HAL Id: jpa-00226799
https://hal.archives-ouvertes.fr/jpa-00226799
Submitted on 1 Jan 1987
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.
NEGATIVE DIFFERENTIAL RESISTANCE OF In0.53Ga0.47As/In0.52Al0.48As RESONANT TUNNELING BARRIERS GROWN BY MBE
S. Muto, T. Inata, Y. Sugiyama, Y. Nakata, T. Fujii, S. Hiyamizu
To cite this version:
S. Muto, T. Inata, Y. Sugiyama, Y. Nakata, T. Fujii, et al.. NEGATIVE DIFFERENTIAL RESIS- TANCE OF In0.53Ga0.47As/In0.52Al0.48As RESONANT TUNNELING BARRIERS GROWN BY MBE. Journal de Physique Colloques, 1987, 48 (C5), pp.C5-453-C5-456. �10.1051/jphyscol:1987595�.
�jpa-00226799�
JOURNAL DE PHYSIQUE
Colloque C5, suppl6ment au noll, Tome 48, novembre 1987
NEGATIVE DIFFERENTIAL RESISTANCE OF I n o . 5 3 G a o ~ 4 , A s / I n o ~ 5 2 A 1 0 0 4 8 A s RESONANT TUNNELING BARRIERS GROWN BY MBE
S. MUTO, T. INATA, Y. SUGIYAMA, Y. NAKATA, T. FUJI1 and S. HIYAMIZU
Fujitsu Laboratories Ltd, 10-1 Morinosato-Wakamiya, Atsugi, Kanagawa , 2 4 3 - 0 1 , Japan
The q u a n t u m - w e l l - w i d t h d e p e n d e n c e o f n e g a t i v e d i f f e r e n t i a l r e s i s t a n c e (NDR) o f an InGaAs/InAlAs r e s o n a n t t u n n e l i n g b a r r i e r (RTB) s t r u c t u r e , l a t t i c e - m a t c h e d t o I n P s u b s t r a t e s , was s t u d i e d . The b e s t NDR c h a r a c t e r i s t i c s e v e r r e p o r t e d ( a p e a k - t o - v a l l e y r a t i o o f 5.5 a t 300K and 13.3 a t 77K w i t h a peak c u r r e n t d e n s i t y o f 4 . 8 ~ 1 0 ~ ~ / c m ~ a t b o t h 77K and 300K) have been a c h i e v e d f o r a r e s o n a n t t u n n e l i n g b a c r i e r d i o d e w i t h a q u a n t u m w e l l w i d t h o f 32.2 A and a b a r r i e r w i d t h o f 46.9 A. We f o u n d t h a t t h e b a n d n o n p a r a b o l i c i t y e n h a n c e s t h e e l e c t r o n t u n n e l i n g o f t h e I n A l A s b a r r i e r l a y e r .
