SXPS studies of single crystalline CdTe/CdS interfaces

The interface formation between CdS and CdTe is investigated by synchrotron induced photoemission measurements at the BESSY II storage ring. CdS and CdTe layers were deposited by thermal evaporation on CdTe and CdS single crystal substrates with two different orientations for each substrate. Surface core level shifts show a passivation of dangling bonds for CdS substrates overgrown by CdTe. TeTe bonds are found even on a 200 nm thick layer of CdS on CdTe. A valence band offset of 1.02 ± 0.05 eV, corresponding to a conduction band offset of −0.09 ± 0.05 eV is determined, independent of the substrate type and orientation and in agreement with measurements of polycrystalline interfaces. This alignment of every bands with a very small barrier for electron transfer and a maximized barrier for hole transport to the electron accepting front contact promises ideal properties for devices like CdS/CdTe hetero junction thin film solar cells.