FAR-INFRARED CYCLOTRON RESONANCE OF PHOTOEXCITED HOT CARRIERS IN INDIUM ANTIMONIDE

(1)

HAL Id: jpa-00221685

https://hal.archives-ouvertes.fr/jpa-00221685

Submitted on 1 Jan 1981

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.

FAR-INFRARED CYCLOTRON RESONANCE OF PHOTOEXCITED HOT CARRIERS IN INDIUM

ANTIMONIDE

E. Otsuka, T. Ohyama, K. Fujii

To cite this version:

E. Otsuka, T. Ohyama, K. Fujii. FAR-INFRARED CYCLOTRON RESONANCE OF PHOTOEX-

CITED HOT CARRIERS IN INDIUM ANTIMONIDE. Journal de Physique Colloques, 1981, 42 (C7),

pp.C7-393-C7-398. �10.1051/jphyscol:1981748�. �jpa-00221685�

(2)

JOURNAL DE PHYSIQUE

Colloque C7, supplément au n°10, Tome 42, octobre 1981 page C7-393

FAR-INFRARED CYCLOTRON RESONANCE OF PHOTOEXCITED HOT CARRIERS IN INDIUM ANTIMONIDE

E. Otsuka, T. Ohyama and K. Fujii

Department of Physios, College of Geneva! Education, Osaka University, Toyonaka, Osaka 560, Japan

Résumé. - Nous avons fait l'expérience de résonance cyclotronique sur les porteurs produits par 1'excitation de lumière

intrinsèque dans InSb, tant de type n que de type p, sous la condition thermique de l'hélium liquide. En voici nos résultats:

tout d'abord, la température des électrons s'élève au-dessus de 40 K, et la constante de temps de refroidissement est à 6,5 ps;

la durée de vie du système des électrons ainsi produits est longue, même de l'ordre de 10 ys dans p-InSb à 4,2 K, tandis que dans le matériau de type n, elle est encore plus longue ; et, nous avons

pu observer en même temps la résonance des électrons que celle des trous, ce qui nous permet de déterminer une nouvelle série de pa- ramètres Luttinger de la bande de valence. Il faut ajouter que l'émission cyclotronique des électrons produits par l'excitation de lumière ressemble à celle de l'excitation électrique.

Abstract. - Cyclotron resonance experiment has been performed at liquid helium temperatures for intrinsically photoexcited carriers both in n- and in p-InSb. Electron temperature above 40 K is observed. Its cooling time constant is found to be 6.5 ys.

Lifetime as long as &10 ys is observed at 4.2 K for the photoexcited electron system in the p-type material. That in the n- type material is even longer. Joint observation of electron and hole resonances in an n-type material has enabled us to determine a new set of Luttinger parameters for the valence band. Cyclo- tron emission like in the case of electric field excitation has been observed also for the photoexcited hot electron system.

1. Introduction

Since the first laser cyclotron resonance on InSb , considerable information of this material has been obtained. The valence band parameters and the steady-state hot electron behaviour have been in-2 vestigated. ' In all the past experiments, free carriers relevant to 3 4 cyclotron resonance observation were made available either by thermal or by electrical means. This situation is rather in contrast with the case for silicon and germanium, where the free carriers which are ab- sent at low temperatures are almost always produced by the band gap light excitation. This paper deals with the behaviour of intrinsically photoexcited free carriers. One can meet electron cyclotron resonance in p-type material and vice versa. In particular, the present work tells a story of hot photoexcited carriers, a good amount of

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1981748

(3)

C7-394 JOURNAL DE PHYSIQUE

i n f o r m a t i o n which may be complementary t o t h e luminescence e x p e r i m e n t a s such r e p o r t e d by U l b r i c h f o r The r e s u l t o b t a i n e d h e r e w i l l a l s o supplement t h e one o b t a i n e d from t h e h o t e l e c t r o n r e s o n a n c e by means o f e l e c t r i c The l a s t b u t n o t l e a s t i m p o r t a n t , cyclo- t r o n e m i s s i o n by i n t r i n s i c a l l y p h o t o e x c i t e d c a r r i e r s , t o o u r knowledge f o r t h e f i r s t t i m e , h a s been o b s e r v e d . T h i s i s a l s o a n o v e l

supplement t o t h e p a s t work by means of e l e c t r i c f i e l d e ~ c i t a t i o n . ~ ' ~ 2. Samples

We have t r i e d t h r e e samples o f InSb a s g i v e n i n T a b l e 1; namely two n-type and one p-type m a t e r i a l s . The t y p i c a l sample s i z e i s 4 ^X 4

X (0.15

-

0.50) mm 3

.

