RAMAN STUDIES OF THE P LOCAL MODE VIBRATION IN P IMPLANTED, LASER ANNEALED Ge

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RAMAN STUDIES OF THE P LOCAL MODE

VIBRATION IN P IMPLANTED, LASER ANNEALED Ge

G. Contreras, A. Compaan, A. Axmann

To cite this version:

G. Contreras, A. Compaan, A. Axmann. RAMAN STUDIES OF THE P LOCAL MODE VIBRA-

TION IN P IMPLANTED, LASER ANNEALED Ge. Journal de Physique Colloques, 1983, 44 (C5),

pp.C5-193-C5-195. �10.1051/jphyscol:1983530�. �jpa-00223115�

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JOURNAL DE PHYSIQUE

Colloque C5, suppl6ment au nO1O, Tome 44, octobre 1983 page C5-193

RAMAN STUDIES OF THE P LOCAL MODE VIBRATION IN P IMPLANTED, LASER ANNEALED G e

G. contreras', A. Cornpaan ++ and A. Axmann*

Max-Planck-Institut ~ % r Festktrrperforschung, Heisenbergstr. 1, 7000 S t u t t g a r t 80, F.R.G.

"Fraunhofer-Institut far Angewandte FestkD~perphysik, E c k e r s t r . 4, 7800 Freiburg, F.R.G.

Resume

-

Nous presentons l e s p e c t r e Raman des v i b r a t i o n s l o c a l i s e e s du phos- p h o r e i m p l a n t e s u b s t i t u t i o n e l lement dans 1 e germanium e t recui t par l a s e r . Le

haut taux de dopage, s u p e r i e u r

a

l a s o l u b i l i t e dans l e volume, permet l ' o b s e r - vation de c e s s p e c t r e s de f a i b l e i n t e n s i t e . Nous en avons determine l a v a r i a - t i o n de l a s e c t i o n e f f i c a c e en f o n c t i o n de l a longueur d'onde du l a s e r . A b s t r a c t

-

We r e p o r t t h e f i r s t observation by Raman s c a t t e r i n g by t h e loca- l i z e d v i b r a t i o n a l mode of P i n P implanted and pulsed l a s e r annealed Ge. The

heavy dose ion implantation followed by pulsed l a s e r annealing have allowed us t o achieve P d e n s i t i e s exceeding t h e normal s o l i d s o l u b i l i t y l i m i t s i n Ge, a f a c t which i s e s s e n t i a l f o r t h e l o c a l mode observations. We have obtained information about t h e p o s i t i o n and i n t e n s i t y of t h e P local mode a s a f u n c t i o n o f t h e implantations dose and i t s resonant Raman behavior a s a f u n c t i o n of l a s e r photon energy.

The band s t r u c t u r e of semiconductors i s changed l i t t l e by t h e presence of high con- c e n t r a t i o n s hydrogenic donor o r acceptor atoms /1,2/. However, i f t h e s e atoms a r e l i g h t e r than t h e h o s t atoms, l o c a l i z e d v i b r a t i o n a l modes can appear a t frequencies above t h a t of t h e Raman phonons / 3 / . Many of t h e s e l o c a l modes have been observed by means of i r a b s o r p t i o n , Raman observations have been l i m i t e d t o boron i n Si /4/.

In t h i s paper we r e p o r t t h e f i r s t observation by Raman spectroscopy of a v i b r a t i o n a l l o c a l mode i n germanium, namely t h a t of s u b s t i t u t i o n a l phosphorus. The samples were P-implanted ( a t 190 keV) and excimer l a s e r annealed /5/ t o produce germanium l a y e r s - - of an estimated t h i c k n e s s %300 nm and dopant concentrations Ne between 2 x 10" and 1 x 10" ~ m - ~ . Doping by implantation was found t o be a b s o l u t e l y necessary f o r t h i s work; previous attempts t o observe t h e l o c a l mode i n bulk doped samples f a i l e d on - . account of t h e small s o l u b i l i t y of P i n Ge (d x 10'' cm-3

1.

Figure 1 shows t h e room temperature Stokes s p e c t r a of t h e Raman phonons and t h e l o c a l mode o f P f o r t h r e e samples with d i f f e r e n t implantation doses. For t h e s e samples t h e phonon obeyed (T2J s e l e c t i o n r u l e s f o r t h e o r i e n t a t i o n of t h e sub- s t r a t e s , t h u s i n d i c a t i n g good epitgxy. The local symmetry around t h e impurity atom i s TZd ( t e t r a h e d r a l ) . Thus t h e local mode should have r15(T1) symmetry. The Raman se- l e c t i o n r u l e s f o r t h i s mode a r e t h e same a s those f o r t h e

rZ5,

phonon. The local 'permanent address :

DADD Fellow, on leave from E.S.F.M.

