Philips Res. Repts 17, 513-517, 1962

R 465

ELECTRON-SPIN RESONANCE OF Fe IN GaAs by R. BLEEKRODE,

J. DIELEMAN

and H. J. VEGTER 539.124.142: 546.68'19

Summary Electron-spin resonance measurements have been carried out at 77 "K on single-crystal GaAs doped with Fe. The resonance patterns can be explained by assuming that Fe3+ ions are on substitutional sites of the GaAs lattice. The spin Hamiltonian parameters are found to be g = 2.0424 ± 0·0004 and lal = (330 ± 2). 10-4 cm-I. Good agreement is found between the value of a determined directly from the finesplitting of the lines and that determined from the angular dependence of the line positions. Résumé Des mesures de la résonance paramagnétique ont été effectuées à 77 "K dans un monocrystal GaAs dopé de Fe. La structure de la résonance s'explique par le fait qu'il se trouve des ions de Fe3+ sur les endroits du réseau crystallin. Comme constantes du spin hamiltonien on a trouvé g = 2.0424 ± 0·0004 et lal = (330 ± 2). 10-4 cm-I. La valeur a directement déduite de la structure fine correspond très bien à la valeur déduite de la disposition des lignes en fonction de I'angle formée par I'axe du crystal et le champ magnétique statique. Zusammenfassung Die Elektronenspinresonanz wurde bei 77 "K in einem mit Fe dotiertem GaAs-Einkristall gemessen. Die Struktur und Winkelabhängigkeit dieser Resonanz lassen sich dadurch erklären, daB sich Fe3+-Ionen auf Gitterplätzen befinden. Als Spin-Hamilton-Konstanten wurden gefunden g = 2·0424 ± 0·0004 und lal = (330 ± 2).10-4 cm-I. Der direkt aus der Feinstruktur gefundene Wert a stimmt gut mit dem aus der Winkelabhängigkeit der Linienlage gefundenen überein.

1. Introduetion During the last few years a number of electron-spin resonance experiments on impurities in semiconductors have been carried out 1,2). In this way valuable information about the position and charge distribution of the impurities has been obtained. In the case of GaAs, preliminary investigations were recently reported for Mn 3,4), Fe 5) and Ni 5). In this paper we describe the results of electron-spin

resonance

2. Experimental

studies on Fe in GaAs.

part

Single-crystal GaAs was doped with Fe by horizontal zone melting. Electrical measurements revealed the doped material to be high-ohmic partly compensated

p-type. A crystal was oriented with the aid of X-ray reflexion techniques. A {IlO} plane and a {11I} plane perpendicular to this {110} plane were cut from the crystal.

514

R. BLEEKRODE.

J. DIELEMAN

and H. J. VEGTER

Measurements were carried out with a Varian V 4500 E.P.R. Spectrometer operating at ')I = 9221 ± 1 Mcfs using 100 kcfs magnetic-field modulation: Spectra were taken at 77 "K for various orientations of the crystal with respect to the static magnetic field. The different orientations were obtained by rotating the crystal about a (110) direction which was kept perpendicular to the static magnetic field. Four typical spectra are shown in figs 1 to 4. These spectra were obtained in the derivative form by scanning the static magnetic field. The additional six sharp lines are due to Mn2+ in cubic-ZnS powder a small quantity of which was added for calibration purposes; e is the angle between the static magnetic field H and a cubic axis.

r

I

Fig. 1. Derivative of the electron paramagnetic resonance absorption signalof Fe in GaAs for e = 0°. The deviations from the base line are due to the presence of small amounts of oxygen and ice in the cooling bath.

Î

dA -dH

~

~M

....wv-

\..

."1"

~ I25OOe,

-H 9=28°

'-Ho

_. Fig. 2. Same as fig. 1;

e = 28°.

ELECTRON-SPIN

515

RESONANCE OF Fe IN GaAs

9"'.1

Fig. 3. Same as fig. 1;

e = 55°.

t

dA

-dH

-H 9=90°

9H2

Fig. 4. Same as fig. 1;

e = 90°.

