ELECTRONIC STRUCTURE OF Zn3As2 AND Cd3As2 FROM X-RAY SPECTRA

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ELECTRONIC STRUCTURE OF Zn3As2 AND Cd3As2 FROM X-RAY SPECTRA

E. Sobczak, H. Sommer

To cite this version:

E. Sobczak, H. Sommer. ELECTRONIC STRUCTURE OF Zn3As2 AND Cd3As2 FROM X-RAY SPECTRA. Journal de Physique Colloques, 1987, 48 (C9), pp.C9-1005-C9-1008.

�10.1051/jphyscol:19879179�. �jpa-00227294�

ELECTRONIC STRUCTURE OF Z n , A s , AND C d , A s , FROM X-RAY SPECTRA

E.

SOBCZAK and H.

SOMMER*

Institute of Physics, Polish Academy of Sciences,

A1.

Lotnikow 32/46, PL-02 668 Warsaw, Poland

" ~ e p a r t m e n t of Chemistry, Karl-Marx-University, Linnestrasse

2,

DDR-701 Leipzig, G. D. R.

The Zn K B z , ~ and As KB2 x - r a y e m i s s i o n s p e c t r a e x c i t e d by f l u o r e s - cence method and t h e Zn K and As K x - r a y a b s o r p t i o n s p e c t r a f o r Zn3As2 and Cd3As2 have been measured by u s i n g a d o u b l e - c r y s t a l x - r a y s p e c t r o m e t e r . The e l e c t r o n b i n d i n g e n e r g i e s f o r Zn3As2 and Cd3As2 have been o b t a i n e d f r o m x - r a y p h o t o e l e c t r o n s p e c t r a . The x - r a y b r e m s s t r a h l u n g i s o c h r o m a t s f r o m b o t h compounds a t t h e pho-

t o n e n e r g y o f 5415 eV have been a l s o s t u d i e d .

A l o t o f d a t a (1,2,3) i s a v a i l a b l e on t h e e l e c t r i c a l and o p t i c a l p r o p e r t i e s o f Zn3As2 and CdsAs2, b u t r e l a t i v e l y l i t t l e i s known a b o u t t h e e l e c t r o n i c band s t r u c - t u r e . The u l t r a v i o l e t and x - r a y p h o t o e l e c t r o n s p e c t r a o f Zn3As2 and Cd3As2 were r e - p o r t e d by B i s h o p e t a l . ( 4 ) . The e l e c t r o n energy l o s s s p e c t r a o f Cd3As2 were s t u d i e d by S c h u l z e ( 5 ) . The Zn La and As M 4 , 5 x - r a y e m i s s i o n s p e c t r a o f Zn3Asz were measured by Domashevskaya and Terekhov ( 6 ) . The Zn K a b s o r p t i o n s p e c t r u m o f Zn3As2 was s t u - d i e d by Adhyapak and N i g a v e k a r ( 7 ) . The t h e o r e t i c a l e n e r g y band s t r u c t u r e s o f Zn3Asz and Cd3As2 i n a h y p o t h e t i c a l f l u o r i t e s t r u c t u r e e m p l o y i n g t h e p s e u d o p o t e n t i a l method have been d e t e r m i n e d b y Lin-Chung ( 8 ) .

I n t h i s work we have i n v e s t i g a t e d t h e v a l e n c e and c o n d u c t i o n bands o f Zn3As2 and Cd3As2 u s i n g x - r a y s p e c t r o s c o p i c methods. The x - r a y e m i s s i o n and a b s o r p t i o n s p e c t r a were s t u d i e d b y means o f a d o u b l e - c r y s t a l x - r a y s p e c t r o m e t e r

(9)

equipped w i t h S i ( 2 2 0 ) c r y s t a l s . The FWHM's o f t h e (1,-1) r o c k i n g c u r v e s r e c o r d e d w i t h Ge Ka and B r Ka r a d i a t i o n were 0.8 eV and 1.0 eV r e s p e c t i v e l y . The x - r a y b r e m s s t r a h l u n g

i s o c h r o m a t s were measured a t t h e p h o t o n e n e r g y o f 5415 eV b y means o f . a n x - r a y vacuum s p e c t r o m e t e r d e s c r i b e d i n d e t a i l s i n R e f . 10. The x - r a y p h o t o e l e c t r o n s p e c t r a were measured u s i n g t h e VG ESCA-3 p h o t o e l e c t r o n s p e c t r o m e t e r .

Pol y c r y s t a l l in e p i e c e s o f Zn3As2 and Cd3As2 were powdered j u s t b e f o r e measure- ments. For t h e x - r a y a b s o r p t i o n measurements t h e powder was mixed w i t h a c e l l u l o s e powder and p r e s s e d i n t o a t a b l e t o f d i a m e t e r 20 rnm.

