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The paper presents the experimental results of the electronic band structure study of the semiconductor crystal clean surface and this surface doped by transition metal or rare earth metal atoms. For clean surfaces of the CdTe crystal the two-dimensional electronic band structure E( k ) dependence was determined for surface states located in the valence band energy region. The doping of the clean surface of CdTe was performed by the controlled, sequential deposition of metal atoms (Fe, Gd or Yb) on the surface. After each deposition the synchrotron radiation was used to measure the resonant photoemission spectra (energy distribution curve – EDC, constant initial states – CIS and constant finale states – CFS). The results of the study showed that in the first stages of the metal atoms' deposition in the range of thickness equal to about 0.5 ML the effect of the crystal clean surface doping occurs. For bigger metal layer deposition the metallic islands electronic structure gave the contribution to the measured spectra. Heating of the sample surface covered by metal atoms leads to the diffusion of the atoms into the sample and results in an increase of the crystal doping and decrease of the metallic islands contribution to the measured spectra.

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.

The aim of the work is to present the XPS and UPS studies of a new kind of material MBE grown -CdYbTe thin layers. The analysis of the valence band electron states was performed for three samples (with different Yb contents and different crystallographic quality) by means of resonant photoemission based on the electronic transition between Yb 4d–4f shells. Analysis of Cd 3d, Te 3d and Yb 4d core levels made by XPS gave the qualitative information about the samples before and after Argon ion sputtering. The photoemission spectra for the CdYbTe sample containing 5% Yb, which corresponds to the limit of Yb solubility, were compared with the spectra of the CdYbTe sample with 1% Yb. By means of resonant photoemission Ytterbium was found in two charge states Yb(+2) and Yb(+3).

The electronic structure of Cd 0.985 Fe 0.015 Te has been studied by resonant photoemission in the synchrotron radiation photon energy range from 48 to 67 eV. Photoemission spectra revealed that Fe contributions to the valence band density of states are situated at 1.2 eV, 4.1 eV and 5.9 eV below the valence band maximum. The contribution of Fe 3d states to the valence band electronic structure was also observed in situ during evaporation of Fe atoms on the clean CdTe(110) surface. Photoemission measurements show that after Fe evaporation and heating to 265°C the CdTe(110)/Fe crystal, a ternary compound Cd 1− x Fe x Te is created in the surface region. The results of photoemission experiments are consistent with the theoretical calculations made by the CPA (coherent potential approximation) method.

Electronic states of 4f samarium ions were investigated by photoemission spectroscopy in samarium-rich CdSmTe sample obtained by MBE. The photon energy of synchrotron radiation allowed to investigate Fano-type resonance and antiresonance. The energy distribution curve spectra were attributed to the Sm 4d-4f transition. The shape of the constant initial states spectra was compared with this one obtained for atomic samarium. PACS numbers: 73.20.At, 79.60.-i, 79.60.Bm

We report a new approach to investigate metal-semiconductor interface formation. Photoemission spectroscopy was applied in order to investigate the clean surface of a Sn0.97 Cr0.03Te crystal and to observe its changes under sequential deposition of small amounts of Cr atoms. In order to analyse the Cr 3d contribution to the valence band, the Fano-type resonance tuned to the Cr 3p-3d transition was used. The experiment was designed to follow the Sno.97Cr0.o3Te/Cr interface formation process. At the clean Sn0.97Cro.o3Te surface, the Cr 3d states contribution to the valence band was found to be positioned 0.8 eV below the Fermi level. After the Cr deposition processes the contribution shifted to a higher binding energy and another contribution 5.8 eV below the Fermi level was also observed. PACS numbers: 79.60.-i, 68.35.Fx

ZnYbTe and CdYbTe thin films were grown by molecular beam epitaxy (MBE) on ZnTe and CdTe buffer layers crystallized on GaAs(100) substrates. At the chosen growth temperature (320°C for CdYbTe and 340°C for ZnYbTe) the maximum concentration of ytterbium was found to be 5% in CdTe and 3% in ZnTe. The layers were characterized by X-ray diffraction, photoluminescence (PL) and reflectivity measurements. X-ray investigations have shown that there was a small admixture of pure YbTe in the samples. From the optical measurements it follows that in CdYbTe and ZnYbTe, Yb can be found both in 2+ (as in YbTe) and 3+ (as in Yb doped II–VI compounds) valence state. The relatively broad PL spectra detected at the energies close to the Yb 3+ 4 f 13 ( 2 F 5 2 → 2 F 7 2 ) transitions indicate that at such a high concentration Yb incorporates with certain inhomogeneity into the crystal lattices of ZnTe and CdTe.