T a b l e 1. Sample c h a r a c t e r i s t i c s

- - - p-

S ample Type

IN^ -

^hlAl Compensation r a t i o

3. E x p e r i m e n t a l P r o c e d u r e s

I n t r i n s i c p h o t o e x c i t a t i o n h a s been done by a xenon f l a s h lamp f o r c y c l o t r o n r e s o n a n c e o b s e r v a t i o n . A t u n g s t e n lamp h a s a l s o been emp- l o y e d f o r o b s e r v i n g c y c l o t r o n e m i s s i o n . We have u s e d f o u r f a r - i n f r a - r e d l a s e r wavelengths f o r c y c l o t r o n r e s o n a n c e a b s o r p t i o n measurement;

namely, 8 4 , 119, 172 and 220 Wm. R e p e t i t i o n f r e q u e n c y o f t h e FIR l a s e r p u l s e s i s 20 Hz w h i l e t h a t o f p h o t o e x c i t a t i o n p u l s e s 10 H z . The w i d t h o f p h o t o p u l s e i s *l

v s

and t h e e n e r g y absorbed by t h e sample h a s been v a r i e d 1 ~ 1 2 . 5 pJ p e r p u l s e . These two f r e q u e n c i e s a r e made i n e v e r y - o t h e r - t u r n s y n c h r o n i s a t i o n . The FIR d e t e c t o r i s an n-type InSb P u t l e y u n i t f o r c y c l o t r o n r e s o n a n c e e x p e r i m e n t and i s an Sb-doped Ge f o r c y c l o t r o n e m i s s i o n e x p e r i m e n t . One always a p p l i e s t h e magnetic f i e l d a l o n g [ l l l ] , up t o t h e s t r e n g t h of 5 T . The ambient t e m p e r a t u r e h a s been changed between 1 . 7 and 4.2 K. When i t was n e c e s s a r y t o d i s - t i n g u i s h t h e p h o t o e x c i t e d c a r r i e r s , h o l e s i n p a r t i c u l a r , from t h e t h e r m a l e q u i l i b r u i m c a r r i e r s a s i n t h e c a s e o f d e a l i n g w i t h an n-type m a t e r i a l , t h e d i f f e r e n t i a l method was t a k e n . 3

4. R e s u l t s

A. C y c l o t r o n Resonance. Both e l e c t r o n and h o l e c y c l o t r o n s i g n a l s have been examined i n t i m e - r e s o l u t i o n . The h o t c a r r i e r n a t u r e , however, i s

(4)

more e v i d e n t and e a s i e r t o ana- l y s e i n t h e e l e c t r o n s i g n a l . A c c o r d i n g l y , w e w i l l p u t more em- p h a s i s on t h e e l e c t r o n s i g n a l and l a t e r mention t h e h o l e s i g n a l j u s t b r i e f l y .

( a ) E l e c t r o n

A t i m e - r e s l o u t i o n s e r i e s o f p h o t o e x c i t e d e l e c t r o n c y c l o t r o n r e s o n a n c e o b t a i n e d a t 8 4 p m from t h e sample C (p-type) i s g i v e n i n F i g . 1. T h i s i s f o r weak e x c i t a - t i o n (1 p J p e r p u l s e ) i n which a l l t h e i n i t i a l l y produced h o l e s can b e accommodated i n t h e ac- c e p t o r s i t e s s o t h a t no h o l e s i g - n a l s a r e s e e n . The d e l a y - t i m e s a f t e r t h e t o p o f t h e p h o t o e x c i t a -