1. I n t r o d u c t i o n
S i n c e t h e p r o p o s a l o f t h e RTB s t r u c t u r e b y T s u and E s a k i i n 1973'). t h e s t u d y o f t h e NDR o f RTBs h a s been l i m i t e d t o GaAs/AlGaAs h e t e r o s t r u c t u r e s . However, o b t a i n e d NDR c h a r a c t e r i s t i c s were n o t s u f f i c i e n t i n v i e w o f p r a c t i c a l a p p l i c a t i o n s t o new f u n c t i o n a l d e v i c e s s u c h a s a r e s o n a n t - t u n n e l i n g h o t e l e c t r o n t r a n s i s t o r (RHET)') a n d a r e s o n a n t - t u n n e l i n g b i p o l a r t r a n s i s t o r ( R B T ) ~ ) . We r e c e n t l y r e p o r t e d 4 ) t h e f i r s t o b s e r v a t i o n o f e x c e l l e n t NDR (a p e a k - t o - v a l l e y r a t i o o f 11.7 a t 77K and 2.0 a t 300K w i t h a peak c u r r e n t d e n s i t y o f 2 . 2 ~ 1 0 ~ ~ / c m ' ) i n a n I n G a A s / I n A l A s RTB s t r u c t u r e , l a t t i c e - m a t c h e d t o InP, i n d i c a t i n g t h e s u p e r i o r i t y o f t h i s m a t e r i a l f o r RTB s t r u c t u r e s o v e r GaAs/AlGaAs h e t e r o s t r u c t u r e s . I n f a c t , t h e I n G a A s / I n A l A s h e t e r o s t r u c t u r e h a s a d v a n t a g e s o v e r t h e c o n v e n t i o n a l GaAs/AlGaAs h e t e r o s t r u c t u r e i n RTB a p p l i c a t i o n s . F i r s t , I n A l A s used f o r t h e b a r r i e r l a y e r has a l i g h t e r e f f e c t i v e mass (0.075111~) t h a n A1,Gal-xAs (m"=0.092m0 a t x=0.3). T h i s means4) t h a t we can e x p e c t e x t r e m e l y h i g h e r t u n n e l i n g c u r r e n t d e n s i t y i n t h e I n G a A s / I n A l A s RTB t h a n i n t h e GaAs/AlGa-As RTB. I n a d d i t i o n , n-InGaAs u s e d f o r e l e c t r o d e l a y e r s has l o w e r p a r a s i t i c r e s i s t a n c e s 5 ) t h a n n-GaAs o f GaAs/AlGaAs RTBs. I n t h i s p a p e r , we s t u d i e d t h e e f f e c t o f q u a n t u m w e l l w i d t h o n I - V c h a r a c t e r i s t i c s o f an InGaAs/InAlAs RTB t o f u r t h e r i m p r o v e i t s NDR.
2. E x p e r i m e n t s
Resonant t u n n e l i n g b a r r i e r s t r u c t u r e s o f I n x A 1 1-xAs(x=0.52, . LB)/InyGal-yAs (~=0.53, LW)/InxA11-xAs(x=0.52, LB) sandwiched between t h i c k Si-doped
n - I n Gal-yAs l a y e r s (y=0.53. ND g r a d e d f r o m 1 x 1 0 ' ~ cm-3 n e a r t h e RTB t o Y
2 x 1 0 ' ~ f a r from t h e RTB) were grown on ( 1 0 0 ) - o r i e n t e d nf-I~P s u b s t r a t e s b y MBE a t a t e m p e r a t u r e o f 470°C. A f t e r t h e g r o w t h , d i o d e s w e r e f a b r i c a t e d b y m a k i n g n o n - a l l o y e d o h m i c c o n t a c t s a t t h e upper and t h e l o w e r n-InGaAs l a y e r s .
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1987595
JOURNAL
DE
PHYSIQUE3. R e s u l t s and d i s c u s s i o n
The peak ( J p ) and t h e x a l l e y ( J V ) c u r r e n t d e n s i t i e s i n t h e NDR r e g i o n o f RTBs w i t h f i x e d LB o f 41.0 A a r e shown i n F i g . 1 %s a f u n c t o i o n o f t h e q u a n t u m w e l l w i d t h (LW). When L W was r e d u c e d f r o m 61.5 A t o 44.0 A, t h e p e a k c u r r e n t d e n s i t y ( J p ) o f t h e NDR r e g i o n i n c r e a s e d m o n o t o n i c a l l y f r o m 2 . 9 ~ 1 0 ~ ~ l c m ' t o 6 . 3 ~ 1 0 ~ ~ l c m ' . A t 77K. t h e v a l l e y c u r r e n t d e n s i t y ( J V ) i n c r e a s e d p r o p o r t i o n a l l y t o Jp, and t h e r e s u l t a n t p e a k - t o - v a l l e y r a t i o s t a y e d a l m o s t c o n s t a n t (10.9-11.7). The v a l l e y c u r r e n t d e n s i t y a t 300K. h o w e v e r , became m i n i m u m when L W i s 52.7 A, w h i c h we r e g a r d e d as b e i n g d u e t o a c r o s s - o v e r o f e v a n e s c e n t - s t a t e c u r r e n t and t h e r m i o n i c c u r r e n t t h r o u g h upper resonant-states.
