- Email: [email protected]
GaAs(110) interface
Surface Science 433–435 (1999) 352–356 www.elsevier.nl/locate/susc
Photoemission study of the reactive Dy/GaAs(110) interface A.N. Chaika a,b, V.A. Grazhulis a,1, A.M. Ionov a, *, P.K. Kashkarov b, S.L. Molodtsov c,d, A.M. Shikin c,d, C. Laubschat d a Institute of Solid State Physics, Russian Academy of Sciences, 142432 Chernogolovka, Russia b Moscow State University, 119899 Moscow, Russia c Institute of Physics, St. Petersburg State University, 198904 St. Petersburg, Russia d Institut fu¨r Oberfla¨chen- und Mikrostrukturphysik, Technische Universita¨t Dresden, D-01062 Dresden, Germany
Abstract The Dy/n-GaAs(110) interface was formed and studied at 100 K and 300 K by photoemission and low-energy electron diffraction (LEED). At both temperatures, formation of the reactive interface was observed beginning from the lowest deposited coverage of Dy (0.03 ML). Least-squares fit analysis of Ga 3d and As 3d core-level PE spectra reveals reacted components, which are related to segregation of substrate atoms and growth of binary (DyMGa and DyMAs) and ternary interfacial compounds. It was found that band bending occurs already at 0.03 ML of Dy coverage. The latter was interpreted in terms of the Fermi-level pinning by defect states that is completed at coverages lower than 0.5 ML. Deposition of Dy at 100 K leads to formation of the disordered interface, as monitored by LEED experiments. At room temperature, LEED patterns for overlayers of Dy in the range between 0.5 and 1 ML show a co-existence of structures with two- and three-fold symmetries. © 1999 Elsevier Science B.V. All rights reserved. Keywords: Low energy electron diffraction; Photoemission; Reactive Dy/GaAs(110) interface; Schottky barrier
1. Introduction There have been numerous studies of interfaces grown by deposition of metals onto semiconductor surfaces. However, up to now deposition of rareearth ( RE) metals has not been investigated sufficiently, although RE overlayers and heterostructures are of particular interest from different points of view. Until recently, photoemission (PE ) studies of RE/GaAs(110) interfaces [1–4] were performed mainly at room temperature (RT ). As a rule, deposition of REs onto GaAs(110) led to reactive interfaces. Studies of the Sm/GaAs(110) interfaces * Corresponding author. Fax: +7 096-576-4111. E-mail address: [email protected] (A.M. Ionov) 1 Deceased.
grown at low temperatures (LT ) [5] revealed that reaction between substrate and Sm overlayers takes place even at 20 K. In this paper, we report a PE and low-energy electron diffraction (LEED) study of the Dy/nGaAs(110) interface grown at 300 K and 100 K.
2. Experimental Clean surfaces of GaAs(110) (4×4.5 mm2) were obtained by cleaving n-type GaAs single crystals (Si-doped, n=6×1017 cm−3) at a base pressure in the range of 10−10 Torr. The interfaces were prepared by in-situ deposition of 99.99%pure Dy metal from an electron-beam cell onto GaAs substrates at LT and RT at pressures lower
0039-6028/99/$ – see front matter © 1999 Elsevier Science B.V. All rights reserved. PII: S0 0 39 - 6 0 28 ( 99 ) 0 01 2 2 -3
A.N. Chaika et al. / Surface Science 433–435 (1999) 352–356
than 5×10−10 Torr. Thicknesses of Dy overlayers ˚ ) were cali(1 monolayer corresponds to 3.2 A brated by a quartz microbalance with an accuracy of 20%. PE experiments were performed at the Berliner Elektronenspeicherring fu¨r Synchrotronstrahlung (BESSY ). Monochromatic radiation (hn=60 eV ) was provided by the 2.1 m toroidal grating monochromator. The overall system resolution was approximately 150 meV and 200 meV in the experiments performed at LT and RT, respectively.
