On the intermetallic compounds indium antimonide, gallium antimonide, and aluminum antimonide

On the intermetallic compounds indium antimonide, gallium antimonide, and aluminum antimonide

Breckenridge, R. G. Physica X X No. 11 Amsterdam Conferenec Semiconductors Blunt, R. F. Hosler, W. R. Frederikse, H. P. R. Becker, J. H. Oshinsky, W...

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Breckenridge, R. G.

Physica X X No. 11 Amsterdam Conferenec Semiconductors

Blunt, R. F. Hosler, W. R. Frederikse, H. P. R. Becker, J. H. Oshinsky, W.

1954

ON THE INTERMETALLIC COMPOUNDS INDIUM ANTIMONIDE, GALLIUM ANTIMONIDE, AND ALUMINUM ANTIMONIDE t) b y R. G. B R E C K E N R I D G E , R. F. BLUNT, W. R. HOSLER, H. P. R. F R E D E R I K S E , J. H. B E C K E R and W. O S H I N S K Y *) National Bureau of Standards, Washington, D.C.U.S.A. I. I n t r o d u c t i o n . The series of intermetallic compounds of the A I n B v type have recently been shown to be of considerable theoretical and practical interest z). We have carried out a series of studies of the electrical resistivity, Hall effect and optical absorption spectra on the compounds InSb, GaSb and A1Sb over a wide range of temperatures from which a preliminary picture of their electronic structure m a y be I

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Fig. 2. Hall coefficient of InSb samples.

deduced. This work, which will be described in greater detail elsewhere, finds, in agreement with other investigators 2) a) 4), t h a t although the compounds have some aspects in common they are characterized b y a n u m b e r of striking features of individual differences. t) Supported in part by Office of Ordnance Research. *) Now at Army Engineering Labs., Fort Belvoir, Virginia.

-- 1073 Physica XX

68

1074 BRECKENRIDGE, BLUNT, HOSLER, FREDERIKSE, Bt~CKER AND OSHINSKY

2. Experimental. T h e samples a v a i l a b l e for m e a s u r e m e n t i n c l u d e d b o t h single a n d p o l y c r y s t a l l i n e s p e c i m e n s m a d e b y m e l t i n g t o g e t h e r m e t a l s of v e r y h i g h c h e m i c a l p u r i t y , usually 99.95% or b e t t e r . T h e r e s u l t i n g ingot was zone m e l t e d in m o s t cases and t h e n ingots were pulled f r o m t h e m e l t using t h e I( y r o p o u 1 o s t e c h n i q u e . T h e u n t r e a t e d samples were a l w a y s p - t y p e b u t could be m a d e n - t y p e b y d o p i n g the m e l t w i t h t e l l u r i u m . U s i n g a d i a m o n d saw samples were c u t f r o m the ingots for t h e v a r i o u s optical and electrical studies and t h e optical s p e c i m e n s were c a r e f u l l y polished. The H a l l a n d r e s i s t i v i t y studies were m a d e o v e r a t e m p e r a t u r e range f r o m liquid nitrogen to t e m p e r a t u r e s n e a r t h e m e l t i n g p o i n t of t h e sample, using d.c. t e c h n i q u e s . The optical studies were made, using c o n v e n t i o n a l e q u i p m e n t , at r o o m t e m p e r a t u r e and a t liquid n i t r o g e n t e m p e r a t u r e ; for m e a s u r e m e n t s at liquid h e l i u m t e m p e r a t u r e an optical cell similar to t h a t designed b y D u e h r i g and M a d o r 5) was used. .3. Results. T h e H a l l c o n s t a n t and r e s i s t i v i t y d a t a for I n S b are s h o w n in Figs. 1 and 2. This d a t a has b e e n a n a l y z e d and confirms m a n y of t h e i n t e r e s t i n g f e a t u r e s p r e v i o u s l y reported. I n particular, t h e m o b i l i t y is v e r y high for electrons, being 2 × 104 c m 2 / v o l t sec at r o o m t e m p e r a t u r e w i t h t h e ratio #,//~p = 29 for s a m p l e SC-5 *).

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Possibly of g r e a t e r i n t e r e s t is t h e c o m b i n a t i o n of t h e optical and electrical d a t a to give a clear picture of t h e e n e r g y gap situation. The optical a b s o r p t i o n d a t a of Fig. 3 indicates a dE]dT = fl .~ - - 2 . 5 × 10- 4 e v / d e g in fairly pure p - t y p e samples. T h e electrical d a t a in t h e intrinsic range h a v e been a n a l y z e d to give

X ( X + I) = (CT3/N 2) exp (fl/k) e x p (-- Eo/kT ) where X -----n/N, N = t h e s a t u r a t i o n n u m b e r of impurities. T h e a p p l i c a t i o n of this relation to one sample is s h o w n in Fig. 4. F r o m t h e slope of this c u r v e E 0 is f o u n d to *) These quantities vary widely from sample to sample although the order of magnitude is well indicated by these figures.