xhe r e s u l t a n t peak-Jo-val l e y r a t i o a t 300K i n c r e a s e d 1 in e a r l y f r o m 2.1 (LW=61,5 A) t o 4.1 (LW=44.0 A). By f u r t h e r r e d u c i n g t h e q y a n t u m w e l l w i d t h t o 32.2 A, we h a v e a c h i e v e d f o r a RTB d i o d e w i t h LB = 46.9 A, a p e a k - t o - v a l l e y r a t i o o f 5.5 w ~ t h a.peak c u r r e n t d e n s i t y of 4 . 8 ~ 1 0 ~ ~ / c m ' a t 300K (Fig. 2). w h i c h i s , as f a r as we know, t h e b e s t NDR o f any RTB s t r u c t u r e .
F i g . 1
. -
lo3% 50 60 70
Well wldrh ( % I
Peak c u r r e n t d e n s i t y ( J p ) and v a l l e y c u r r e n t d e n s i t y ( J V ) o f I n G a A s / I n A l A s r e s o n a n t t u n n e l i n g b a r r i e r d i o d e s a t 7 7 K a s a f u n c t i o n o f q u a n t u m we1 1 w i d t h , LW.
-
F i g . 2e! ! !r>r/ c u r r e n t - v o l t a g e (I-V)
-
c h a r a c t e r i s o t i c s o f a nLnGaAs(46.9 A ) / I n A l A s ( 3 2 . 2
:
2 0A ) r e s o n a n t t u n n e l i n g
- 5
0 0 b a r r ~ e r d i o d e w ~ t h a n; 0 0 3 0 6 0 9 1 2 1 5
u Voltage ( V ) e f f e c t i v e c o n t a c t a r e a o f
6x6 urn2.
Obtained p e a k - t o - v a l l e y r a t i o s o f InGaAsjInAlAs RTBs a t 77K a r e summarized i n F i g . 3 as a f u n c t i o n o f J p , c o n t r a s t e d w i t h d a t a o f GaAsIAlGaAs ( i n c l u d i n g G a A s l A l A s ) RTBS~-'). The a d v a n t a g e o f I n G a A s j I n A l A s RTBs o v e r c o n v e n t i o n a l GaAs/AlGaAs RTBs i s o b v i o u s . The NOR r e q u i r e d ( J p o f a b o u t
l o 5
~ / c m ' and J p / J V o v e r 10) f o r an e m i t t e r b a r r i e r o f t h e n e w - f u n c t i o n a l t r a n s i s t o r (RHET) i s shown b y t h e s h a d e d area. As seen, some o f t h e I n G a A s / I n A l A s RTBs n e a r l y meet t h e r e q u i r e m e n t .F i g . 3
1 5 1 , , 1 ,
. . . , . .
. , , , . , ,-
P e a k - t o - v a l l e y r a t i o ( J p / J V ) o f F i g . 2 a s a f u n c t i o n o f t h e p e a k c u r r e n t d e n s i t y (Jp). Data f o r GaAs/AlGaAs RTBs a r e a l s o p l o t t e d : ( 0 ) a f t e r r e f . 6, (A) a f t e r r e f . 7,
I o3 I o4 I o5 I o6
Peak current denaty lA/crn2) (H) a f t e r r e f . 8 , a n d ( A ) a f t e r r e f . 9.
I n t h e I n G a A s / I n A l A s RTBs, b a n d n o n p a r a b o l i c i t y i s e x p e c t e d t o p l a y a n i m p o r t a n t r o l e i n t h e NDR c h a r a c t e r i s t i c s , p a r t l y due t o t h e s m a l l e n e r g y band g a p o f InGaAs (Eg i s 0.76 eV a t 300K). T h e r e f o r e , we p e r f o r m e d a s i m p l e t u n n e l i n g m o d e l c a l c u l a t i o n 5 ) t a k i n g t h e band n o n p a r a b o l i c i t y i n t o account.