1.5 2.0 z5 t i o n p u l s e a r e i n d i c a t e d on t h e

M A G N E T I C F I E L D ( T )

r i g h t . A l l s i g n a l s d i s a p p e a r F i g . 1 Time-resolved c y c l o t r o n a f t e r a s u f f i c i e n t l a p s e o f t i m e .

resonance t r a c e s o f ~ h o t o e x c i t e d _The signal indicated ICR is the e l e c t r o n s i n t h e sample C

s o - c a l l i m p u r i t y c y c l o t r o n r e s o - nance314 a s s o c i a t e d w i t h t h e do-

l o n g l a p s e o f t i m e . I n o r d e r n o r s t a t e s , which e x i s t i n t h e p-type m a t e r i a l a s w e l l . Those i n d i c a t e d Cl and C2 a r e t h e con-

,

d u c t i o n e l e c t r o n c y c l o t r o n r e s - onance a r i s i n g from t h e t r a n s i -

-

t o s t u d y t h e p u r e l y t r a n s i e n t F i g . 2 Time v a r i a t i o n s o f v a r i o u s p r o c e s s o f t h e p h o t o e x c i t e d e- q u a n t i t i e s o b t a i n e d from F i g . 1

'<a A A A

* * ^A a

6t -

* *

A 1

O O o :

o

l e c t r o n s , a c c o r d i n g l y , u s e of a

t i o n s O+ + l+ and 0- + I , _U ⁰

where t h e numerals a r e t h e Lan-

:

^AI C R + C I .C2 -loo--

ICR r ^Y

dau quantum numbers and s i g n s _>

-

s t a n d f o r t h e s p i n o r i e n t a t i o n . ⁰c1

-

G.d

S i g n a l s a r e s i m i l a r i n n-type $ samples b u t one a r r i v e s a t t h e ₀₀₁ t h e r m a l e q u i l i b r i u m resonance

0 2 4 6 8 10 12 14 16

l i n e s of I C R and Cl a f t e r a D e l a y T i m e ( p s )

(5)

C7-396 JOURNAL DE PHYSIQUE

p-type sample i s more c o n v e n i e n t . Time dependence of v a r i o u s q u a n t i - t i e s o b t a i n e d from F i g . 1 i s g i v e n i n F i g . 2. The sum o f t h e s i g n a l i n t e n s i t i e s , ICT

+

Cl + C 2 , remains p r a c t i c a l l y c o n s t a n t f o r t h e f i r s t 10 p s and t h e n s t a r t s decaying a t a t i m e c o n s t a n t of % l 3 u s ( n o t v i s i - b l e on t h e time s c a l e of F i g . 1 ) . The r a t i o of t h e two conduction e-

l e c t r o n s i g n a l i n t e n s i t i e s , C2/C1, y i e l d s an e x p l i c i t i d e a o f e l e c t r o n t e m p e r a t u r e TE. T h a t a s h i g h a s 4 0 K h a s been achieved r i g h t a f t e r t h e p u l s e . The t i m e c o n s t a n t f o r c o o l i n g t o t h e l a t t i c e t e m p e r a t u r e TL i s found t o be s 6 . 5

u s .

When one i n c r e a s e s t h e e x c i t a t i o n i n t e n - s i t y s o as t o make t h e f r e e c a r r i e r s o v e r f l o w t h e i m p u r i t y s i t e s , r e s - onance l i n e s broaden and come t o a complete o v e r l a p p i n g r i g h t a f t e r t h e p h o t o p u l s e . The p h o t o e x c i t e d c a r r i e r s i g n a l i n t e n s i t y i s charac- t e r i s e d by an i n i t i a l f a s t decay, h a v i n g a t i m e c o n s t a n t of s 1 . 5 V s , common t o e l e c t r o n s and h o l e s , and a l s o n e a r l y common t o a l l t h e t h r e e samples. Then, such a p r o c e s s a s shown i n F i g . 2 f o l l o w s . For n-type m a t e r i a l s , t h e e v e n t u a l decay of t h e e l e c t r o n s i g n a l s i s v e r y slow, t h e o f f - e q u i l i b r i u m p a r t of t h e Cl a s w e l l a s ICR l i n e b e i n g observa- b l e even a f t e r t h e l a p s e of a few m i l l i s e c o n d s .

