Probing the interface and microstructures in CdS/CuInSe2 and InGaAsN/GaAs heterojunctions by synchrotron radiation

Measurements of angular dependence of x-ray fluorescence (ADXRF), x-ray absorption fine structure (XAFS), and grazing incidence x-ray scattering (GIXS) using synchrotron radiation were utilized to study the migration of constituent atoms, microstructures, and interface morphology in two sets of heterostructures consisting of CuInSe2 (single crystal)/CdS and InxGa1-xAs1-yNy/GaAs compounds. Both systems are useful for the development of innovative high efficiency solar cells. By comparing the ADXRF and XAFS data of a CdS-coated and a bare CuInSe2 single crystal, changes in the depth profile of atoms and their local structures due to CdS coating can be investigated with well-defined stoichiometry. Our results indicate that both Cu and Se atoms have migrated into the CdS layer in the heterojunction while In atoms remain practically intact in the CuInSe2 single crystal. For a study of the InxGa1-xAs1-yNy system, our XAFS results show a sp3 hybridized bonding configuration for N atoms, indicating that the N impurities most likely substitute for As sites in the compounds GaAs1-yNy and InxGa1-xAs1-yNy. Within experimental uncertainties, the results of In K-edge XAFS indicate that the In-As interatomic distance remains essentially the same as in InAs. Further, GIXS measurements confirm that In0.08Ga0.92As0.97N0.03 thin films can indeed form very smooth interfaces with GaAs. (author)