ON THE INTERMETALLIC COMPOUNDS

InSb, G a S b

AND A 1 S b

1075

b e 0.23 e.v. c o r r e s p o n d i n g t o a r o o m t e m p e r a t u r e e n e r g y g a p of 0.16 e.v. T h e c u t - o f f w a v e l e n g t h a t 13°K (Fig. 3) f o r a r a t h e r p u r e single c~ystal is also f o u n d t o b e 0.23 e.v. O u r o b s e r v a t i o n s t e n d t o c o n f i r m t h e s u g g e s t i o n of B u r s t e i n s) t h a t t h e e l e c t r o n i c s t r u c t u r e is c h a r a c t e r i z e d b y a n u n u s u a l l y low d e n s i t y of e l e c t r o n i c s t a t e s n e a r t h e b o t t o m of t h e c o n d u c t i o n b a n d , h e n c e t h e F e r m i level is n o r m a l l y l o c a t e d a t a c o n s i d e r a b l e d i s t a n c e a b o v e t h e b o t t o m of t h e c o n d u c t i o n b a n d . (

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1076

ON TIIE INTERMETALLIC COMPOUNDS InSb, GaSb AND AISb

low, ca. 100 c m 2 / v o l t sec a t r o o m t e m p e r a t u r e , p r e s u m a b l y d u e t o t h e i m p u r i t y of our samples. The optical absorption spectra are complex. For p-type samples the r e s u l t s a r e s h o w n i n Fig. 6. T h e f o r b i d d e n g a p c o r r e s p o n d s t o 1.52 e.v. a t r o o m t e m p e r a t u r e , a n d fl is - - 3.5 X 10 - 4 e v / d e g . F o r n - t y p e T e - d o p e d A1Sb, t h e a b s o r p t i o n s p e c t r u m is r a d i c a l l y a l t e r e d as s h o w n i n Fig. 7. T h e f u n d a m e n t a l a b s o r p t i o n edge is u n c h a n g e d , b u t t h e b a n d i n t h e i n f r a r e d a t 1.6/~ o b s e r v e d i n t h e p - t y p e m a t e r i a l h a s d i s a p p e a r e d a n d a n e w b a n d a t ca. 4.0/~ h a s a p p e a r e d . A t e n t a t i v e e x p l a n a t i o n f o r t h e s e a n d o t h e r o b s e r v a t i o n s i n t e r m s of a l a t t i c e d i s o r d e r m o d e l will b e p r e s e n t e d elsewhere. i

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I n s u m m a r y , we see t h e n t h a t t h e c h a r a c t e r of t h e i n t e r m e t a l l i c c o m p o u n d s c h a n g e s i n a r a t h e r m a r k e d w a y e v e n t h o u g h t h e e l e c t r o n i c s t r u c t u r e is p r e s u m a b l y t h e s a m e . I n S b s e e m s t o b e a n o m a l o u s i n t h a t t h e d e n s i t y of e l e c t r o n i c s t a t e s n e a r t h e b o t t o m of t h e c o n d u c t i o n b a n d is r e m a r k a b l y low. G a S b o n t h e o t h e r h a n d b e h a v e s as a n a l m o s t i d e a l s e m i c o n d u c t o r w i t h n o s t r i k i n g p e c u l i a r i t i e s . T h e b a s i c e l e c t r o n i c p r o p e r t i e s of A1Sb a p p a r e n t l y a r e n o T m a l b u t we f i n d a n u n u s u a l n u m b e r of " i m p u r i t y " s t a t e s i n t h e f o r b i d d e n g a p w h i c h s e e m d u e t o l a t t i c e d i s o r d e r .

4. Acknowledgment. T h e figures i n c l u d e d i n t h i s p a p e r a r e r e p r o d u c e d w i t h t h e p e r m i s s i o n o f t h e E d i t o r of t h e P h y s i c a l R e v i e w . Received 27-7-54.

REFERENCES I) 2) 3) 4) 5) 6)

W e I k e r, H., Z. Naturforschung 7a (1952) 744; 8a (1953) 248. W e i s s, H., Z. Naturforschung 8a (1953) 463. L e i f e r , H. N. and D u n l a p , W. C., Bull. Am. phys. Soc. 29 (1954) 33. Justi, E. and L a u t z , G.,Abh. Braunsch. wiss. Ges. V(1953) 36. Duehrig, W.H. and M a d o r , I . L . , R e v . sci. lnstr. 23(1952) 421. B u r s t e i n , E., Phys. Rev. 98 (1954) 632."