( b ) Hole

Within t h e magnetic f i e l d o f 5 T, o n l y two quantum l i n e s of h o l e c y c l o t r o n r e s o n a n c e , t h e t r a n s i t i o n s O O +- l1 and lO + 21, a f t e r t h e Hensel-Suzuki

notation^,^

a r e o b s e r v a b l e . These s i g n a l s have been o b t a i n e d w i t h t h e h e l p of t h e d i f f e r e n t i a l method. They a r e s e e n o n l y f o r t h e f i r s t r a p i d l y decaying s t a g e a f t e r an e x c e s s i v e e x c i t a t i o n , c h a r a c t e r i s e d by t h e t i m e c o n s t a n t o f 1 . 5 vs. The t r a n s i t i o n l O + 21 i s o u t o f s c a l e a t t h e FIR l a s e r wavelength o f 84 pm. The h o l e obser- v a t i o n h a s been e a s i e r i n n-type m a t e r i a l . T h i s tendency i s c o n s i s t - e n t w i t h o u r e x p e r i e n c e i n Ge and S i . The l i n e - s h a p e of t h e t r a n - s i t i o n l O +- 21 i s e x a m i n e d a t 2 2 0 pm and a l s o a t 1 1 9 um f o r t h e sample A

( n - t y p e ) . I t i s found t o be r a t h e r l i t t l e a f f e c t e d by e x c i t a t i o n i n - t e n s i t y . Assuming a p e r f e c t L o r e n t z i a n , t h e c o l l i s i o n r a t e o f h o l e s i s e s t i m a t e d t o be 1 . 8 X 10 l2 s - l f o r t h i s sample under s t r o n g ex- c i t a t i o n .

( c ) L u t t i n g e r Parameters

One by-product of t h e p r e s e n t p h o t o e x c i t e d c a r r i e r c y c l o t r o n r e s - onance experiment i s t h e d e t e r m i n a t i o n o f t h e L u t t i n g e r p a r a m e t e r s of t h e v a l e n c e band.'' I n terms of f o u r FIR l a s e r wavelengths, t h e mag- n e t i c f i e l d dependence of t h e c a r r i e r c y c l o t r o n masses i s examined f o r two h o l e quantum l i n e s and a l s o f o r e l e c t r o n c y c l o t r o n t r a n s i t i o n s Cl and C2 o b t a i n e d from t h e sample A. A j o i n t f i t t i n g p r o c e d u r e f o r h o l e s and e l e c t r o n s a f t e r t h e c a l c u l a t i o n by ~ i d ~ e o n - ~ r o w n l ~ y i e l d s a

(6)

new set of the Luttinger parameters;

namely, yL = 38.5 0.5, y2 L = l8.1 t 1.0 and y3 L = 18.0 0.7. These are somewhat different from the de-

Oj

termination by pidgeon-~rownl~ and

EZ1

that by Ranvaud e t al. Participation

g

of the electron signals, Cl and C2, a 0

in the determination of the valence

8

a band parameters is a distinct fea- O

ture of the photoexcitation experi-

5

ment

. E

^R

n

^4.2 ^K

Electric F i e l d

P h o t o e x c i t a t i o n ( t u n g s t e n lamp)

B. Cyclotron Emission. Cyclotron - - . . - - L d

0 1 2 3 4

emission from the photoexcited hot _MAGHETIC_FIELD _(T) electron system is observed very

clearly for the sample B (n-type).

Upon changing the magnetic field, a Fig. 3 Cyclotron emission by two different kinds of excita- peak appears when the cyclotron en- tion observed in the sample B ergy meets the maximum photoresponse

of the detector. A typical signal trace obtained by the tungsten lamp excitation (1 ms, 30 Hz) is given in Fig. 3 together with, for compar- ison, a signal obtained by the electric field excitation (1 ms, 30 Hz, 30 V/cm). To our knowledge, the cyclotron emission from the intrinsically photoexcited hot carriers has never been observed before. The xenon lamp excitation has met a poorer signal-to-noise ratio and a

long tail on the higher magnetic field side possibly reflecting the higher kH or higher Landau level cyclotron emission.

