounced as i n n-GaAs. The r e s u l t s are shown i n f i g u r e s 3, 4. The hole d e n s i t y of t h e Ga- bent specimen i n f i g u r e 3a i s lowered by n e a r l y 3 ~ 1 0 ~ ~ r n - ~ (curve 2) w i t h respect t o t h e as-grown ma- t e r i a l (curve 1 ) . The shape o f t h e I n p ( l / T ) - c u r v e i s s l i g h t l y d i f f e r e n t from curve 1. Curve 3 i n d i c a t e s t h a t p r a c t i c a l l y no contamination occured. The de- crease i n m o b i l i t y ( F i g . 3b) i s o n l y a few percent.
d u r i n g deformation i s again n e g l i g i b l e (curve 3 ) . The m o b i l i t y ( F i g . 4b) i s o n l y s l i g h t l y lowered i n t h e deformed sample ( c u r v e 2) w h i l e i n t h e c o n t r o l specimen (3) i t even exceeds t h e as-grown m a t e r i a l . So f o r b o t h signs o f bending t h e d i s l o c a t i o n e f f e c t s a r e o f t h e donor type i n p-material, and As-bending provides the weaker e f f e c t .
F i g . 3a : Hole c o n c e n t r a t i o n o f a Ga-bent sample versus r e c i p r o c a l temperature.
F i g . 3b : Temperature dependence o f H a l l m o b i l i t y f o r t h e same sample.
For t h e As-bent specimen i n f i g u r e 4a t h e acceptor e f f e c t f o r holes i s weaker than f o r t h e Ga-bent sam- p l e , b u t curve 2 shows a steeper slope. Contamination
F i g . 4a : Hole c o n c e n t r a t i o n versus r e c i p r o c a l tem- p e r a t u r e f o r an As-bent sample.
F i g . 4b : Temperature dependence o f H a l l m o b i l i t y f o r t h e same sample.
4 . Discussion.- T h e o r e t i c a l r e s u l t s on t h e e l e c t r o n l e v e l s a t As-.and Ga-dislocations a r e n o t a v a i l a b l e . I n t h e o n l y t h e o r e t i c a l work on t h e s u b j e c t /lo/ the d i s l o c a t i o n s are assumed t o be i n t h e s h u f f l e s e t which i s n o t r e a l i s t i c /11/. Labusch and Schroter /4/
D. (;winner and R. L a b ~ ~ s c h C6-79
have suggested t h a t t h e n e u t r a l A s - d i s l o c a t i o n has a - References
f u l l d i s l o c a t i o n band and t h e n e u t r a l G a - d i s l o c a t i o n /I/ P e t r o f f , p. and Hartman, R.L., J. ~ p p l . phys. 5
has an empty band. Furthermore, because o f the i o n i - (1974) 3899.
c i t y o f t h e bonds i n GaAs, t h a t t h e As-band i s a t a /2/ Metz, S., Appl. Phys. ~ e t t . - 30 (1977) 296.
h i g h e r energy l e v e l t h a n t h e Ga-band. I n t h e presen- 131 Labusch, R - , S c h r o t e r , Y., I n s t . Phys. Conf.
Ser. 23 (1975) 56.
ce o f b o t h t y p e s and o v e r a l l - n e u t r a l i t y o f a l l
Bohm, K. and Gwinner, D., Appl. Phys. 17 (1978)
d i s l o c a t i o n s t h i s would a u t o m a t i c a l l y l e a d t o i n t e r - -
155.
n a l compensation and r e s u l t i n a l i n e charge o f /4/ Labusch, R., S c h r o t e r , W., " D i s l o c a t i o n s . Col- o p p o s i t e s i g n on b o t h d i s l o c a t i o n types. Both t y p e s l e c t i v e T r e a t i s e " , ed. F.N.R. Nabarro, (M: Dek-
k e r ) 1974, i n p r i n t . would t h e n possess a p a r t l y f i l l e d band w i t h a
/ 5 / H i r t h , J .P. and Lothe, J . , "Theory o f D i s l o c a - common o c c u p a t i o n l i m i t F t h a t depends t o some extent t i o n s " , (Mc G r a w - H i l l , New York), 1968, 353.
on t h e r a t i o between As- and G a - d i s l o c a t i o n s . /6/ Kravchenko, A.F., P a l k i n , A.M. and Ruleva, V.P.
