We studied the structural and electronic properties of the ZnTe/CdTe(100) interface with reflection high-energy electron diffraction and angle-resolved synchrotron radiation photoemission spectroscopy (ARPES). ZnTe overlayers grown at 300 °C on CdTe(100) were fully strained and pseudomorphic up to ≊16 Å. Beyond this coverage the ZnTe film starts to gradually relax the 6.6% in-plane lattice strain. Complete relaxation is reached at a ZnTe coverage of ∼300 Å. A valence-band offset of ΔEv=0.00±0.05 eV was measured with ARPES at the Γ point. This propitious band lineup may allow for the use of a ZnTe intermediate layer at metal/CdTe structures to induce ohmic back contacts in CdS/CdTe heterojunction solar cells.
We report first-principles band structure calculations that show that ZnSe/CuInSe2 has a significant valence band offset (VBO, ΔEv): 0.70±0.05 eV for the relaxed interface and 0.60±0.05 eV for the coherent interface. These large values demonstrate the failure of the common anion rule. This is traced to a stronger Cu,d-Se,p level repulsion in CuInSe2 than the Zn,d-Se,p repulsion in ZnSe. The VBO was then studied by synchrotron radiation soft x-ray photoemission spectroscopy. ZnSe overlayers were sequentially grown in steps on n-type CuInSe2(112) single crystals at 200 °C. In situ photoemission measurements were acquired after each growth in order to observe changes in the valence band electronic structure as well as changes in the In 4d and Zn 3d core lines. Results of these measurements reveal that the VBO is ΔEv=0.70±0.15 eV, in good agreement with the first-principles prediction.
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