-

^I.P.N. ^Mexico

++ Permanent address :

Von Humboldt Foundation Fellow, on leave from Kansas State University, Dept. of Physics, Cardwell Hall, Manhattan, Kansas 66506, U.S.A.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1983530

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C5-194 JOURNAL DE PHYSIQUE

mode, however, i s i r - a c t i v e /6/ w h i l e t h e phonon i s n o t . F o r t h e two samples w i t h t h e

-

1

l o w e s t doses t h e l o c a l mode peaks a t 336 t 1 cm

.

^{I t}s h i f t s t o 342

+

1 cm-I f o r t h e sample w i t h 6 x 1016 2

P/cm

.

I n f r a r e d s p e c t r a o f Li-compensated P-doped Ge show a l o c a l mode a t 343 cm-I a t l i q u i d n i t r o g e n t e m p e r a t u r e /6/. We n o t e t h a t t h e t h r e e s p e c t r a o f F i g . 1 show no s h i f t i n t h e phonon f r e q u e n c y o f t h e doped l a y e r w i t h r e - s p e c t t o t h a t o f p u r e Ge (300 cm-'), i n agreement w i t h p r e v i o u s work a t l o w e r d e n s i -

t i e s / 7 / . The l o c a l mode f r e q u e n c y can be o b t a i n e d f r o m t h e s i m p l i f i e d mass d e f e c t s e c u l a r e q u a t i o n / 8 / :

w h i c h assumes t h a t t h e f o r c e c o n s t a n t s a r e t h e same f o r P-Ge as f o r Ge-Ge p a i r s . I n Eq. (1) wM = 280 cm-I i s t h e f r e q u e n c y o f t h e maximum i n t h e d e n s i t y of TO phonons and E = 1-Mp/MGe = 0.57 t h e mass d e f e c t parameter. E q u a t i o n ( 1 ) y i e l d s f o r t h e l o c a l mode f r e q u e n c y o f P i n Ge up = 340 cm-I i n r a t h e r good agreement w i t h t h e ex- p e r i m e n t s . The i n c r e a s e o f up f o r t h e h i g h e s t i m p l a n t a t i o n dosage may be due t o de- v i a t i o n f r o m t h e i s o l a t e d P-atom model i m p l i c i t i n Eq. ( I ) , i . e . , t o t h e presence of P-P p a i r s .

RAMAN SHIFT (cm-')

16 16 2

F i g . 1

-

Raman s p e c t r a o f t h e P l o c a l mode f o r t h e 1 x 10 /cm2, 2 x 10 /cm and 6 x 1i16/cm P i m p l a n t e d and p u l s e l a s e r annealed Ge. E x c i t i n g l a s e r l i n e 2 h =

5682

.

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We have measured t h e s p e c t r a of F i g . 1 f o r v a r i o u s l a s e r f r e q u e n c i e s between 1.8 and 3 . 1 eV. F i g u r e 2 shows t h e r a t i o o f t h e i n t e g r a t e d s t r e n g t h o f t h e phonon t o t h a t o f t h e l o c a l mode v e r s u s l a s e r photon energy. The maximum seen i n F i g . 2.2 eV c o r r e s - ponds t o t h e resonance o f t h e phonon between t h e El and t h e El

+

Al gaps / 9 / . Thus t h e phonon r e s o n a t e s much more s t r o n g l y t h a n t h e l o c a l mode, a f a c t which must be a t t r i b u t e d - t o k - n o n c o n s e r v a t i o n i n t h e Raman s c a t t e r i n g mechanism o f t h e l o c a l mode.

PHOTON ENERGY ( e V )

F i g . 2

-

R a t i o o f t h e i n t e g r a t e d Raman i n t e n s i t y o f t h e zone c e n t e r o p t i c a l phonon o f Ge t o t h e P l o c a l mode f o r d i f f e r e n t photon e n e r g i e s o f t h e e x c i t i n g l a s e r l i n e . The sample used was P i m p l a n t e d (dose 6 x 1016 and l a s e r annealed Ge.

ACKNOWLEDGEMENTS

We would l i k e t o thank T.P. M a r t i n f o r t h e use o f t h e excimer l a s e r , G. K i s e l a f o r s u b s t r a t e p r e p a r a t i o n , and H. B r e i t s c h w e r d t f o r i n f r a r e d measurements.

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