F should be i n c r e a s i n g w i t h an i n c r e a s i n g f r a c t i o n Sov. Phys. Semicond. 1 (1968) 922.
o f A s - d i s l o c a t i o n s . /7/ L i n , A.L. and Bube, R., J . Appl. Phys. 46 (1975)
5302.
T h i s model p r e d i c t s t h a t a m i x t u r e o f b o t h
/8/ E s q u i v e l , A.L.. Sen, S. and L i n , W.N., J. Appl.
k i n d s o f d i s l o c a t i o n s can compensate s h a l l o w donors Phys. f?l (1976) 2588.
as w e l l as s h a l l o w a c c e p t o r s and t h u s reduce t h e /9/ S c h e l l , H.A., A. Y e t a l l k d . 48 (1957) 158. -
c a r r i e r d e n s i t y i n n- and P-type m a t e r i a l , if o n l y / l o / berg, S., Phys. S t a t u s S o l i d i , r e c e i v e d J U ~ Y , t h e coimnon Fermi l e v e l o f t h e n e u t r a l d i s l o c a t i o n 1978.
m i x t u r e i s n e a r t h e m i d d l e of t h e gap. Furthermore, G o t t s c h a l k, H., Patzer, G. and Alexander, H., Phys. S t a t u s S o l i d i ( a ) 45 (1978) 207.
a t a c o n s t a n t t o t a l d i s l o c a t i o n d e n s i t y , t h e c a r r i e r d e n s i t y i n n - m a t e r i a l s h o u l d be more reduced w i t h a h i g h e r f r a c t i o n o f G a - d i s l o c a t i o n s w h i l e t h e oppo- s i t e h o l d s i n p - m a t e r i a l . On t h e o t h e r hand, i f t h e r a t i o o f Ga- t o A s - d i s l o c a t i o n s i s constant, t h e c a r r i e r d e n s i t y i n p- and n - t y p e m a t e r i a l s h o u l d be d e c r e a s i n g w i t h i n c r e a s i n g t o t a l d i s l o c a t i o n d e n s i t y .
U n f o r t u n a t e l y i t was n o t p o s s i b l e t o p r e p a r e s u i t e d TEM-foils from o u r h i g h l y deformed samples, so t h a t a q u a n t i t a t i v e check on t h e s e c o n j e c t u r e s i s n o t p o s s i b l e . Q u a l i t a t i v e l y a l l p r e d i c t i o n s o f t h e model e x c e p t one a r e c o n f i nned, t h e unconfirmed p r e - d i c t i o n b e i n g t h a t i n p - m a t e r i a l t h e c a r r i e r d e n s i t y should be more reduced w i t h a h i g h e r c o n t e n t o f As- d i s l o c a t i o n s . However, s i n c e we have no q u a n t i t a t i v e c o n t r o l o f t h e d i s l o c a t i o n d e n s i t y , t h i s e f f e c t may be due t o a h i g h e r t o t a l d e n s i t y i n t h e Ga-bent spe- cimen.
Acknowledgement.- The a u t h o r s w i s h t o thank P r o f e s - s o r P. Haasen f o r h i s a d v i c e and t h e p e r m i s s i o n t o c a r r y o u t t h e experiments a t I n s t i t u t f u r M e t a l l p h y - s i k , U n i v e r s i t a t G o t t i n g e n , W. Germany. H e l p f u l d i s c u s s i o n s w i t h P r o f e s s o r W . S c h r o t e r a r e g r a t e f u l - l y acknowledged t o o . T h i s r e s e a r c h was p a r t l y spon- sored by Sonderforschungsbereich 126, G o t t i n g e n -
C l a u s t h a l , Deutsche Forschungsgemeinschaft.
