- Email: [email protected]
Electroreflectance at a semiconductor-electrolyte interface: Infrared measurements
Volume 23, n u m b e r 1
PHYSICS
L B. O. Seraphin and N. Bottka, P h y s . Rev. L e t t e r s 15 (1965) 104. 2. B . O . S e r a p h i n , P h y s . R e v . 140 (1965) A1716. 3. B. O. Seraphin and N. Bottka, P h y s . Rev. 145 (1966) 628. 4. K . L . S h a k l e e , F . H . Pollak and M. Cardona, P h y s . Rev. L e t t e r s 15 (1965) 883. 5. A. K. Ghosh, to be published. 6. U. G e r h a r d t , P h y s . R e v . L e t t e r s 15 (1965) 401; P h y s . Status Solidi 11 (1965) 801. 7. F. H e r m a n , R . L . K o r t u m , C . D . Kuglin and R. A. Short,
ELECTROREFLECTANCE INTERFACE:
LETTERS
8. 9. 10. 11.
3 O c t o b e r 1966
Quantum T h e o r y of A t o m s , M o l e c u l e s and the Solid State; ed. P . O . L~wdin (Academic P r e s s , New York), to be published. D. B r u s t , P h y s . R e v . 1 3 6 (1964) A1337. H. E h r e n r e i c h , H . R . Phillip and J. C. P h i l l i p s , Phys. Rev. L e t t e r s 8 (1962) 59. D . B r u s t , J . C . P h i l l i p s and F . B a s s a n i , P h y s . R e v . L e t t e r s 9 (1962) 94. E . O . K a n e , P h y s . R e v . 146 (1966) 558.
AT A SEMICONDUCTOR-ELECTROLYTE INFRARED MEASUREMENTS *
M. C A R D O N A , K. L. SHAKLEE and F . H. P O L L A K Physics Department, Brown University, Providence, Rhode Island, USA R e c e i v e d 18 A u g u s t 1966
M e a s u r e m e n t s of e l e c t r o r e f l e c t a n c e at a s e m i - c o n d u c t o r electorlyte i n t e r f a c e in the i n f r a r e d region to about 0.6 eV a r e r e p o r t e d .
We have extended the r a n g e of m e a s u r e m e n t s of e l e c t r o r e f l e c t a n c e at a s e m i c o n d u c t o r - e l e c t r o lyte i n t e r f a c e [1] into the i n f r a r e d r e g i o n to about 0.6 eV. This has b e e n a c c o m p l i s h e d by p la c i n g the s a m p l e as c l o s e as p o s s i b l e to the window of the c e l l containing the e l e c t r o l y t e (~0.1 N KC1 in H20) , while s t i l l m a in ta in in g a thin l a y e r of e l e c t r o l y t e (~0.1 mm), so that the a b s o r p t i o n of the w a t e r is r e d u c e d to a m i n i m u m . W a t e r has s t r o n g a b s o r p t i o n in the n e a r i n f r a r e d which l i m i t e d our previous m e a s u r e m e n t s . There are strong abs o r p t i o n peaks at 0.9 eV (~ ~ 1 0 c m - 1 ) and 0.64 eV (~ ~ 5 0 c m - 1 ) , the f o r m e r peak due to the v i b r a tions of the O- H bond. The above l i m i t a t i o n m a y a l s o be o v e r c o m e by the use of s o m e o r g a n i c e l e c t r o l y t e s such as KCNS or t e t r a e t h y l a m m o nium b r o m i d e d i s s o l v e d in a c e t o n i t r i l e o r p r o p y lene c a r b o n a t e [2]. The e x p e r i m e n t a l technique is s i m i l a r to that which has been used in our p r e v i o u s e l e c t r o r e f l e c t a n c e m e a s u r e m e n t s [1]. H o w e v e r , in the p r e s e n t c a s e a P e r k i n - E l m e r Model 98 m o n o c h r o m a t o r and a PbS c e l l w e r e used. A p o r t i o n of the incident light was chopped at 200 c / s and a 80 c / s modulating signal was applied to the s a m p l e . The 200 c / s signal was d e t e c t e d by a * Supported by the National Science Foundation and the A r m y R e s e a r c h Office, D u r h a m .
InSb (5
O
Eo
(.9
I
$
Ge
c
"~ /~ Geo.93Sio.07
%
% x =
0
\
-8
l
0.8
I0
V
I
1.2
ENERGY (ev~
Fig. 1. E l e c t r o r e f l e c t a n c e s p e c t r u m of Ge, A Ge-Si a l loy (7% Si), and InSb in the e n e r g y r a n g e 0.7 - 1.2 eV at room temperature.
