- Email: [email protected]
Recent work on group III antimonides and arsenides
FLOATING ZONE CRYSTALLIZATION OF SILICON
1065
f o u n d t o o c c u r a l o n g t h e r o d axis. Single c r y s t a l s are o b t a i n e d m o r e r e a d i l y if a seed c r y s t a l is u s e d o n o n e side a n d if t h e i n i t i a l f l o a t i n g l i q u i d zone is f o r m e d a t t h e j o i n t w i t h p o l y c r y s t a l l i n e silicon. T h e f l o a t i n g zone is t h e n m a d e t o t r a v e l a l o n g t h e p o l y c r y s t a l l i n e m a s s w h i l e a single c r y s t a l f o r m s f r o m t h e seed. E f f e c t i v e p u r i f i c a t i o n b y successive zone m e l t i n g h a s b e e n o b s e r v e d in m o s t s a m p l e s . Single c r y s t a l s w i t h r e s i s t i v i t i e s u p t o s e v e r a l h u n d r e d o h m - c m h a v e b e e n p r e p a r e d , d i s p l a y i n g w i t h o u t e x c e p t i o n p - t y p e c o n d u c t i o n . W e believe t h a t t h e r e m a i n i n g i m p u r i t y in t h e s e c r y s t a l s is e s s e n t i a l l y B o r o n w h i c h c a n n o t be e f f e c t i v e l y s e g r e g a t e d b y zone m e l t i n g . F o r t h e a p p l i c a t i o n of t h e f l o a t i n g zone m e t h o d t h e silicon m u s t be a v a i l a b l e in t h e s h a p e of r o d s or a t l e a s t as pieces w h i c h c a n b e w e l d e d t o g e t h e r to f o r m a r o d of i r r e g u l a r s h a p e . I n t h e case in w h i c h o n l y p o w d e r is a v a i l a b l e as s t a r t i n g m a t e r i a l , t h e p o w d e r c a n be p r e s s e d h y d r o s t a t i c a l l y i n t o a rod w i t h o u t t h e use of a n y b i n d e r 4). S u c h p r e s s e d r o d s h a v e b e e n s u c c e s s f u l l y t u r n e d i n t o silicon c r y s t a l s b y m e a n s of t h e floating zone equipment. I n c o n c l u s i o n t h r e e s i g n i f i c a n t a d v a n t a g e s of t h e f l o a t i n g zone m e t h o d s h o u l d be emphasized : 1. A v o i d a n c e of i m p u r i t i e s o r i g i n a t i n g f r o m a c o n t a i n e r for t h e m e l t or f r o m a heater element. 2. P o s s i b l e a p p l i c a t i o n to m a t e r i a l s w i t h m e l t i n g p o i n t s e v e n h i g h e r t h a n t h a t of silicon. 3. P r e p a r a t i o n of single c r y s t a l s f r o m r e l a t i v e l y s m a l l q u a n t i t i e s of r a w m a t e r i a l . Received 30-6-54. REFERENCES 1) K e c k , P.H. at,d v a n H o r n , W., Phys. Rev.!Jl (1953) 512. 2) K e c k , P. H. and G o l a y , M. J. E., Phys. Rev. 8.t) (1953) 1297; N e c k , P. H., v a n H o r n , W., S o l e d , J. and M a c D o n a l d , A., Rev. sei. Instr. :~5 (1954) 331; E m e i s , R., Z. Naturforschg. 9a (1954) 67; M fill e r, S., Z. Naturforsehg..t)b (1954) 504. 3) K e c k , P.H., G r e e n , M. and P o l k , M. L.,J. appl. Phys. 24 (1953) 1479. 4) B l a c k b u r n , A. R. and S h e v l i n , T . S . , J . Am. cer. Soe.:14 (1951) 237.
