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The facet effect in epitaxial GaAs
Solid State Communications, Vol. 5, pp. 727-729, 1967. Pergamon Press Ltd. Printed in Great Britain
THE FACET EFFECT IN EPITAXIAL GaAs B.D. Joyce andJ.B. MuIItn Royal Radar Establishment, Malvern, Worcs., U.K. (Received 29 June 1967 by C.W. McCombie)
Direct evidence for a vapour growth “Facet-Effect” has been obtained using Te during the epitaxtal deposition of gallium arsenide. The effect is a feature of growth on several low-index planes. •~
IN THE melt-growth of semiconductor crystals the Facet Effect is an established and well investigated phenomenon. The effect is the spedftc characteristic change which occurs in the 4 value of the interface coefficient when the nature of thedistribution growth surface changesk from a non-faceted type to a faceted type. The change from a non-faceted surface to a faceted surface may represent a change in the orientation of the surface of only a fraction of a degree. The facet effect is therefore a special case of the orientation-dependence of k*. Facets of type [1111 or [1111 show marked effects for various solute elements in indium antimonide1, germanium2, gallium antimonide3 and gallium arsenide.4 6 A (100) facet effect for the case of tellurium in indium antimontde8 which is almost as large’ as the (111) facet effect has also been reported. The phenomenon is probably a significant feature of the faceted growth of all materials and is not confined to semiconductor crystals; yttrium aluminium garnet9, for example, shows the effect, Although the facet effect is conventionally associated with the melt-growth of crystals direct evidence that an equivalent phenomena can occur in the vapour growth of the crystals has now been obtained. The presentation of this evidence is the purpose of this communication,
crystals were first vapour etched in situ to remove approximately 5 ~.xfrom the surface. This was done by maintaining the source at 800°Cand the seed C. byThen an epitaxtal layer wasto grown on atthe850° seed reducing its temperature 750°C. Approximately 10 ii thick ‘~ Te doped layers were deposited on to (Ill) Ga seeds at the rate of 20 ~i/hr. Seed crystals which were ortentated to within a quarter of a degree of a singular plane generally developed an epitaxial layer which had adjacent regions of both faceted and non-faceted growth. The distribution of ~Te in these layers was then recorded by placing the epttaxial surface in contact with Microtex X-ray film for a suitable period and then developing the autoradiograph by the recommended method. The resuits obtained from growing a typical layer on a (Ill) Ga orientated substrate are shown in Figs. 1(a) and 1 (b). -
The photographic evidence of the development of the (III) Ga facet in Fig. 1 (a) can be compared with the autoradiographic evidence of the ~6Te distribution in Fig. 1(b). The identity of the (III) Ca facet was confirmed by careful X-ray measurements. The shape and extent of the region of faceted growth is exactly equivalent to that of the region of higher “~6Teconcentration which extends a quarter of the way across the slice from one side. Additionally, right at the edge of the three corners of the triangularshaped slice are narrow outlines representing very Te-rich growth; these regions are the result of growth on small edge facets of the type equivalent to till) As. It is clear that although
The experimental evidence was obtained by using radioactive tracers during the epitaxial deposition of GaAs. A ‘2~Te doped GaAs source was transported onto a single crystal substrate using a conventional A5CI,, /H 9 Accurately orientated 2 reactiveseed transthere is effect thea till) significant As facet and effect striking is even (III) greater. Ga facet port medium. 727 -
728
THE FACET EFFECT IN EPITAXIA.L GaAs
Vol. 5, No. 9
Ã~
_
~,
__
(a)
FIG1
(b)
Effect of [1111 facets on ‘~Tesegregation. (a) Photograph of epitaxial surface showing facetted areas. (b) Autoradlograph of same surface showing Te distribution (light areas are Te-rich). The magnitude of the facet ratio R, the ratio of 4 off a facet has not yet been k* on a facetThe to Icaccurate measured. measurement of R is affected by surface growth phenomena and wiU be reported elsewhere. It Is worth noting that in addition to the till) facets both the (100) and [110) facets show the effect. Previous evidence of orientation dependent distribution effects for impurities in vapour_ grown GaAs have been reported by Williams ° and Moest. ‘-~ Whilst Williams’ results could be taken to indicate the possibility of a facet effect specific evidence on facet development or on the possibility of a facet effect was not discussed, -
Facet development is not only critically dependent on precise substrate orientation but also on the growth conditions. Precisely oriented substrates do not necessarily produce faceted growth. It is possible some of the variability in Williams results or in the orientation effects for impurity Incorporation in vapour-growth GaP reported by Groves~ could be attributed to the capriciousness of facet development during epitaxy. Acknowledgements Useful discussion with our colleagues are gratefully acknowledged. The authors are indebted to B, W. Straughan, R. C. Clarke, 0. Jones and R. Cottrell for their assistance in this work. By permission of the Controller, Her Britannic Majesty’s Stationery Office, Crown copyright reserved.