37
Volume 23, n u m b e r 1
PHYSICS
lock-in amplifier, whose output was connected to a s e r v o m e c h a n i s m c o n t r o l l i n g t h e s l i t - w i d t h of t h e m o n o c h r o m a t o r . T h i s s e r v o t h u s k e e p s t h e l o c k - i n a m p l i f i e r o u t p u t c o n s t a n t . T h e 80 c / s s i g n a l f r o m t h e d e t e c t o r w a s s e n t to a s e c o n d l o c k - i n a m p l i f i e r t h e o u t p u t of w h i c h w a s c o n n e c t e d to a s t r i p - c h a r t r e c o r d e r . T h e r e c o r d e d s i g n a l i s t h u s d i r e c t l y p r o p o r t i o n a l to t h e r a t i o A R / R [3]. Shown in fig. 1 i s t h e e l e c t r o r e f l e c t a n c e s p e c t r u m of G e , a G e - S i a l l o y (7% Si), a n d InSb i n t h e e n e r g y r a n g e 0.7 - 1.2 e V a t r o o m t e m p e r a t u r e . T h e o b s e r v e d e n e r g i e s of t h e E o ( 0 . 8 0 0 + 0.005 e V [ 3 , 4 ] ) a n d E o + a o ( 1 . 0 8 2 ± 0.005 e V [ 3 ] ) p e a k s of Ge a r e in good a g r e e m e n t w i t h o t h e r m e a s u r e m e n t s . T h e s h a p e s of t h e s e p e a k s a r e s i m i l a r to t h o s e of t h e s a m e t r a n s i t i o n s m e a s u r e d in o t h e r m a t e r i a l s [1]. T h e o b s e r v e d e n e r g y of t h e E o p e a k f o r t h e G e - S i a l l o y (1.042 ± 0 . 0 0 5 eV) i n d i c a t e s a l i n e a r v a r i a t i o n of t h e F25, - F 2, gap w i t h Si c o n centration. The entire electroreflectance spect r u m of a s e r i e s of G e - S i a l l o y s i s p r e s e n t l y b e ing s t u d i e d . P r e l i m i n a r y r e s u l t s y i e l d a v a l u e of 4.1 + 0.1 eV f o r t h e e x t r a p o l a t i o n of t h e 1"25, - F 2, g a p to 100% Si. T h e s t r u c t u r e in t h e s p e c t r u m of InSb i s b e l i e v e d , to b e due to t h e s p i n - o r b i t s p l i t b a n d a t k = 0 (E o + 4 0 ) . T h e e n e r g y of t h i s p e a k (0.990 + 0.005 eV) t o g e t h e r w i t h t h e v a l u e of E o (0.17 e V [5] ) a t r o o m t e m p e r a t u r e y i e l d s a v a l u e
LETTERS
3 O c t o b e r 1966
of 0.82 e V f o r Ao, in good a g r e e m e n t w i t h t h e r u l e (A 1 = 0 . 5 8 e V [ 1 , 6 ] ) . T h e e x t e n s i o n of t h e e l e c t r o l y t e t e c h n i q u e of electroreflectance into the near infrared makes it p o s s i b l e to i n v e s t i g a t e (1) t h e d i r e c t e d g e of a n u m b e r of o t h e r m a t e r i a l s s u c h a s G a S b (2), t h e e f f e c t s of u n i a x i a l s t r e s s on t h e e l e c t r o r e f l e c t a n c e s p e c t r u m of t h e d i r e c t e d g e of G e , G a S b , e t c . , a n d (3) e l e c t r o t r a n s m i s s i o n of m a t e r i a l s s u c h a s Ge a n d Si. T h e u s e of o r g a n i c s o l v e n t s m a k e s it p o s s i b l e to s t u d y e l e c t r o r e f l e c t a n c e o v e r a b r o a d t e m p e r a t u r e r a n g e ( - 5 0 to 2 5 0 o c for propylene carborate).