3. Results and discussion PE spectra of Ga 3d and As 3d core levels taken at 300 K and 100 K are shown in Fig. 1a and b, respectively. In these figures dots correspond to the experimental points, while solid lines are results of multi-peak least-squares fit analysis. Subspectra shown are individual components used in the spectra decomposition. Both Ga 3d and As 3d PE spectra for freshly cleaved GaAs(110) surfaces are well described by two spin–orbit-split doublets originating from the surface and bulk atoms (bottom spectra in Fig. 1a and b). The lineshapes exploited during fitting are combinations of Lorentzian profiles convoluted by a Gaussian, with linewidth depending on the experimental resolution. The obtained spin–orbit splittings (0.44±0.02) eV and (0.70±0.02) eV, as well as the surface core level shifts (0.31±0.03) eV and (0.40±0.03 eV ) for Ga 3d and As 3d core levels, respectively, were found to be in good agreement with previously published values [6 ]. As seen in Fig. 1a and b, already at very low Dy coverages (0.03 ML) the surface and bulk doublets shift to lower binding energies (BEs) due to the band bending. In addition, the appearance of reacted components and attenuation of the surface and bulk doublets are observed. Additional reacted components were settled as doublets with spin–orbit splittings and branch intensity ratios derived from fitting of the PE spectra for clean GaAs(110), while their energy positions and linewidths were allowed to vary. It was found that at both temperatures the surface components become undetectable, beginning from 0.5 ML, while the
353
bulk doublets are still monitored up to 2 ML coverage. Attenuation rates for the surface and bulk doublets are larger at 300 K, indicating stronger chemical reactions at RT. For distribution curves taken at LT, we used only one reacted doublet to fit Ga 3d and As 3d spectra, while it was necessary to consider at least two reacted components to simulate spectra recorded from the interface grown at RT. Linewidths of the reacted doublets are larger than those of the unreacted components, pointing to the formation of different interfacial compounds. The reacted components measured at 100 K and 300 K move to lower BEs with increasing Dy coverage. Thereby, BE variations are stronger for the Ga-derived than for As-originating reacted doublets (compare spectra in Fig. 1a and b). Linewidths of the reacted components of Ga 3d PE spectra taken at 300 K, which are similar to values obtained for the surface and bulk doublets, suggest formation of close to single-phase DyMGa and DyMAs chemical compounds. As seen from Ga 3d PE spectra, relative contributions of different DyMGa compounds depend on deposited coverage. The reacted doublet appearing at 1 ML coverage and dominating at 2 ML in Ga 3d PE spectra taken at RT might be related to segregated Ga atoms; BE of the 3d component of this 3/2 doublet (18.7 eV ) corresponds to that known for elemental Ga. For optimal fitting of As 3d PE spectra measured at RT (see Fig. 1a) we used two additional reacted doublets as well. One of them shifts by 0.3 eV to lower BEs for coverages between 0.1 and 2 ML, and contributes more than 85% to the total signal at 2 ML coverage. In PE spectra recorded at 100 K, the reacted components move continuously to lower BEs when going from 0.07 ML to 2 ML. At 2 ML, BEs of 3d components of these doublets are 18.95 eV 5/2 and 40.65 eV for Ga 3d and As 3d, respectively. These values are more than 0.5 eV larger than those of the reacted components measured in the case of the RT interface. Lower relative contributions of the reacted components into intensities of PE spectra taken for the 100 K interface as compared to that for the RT interface (see above) demonstrate partial suppression of Dy–substrate reaction. Deposition of 2 ML of Dy leads to a
354
A.N. Chaika et al. / Surface Science 433–435 (1999) 352–356
(a)
(b)
Fig. 1. PE spectra of Ga 3d and As 3d core levels taken from (a) 300 K and (b) 100 K interfaces for different coverages of Dy. The spectra have been background subtracted and normalized to the same height. Here, solid circles represent experimental points, solid lines show results of a least-squares fit analysis. Dashed subspectra denote surface and bulk fitting components ( labeled s and b, respectively), whereas dotted subspectra indicate reacted contributions [ labeled r in (b)].