5. Discussion

One of the most striking features of the present research would be the long lifetime of the photoexcited carrier system. When electrons and holes are photoexcited in large quantity, a part of them will fill up all the ionised impurity centres. Then, free carriers d e t r o p

will recombine within themselves. The initial common time constant of 1.5 us observed in the case of a strong excitation seems to account for this process with possible inclusion of the recombination v i a exciton formation. The subsequent stage is considered to be reflecting the extremely long life of the neutralised donors. The excess electrons in this stage will be distributed, in quasi-equilibrium, over the donor states and the conduction band. They will eventually fall to the acceptor levels. The final stay before the fall would be at the donor states. The time spent till the last deneutralisation of

(7)

C7-398 JOURNAL DE PHYSIQUE

t h e a c c e p t o r s t a t e s may depend on t h e c o n c e n t r a t i o n , d i s t r i b u t i o n a n d t h e d e g r e e o f compensation o f t h e i m p u r i t i e s . I t would n o t b e t o o s u r p r i s i n g t o f i n d s u c h a l o n g d e c a y t i m e a s a few m i l l i s e c o n d s i n some sample.

6. C o n c l u s i o n s

Through o b s e r v i n g c y c l o t r o n r e s o n a n c e and c y c l o t r o n e m i s s i o n , t h e d e c a y p r o c e s s and t h e h o t n a t u r e o f t h e p h o t o e x c i t e d c a r r i e r s b o t h i n n- and i n p - t y p e I n S b h a v e b e e n examined. Long l i f e t i m e o f photo- e x c i t e d e l e c t r o n s , o f t h e o r d e r o f 10 US i n a p - t y p e a n d e v e n l o n g e r i n o t h e r n - t y p e m a t e r i a l s , h a s b e e n confim.ec? i n t h i s d i r e c t g a p s e m i - c o n d u c t o r . E l e c t r o n t e m p e r a t u r e c a n r e a d i l y b e e l e v a t e d above 40 K and a c o o l i n g t i m e o f s 6 . 5 u s h a s b e e n o b s e r v e d a t t h e l a t t i c e tem:

p e r a t u r e o f 4.2 K. J o i n t o b s e r v a t i o n o f e l e c t r o n and h o l e c y c l o t r o n r e s o n a n c e s y i e l d s a s l i g h t l y m o d i f i e d s e t o f t h e L u t t i n g e r p a r a m e t e r s f o r t h e v a l e n c e band.

R e f e r e n c e s

1. K . J . B u t t o n , B. Lax and C.C. B r a d l e y : Phys Rev. L e t t . 2 1 (1968) 350.

2 . R. Ranvaud, H.-R. T r e b i n , U. R o s s l e r and F . H . P o l l a k : Phys. Rev.

B20 (1979) 701.

3. K.L.I. Kobayashi and E . Otsuka: J. Phys. Chem. S o l i d s

35

(1974) 839.

4. 0. Matsuda and E. Otsuka: J. Phys. Chem. S o l i d s

40

(1979) 819.

5. R. U l b r i c h : Phys. Rev. B 8 (1973) 5719.

6 . E . Gornik: Phys. Rev. L e t t .

29

(1972) 595.

7. K.L.I. Kobayashi, K . F . Komatsubara a n d E . O t s u k a : Phys. Rev. L e t t . 30 (1973) 702.

8. J . C . H e n s e l a n d R. S u z u k i : Phys. Rev. ( 1 9 7 4 ) ~ 4219.

9. E. O t s u k a , K. Murase a n d J. I s e k i : J. Phys. Soc. J p n .

21

(1966) 1104.

10. E. O t s u k a , T . Ohyama a n d K . Murase: J . Phys. Soc. J p n .

5

(1968) 729.

.11. J . M . L u t t i n g e r : Phys. Rev.

102

(1956) 1030.

12. C.R. Pidgeon a n d R.N. Brown: Phys. Rev.

146

(1966) 575.