A c c o r d i n g t o Kane's k m p p e r t u r b a t i o n 1 0 ) , o n e - d i m e n s i o n a l S c h r u d i n g e r e q u a t i o n o f t h e e n v e l o p e - f u n c t i o n can be m o d i f i e d t o ( i n b o t h InGaAs and I n A l A s l a y e r s )
Here, z i s t h e c o o r d i n a t e n o r m a l t o t h e i n t e r f a c e , E i s e l t c t r p n k i n e t i c e n e r g y i n t h e z d i r e c t i o n , and egergy-dependent e f f e c t i v e mass m (E) i s d e f i n e d , u s i n g e l e c t r o n e f f e c t i v e mass m
,
b yQ Q
m (E) = m [ l t [ ~ - ( m * / m ~ ) ] ~ ~ / ~ ~ ] . (2)
Note t h a t t h e k i n e t i c e n e r g y E Q i s n e g a t i v e i f an elecJron i s t u n n e l i n g t h r o u g h I n A l A s b a r r i e r l a y e r s , a n d m (E) i s s m a l l e r t h a n m
.
As f o r t h e c o n t i n u i t y c o n d i t i o n s a t t h e i n t e r f a c e , we assumed t h a t b o t hY ( z ) and
d
~ ( z )m'"'(~) dz
be c o n t i n u o u s , w h i c h i s i n a c c o r d a n c e w i t h x r e s u l t o f t h e e n v e l o p e - f u n c t i o n a p p r o x i ~ a t i o n b y ~ a s t a r d " ) e x c e p t f o r t h e m2'/m0 t e r m i n eq. (2).
The peak c u r r e n t d e n s i t i e s (Jp) c a l c u l a t e d i n t h e above way a r e shown as t h e s o l i d c u r v e i n F i g . 45). E x c e l l e n t a g r e e m e n t w i t h t h e o b s e r v e d ,Jp i s o g t a i n e d . The dashed c u r v e i s produced b y assuming t h e p a r a b o l i c band (m (E) =
m i n eq. (2)). The r e a s o n f o r t h e i n c r e a s e d J p d u e t o t h e n o n p a r a b o l i c i t y i s e x p l a i n e d next. I n t h e r e s o n a r i t t u n n e l i n g o f t h e InAlAs/InGaAs RTB, due t o t h e l a r g e c o n d u c t i o n b a n d d i s c o n t i n u i t y ( A E ~ ) o f 0.53 evl') a t t h e i n t e r f a c e , e l e c t r o n s t u n n e l t h r o u g h t h e I n A l A s b a r r i e r l a y e r w i t h a l a r g e n e g a t i v e k i n e t i c e g e r g y ( a r o u n d -0.4 eV). T h e r e f o r e , t h e e n e r g y - d e p e n d e n t e f f e c t i v e mass, m (E), i n t h e b a r r i e r l a y e r i s c o n s i d e r a b l y reduced t o y i e l d a h i g h e r t u n n e l i n g p r o b a b i l i t y and a h i g h e r peak c u r r e n t d e n s i t y t h a n t h e p a r a b o l i c a p p r o x i m a t i o n . Thus, t h e h i g h e l e c t r o n t u n n e l i n g p r o b a b i l i t y of I n A l A s b a r r i e r l a y e r due t o a l i g h t e l e c t r o n mass i s enhanced b y t h e n o n p a r a b o l i c i t y o f t h e l a y e r .
C5 -45 6 JOURNAL DE PHYSIQUE
F i g . 4
7 7 K
E f f e c t o f n o n p a r a b o l i c i t y on t h e q u a n t u m - w e l l - w i d t h dependence o f peak c u r r e n t d e n s i t y (Jp) o f InGaAs/
Meosured I n A l As r e s o n a n t - t u n n e l i n g
b a r r i e r .