Hrostowski, H.J. T a n e n b a u m , M. 1954
Physica XX No. I 1 Amsterdam Conference Semiconductors
R E C E N T W O R K ON G R O U P III A N T I M O N I D E S A N D ARSENIDES by H. J. HROSTOWSKI and M. TANENBAUM Bell Telephone Laboratories, Murray Hill, N. J., U.S.A. Of t h e m a n y k n o w n s e m i c o n d u c t i n g c o m p o u n d s , t h o s e f o r m e d b y r e a c t i o n of a G r o u p I I I e l e m e n t w i t h o n e of G r o u p V are m o s t closely a k i n t o t h e G r o u p I V s e m i c o n d u c t o r s 1). T h i s p a p e r d e s c r i b e s s o m e of o u r r e c e n t w o r k o n a n u m b e r of t h e s e compounds. T h e a n t i m o n i d e s were p r e p a r e d b y m e l t i n g t o g e t h e r s t o i c h i o m e t r i c a m o u n t s of t h e e l e m e n t s . T h e a r s e n i d e s were p r e p a r e d b y r e a c t i n g t h e c o m p o n e n t s in sealed q u a r t z
1066
H . J . HROSTOWSKI AND M. TANENBAUM,
tubes at high temperature. A n t i m o n y was purified by zone refining 2), arsenic by v a c u u m sublimation. Although I n S b is the only c o m p o u n d of this t y p e which seems completely stable at its melting point, GaSb and AISb are sufficiently stable to obtain crystals b y the pulling technique 3). InAs and GaAs b o t h decompose a t their me lt i n g points. All of these compounds except A1Sb are e x t r e m e l y stable under ordinary atmospheric conditions. Some of t h e room t e m p e r a t u r e electrical properties of these semiconductors are compared with those of Ge and Si 4) inTable I. The energy gaps (first column) were determined from the long w a v e - l e n g t h limits of absorption in t h e infrared. This m e t h o d yields more reliable values for non-degenerate materials t h a n those obtained from studies of c o n d u c t i v i t y versus t e m p e r a t u r e since it involves no assumptions a bout effective masses of cha~ge carriers or t e m p e r a t u r e dependence of mobilities. The lowest observed carrier concentration in cm --~ are listed in the second column of Table I. E x c e p t for InSb, which has been extensively zone refined, these are several orders of m ag n i t u d e higher t h a n the l014 c m , 3 necessary to a t t a i n limiting mobility values in Ge and Si. Electron and hole mobilities, given in colums three and four in cm 2 v o l t -1 sec - 1 , were obtained from measurements of Hall effect and conductivity. The d a t a for InSb, GaSb, Si and Ge are for single crystal material. Magnetoresistance studies on oriented single crystals of ~nSb and GaSh indicate t h a t the energy surfaces of these compounds are spherical. Mobilities derived from the magnetoresistance data are in reasonable agreement with the Hall mobilities. TABLE I Some room temperature properties of group III antimonides and arsenides E o (eV) . or p p,. /.~p 10 Is InSb 0.18 77,000 1250 5 X 1016 InAs 0.35 >15,000 10 tv 0.77 70O GaSb 2500 7 X 10Iv GaAs 1.45 > 200 10 n AlSb , ~ 100 1.7 --.,]00 1014 1820 Ge 0.68 3800 10 *4 Si I.I0 1300 500 In degenerate n-type InSb an anomalous optical behavior has been observed by Tanenbaum and B r i g g s 6). The absorption limit for pure material occurred at 7.0 microns and shifted to shorter wavelength with increasing i m p u r i t y concentration. Recently, B u r s t e i n 6) had advanced an explanation of this effect which depends on the v e r y small effective mass of electrons in InSb and the associated low density of states in the conduction band. The absorption limit in degenerate n-type InSb involves a transition from the valence band to the lowest unfilled level in the conduction band. Since this is a considerable height above the b o t t o m of the conduction band in highly degenerate samples, the absorption edge depends strongly on electron density. We have investigated the absorption limits of a series of degenerate n-type samples of v ar y i n g electron density. The results are shown in Figure 1 in which the solid curve is drawn through the experimental points. Comparison of this with the calculated (dotted) curve confirms the dependence of E o, the optical energy gap, on n. However, the functional relationship is more complicated t h a n predicted by simple theory. A similar anomalous behavior has been observed with InAs, b u t the m a x i m u m shift am o u n t s to only 0.7 microns in this case.
RECENT
WORK
ON GROUP
Ill A N T I M O N I D E S
AND
ARSENIDES
1067
A m o r e d e t a i l e d a c c o u n t of t h i s w o r k will b e p u b l i s h e d i n t h e P h y s i c a l R e v i e w . 0.7
//
0.6--
t~
05-
/J
0.4-E (eV)0.3
i
2
25
~
3
~ "
4 ~.(a)
~°~'a'a"'~ ljJJ 0.2
"=5
A
_..,~-=.-L%'~_ ~ __ .