disruption of the surface layers of GaAs, followed by formation of a region with intermixed Dy, Ga, and As atoms. As it can be assumed from the derived linewidths and energy positions of the reacted components, this intermixed layer is rather inhomogeneous and consists of DyMGaMAs interfacial compounds. Valence-band PE spectra shown in Fig. 2a and b also reveal different behavior of the Dy/GaAs(110) interfaces grown at 100 K and 300 K. For the RT interface, the Dy 4f signal grows up already at 0.1 ML coverage. It shifts to lower binding energies from 5.5 eV to 5.0 eV between 0.1 and 2 ML. It was observed in Ref. 7 that Dy 4f multiplet in DySb locates at about 5 eV
BE. We assume similar BE of the 4f multiplet in DyMAs compound. This fact, together with the dominating segregation component in the Ga 3d PE spectrum taken at 2 ML, suggests that in this coverage range Dy atoms deposited onto the GaAs(110) interface at 300 K are bonded primarily with As atoms. At 100 K, the 4f multiplet shifts slightly towards E from 6 eV BE at 0.33 ML to 5.85 eV BE at F 2 ML. The energy positions of the Dy 4f signals measured at 2 ML are different for the RT and LT depositions (see spectra in Fig. 2a, b). The following model of the 100 K interface formation can be proposed, based on the observed behavior of the Dy 4f, Ga 3d, and As 3d core-level PE
A.N. Chaika et al. / Surface Science 433–435 (1999) 352–356
355
Fig. 3. Shifts of the Fermi energy relative to the valence band maximum ( VBM ) derived from core-level PE spectra upon formation of the RT and LT interfaces.
Fig. 2. Valence-band PE spectra taken from (a) 300 K and (b) 100 K interfaces for different coverages of Dy.
spectra: at the initial stage of Dy deposition, disruption of the surface layers of the substrate and formation of inhomogeneous intermixed DyMGaMAs compounds occurs. At thick coverages, a thin film of Dy metal grows onto the disrupted interface. At the initial stages of the LT deposition, LEED experiments show a typical two-fold symmetry LEED pattern of GaAs(110) superimposed by a diffuse background. Only background was observed at coverages exceeding 1 ML. Upon the RT deposition, a co-existence of various ordered structures was indicated by the LEED measurements: in the coverage range from 0.5 ML to 1 ML, patterns with two- and three-fold symmetries were monitored. In Fig. 3 we present the energy position of the
Fermi level relative to the valence-band maximum ( VBM ) as a function of Dy coverage. At both temperatures, the Schottky-barrier formation is completed already at coverages less than 0.5 ML. The latter is quite consistent with the defect model [8]. Note, that Schottky-barrier values obtained are different for the interfaces formed at RT and LT: (0.40±0.05) eV for the 100 K interface and (0.70±0.05) eV for the 300 K interface. We can propose two possible explanations for the observed formation of different Schottky-barriers. Firstly, the different Schottky-barrier values may result from specific chemistry in the interfacial region that could be expected from PE and LEED data. Spicer et al. [8] showed that there is a strong dependence of the Fermi-level position on interfacial chemistry at the Al/GaAs interface. An increase of the barrier height due to AlMAs reaction was observed after annealing of the interface. From the advanced unified defect model [8], one would expect an increase in the Schottky-barrier height with decrease of As antisite defect concenGa tration at the interface after annealing. The above presented PE data suggest that this scenario might be possible for Dy/GaAs(110) as well. Secondly,
356
A.N. Chaika et al. / Surface Science 433–435 (1999) 352–356
we cannot discard the possibility of the photovoltaic effects.
4. Conclusion The reactive Dy/GaAs(110) interface was studied at 100 K and 300 K. At RT, the obtained PE data indicate segregation of Ga atoms and growth of DyMAs interfacial compounds for coverages between 0.5 and 2 ML. The low-temperature experiments reveal disruption of the GaAs surface at the initial stages of Dy deposition, followed by formation of ternary DyMGaMAs phases. Our LEED experiments give co-existence of two- and three-fold symmetry patterns for the RT interface in the range of coverages between 0.5 and 1 ML; they evidence, however, formation of the disordered interface at LT. Different Schottky-barrier values were observed for the 100 K and 300 K interfaces.