Io3 40 50 6 0 70
Well width ( 8 )
I n summary, we h a v e s t u d i e d t h e q u a n t u m - w e l l - w i d t h d e p e n d e n c e o f n e g a t i v e d i f f e r e n t i a l r e s i s t a n c e (NDR) o f an InGaAs/InAlAs r e s o n a n t t u n n e l i n g b a r r i e r s t r u c t u r e , l a t t i c e - m a t c h e d t o I n P s u b s t r a t e s . T h e b e s t NDR c h a r a c t e r i s t i c s e v e r r e p o r t e d (a p e a k - t o - v a l l e y r a t i o o f 5.5 a t 300K and 13.3 a t 77K w i t h a peak c u r r e n t d e n s i t y o f 4 . 8 ~ 1 0 ~ ~ / c m ' a t b o t h 77K and 300K) have been achieoved f o r a r e s o n a n t t u n n e l i n g b a r r i e r daode w i t h a quantum w e l l w i d t h o f 32.2 A a n d a b a r r i e r w i d t h o f 46.9 A. We f o u n d t h a t t h e b a n d n o n p a r a b o l i c i t y enhances t h e l i g h t e l e c t r o n mass and e l e c t r o n t u n n e l i n g o f t h e I n A l As b a r r i e r 1 ayer.
Acknowledgments
The a u t h o r s a r e g r a t e f u l t o T. Yamaoka, K. Dazai, 0. Ryuzan, and T. M i s u g i f o r t h e i r s u p p o r t o f t h i s work.
References
1 ) R. Tsu and L. Esaki: Appl. Phys. L e t t .
22
(1973) 562.2) N. Yokoyama, K. Imamura, S. Muto, S. Hiyamizu, and H. N i s h i : Jpn. J. Appl. Phys.
24
(1985) L853.3 ) T. F u t a t s u g i , Y. Yamaguchi, K. I s h i , K. Imamura, S. M u t o ,
N. Yokoyama, and A. S h i b a t o m i : IEDM 1986, Tech. Dig. p286. Also, F. Capasso, S. Sen, A.C. Gossard. A.L. Hutchinson, and
J.H. E n g l i s h : IEEE E l e c t o n Device L e t t .
EDL-7
(1986) 573.4) T. I n a t a , S. M u t o , Y. N a k a t a , T. F u j i i , H. O h n i s h i , and S. H i y a m i z u : Jpn. J. A p p l . Phys.
25
(1986) L983.5) S. Muto, T. I n a t a , Y. Sugiyama, Y. Nakata, T. F u j i i , H. Ohnishi, and S. Hiyamizu: Jpn. J. Appl. Phys.
26
(1987) L220.6 ) S. M u t o , S. H i y a m i z u , a n d N. Y o k o y a m a : P r o c e e d i n g s o f H i g h - S p e e d E l e c t r o n i c s , Stockholm, 1986 ( S p r i nger-Verl ag, H e i d e l berg, 1987) pp.72-78.
7) M. T s u c h i y a , H. S a k a k i , and J. Y o s h i n o : Jpn. J. Appl. Phys.
3
(1985) L466.
M. T s u c h i y a and H. S a k a k i : Jpn. J. A p p l . Phys.
3
( 1 9 8 6 ) L185.M. T s u c h i y a a n d H. S a k a k i : A p p l . Phys. L e t t .
9
( 1 9 8 6 ) 88.8 ) W.D. Goodhue, T.C.L.G. S o l l n e r , H.Q. Le, E.R. Brown, and B.A. Vojak: Appl. Phys. L e t t .
49
( 1 9 8 6 ) 1086.9 ) H. Morkoc, J. Chen, U.K. Reddy, T. Henderson, and S. L u r y i : Appl. Phys. L e t t .
9
(1986) 70.10) E.O. Kane: J. Phys. Chem. S o l i d s
1
(1957) 249.11) G. B a s t a r d : Phys. Rev. @ (1981) 5693.
1 2 ) Y. Sugiyama, T. I n a t a , T. F u j i i , Y. N a k a t a , S. Muto, and S.
Hiyamizu: Jpn. J. Appl. Phys.