The Zn and As f l u o r e s c e n c e r a d i a t i o n was e x c i t e d w i t h a t u n g s t e n x - r a y t u b e . The W L B 1 and Zn e m i s s i o n l i n e s f r o m t u n g s t e n and z i n c m e t a l s were used f o r t h e c a l i b r a t i o n o f t h e e n e r g y s c a l e o f t h e Zn KB2,5 e m i s s i o n band s p e c t r a . The W LB1 e m i s s i o n l i n e f r o m t h e x - r a y t u b e would be superimposed w i t h t h e Zn K a b s o r p t i o n

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19879179

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spectrum, t h e r e f o r e we used a molybdenum x - r a y tube f o r t h e Zn K a b s o r p t i o n s t u d i e s , and t h e Au Lal emission l i n e from a v e r y t h i n g o l d f o i l f i x e d t o one o f t h r e e sample h o l d e r s was used f o r t h e c a l i b r a t i o n o f energy s c a l e o f t h e Zn K a b s o r p t i o n spectrum.

I n the case o f t h e As spectra the Br Kal, Br Ka2 and As KB1 were used as r e f e r e n c e l i n e s f o r the energy s c a l e c a l i b r a t i o n .

To m i n i m i z e e r r o r s i n t h e energy p o s i t i o n s o f each p a i r o f t h e Zn KP2,5 emission and As Kb2 emission, and As K a b s o r p t i o n s p e c t r a from two i n v e s t i g a t e d compounds, t h e measurements were done i n such a way, t h a t the three-sample h o l d e r moved stepwise and p u t samples i n t o p r i m a r y x - r a y beam s u c c e s i v e l y one by one f o r each a n g l e p o s i - t i o n o f t h e spectrometer.

To l o c a l i z e t h e Fermi l e v e l on t h e a b s o l u t e energy s c a l e o f t h e x - r a y s p e c t r a we have s t u d i e d t h e Zn KB1,3 and As KBl,3 emission l i n e s and the Zn 3p3/2 and As 3 p 3 / 2 b i n d i n g e n e r g i e s from p h o t o e l e c t r o n s p e c t r a .

TABLE 1. The b i n d i n g energies o f e l e c t r o n s o f Zn3As2 and Cd3As2 r e l a t i v e t h e Fermi l e v e l ( C I S c o r r e c t e d ) .

1 eve 1 ER (eV) l e v e l ER (eV)

I n F i g . 1 t h e Zn KB2,5 emission bands from Zn3As2 and Zn-metal and t h e Zn K a b s o r p t i o n spectrum from Zn3As2 a r e shown i n t h e a b s o l u t e energy scale. The emission s p e c t r a have been normalized w i t h respect t o t h e Z n KB1,3 emission l i n e s . The i n t e n - s i t y r a t i o o f t h e Zn KB2,5 and Zn K B I , ~ l i n e s i s equal t o 0.014 f o r Zn3As2. A f t e r t h i s n o r m a l i z a t i o n t h e i n t e n s i t y r a t i o o f t h e Zn KB2,5 emission from Zn3As2 t o t h a t from Zn-metal y i e l d s 1.08.

9640

€F 9680

photon energy lev)

FIG. 1 . The Zn KB2,5 emission s p e c t r a from Zn3As2 and Zn-metal, and t h e Zn K a b s o r p t i o n spectrum from Zn3As2.

11840

E~ ¹¹⁹⁰⁰

photon energy (eV)

FIG. 2. The As KB2 emission and As K a b s o r p t i o n spectra from Zn3As2 and Cd3As2 compounds.

l i z e d w i t h r e s p e c t t o t h e As e m i s s i o n l i n e s . The i n t e n s i t y r a t i o o f t h e As KB2 and As KBl,3 l i n e s i s much b i g g e r t h a n i n t h e case o f Zn Kf32,5 and i s equal t o 0.0564 and 0.0570 f o r Zn3As2 and Cd3As2 s p e c t r a r e s p e c t i v e l y , what means t h a t t h e v a l e n c e e l e c t r o n s a r e l o c a l i z e d around t h e As i o n i n t h e s e compounds.

The As K a b s o r p t i o n spectrum i s u n l i k e t o t h e Zn K a b s o r p t i o n spectrum f r o m Zn3As2, due t o a d i f f e r e n t symmetry o f t h e s u r r o u n d e n i n g f o r b o t h t y p e s o f i o n s : Zn i o n s a r e t e t r a h e d r a l l y c o o r d i n a t e d and each As i o n i s surrounded by Zn i o n s a t s i x o f t h e e i g h t c o r n e r s o f a d i s t o r t e d cube.

