ESR and x-ray analysis of the ternary semiconductors CuAlS2, CuInS2 and AgGaS2

Solid State Communications,

Vol. 12, pp. 48 1—483, 1973.

Pergamon Press.

Printed in Great Britain

ESR AND X-RAY ANALYSIS OF THE TERNARY SEMICONDUCTORS CuAIS2, CuInS2 AN]) AgGaS2 G. Brandt, A. Räuber and J. Schneider Institut für Angewandte Festkorperphysik der Fraunhofer-Gesellschaft, Freiburg i. Br., Germany (Received 13 November 1972 by M Cardona) 3~-impurityions in CuA1S The electron spin resonance (ESR) of Fe 2, CuInS2 and AgGaS2 has been analysed. In addition, the crystallographic parameters a, c and x~.were determined by X-ray diffraction techniques.

WE HAVE recently shown the capabilities electron spin resonance (ESR) has in structure analysis of the large of ternary semiconductors which crystallize in theclass tetragonal chalcopyrite (ch) structure, 142d. This was demonstrated by an ESR-analysis of the representative system CuGaS 3~.1 2 Fe In this letter, we want to present complementary data for the isomorphous compounds CuA1S 2, CuInS2 and AgGaS 2. The experimental procedure was the same as that described in reference(1).

measuring the angular dependence of an ESR line upon rotating the crystal around itsthe tetragonal with 1 Under this geometry, magneticc-axis, inequivaHi lencec. of the two metal sites in the ch-structure can be seen by a splitting of a fine Structure transition. This then also enables a very direct determination’ of the clockwise and counterclockwise rotation of the sulfur ligand tetrahedra around their common c-axis by the 3~).At an ideal trivalent metal site, the angle ±r(Fe angle r is related to the free parameter of the ch-structure,x1, by the expression’

Single crystals of CuAIS2, CuInS2 and AgGaS2 were grown by chemical transport reaction. As in the case of CuGaS2, it was found traces of iron impurities in these crystals leadthat to strong absorption

tg T

4x,—1 4 Xf

(2) 3~.signals

site for splitting couldThe notmagnetic be resolved CuInSof the Fe 2, because of the large inhomogeneous broadening of the ESR lines resulting 5 ligands. Here, from the nuclear moments of the In” the width of the central —1/2 + 1/2 fine structure transition was 58G forHllc. The corresponding values for CuGaS2 and AgGaS2 arevalues muchwere smaller, 17, CuA1S2, 34 and 16G, respectively. These determined at 77K. At lower temperature, no further line narrowing was observed. A summary of ESR parameters determined for Fe3~.impurityions on, presumably,

in the visible spectral region.’ For AgGaS2, this effect was lessions pronounced. Typical of Fe~-impurity on trivalent sites inESR-spectra CuA1S 2, CuInS2 and AgGaS2 recorded at 35GHz, at 77K and under HLIc are shown in Fig. 1. For comparison,3~has the previously also been reported’inspectrum of CuGaS2 : Fe are described by included Fig. 1. The ESR-spectra the spin Hamiltonian appropriate to Fe3~-ionsin tetragonal symmetry,’ =

=

—*

g~3H S +D(S~ 35/12)

trivalent metal sites in CuAIS

—

AgGaS2 is given in Table 1.

+(7/36)F[S~ —(95/l4)S~+ 81/16] + (a/6) [S~+ S~+ S 707/16]. (1)

2, CuGaS2 ~ CuInS2 and

We have also determined the crystallographic parameters of these compounds using X-ray diffraction techniques: The lattice constants a and c were evaluated using Debye-Scherrer powder data and the computer

—

From the spectrum Hjjc, the quantitiesg,,D and a + (2/3)Fwere obtained. The cubic crystal field parameter, a, can be determined independently by

program package X-RAY-SYSTEM. This program 481

482

ESR AND X-RAY ANALYSIS OF CuAIS2, CuInS2 AND AgGaS2

Vol. 12, No.6

3~in ternary type XYS Table 1. ESR parameters ofFe hosts,ofatthe 77K, Crystalfield are giveh 4cm1. Their sign has been determined2tochalcopyrite be equal to that cubic parameter parameters a which is known to in units of 10 be positive’ CuA1S 2 CuGaS2 CuInS2 AgGaS2 g, D

2.020(1) 900(1)

2.024(1) 1886(1)

2.022(1) 990(2)

2.019(1) 4871(2)

a+~-F 90(1) 103(1) 66(2) 71(2 3~)I 5.l(l)° 5.l5(lO)° 10.9(2)° jr(Fe Table 2 Crystallographic parameters of CuA IS 2, CuGaS2,’ Cu!nS2 and AgGaS2 determined —

by X-ray diffraction at 300K CuAIS2 a(A) c(A) Xf

c/a3~) r(Me

5.3336(5) 10.444(2) 0.268(4) 1.958 + 2.10(4)

CuGaS2 5.351(1) 10.480(5) 0.272(5) 1.958 +2.6°(6)