.
.
.
'--P~"
.
7
0.1
o 1017
I 2
I 4
I I I e 8 1018
Fig. 1. D e p e n d e n c e of .......
n
I 2
I 4
I I I 6 8 IOtg
I 2
a n d X o n n (cm - a ) i n I n S b calculated experimental © single c r y s t a l s a m p l e s /X p o l y c r y s t a l l i n e s a m p l e s . E o
Received 3-7-54. REFERENCES I) 2) 3) 4) 5) 6)
W e 1 k e r, H., Z. Naturforsch. 7a (1952) 744. P f a n n , W . G . , J . Metals4 (1952) 747. T e a l , G. K. and L i t t l e , J. B., Phys. Rev. 78 (1950) 647. M o r i n , F . J . and M a l t a , J . P . , i n p r e s s . Tanenbaum, M. and B r i g g s , H.B., Phys. Rev. t~! (1953) 1561. Burstein, E., Phys. Rev. 98 (1954) 632.
B u s c h , G. W i n k l e r , U. 1954
Physica XX No. 11 Amsterdam Conference Semiconductors
ELEKTRISCHE EIGENSCHAFTEN D E R INTERMETALLISCHEN VERBINDUNGEN Mg2 Si, Mg2Ge, Mg2Sn UND Mg2 Pb yon
G. BUSCH und U. W I N K L E R
Physikalisches Institut der Eidgen6ssischen Teehnischen Hochschule, Zfirich, Schweiz Die i n t e r m e t a l l i s c h e n V e r b i n d u n g e n w u r d e n y o n Z i n t 1 1) i n zwei K l a s s e n eingeteilt, i n die eine m i t m e t a l l i s c h e n G i t t e r n u n d i n die a n d e r e m i t sog. " n i c h t m e t a l l i s c h e n " G i t t e r n . Die n i c h t m e t a l l i s c h e n S t r u k t u r e n w e r d e n d u t c h die M e t a l l e d e r e r s t e n
1065
f o u n d t o o c c u r a l o n g t h e r o d axis. Single c r y s t a l s are o b t a i n e d m o r e r e a d i l y if a seed c r y s t a l is u s e d o n o n e side a n d if t h e i n i t i a l f l o a t i n g l i q u i d zone is f o r m e d a t t h e j o i n t w i t h p o l y c r y s t a l l i n e silicon. T h e f l o a t i n g zone is t h e n m a d e t o t r a v e l a l o n g t h e p o l y c r y s t a l l i n e m a s s w h i l e a single c r y s t a l f o r m s f r o m t h e seed. E f f e c t i v e p u r i f i c a t i o n b y successive zone m e l t i n g h a s b e e n o b s e r v e d in m o s t s a m p l e s . Single c r y s t a l s w i t h r e s i s t i v i t i e s u p t o s e v e r a l h u n d r e d o h m - c m h a v e b e e n p r e p a r e d , d i s p l a y i n g w i t h o u t e x c e p t i o n p - t y p e c o n d u c t i o n . W e believe t h a t t h e r e m a i n i n g i m p u r i t y in t h e s e c r y s t a l s is e s s e n t i a l l y B o r o n w h i c h c a n n o t be e f f e c t i v e l y s e g r e g a t e d b y zone m e l t i n g . F o r t h e a p p l i c a t i o n of t h e f l o a t i n g zone m e t h o d t h e silicon m u s t be a v a i l a b l e in t h e s h a p e of r o d s or a t l e a s t as pieces w h i c h c a n b e w e l d e d t o g e t h e r to f o r m a r o d of i r r e g u l a r s h a p e . I n t h e case in w h i c h o n l y p o w d e r is a v a i l a b l e as s t a r t i n g m a t e r i a l , t h e p o w d e r c a n be p r e s s e d h y d r o s t a t i c a l l y i n t o a rod w i t h o u t t h e use of a n y b i n d e r 4). S u c h p r e s s e d r o d s h a v e b e e n s u c c e s s f u l l y t u r n e d i n t o silicon c r y s t a l s b y m e a n s of t h e floating zone equipment. I n c o n c l u s i o n t h r e e s i g n i f i c a n t a d v a n t a g e s of t h e f l o a t i n g zone m e t h o d s h o u l d be emphasized : 1. A v o i d a n c e of i m p u r i t i e s o r i g i n a t i n g f r o m a c o n t a i n e r for t h e m e l t or f r o m a heater element. 