Acknowledgements We would like to thank Th. Gantz and J. Boysen ( Technische Universita¨t Dresden) and BESSY staff
for providing experimental equipment and kind support. This work was partially supported by the Russian Foundation for Basic Research, grant N96-02-175532 and the Ministry of Science of Russia, grants SAS N95-1.4, 95-2.6 and ‘Atomic layers’.
References [1] M. Grioni, J.J. Joyce, J.H. Weaver, Phys. Rev. B 32 (1985) 962. [2] J.H. Weaver, M. Grioni, J.J. Joyce, M. Del Giudice, Phys. Rev. B 31 (1985) 5290. [3] M. Prietsch, C. Laubschat, M. Domke, G. Kaindl, Phys. Rev. B 38 (1988) 10655. [4] J.-H. Oh, J. Chung, H.-D. Kim, Y.-H. Choe, S.-J. Oh, S.-M. Chung, A. Kakizaki, T. Ishii, J. Electron Spectrosc. Relat. Phenom. 83 (1997) 77. [5] T. Komeda, S.G. Anderson, J.M. Seo, M.C. Schabel, J.H. Weaver, J. Vac. Sci. Technol. A 9 (1985) 1964. [6 ] D.E. Eastman, T.-C. Chiang, P. Heimann, F.J. Himpsel, Phys. Rev. Lett. 45 (1980) 656. [7] M. Campagna, E. Bucher, G.K. Wertheim, D.N.E. Buchanan, L.D. Longinotti, in: Photoemission in Solids 2 , Springer, Berlin, 1978, p. 241. [8] W.E. Spicer, Z. Lilliental-Weber, E. Weber, N. Newman, T. Kendelewicz, R. Cao, C. McCants, P. Mahowald, K. Miyano, I. Lindau, J. Vac. Sci. Technol. B 6 (1988) 1245.
Photoemission study of the reactive Dy/GaAs(110) interface A.N. Chaika a,b, V.A. Grazhulis a,1, A.M. Ionov a, *, P.K. Kashkarov b, S.L. Molodtsov c,d, A.M. Shikin c,d, C. Laubschat d a Institute of Solid State Physics, Russian Academy of Sciences, 142432 Chernogolovka, Russia b Moscow State University, 119899 Moscow, Russia c Institute of Physics, St. Petersburg State University, 198904 St. Petersburg, Russia d Institut fu¨r Oberfla¨chen- und Mikrostrukturphysik, Technische Universita¨t Dresden, D-01062 Dresden, Germany
Abstract The Dy/n-GaAs(110) interface was formed and studied at 100 K and 300 K by photoemission and low-energy electron diffraction (LEED). At both temperatures, formation of the reactive interface was observed beginning from the lowest deposited coverage of Dy (0.03 ML). Least-squares fit analysis of Ga 3d and As 3d core-level PE spectra reveals reacted components, which are related to segregation of substrate atoms and growth of binary (DyMGa and DyMAs) and ternary interfacial compounds. It was found that band bending occurs already at 0.03 ML of Dy coverage. The latter was interpreted in terms of the Fermi-level pinning by defect states that is completed at coverages lower than 0.5 ML. Deposition of Dy at 100 K leads to formation of the disordered interface, as monitored by LEED experiments. At room temperature, LEED patterns for overlayers of Dy in the range between 0.5 and 1 ML show a co-existence of structures with two- and three-fold symmetries. © 1999 Elsevier Science B.V. All rights reserved. Keywords: Low energy electron diffraction; Photoemission; Reactive Dy/GaAs(110) interface; Schottky barrier
1. Introduction There have been numerous studies of interfaces grown by deposition of metals onto semiconductor surfaces. However, up to now deposition of rareearth ( RE) metals has not been investigated sufficiently, although RE overlayers and heterostructures are of particular interest from different points of view. Until recently, photoemission (PE ) studies of RE/GaAs(110) interfaces [1–4] were performed mainly at room temperature (RT ). As a rule, deposition of REs onto GaAs(110) led to reactive interfaces. Studies of the Sm/GaAs(110) interfaces * Corresponding author. Fax: +7 096-576-4111. E-mail address: [email protected] (A.M. Ionov) 1 Deceased.
