In the DAISY-MAT system， the sample preparation system is directly connected to the analysis chambers to avoid sample contamination due to sample handling in air.Photoelectron spectroscopy studies have been performed using a Physical Electr... In the DAISY-MAT system， the sample preparation system is directly connected to the analysis chambers to avoid sample contamination due to sample handling in air.Photoelectron spectroscopy studies have been performed using a Physical Electronics PHI 5700 multitechnique surface analysis system with a monochromatized Al anode X-ray source (X-ray photoelectron spectroscopy (XPS)，hm=1486.6eV) and an He discharge lamp (UPS， 21.2eV).The core level lines are analysed with respect to binding energies and different chemical components after a curve fitting procedure using Voigt line profiles. Binding energies are given with respect to the Fermi level， calibrated with sputter cleaned Ag samples prior to every experiment. The binding energies of the core levels of CdTe and ZnTe with respect to the valence band maximum have been determined using the statistical average from large number of polycrystalline samples. The values for CdTe have been published elsewhere [9].
3.1. CdTe/ZnTe interface
XPS core level and UPS valence band spectra for different ZnTe deposition times and therefore ZnTe coverage are show in Fig. 1. As expected with increasing ZnTe coverage， the Cd3d5/2 emissions disappear while the Zn2p3/2 adsorbate emissions appear. After a deposition time of 1092 s， no Cd
emissions remain in the spectra. The valence band spectra
show a continuous change from pure CdTe valence band to
pure ZnTe. No evidence for interfacial reaction is observed in
the core and valence spectra.
The binding energies of the core levels with respect to the
binding energies of the valence band maximum for CdTe and
ZnTe are BEVBM(Cd3d5/2)=404.39F0.05 eV and BEVBM
(Zn2p3/2)=1021.11F0.05 eV， respectively. Therefore， the
valence band position with respect to the Fermi level can be
calculated. The determined position of the valence band
maximum using the Cd3d5/2 and Zn2p3/2 emissions and the
valence band offset are shown in Fig. 2. The offset values
scatter only slightly with thickness， indicating a reliable
determination. The valence band offset for the CdTe/ZnTe
interface is determined as 0.1F0.1 eV， with the valence band
maximum of ZnTe above that of CdTe. This result agrees to a
previous investigation of CdTe/ZnTe interface prepared by
physical vapour deposition [10]， indicating no change of the
interfacial barrier height induced by the sputter deposition
process. Using bulk band gaps of 1.49 eV for CdTe and 2.3
eV for ZnTe， the valence band offset corresponds to a
conduction band offset of 0.91F0.1 eV. 展开
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