2. P o s s i b l e a p p l i c a t i o n to m a t e r i a l s w i t h m e l t i n g p o i n t s e v e n h i g h e r t h a n t h a t of silicon. 3. P r e p a r a t i o n of single c r y s t a l s f r o m r e l a t i v e l y s m a l l q u a n t i t i e s of r a w m a t e r i a l . Received 30-6-54. REFERENCES 1) K e c k , P.H. at,d v a n H o r n , W., Phys. Rev.!Jl (1953) 512. 2) K e c k , P. H. and G o l a y , M. J. E., Phys. Rev. 8.t) (1953) 1297; N e c k , P. H., v a n H o r n , W., S o l e d , J. and M a c D o n a l d , A., Rev. sei. Instr. :~5 (1954) 331; E m e i s , R., Z. Naturforschg. 9a (1954) 67; M fill e r, S., Z. Naturforsehg..t)b (1954) 504. 3) K e c k , P.H., G r e e n , M. and P o l k , M. L.,J. appl. Phys. 24 (1953) 1479. 4) B l a c k b u r n , A. R. and S h e v l i n , T . S . , J . Am. cer. Soe.:14 (1951) 237.
Hrostowski, H.J. T a n e n b a u m , M. 1954
Physica XX No. I 1 Amsterdam Conference Semiconductors
R E C E N T W O R K ON G R O U P III A N T I M O N I D E S A N D ARSENIDES by H. J. HROSTOWSKI and M. TANENBAUM Bell Telephone Laboratories, Murray Hill, N. J., U.S.A. Of t h e m a n y k n o w n s e m i c o n d u c t i n g c o m p o u n d s , t h o s e f o r m e d b y r e a c t i o n of a G r o u p I I I e l e m e n t w i t h o n e of G r o u p V are m o s t closely a k i n t o t h e G r o u p I V s e m i c o n d u c t o r s 1). T h i s p a p e r d e s c r i b e s s o m e of o u r r e c e n t w o r k o n a n u m b e r of t h e s e compounds. T h e a n t i m o n i d e s were p r e p a r e d b y m e l t i n g t o g e t h e r s t o i c h i o m e t r i c a m o u n t s of t h e e l e m e n t s . T h e a r s e n i d e s were p r e p a r e d b y r e a c t i n g t h e c o m p o n e n t s in sealed q u a r t z
1066
H . J . HROSTOWSKI AND M. TANENBAUM,
tubes at high temperature. A n t i m o n y was purified by zone refining 2), arsenic by v a c u u m sublimation. Although I n S b is the only c o m p o u n d of this t y p e which seems completely stable at its melting point, GaSb and AISb are sufficiently stable to obtain crystals b y the pulling technique 3). InAs and GaAs b o t h decompose a t their me lt i n g points. All of these compounds except A1Sb are e x t r e m e l y stable under ordinary atmospheric conditions. Some of t h e room t e m p e r a t u r e electrical properties of these semiconductors are compared with those of Ge and Si 4) inTable I. The energy gaps (first column) were determined from the long w a v e - l e n g t h limits of absorption in t h e infrared. This m e t h o d yields more reliable values for non-degenerate materials t h a n those obtained from studies of c o n d u c t i v i t y versus t e m p e r a t u r e since it involves no assumptions a bout effective masses of cha~ge carriers or t e m p e r a t u r e dependence of mobilities. The lowest observed carrier concentration in cm --~ are listed in the second column of Table I. E x c e p t for InSb, which has been extensively zone refined, these are several orders of m ag n i t u d e higher t h a n the l014 c m , 3 necessary to a t t a i n limiting mobility values in Ge and Si. Electron and hole mobilities, given in colums three and four in cm 2 v o l t -1 sec - 1 , were obtained from measurements of Hall effect and conductivity. The d a t a for InSb, GaSb, Si and Ge are for single crystal material. Magnetoresistance studies on oriented single crystals of ~nSb and GaSh indicate t h a t the energy surfaces of these compounds are spherical. Mobilities derived from the magnetoresistance data are in reasonable agreement with the Hall mobilities. TABLE I Some room temperature properties of group III antimonides and arsenides E o (eV) . or p p,. /.