grown at low temperatures (LT ) [5] revealed that reaction between substrate and Sm overlayers takes place even at 20 K. In this paper, we report a PE and low-energy electron diffraction (LEED) study of the Dy/nGaAs(110) interface grown at 300 K and 100 K.
2. Experimental Clean surfaces of GaAs(110) (4×4.5 mm2) were obtained by cleaving n-type GaAs single crystals (Si-doped, n=6×1017 cm−3) at a base pressure in the range of 10−10 Torr. The interfaces were prepared by in-situ deposition of 99.99%pure Dy metal from an electron-beam cell onto GaAs substrates at LT and RT at pressures lower
0039-6028/99/$ – see front matter © 1999 Elsevier Science B.V. All rights reserved. PII: S0 0 39 - 6 0 28 ( 99 ) 0 01 2 2 -3
A.N. Chaika et al. / Surface Science 433–435 (1999) 352–356
than 5×10−10 Torr. Thicknesses of Dy overlayers ˚ ) were cali(1 monolayer corresponds to 3.2 A brated by a quartz microbalance with an accuracy of 20%. PE experiments were performed at the Berliner Elektronenspeicherring fu¨r Synchrotronstrahlung (BESSY ). Monochromatic radiation (hn=60 eV ) was provided by the 2.1 m toroidal grating monochromator. The overall system resolution was approximately 150 meV and 200 meV in the experiments performed at LT and RT, respectively.
3. Results and discussion PE spectra of Ga 3d and As 3d core levels taken at 300 K and 100 K are shown in Fig. 1a and b, respectively. In these figures dots correspond to the experimental points, while solid lines are results of multi-peak least-squares fit analysis. Subspectra shown are individual components used in the spectra decomposition. Both Ga 3d and As 3d PE spectra for freshly cleaved GaAs(110) surfaces are well described by two spin–orbit-split doublets originating from the surface and bulk atoms (bottom spectra in Fig. 1a and b). The lineshapes exploited during fitting are combinations of Lorentzian profiles convoluted by a Gaussian, with linewidth depending on the experimental resolution. The obtained spin–orbit splittings (0.44±0.02) eV and (0.70±0.02) eV, as well as the surface core level shifts (0.31±0.03) eV and (0.40±0.03 eV ) for Ga 3d and As 3d core levels, respectively, were found to be in good agreement with previously published values [6 ]. As seen in Fig. 1a and b, already at very low Dy coverages (0.03 ML) the surface and bulk doublets shift to lower binding energies (BEs) due to the band bending. In addition, the appearance of reacted components and attenuation of the surface and bulk doublets are observed. Additional reacted components were settled as doublets with spin–orbit splittings and branch intensity ratios derived from fitting of the PE spectra for clean GaAs(110), while their energy positions and linewidths were allowed to vary. It was found that at both temperatures the surface components become undetectable, beginning from 0.5 ML, while the
353
bulk doublets are still monitored up to 2 ML coverage. Attenuation rates for the surface and bulk doublets are larger at 300 K, indicating stronger chemical reactions at RT. For distribution curves taken at LT, we used only one reacted doublet to fit Ga 3d and As 3d spectra, while it was necessary to consider at least two reacted components to simulate spectra recorded from the interface grown at RT. Linewidths of the reacted doublets are larger than those of the unreacted components, pointing to the formation of different interfacial compounds. The reacted components measured at 100 K and 300 K move to lower BEs with increasing Dy coverage. Thereby, BE variations are stronger for the Ga-derived than for As-originating reacted doublets (compare