References 1. K.L.Shaklee, F . H . P o l l a k and M.Cardona, Phys. Rev. L e t t e r s 15 (1965) 883; A. G. Thompson, M. Cardona, K. L. Shaklee and J. C. Woolley, P h y s . R e v . 146 (1966) 601; M. Cardona, K. L. Shaklee and F. H. Pollak, submitted to Phys. Rev. 2. We a r e grateful to Dr. R . M a r i c l e of the Cyanamid Corp. for suggesting the use of these electrolytes. 3. W.E. Engeler, H. F r i t z s c h e , M. Garfinkel and J. J. Tiemann, P h y s . R e v . L e t t e r s 14 (1965) 1069. 4. B . O . S e r a p h i n , R . B . H e s s and N. Bottba, J.Appl. Phys. 36 (1965) 2242. 5. O.Madelung in Physics of III-V compounds (J.Wiley and Sons, Inc., New York, 1964)p. 53. 6. K.L.Shaklee, M . C a r d o n a and F . H . P o l l a k , Phys. Rev. L e t t e r s 16 (1966) 48.
ELECTRONIC CONTRIBUTION TO ULTRASONIC ATTENUATION
THE IN
NORMAL INDIUM
STATE
E . S. BLISS a n d J . A. R A Y N E
Carnegie Institute of Technology, Pittsburgh, Pennsylvania Received 18 August 1966
This paper r e p o r t s the anisotropy and frequency dependence of the n o r m a l electronic attenuation of longitudinal sound waves in very pure single c r y s t a l s of indium.
T h e c r y s t a l s w e r e g r o w n f r o m 99.9999+% p u r e starting material and were spark cut for propag a t i o n n o r m a l to t h e (100), (001), (110), (011) a n d (111) p l a n e s . R e l a t i v e a t t e n u a t i o n m e a s u r e m e n t s w e r e m a d e in t r a n s m i s s i o n , u s i n g t h e p u l s e c o m p a r i s o n t e c h n i q u e , a t f r e q u e n c i e s up to 210 Mc/sec. For the frequency and temperature ranges investigated the samples satisfied the limiting con38
d i t i o n ql >> 1, w h e r e q i s t h e p h o n o n w a v e n u m b e r a n d l i s t h e e l e c t r o n i c m e a n f r e e p a t h . In t h i s l i m it, t h e n o r m a l s t a t e e l e c t r o n i c a t t e n u a t i o n f o r l o n g i t u d i n a l w a v e s i s g i v e n b y [1]
w h e r e R i s t h e r e c i p r o c a l of t h e G a u s s i a n c u r v a t u r e of t h e F e r m i s u r f a c e , K x i s t h e r e l e v a n t d e -
PHYSICS
L B. O. Seraphin and N. Bottka, P h y s . Rev. L e t t e r s 15 (1965) 104. 2. B . O . S e r a p h i n , P h y s . R e v . 140 (1965) A1716. 3. B. O. Seraphin and N. Bottka, P h y s . Rev. 145 (1966) 628. 4. K . L . S h a k l e e , F . H . Pollak and M. Cardona, P h y s . Rev. L e t t e r s 15 (1965) 883. 5. A. K. Ghosh, to be published. 6. U. G e r h a r d t , P h y s . R e v . L e t t e r s 15 (1965) 401; P h y s . Status Solidi 11 (1965) 801. 7. F. H e r m a n , R . L . K o r t u m , C . D . Kuglin and R. A. Short,
ELECTROREFLECTANCE INTERFACE:
LETTERS
8. 9. 10. 11.
3 O c t o b e r 1966
Quantum T h e o r y of A t o m s , M o l e c u l e s and the Solid State; ed. P . O . L~wdin (Academic P r e s s , New York), to be published. D. B r u s t , P h y s . R e v . 1 3 6 (1964) A1337. H. E h r e n r e i c h , H . R . Phillip and J. C. P h i l l i p s , Phys. Rev. L e t t e r s 8 (1962) 59. D . B r u s t , J . C . P h i l l i p s and F . B a s s a n i , P h y s . R e v . L e t t e r s 9 (1962) 94. E . O . K a n e , P h y s . R e v . 146 (1966) 558.
AT A SEMICONDUCTOR-ELECTROLYTE INFRARED MEASUREMENTS *
M. C A R D O N A , K. L. SHAKLEE and F . H. P O L L A K Physics Department, Brown University, Providence, Rhode Island, USA R e c e i v e d 18 A u g u s t 1966
M e a s u r e m e n t s of e l e c t r o r e f l e c t a n c e at a s e m i - c o n d u c t o r electorlyte i n t e r f a c e in the i n f r a r e d region to about 0.6 eV a r e r e p o r t e d .