Additionallines with lower intensity were found at very low magnetic fields. The behaviour of these lines has not yet been investigated. 3. Interpretation

The pattern in fig. 1 closely resembles the pattern one can expect theoretically for a 3d5 configuration in a cubic crystalline field with the static magnetic field parallel to a cubic axis. In this case it is known that the ratio of the splitting between the first and fifth, and the second and fourth fine-structure lines is 5 : 4 up to second-order terms in the fine-splitting parameter. The ratio was

516

R. BLEEKRODE.

J. DIELEMAN

and H. J. VEGTER

found to be 5·00 : 3·98. For the given configuration one can also deduce that the ratio of the intensities of the various fine-structure lines is 8 : 5 : 9 : 5 : 8. Experimentally we found 8 : 5 for the ratio of the intensities of the first and second as well as for the :fifthand fourth fine-structure lines. The intensity of the central line was found to be somewhat larger than expected. According to Kronig and Bouwkamp 6) the positions of the fine-structure lines in the case of lal «f3H are given by the following formulas: 1 Transition - - --7 2 H = Ho Transitions

H

2

10

+ -3

3

±-

2

H = Ho .. Transitions

1

+ -:

5 2

±-

a2 4> (7 - 25 4» Ho

+ ... ,

1

+- -+

5

±-

2

+--+

= Ho =r=

± -: 2

(1-

54» a - -

5

~

(3

+ 178 4> -

625 4>2)

~

(1)

-,+ ..., ~

3 2

±-:

2 (1- 5 4» a

+ -53 4> (1-

a2

7 4» -

Ho

+ ... ,

where 4> = al2a22 + a22a32 + a32al2 and al, «a and a3 are the direction cosines of the static magnetic field with respect to the cubic axes. Further, Ho is defined by hv = gf3Ho and a is the cubic-field-splitting parameter. Higher-order terms could be neglected in this case. The absolute value of a deduced from fig. lis equal to lal = (330 ± 2). 10-4 cm-I. To see whether the angular dependence of the positions of the fine-structure lines agrees with the expected dependence, this value of a was substituted in (1). The calculated line positions are given in fig. 5 (solid lines) and we see that the experimentalline positions indicated by crosses fit these curves fairly well. The isotropic g value is found to be g = 2·0424 ± 0·0004. For e = 0°, the line width of the centralline is 51·6 oersteds and the line width of the othér lines 53·4 oersteds. The width reported by De Wit and Estle 5) for 1·3 OK amounts to 54 oersteds. A comparison between these values suggests that this width is entirely due to the interaction of the magnetic moment of the Fe3+ impurity with the magnetic moments of Ga and As. The values reported by De Wit and Estle for a and gat 1·3 OK are lal = (340 ± 1). 10-4 cm-I and g = 2·0453 ± 0·0006. The .differences may be attributed to the lower temperature at which their measurements were carried out. Our results indicate that Fe3+ ions are incorportaed on substitutional sites of the GaAs lattice.

,---------------------------ELECTRON-SPIN

RESONANCE

-

517

OF Fe IN GaAs

90°',..-----,----

e

t

00 2200

LT +-'-----L--i 2500

j~

i~~

3000 Ho 3400 3800 --_ H (Oersteds)

4200 ,H)

Fig. 5. Angular dependence of the positions of the fine-structure lines.

Acknowledgement The authors wish to thank Mr Th. P. M. Meeuwsen ofthe X-ray department for careful orientation of the crystal and Mr O. van Ommeren for his skilful help with the experiments. Eindhoven, October 1962

REFERENCES 1) G. W. Ludwig 2) 3) 4) 5) 6)

and H. H. Woodbury, Solid State Physics, Vol. 13, edited by F. Seitz and D. Turnbull, Academic Press Inc., 1962, p. 223. J. S. van Wieringen, Progress in Semiconductors 6, 201-231, 1962. N. Almeleh and B. Goldstein, Bull. Am. phys. Soc. 7, 250, 1962. R. Bleekrode, J. Dieleman and H. J. Vegter, Physics Letters, 2, 355-356, 1962. M. De Wit and T. L. estle, Bull. Am. phys. Soc. 7, 449, 1962. R. de L. Kronig and C. J. Bouwkamp, Physica 6, 290-298, 1939.