References • 1.
HULME K. F. and MULLIN J. B., Phil. Mag. 4, 1286 (1959).
2.
DIXHOFF J.A.M., Solid State Electron 1, 202 (1960).
3.
HALL R. N. and RACETTE J. H.,
4.
LEMAY C. Z.,
J. Appl. Phys. 32, 856 (1961).
J. Appi. Phys. 34, 439 (1963).
-
Vol. 5, No. 9
THE FACET EFFECT IN EPITAXIAL GaAs
729
5.
CRONIN G. R., LARRABEE G. B. and OSBORNE J. F., J. Electrochem. Soc.
6.
STRAUSS A.J., J. Appi. Phys. 30, 559 (1959).
7.
MULLIN J. B., Unpublished work.
8.
BARDSLEY W. and COCKAYNE B., J. Phys. Chem. Solids. Supplement, Proceedings Inter-
9.
national Conference on Crystal Growth, Boston 20-24 june (1966). FINCH W. F. and MEHAL E.W., J. Electrochem. Soc. 111, 814 (1964).
10. WILLIAMS F.V., J. Electrochem. Soc. 111, 886 11. MOEST R.R.,, J. Electrochem. Soc. 12. GROVES W. 0.,
113, 292 (1966).
(1964).
113, 141 (1966).
J. Phys. Chem. Solids, Supplement, Proceedings of Conference on Crystal
Growth, Boston, 20-24 June
(1966).
Deutlicher einer “Facettewirkung” ‘~5Teist, w~hrend derBewels epitaktischen Absetzung von Galliumarsenid von der Gasphase, erhalten worden. Die Wirkung ist eine Eigenschaft von Wuchs auf einigen Ebenen mit niedrigen Indexzahlen.
THE FACET EFFECT IN EPITAXIAL GaAs B.D. Joyce andJ.B. MuIItn Royal Radar Establishment, Malvern, Worcs., U.K. (Received 29 June 1967 by C.W. McCombie)
Direct evidence for a vapour growth “Facet-Effect” has been obtained using Te during the epitaxtal deposition of gallium arsenide. The effect is a feature of growth on several low-index planes. •~
IN THE melt-growth of semiconductor crystals the Facet Effect is an established and well investigated phenomenon. The effect is the spedftc characteristic change which occurs in the 4 value of the interface coefficient when the nature of thedistribution growth surface changesk from a non-faceted type to a faceted type. The change from a non-faceted surface to a faceted surface may represent a change in the orientation of the surface of only a fraction of a degree. The facet effect is therefore a special case of the orientation-dependence of k*. Facets of type [1111 or [1111 show marked effects for various solute elements in indium antimonide1, germanium2, gallium antimonide3 and gallium arsenide.4 6 A (100) facet effect for the case of tellurium in indium antimontde8 which is almost as large’ as the (111) facet effect has also been reported. The phenomenon is probably a significant feature of the faceted growth of all materials and is not confined to semiconductor crystals; yttrium aluminium garnet9, for example, shows the effect, Although the facet effect is conventionally associated with the melt-growth of crystals direct evidence that an equivalent phenomena can occur in the vapour growth of the crystals has now been obtained. The presentation of this evidence is the purpose of this communication,
crystals were first vapour etched in situ to remove approximately 5 ~.xfrom the surface. This was done by maintaining the source at 800°Cand the seed C. byThen an epitaxtal layer wasto grown on atthe850° seed reducing its temperature 750°C. Approximately 10 ii thick ‘~ Te doped layers were deposited on to (Ill) Ga seeds at the rate of 20 ~i/hr. Seed crystals which were ortentated to within a quarter of a degree of a singular plane generally developed an epitaxial layer which had adjacent regions of both faceted and non-faceted growth. The distribution of ~Te in these layers was then recorded by placing the epttaxial surface in contact with Microtex X-ray film for a suitable period and then developing the autoradiograph by the recommended method. The resuits obtained from growing a typical layer on a (Ill) Ga orientated substrate are shown in Figs. 1(a) and 1 (b). -