We have extended the r a n g e of m e a s u r e m e n t s of e l e c t r o r e f l e c t a n c e at a s e m i c o n d u c t o r - e l e c t r o lyte i n t e r f a c e [1] into the i n f r a r e d r e g i o n to about 0.6 eV. This has b e e n a c c o m p l i s h e d by p la c i n g the s a m p l e as c l o s e as p o s s i b l e to the window of the c e l l containing the e l e c t r o l y t e (~0.1 N KC1 in H20) , while s t i l l m a in ta in in g a thin l a y e r of e l e c t r o l y t e (~0.1 mm), so that the a b s o r p t i o n of the w a t e r is r e d u c e d to a m i n i m u m . W a t e r has s t r o n g a b s o r p t i o n in the n e a r i n f r a r e d which l i m i t e d our previous m e a s u r e m e n t s . There are strong abs o r p t i o n peaks at 0.9 eV (~ ~ 1 0 c m - 1 ) and 0.64 eV (~ ~ 5 0 c m - 1 ) , the f o r m e r peak due to the v i b r a tions of the O- H bond. The above l i m i t a t i o n m a y a l s o be o v e r c o m e by the use of s o m e o r g a n i c e l e c t r o l y t e s such as KCNS or t e t r a e t h y l a m m o nium b r o m i d e d i s s o l v e d in a c e t o n i t r i l e o r p r o p y lene c a r b o n a t e [2]. The e x p e r i m e n t a l technique is s i m i l a r to that which has been used in our p r e v i o u s e l e c t r o r e f l e c t a n c e m e a s u r e m e n t s [1]. H o w e v e r , in the p r e s e n t c a s e a P e r k i n - E l m e r Model 98 m o n o c h r o m a t o r and a PbS c e l l w e r e used. A p o r t i o n of the incident light was chopped at 200 c / s and a 80 c / s modulating signal was applied to the s a m p l e . The 200 c / s signal was d e t e c t e d by a * Supported by the National Science Foundation and the A r m y R e s e a r c h Office, D u r h a m .
InSb (5
O
Eo
(.9
I
$
Ge
c
"~ /~ Geo.93Sio.07
%
% x =
0
\
-8
l
0.8
I0
V
I
1.2
ENERGY (ev~
Fig. 1. E l e c t r o r e f l e c t a n c e s p e c t r u m of Ge, A Ge-Si a l loy (7% Si), and InSb in the e n e r g y r a n g e 0.7 - 1.2 eV at room temperature.
37
Volume 23, n u m b e r 1
PHYSICS
lock-in amplifier, whose output was connected to a s e r v o m e c h a n i s m c o n t r o l l i n g t h e s l i t - w i d t h of t h e m o n o c h r o m a t o r . T h i s s e r v o t h u s k e e p s t h e l o c k - i n a m p l i f i e r o u t p u t c o n s t a n t . T h e 80 c / s s i g n a l f r o m t h e d e t e c t o r w a s s e n t to a s e c o n d l o c k - i n a m p l i f i e r t h e o u t p u t of w h i c h w a s c o n n e c t e d to a s t r i p - c h a r t r e c o r d e r . T h e r e c o r d e d s i g n a l i s t h u s d i r e c t l y p r o p o r t i o n a l to t h e r a t i o A R / R [3]. Shown in fig. 1 i s t h e e l e c t r o r e f l e c t a n c e s p e c t r u m of G e , a G e - S i a l l o y (7% Si), a n d InSb i n t h e e n e r g y r a n g e 0.7 - 1.2 e V a t r o o m t e m p e r a t u r e . T h e o b s e r v e d e n e r g i e s of t h e E o ( 0 . 8 0 0 + 0.005 e V [ 3 , 4 ] ) a n d E o + a o ( 1 . 0 8 2 ± 0.005 e V [ 3 ] ) p e a k s of Ge a r e in good a g r e e m e n t w i t h o t h e r m e a s u r e m e n t s . T h e s h a p e s of t h e s e p e a k s a r e s i m i l a r to t h o s e of t h e s a m e t r a n s i t i o n s m e a s u r e d in o t h e r m a t e r i a l s [1]. T h e o b s e r v e d e n e r g y of t h e E o p e a k f o r t h e G e - S i a l l o y (1.042 ± 0 . 