~p 10 Is InSb 0.18 77,000 1250 5 X 1016 InAs 0.35 >15,000 10 tv 0.77 70O GaSb 2500 7 X 10Iv GaAs 1.45 > 200 10 n AlSb , ~ 100 1.7 --.,]00 1014 1820 Ge 0.68 3800 10 *4 Si I.I0 1300 500 In degenerate n-type InSb an anomalous optical behavior has been observed by Tanenbaum and B r i g g s 6). The absorption limit for pure material occurred at 7.0 microns and shifted to shorter wavelength with increasing i m p u r i t y concentration. Recently, B u r s t e i n 6) had advanced an explanation of this effect which depends on the v e r y small effective mass of electrons in InSb and the associated low density of states in the conduction band. The absorption limit in degenerate n-type InSb involves a transition from the valence band to the lowest unfilled level in the conduction band. Since this is a considerable height above the b o t t o m of the conduction band in highly degenerate samples, the absorption edge depends strongly on electron density. We have investigated the absorption limits of a series of degenerate n-type samples of v ar y i n g electron density. The results are shown in Figure 1 in which the solid curve is drawn through the experimental points. Comparison of this with the calculated (dotted) curve confirms the dependence of E o, the optical energy gap, on n. However, the functional relationship is more complicated t h a n predicted by simple theory. A similar anomalous behavior has been observed with InAs, b u t the m a x i m u m shift am o u n t s to only 0.7 microns in this case.
RECENT
WORK
ON GROUP
Ill A N T I M O N I D E S
AND
ARSENIDES
1067
A m o r e d e t a i l e d a c c o u n t of t h i s w o r k will b e p u b l i s h e d i n t h e P h y s i c a l R e v i e w . 0.7
//
0.6--
t~
05-
/J
0.4-E (eV)0.3
i
2
25
~
3
~ "
4 ~.(a)
~°~'a'a"'~ ljJJ 0.2
"=5
A
_..,~-=.-L%'~_ ~ __ .
.
.
.
'--P~"
.
7
0.1
o 1017
I 2
I 4
I I I e 8 1018
Fig. 1. D e p e n d e n c e of .......
n
I 2
I 4
I I I 6 8 IOtg
I 2
a n d X o n n (cm - a ) i n I n S b calculated experimental © single c r y s t a l s a m p l e s /X p o l y c r y s t a l l i n e s a m p l e s . E o
Received 3-7-54. REFERENCES I) 2) 3) 4) 5) 6)
W e 1 k e r, H., Z. Naturforsch. 7a (1952) 744. P f a n n , W . G . , J . Metals4 (1952) 747. T e a l , G. K. and L i t t l e , J. B., Phys. Rev. 78 (1950) 647. M o r i n , F . J . and M a l t a , J . P . , i n p r e s s . Tanenbaum, M. and B r i g g s , H.B., Phys. Rev. t~! (1953) 1561. Burstein, E., Phys. Rev. 98 (1954) 632.
B u s c h , G. W i n k l e r , U. 1954
Physica XX No. 11 Amsterdam Conference Semiconductors
ELEKTRISCHE EIGENSCHAFTEN D E R INTERMETALLISCHEN VERBINDUNGEN Mg2 Si, Mg2Ge, Mg2Sn UND Mg2 Pb yon
G. BUSCH und U. W I N K L E R
Physikalisches Institut der Eidgen6ssischen Teehnischen Hochschule, Zfirich, Schweiz Die i n t e r m e t a l l i s c h e n V e r b i n d u n g e n w u r d e n y o n Z i n t 1 1) i n zwei K l a s s e n eingeteilt, i n die eine m i t m e t a l l i s c h e n G i t t e r n u n d i n die a n d e r e m i t sog. " n i c h t m e t a l l i s c h e n " G i t t e r n . Die n i c h t m e t a l l i s c h e n S t r u k t u r e n w e r d e n d u t c h die M e t a l l e d e r e r s t e n