The photographic evidence of the development of the (III) Ga facet in Fig. 1 (a) can be compared with the autoradiographic evidence of the ~6Te distribution in Fig. 1(b). The identity of the (III) Ca facet was confirmed by careful X-ray measurements. The shape and extent of the region of faceted growth is exactly equivalent to that of the region of higher “~6Teconcentration which extends a quarter of the way across the slice from one side. Additionally, right at the edge of the three corners of the triangularshaped slice are narrow outlines representing very Te-rich growth; these regions are the result of growth on small edge facets of the type equivalent to till) As. It is clear that although
The experimental evidence was obtained by using radioactive tracers during the epitaxial deposition of GaAs. A ‘2~Te doped GaAs source was transported onto a single crystal substrate using a conventional A5CI,, /H 9 Accurately orientated 2 reactiveseed transthere is effect thea till) significant As facet and effect striking is even (III) greater. Ga facet port medium. 727 -
728
THE FACET EFFECT IN EPITAXIA.L GaAs
Vol. 5, No. 9
Ã~
_
~,
__
(a)
FIG1
(b)
Effect of [1111 facets on ‘~Tesegregation. (a) Photograph of epitaxial surface showing facetted areas. (b) Autoradlograph of same surface showing Te distribution (light areas are Te-rich). The magnitude of the facet ratio R, the ratio of 4 off a facet has not yet been k* on a facetThe to Icaccurate measured. measurement of R is affected by surface growth phenomena and wiU be reported elsewhere. It Is worth noting that in addition to the till) facets both the (100) and [110) facets show the effect. Previous evidence of orientation dependent distribution effects for impurities in vapour_ grown GaAs have been reported by Williams ° and Moest. ‘-~ Whilst Williams’ results could be taken to indicate the possibility of a facet effect specific evidence on facet development or on the possibility of a facet effect was not discussed, -
Facet development is not only critically dependent on precise substrate orientation but also on the growth conditions. Precisely oriented substrates do not necessarily produce faceted growth. It is possible some of the variability in Williams results or in the orientation effects for impurity Incorporation in vapour-growth GaP reported by Groves~ could be attributed to the capriciousness of facet development during epitaxy. Acknowledgements Useful discussion with our colleagues are gratefully acknowledged. The authors are indebted to B, W. Straughan, R. C. Clarke, 0. Jones and R. Cottrell for their assistance in this work. By permission of the Controller, Her Britannic Majesty’s Stationery Office, Crown copyright reserved.
References • 1.
HULME K. F. and MULLIN J. B., Phil. Mag. 4, 1286 (1959).
2.
DIXHOFF J.A.M., Solid State Electron 1, 202 (1960).
3.
HALL R. N. and RACETTE J. H.,
4.
LEMAY C. Z.,
J. Appl. Phys. 32, 856 (1961).
J. Appi. Phys. 34, 439 (1963).
-
Vol. 5, No. 9
THE FACET EFFECT IN EPITAXIAL GaAs
729
5.
CRONIN G. R., LARRABEE G. B. and OSBORNE J. F., J. Electrochem. Soc.
6.
STRAUSS A.J., J. Appi. Phys. 30, 559 (1959).
7.
MULLIN J. B., Unpublished work.
8.
BARDSLEY W. and COCKAYNE B., J. Phys. Chem. Solids. Supplement, Proceedings Inter-
9.
national Conference on Crystal Growth, Boston 20-24 june (1966). FINCH W. F. and MEHAL E.W., J. Electrochem. Soc. 111, 814 (1964).
10. WILLIAMS F.V., J. Electrochem. Soc. 111, 886 11. MOEST R.R.,, J. Electrochem. Soc. 12. GROVES W. 0.,
113, 292 (1966).
(1964).
113, 141 (1966).
J. Phys. Chem. Solids, Supplement, Proceedings of Conference on Crystal
Growth, Boston, 20-24 June
(1966).
Deutlicher einer “Facettewirkung” ‘~5Teist, w~hrend derBewels epitaktischen Absetzung von Galliumarsenid von der Gasphase, erhalten worden. Die Wirkung ist eine Eigenschaft von Wuchs auf einigen Ebenen mit niedrigen Indexzahlen.