-

_In

g

1 FIG. 3. The x - r a y b r e m s s t r a h l u n g

-

isochromats from Zn3As2 and Cd3As2 ^2.

a t t h e photon energy o f 5415 eV.

c al

4- C

.-

0 20

energy above Fermi level (ev)

The x - r a y b r e m s s t r a h l u n g isochromats ( B I S ) f r o m Zn3As2 and Cd3As2 ( ~ i g .

3 )

show t h e d i s t r i b u t i o n o f e l e c t r o n s t a t e s i n t h e c o n d u c t i o n band. I t was d i s c o v e r e d (111, t h a t t h e BIS s p e c t r a a t t h e photon energy o f 5415 eV show m a i n l y t h e d e n s i t y o f p - t y p e e l e c t r o n s t a t e s due t o symmetry dependent c r o s s - s e c t i o n s f o r BIS.

-20 -10 0 0 20

energy relative Fermi level (eV) energy above Ferrni level (eVf

F I G . 4 . C o m p a r i s o n o f t h e x - r a y e m i - F I G . 5 . C o m p a r i s o n o f t h e x - r a y a b s o r - s s i o n s p e c t r a from Zn3As2 w i t h t h e p t i o n s p e c t r a w i t h t h e x - r a y bremsstrah- x - r a y p h o t o e l e c t r o n spectrum r e p o r t e d l u n g isochromat f r o m Zn3As2.

by B i s h o p e t a l . ( 4 ) .

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I n F i g . 4 we compare o u r x - r a y v a l e n c e band s p e c t r a o f Zn3As2 w i t h t h e x - r a y p h o t o e l e c t r o n spectrum (XPS) by B i s h o p e t a l . ( 4 ) . The x - r a y K emission s p e c t r a g i v e i n f o r m a t i o n on t h e p - t y p e v a l e n c e s t a t e s o n l y , whereas t h e XPS spectrum shows t h e t o t a l d e n s i t y o f s t a t e s modulated by t h e symmetry dependent c r o s s - s e c t i o n s l i k e i n t h e case o f BIS.

I n t h e case o f Zn3As2 we have g o t i n t h i s work a f u l l i n f o r m a t i o n on t h e p - t y p e d e n s i t y o f s t a t e s i n t h e v a l e n c e and c o n d u c t i o n bands ( ~ i ~ . 4 and 5 ) . From compari- son o f t h e x - r a y a b s o r p t i o n s p e c t r a w i t h BIS we can i n t e r p r e t t h a t t h e p - s t a t e s i n t h e c o n d u c t i o n band a r e l o c a l i z e d m a i n l y around Zn ions, whereas i n t h e v a l e n c e band they a r e l o c a l i z e d around t h e As i o n s .

Acknowledgment

We t h a n k P r o f e s s o r W . Zdanowicz f o r s u p p l y i n g t h e Zn3As2 and Cd3As2 samples.

References

1 . W. Zdanowicz, I I -V Compounds, i n : L a n d o l t - B G r n s t e i n , New S e r i e s , Group I l l , V o l . 17/e, s p r i n $ e r Y V e r l a g , B e r l i n , 1983, pp. 178-249.

2. V.B. Lazarev, V.Ya. Shevchenko, Ya.H. G r i n b e r g and V.V. Sobolev, Semiconductor Compounds o f t h e A ~ Group ( i n Russian), Nauka, Moskva, B ~ 1978.

3. P r o c . F i r s t I n t e r n . Symp. Phys. Chem. I I-V Comp., M o g i l a n y (Poland), 1980, e d i t e d by M.J. G e l t e n and L. Zdanowicz, Eindhoven U n i v . , Eindhoven, 1981.

4. S . Bishop, N. Shevchik and M. Cardona, Proc. I V I n t e r n . Conference on Vacuum U l t r a v i o l e t R a d i a t i o n P h y s i c s , Hamburg, 1974, p. 497.

5. S . S c h u l t z e , i n Ref. 3, p.115.

6. E.P. Domashevskaya and V.A. Terekhov, Proc. X84 Confer. on X-Ray and I n n e t - S h e l l Processes i n Atoms, M o l e c u l e s and S o l i d s , e d i t e d by A. M e i s e l and J . F i n s t e r , K a r l - M a r x - U n i v e r s i t z t , L e i p z i g , 1984, pp. 357-374.

7. S.V. Adhyapak and A.S. N i g a v e k a r , J . Phys. Chem. S o l i d s

2

(1978) 171.

8. P.J. Lin-Chung, Phys. Rev.

188

(1969) 1272.

9. J. T i l g n e r , Exp. Tech. Phys. 24 (1976) 289.

10. E. Sobczak and K. Persy, phys=a S c r i p t a

2

(1980) 88.

1 1 . E. Sobczak and J. A u l e y t n e r , ( t h i s c o n f e r e n c e ) .