B.A. Orlowski

Experimental surface band structure of CdTe(110)

Abstract Angle-resolved photoemission and constant-final-state (CFS) spectroscopy are performed with synchrotron radiation to determine the experimental surface band structure E ( k ∥ ) along the high symmetry lines ГX′MXГgG of in situ cleaved CdTe(110). In order t distinguish between surface and bulk related features we utilized the k ⊥ dispersion behaviour of surface states by photon energy dependent normal emission spectra and off-normal CFS spectra at several critical points of the surface Brillouin zone (BZ) as well as their particular k ∥ dispersion and polarization behaviour. Three surface states and one surface resonance are clearly identified, whereas the resonance is only visible in the second surface BZ. In particular, the energy position of the anion derived dangling bond state with respect to the bulk valence band maximum Γ 8 is determined. The surface band structure is compared with previous experimental and theoretical results.

Oxide formation on the CdTe(111)A (1×1) surface

A CdTe(1 11)A (I X 1) surface, prepared in situ by argon ion bombardment and annealing (at 250°C), was oxidized at the pressure of 1 X 10 -5 -5 X 10 -5 Torr of molecular oxygen excited by the hot filament of the ion gauge. The surface atomic structure was studied by low-energy electron diffraction (LEED). The surface chemical composition and the oxidation process were monitored by recording the energy position and shape of Te 3d, Cd 3d, O 1 s and C Is core level peaks by X-ray photoemission spectroscopy. The excess of Te on the clean CdTe(111)A (1 × 1) surface was detected. Then, the increase of oxygen bound on the surface was observed as a function of the gas exposure. Symptoms of selective oxidation of Te atoms on the surface and in subsurface region were revealed.

Structural and chemical studies of the Cd1−xFexSe semimagnetic semiconductors

The polycrystalline samples of Cd1−xFexSe with different nominal compositions were studied by X-ray diffraction and atomic absorption spectrometry methods. The crystal structure of these compounds was determined as a hexagonal one of the wurtzite type. The structural homogeneity of the samples (except one) was ascertained and the lattice parameters were calculated. The chemical studies revealed the small differences between the nominal and real iron concentrations in all samples. The relationship between the lattice parameters and chemically determinated iron concentrations is presented. The limit of solubility of iron in CdSe was not observed in the range of the investigated compositions.

Photoemission study of EuS/PbS electronic structure

Abstract The ultraviolet photoemission and resonant photoemission spectroscopy were used to study the electronic structure of EuS/PbS multilayers with the contribution of europium’s 4f orbitals to the density of states of the valence band. The valence band photoemission spectra of galena and europium monosulfide layers show good agreement with theoretical density of state computations. The relative ratio of Eu 3+ and Eu 2+ ions located at the surface of EuS layer strongly depends on conditions of preparation procedures of the sample surface. For the buried EuS layer only Eu 2+ ions were observed.

Rare earth 4f states in AIV1-xRExBVI diluted magnetic semiconductors

Abstract Resonant photoemission spectroscopy has been applied to study the group of Pb 1− x RE x B VI (RE=Eu, Gd; B=Te, Se, S) diluted magnetic semiconductors. Energy distribution curves, as well as constant-initial-state or constant-final-state photoemission spectra have been taken for photon energies near to the intra-ion Eu 4d→4f or Gd 4d→4f transitions. The Eu 4f and Gd 4f contributions to the electronic structures of the crystals have been determined by comparison of photoemission spectra taken on and off resonance. The localized character of the Eu(Gd) 4f 7 shell has been confirmed by the analysis of the shape of the corresponding spectral feature. The influence of the host crystal ionicity on the position of the RE 4f shells with respect to the valence band is discussed.

Mn 3d derived contribution to the valence band of MBE grown cubic MnTe

Photoemission spectroscopy was applied to determine the valence band density-of-states in zinc blende MnTe grown by MBE on a CdTe(100) substrate. The Mn 3d derived contribution to the electronic structure was revealed by resonant photoemission experiments. Our experimental results are compared to the available configuration-interaction cluster models. An important role of the core hole screening (through charge transfer from ligand orbitals) on the whole Mn 3d derived photoemission spectrum (including the satellite structure observed below the valence band) was clearly confirmed.

Surface band structure of CdTe(111)-2 × 2 by angle-resolved photoemission

Abstract The surface band structure of non-cleavable CdTe(111)-2 × 2 reconstructed surfaces is determined by means of angle-resolved photoemission and constant-final-state (CFS) spectroscopy. The experiments were performed with He I radiation and synchrotron radiation from the DORIS II storage ring at HASYLAB. High-quality (111)-2 × 2 surfaces were prepared by sputtering and annealing controlled by electron diffraction (LEED and RHEED). In order to distinguish between surface and bulk related emissions in the spectra we utilized, besides the criteria that the k ∥ dispersion of surface states should reveal the 2 × 2 periodicity of the surfac mesh, also photon energy dependent CFS series at several critical points of the surface Brillouin zone. The data on CdTe(111) will be compared with experimental and theoretical results which are available for the electronically similar GaAs(111) surface.

X-ray and ultraviolet photoemission study of electronic structure of Sn1 xMnxTe MBE layers

X-ray photoelectron and ultraviolet resonant photoemission spectroscopy was used to study the Sn0:96Mn0:04Te MBE layers. The surface chemical composition of the samples after different treatment conditions was studied by means of XPS. Resonant photoemission spectroscopy with application of the synchrotron radiation was applied to investigate the electronic structure and the contribution of Mn 3d electrons to the valence band of Sn0:96Mn0:04Te layers. The contribution of the Mn 3d electrons to the valence band electronic structure appears at the valence band with the maximum located at 4.0 eV below the valence band edge. 2002 Published by Elsevier Science B.V.

Photoemission study of Gd atoms on CdTe(100) surface

Abstract A few monolayers of Gd atoms were evaporated on a clean CdTe(p)(100) (bulk crystal) and CdTe(n)(100) (epitaxial layer) surface. Constant initial state (CIS) spectra were measured at the Gd4d → Gd4f Fano resonance (in the photon energy range of 140–160 eV) both after evaporation and heating processes. The binding energy of the Gd4f state was determined after Gd evaporation (9.43 and 9.50 eV for p- and n-type crystals, respectively) and after heating (9.00 and 9.80 eV). Energy distribution curves (EDCs) measured in the photon energy range (50–100 eV) show additional density of states at the valence band edge only for CdTe(n)/Gd crystal.

Optical and photoemission study of surface electronic states and surface oxidation on CdTe(110)

Abstract Surface differential reflectivity and surface sensitive electron spectroscopies have been applied to study the optical properties of CdTe(110) surface. The comparison of the results acquired for the surfaces prepared by two different methods (cleavage and Ar + ion sputtering) enabled us to propose a model explaining the experimental results in a coherent way.