0 0 5 eV) i n d i c a t e s a l i n e a r v a r i a t i o n of t h e F25, - F 2, gap w i t h Si c o n centration. The entire electroreflectance spect r u m of a s e r i e s of G e - S i a l l o y s i s p r e s e n t l y b e ing s t u d i e d . P r e l i m i n a r y r e s u l t s y i e l d a v a l u e of 4.1 + 0.1 eV f o r t h e e x t r a p o l a t i o n of t h e 1"25, - F 2, g a p to 100% Si. T h e s t r u c t u r e in t h e s p e c t r u m of InSb i s b e l i e v e d , to b e due to t h e s p i n - o r b i t s p l i t b a n d a t k = 0 (E o + 4 0 ) . T h e e n e r g y of t h i s p e a k (0.990 + 0.005 eV) t o g e t h e r w i t h t h e v a l u e of E o (0.17 e V [5] ) a t r o o m t e m p e r a t u r e y i e l d s a v a l u e
LETTERS
3 O c t o b e r 1966
of 0.82 e V f o r Ao, in good a g r e e m e n t w i t h t h e r u l e (A 1 = 0 . 5 8 e V [ 1 , 6 ] ) . T h e e x t e n s i o n of t h e e l e c t r o l y t e t e c h n i q u e of electroreflectance into the near infrared makes it p o s s i b l e to i n v e s t i g a t e (1) t h e d i r e c t e d g e of a n u m b e r of o t h e r m a t e r i a l s s u c h a s G a S b (2), t h e e f f e c t s of u n i a x i a l s t r e s s on t h e e l e c t r o r e f l e c t a n c e s p e c t r u m of t h e d i r e c t e d g e of G e , G a S b , e t c . , a n d (3) e l e c t r o t r a n s m i s s i o n of m a t e r i a l s s u c h a s Ge a n d Si. T h e u s e of o r g a n i c s o l v e n t s m a k e s it p o s s i b l e to s t u d y e l e c t r o r e f l e c t a n c e o v e r a b r o a d t e m p e r a t u r e r a n g e ( - 5 0 to 2 5 0 o c for propylene carborate).
References 1. K.L.Shaklee, F . H . P o l l a k and M.Cardona, Phys. Rev. L e t t e r s 15 (1965) 883; A. G. Thompson, M. Cardona, K. L. Shaklee and J. C. Woolley, P h y s . R e v . 146 (1966) 601; M. Cardona, K. L. Shaklee and F. H. Pollak, submitted to Phys. Rev. 2. We a r e grateful to Dr. R . M a r i c l e of the Cyanamid Corp. for suggesting the use of these electrolytes. 3. W.E. Engeler, H. F r i t z s c h e , M. Garfinkel and J. J. Tiemann, P h y s . R e v . L e t t e r s 14 (1965) 1069. 4. B . O . S e r a p h i n , R . B . H e s s and N. Bottba, J.Appl. Phys. 36 (1965) 2242. 5. O.Madelung in Physics of III-V compounds (J.Wiley and Sons, Inc., New York, 1964)p. 53. 6. K.L.Shaklee, M . C a r d o n a and F . H . P o l l a k , Phys. Rev. L e t t e r s 16 (1966) 48.
ELECTRONIC CONTRIBUTION TO ULTRASONIC ATTENUATION
THE IN
NORMAL INDIUM
STATE
E . S. BLISS a n d J . A. R A Y N E
Carnegie Institute of Technology, Pittsburgh, Pennsylvania Received 18 August 1966
This paper r e p o r t s the anisotropy and frequency dependence of the n o r m a l electronic attenuation of longitudinal sound waves in very pure single c r y s t a l s of indium.
T h e c r y s t a l s w e r e g r o w n f r o m 99.9999+% p u r e starting material and were spark cut for propag a t i o n n o r m a l to t h e (100), (001), (110), (011) a n d (111) p l a n e s . R e l a t i v e a t t e n u a t i o n m e a s u r e m e n t s w e r e m a d e in t r a n s m i s s i o n , u s i n g t h e p u l s e c o m p a r i s o n t e c h n i q u e , a t f r e q u e n c i e s up to 210 Mc/sec. For the frequency and temperature ranges investigated the samples satisfied the limiting con38
d i t i o n ql >> 1, w h e r e q i s t h e p h o n o n w a v e n u m b e r a n d l i s t h e e l e c t r o n i c m e a n f r e e p a t h . In t h i s l i m it, t h e n o r m a l s t a t e e l e c t r o n i c a t t e n u a t i o n f o r l o n g i t u d i n a l w a v e s i s g i v e n b y [1]
w h e r e R i s t h e r e c i p r o c a l of t h e G a u s s i a n c u r v a t u r e of t h e F e r m i s u r f a c e , K x i s t h e r e l e v a n t d e -