Cu! nS2

AgGaS2

5.523(4) 11.12(2) 0.214(7) 2.013 —3.8°(7)

5.754(2) 10.295(6) 0.304(6) 1.789 +6.9°(6)

Table 3. Interatomic bond distances, in A units, and bond angles ofthe ternary type XYS 2 chalcopyrite compounds Cu.4 iS2, CuGaS2, CuInS2 and AgGaS2, as evaluated from the X-ray diffraction data quoted in Table 2

*

*

*

X—S Y—S S—X—S S—X—S S—Y—S S—Y----S

CuA1S2

CuGaS2

CuInS2

AgGaS2

2.351 2.239 112.5° 108.0° 108.7°

2.372 2.235 112.9° 107.8° 108.2° 110.1°

2.288 2.517 105.2°

2.605 2.235 120.6°

111.60

104.10

112.9°

109.7°

107.70

109.30

109.90

S—S axis perpendicular to the c-axis.

package was also used together with intensity data, obtained by conventional Buerger precession techniques (MoKa), to evaluate the free parameter Xf. Results are given in Table 2. The values quoted for a and c are in fair agreement with previously 2 It should be those emphasized that reported by Hahn et data at were obtained on samples of our crystallographic rather high crystalline perfection. This is evidenced by the order of magnitude agreement in linewidth of the fine structure transitions for a given host, see Fig. 1. In particular, serious deviations from stoichiometry can not be prominent in our samples, since they would lead to a strong broadening of the outer fine structure transitions.

Once a, c and X, are known, all interatomic bond distances and bond angles can be determined for a ch-compound. Representative data are given in Table 3. It is noted that deviations from perfect tetrahedral sulfur ligand geometry are much more severe around I than around a group covalency III metal ion. This is aa group consequence of the stronger of the latter. The effect is even more pronounced for metal ions in group II—IV—V 3 and CdSiP 2 compounds, as ZnSIP2 2

.~

In a rigid sphere lattice model, a deviation of the free parameter from its ideal value of 1/4 is directly related to the difference in radii of the monovalent and trivalent metal ions. Thus, the exceptionally large value of x~—l/4,observed for A8GaS2, and its negative X~

ESR AND X-RAY ANALYSIS OF CuAIS2, CuInS2 AND AgGaS2

Vol. 12, No.6

483

stood. sign, observed for CuInS2, can be qualitatively under-

CuALS2:

—~-—---4—-.—4-—--—~-— H (Gauss)

5000

CuGaS

10000

20000

from the X-ray diffraction data. These discrepancies may possibly be accounted for by admitting a slight displacement of the sulfur ligands around the Fe3~-impurity ion from the normal position they had around a Me3~-hostlattice site. This distortion can not alter the local symmetry at the Fe3~-impuritysite, but would lower the symmetry of its sulfur ligands.

3 2

Fe

A9GaS

Acknowledgements We wish to thank F. Friedrich for growing the crystals and K. Sambeth for technical assistance in taking the ESR-data.

3~ 2

I

15000

Trends indicated for some of the ESR-parameters listed in Table 1 are not in direct agreement with expectations derived from the crystallographic data. For example, the unusual large value found for the axial field parameter D in AgGaS2 is surprising, in view of the almost ideal tetrahedral sulfur arrangement around 3~), as determined by In ESR, are seen be systematically the gallium site.* addition, thetotilting angles r(Fe larger than the host lattice values, r(Me3~),as derived

—

Fe

I

I

5000

10000

I

—

15000

20000 H(Gouss)

FIG. 1. ESR-spectra of Fe3~-ionsin CulnS 2, CuAIS2, CuGaS2 and AgGaS2, recorded under c at 35GHz and 77K. The maximum field strength of the magnet was 17kG. Thus, some lines in the ESR-spectrum of large CuGaS2 value ofD. and AgGaS2 For AgGaS are missing, because of the 2, this leads to a reversal of the usual order of the fine structure transitions.

Ru

*

In contrast to the ESR-data, but in agreement with 69 nuclear quadrupole coupling constant is deexpectations based on the crystallographic structure, the Ga finitely smaller in AgGaS2 than in CuGaS2 HAEBERLEN U. and SPIESS H.W., Private communication.

REFERENCES 1. 2.

SCHNEIDER J., RAUBER A. and BRANDT G., J. Phys. Oiem. Solids, in press. HAHN H., et aL,Z. anorg. aug. Chem. 271, 153 (1953).

3.

ABRAHAMS S.C. and BERNSTEIN J.L.,J. chem. Phys. 52, 5607 (1970).

4.

ABRAHAMS S.C. andBERNSTEIN J.L.,J. chem. Phys. 55, 796(1971). 3~-Fremdionenwurde in CuAIS Die Elektronen Spin Resonanz von Fe 2, CuInS2 und AgGaS2 analysiert. Zusätzlich wurden die kristallographischen Parametera, c und x,. bestimmt.