spectra in Fig. 1a and b). Linewidths of the reacted components of Ga 3d PE spectra taken at 300 K, which are similar to values obtained for the surface and bulk doublets, suggest formation of close to single-phase DyMGa and DyMAs chemical compounds. As seen from Ga 3d PE spectra, relative contributions of different DyMGa compounds depend on deposited coverage. The reacted doublet appearing at 1 ML coverage and dominating at 2 ML in Ga 3d PE spectra taken at RT might be related to segregated Ga atoms; BE of the 3d component of this 3/2 doublet (18.7 eV ) corresponds to that known for elemental Ga. For optimal fitting of As 3d PE spectra measured at RT (see Fig. 1a) we used two additional reacted doublets as well. One of them shifts by 0.3 eV to lower BEs for coverages between 0.1 and 2 ML, and contributes more than 85% to the total signal at 2 ML coverage. In PE spectra recorded at 100 K, the reacted components move continuously to lower BEs when going from 0.07 ML to 2 ML. At 2 ML, BEs of 3d components of these doublets are 18.95 eV 5/2 and 40.65 eV for Ga 3d and As 3d, respectively. These values are more than 0.5 eV larger than those of the reacted components measured in the case of the RT interface. Lower relative contributions of the reacted components into intensities of PE spectra taken for the 100 K interface as compared to that for the RT interface (see above) demonstrate partial suppression of Dy–substrate reaction. Deposition of 2 ML of Dy leads to a
354
A.N. Chaika et al. / Surface Science 433–435 (1999) 352–356
(a)
(b)
Fig. 1. PE spectra of Ga 3d and As 3d core levels taken from (a) 300 K and (b) 100 K interfaces for different coverages of Dy. The spectra have been background subtracted and normalized to the same height. Here, solid circles represent experimental points, solid lines show results of a least-squares fit analysis. Dashed subspectra denote surface and bulk fitting components ( labeled s and b, respectively), whereas dotted subspectra indicate reacted contributions [ labeled r in (b)].
disruption of the surface layers of GaAs, followed by formation of a region with intermixed Dy, Ga, and As atoms. As it can be assumed from the derived linewidths and energy positions of the reacted components, this intermixed layer is rather inhomogeneous and consists of DyMGaMAs interfacial compounds. Valence-band PE spectra shown in Fig. 2a and b also reveal different behavior of the Dy/GaAs(110) interfaces grown at 100 K and 300 K. For the RT interface, the Dy 4f signal grows up already at 0.1 ML coverage. It shifts to lower binding energies from 5.5 eV to 5.0 eV between 0.1 and 2 ML. It was observed in Ref. 7 that Dy 4f multiplet in DySb locates at about 5 eV
BE. We assume similar BE of the 4f multiplet in DyMAs compound. This fact, together with the dominating segregation component in the Ga 3d PE spectrum taken at 2 ML, suggests that in this coverage range Dy atoms deposited onto the GaAs(110) interface at 300 K are bonded primarily with As atoms. At 100 K, the 4f multiplet shifts slightly towards E from 6 eV BE at 0.33 ML to 5.85 eV BE at F 2 ML. The energy positions of the Dy 4f signals measured at 2 ML are different for the RT and LT depositions (see spectra in Fig. 2a, b). The following model of the 100 K interface formation can be proposed, based on the observed behavior of the Dy 4f, Ga 3d, and As 3d core-level PE
A.N. Chaika et al. / Surface Science 433–435 (1999) 352–356
355
Fig. 3. Shifts of the Fermi energy relative to the valence band maximum ( VBM ) derived from core-level PE spectra upon formation of the RT and LT interfaces.
Fig. 2. Valence-band PE spectra taken from (a) 300 K and (b) 100 K interfaces for different coverages of Dy.
spectra: at the initial stage of Dy deposition, disruption of the surface layers of the substrate and formation of inhomogeneous intermixed DyMGaMAs compounds occurs. At thick coverages, a thin film of Dy metal grows onto the disrupted interface. At the initial stages of the LT deposition, LEED experiments show a typical two-fold symmetry LEED pattern of GaAs(110) superimposed by a diffuse background. Only background was observed at coverages exceeding 1 ML. Upon the RT deposition, a co-existence of various ordered structures was indicated by the LEED measurements: in the coverage range from 0.5 ML to 1 ML, patterns with two- and three-fold symmetries were monitored. In Fig. 3 we present the energy position of the
Fermi level relative to the valence-band maximum ( VBM ) as a function of Dy coverage. At both temperatures, the Schottky-barrier formation is completed already at coverages less than 0.5 ML. The latter is quite consistent with the defect model [8]. Note, that Schottky-barrier values obtained are different for the interfaces formed at RT and LT: (0.40±0.05) eV for the 100 K interface and (0.70±0.05) eV for the 300 K interface. We can propose two possible explanations for the observed formation of different Schottky-barriers. Firstly, the different Schottky-barrier values may result from specific chemistry in the interfacial region that could be expected from PE and LEED data. Spicer et al. [8] showed that there is a strong dependence of the Fermi-level position on interfacial chemistry at the Al/GaAs interface. An increase of the barrier height due to AlMAs reaction was observed after annealing of the interface. From the advanced unified defect model [8], one would expect an increase in the Schottky-barrier height with decrease of As antisite defect concenGa tration at the interface after annealing. The above presented PE data suggest that this scenario might be possible for Dy/GaAs(110) as well. Secondly,
356
A.N. Chaika et al. / Surface Science 433–435 (1999) 352–356
we cannot discard the possibility of the photovoltaic effects.
4. Conclusion The reactive Dy/GaAs(110) interface was studied at 100 K and 300 K. At RT, the obtained PE data indicate segregation of Ga atoms and growth of DyMAs interfacial compounds for coverages between 0.5 and 2 ML. The low-temperature experiments reveal disruption of the GaAs surface at the initial stages of Dy deposition, followed by formation of ternary DyMGaMAs phases. Our LEED experiments give co-existence of two- and three-fold symmetry patterns for the RT interface in the range of coverages between 0.5 and 1 ML; they evidence, however, formation of the disordered interface at LT. Different Schottky-barrier values were observed for the 100 K and 300 K interfaces.
Acknowledgements We would like to thank Th. Gantz and J. Boysen ( Technische Universita¨t Dresden) and BESSY staff
for providing experimental equipment and kind support. This work was partially supported by the Russian Foundation for Basic Research, grant N96-02-175532 and the Ministry of Science of Russia, grants SAS N95-1.4, 95-2.6 and ‘Atomic layers’.
References [1] M. Grioni, J.J. Joyce, J.H. Weaver, Phys. Rev. B 32 (1985) 962. [2] J.H. Weaver, M. Grioni, J.J. Joyce, M. Del Giudice, Phys. Rev. B 31 (1985) 5290. [3] M. Prietsch, C. Laubschat, M. Domke, G. Kaindl, Phys. Rev. B 38 (1988) 10655. [4] J.-H. Oh, J. Chung, H.-D. Kim, Y.-H. Choe, S.-J. Oh, S.-M. Chung, A. Kakizaki, T. Ishii, J. Electron Spectrosc. Relat. Phenom. 83 (1997) 77. [5] T. Komeda, S.G. Anderson, J.M. Seo, M.C. Schabel, J.H. Weaver, J. Vac. Sci. Technol. A 9 (1985) 1964. [6 ] D.E. Eastman, T.-C. Chiang, P. Heimann, F.J. Himpsel, Phys. Rev. Lett. 45 (1980) 656. [7] M. Campagna, E. Bucher, G.K. Wertheim, D.N.E. Buchanan, L.D. Longinotti, in: Photoemission in Solids 2 , Springer, Berlin, 1978, p. 241. [8] W.E. Spicer, Z. Lilliental-Weber, E. Weber, N. Newman, T. Kendelewicz, R. Cao, C. McCants, P. Mahowald, K. Miyano, I. Lindau, J. Vac. Sci. Technol. B 6 (1988) 1245.