Migration of constituent atoms and interface morphology in a heterojunction between CdS and CuInSe2 single crystals

Angular dependence of x-ray fluorescence (ADXRF), x-ray absorption fine str ucture (XAFS), and grazing incidence x-ray scattering measurements were car ried out using synchrotron radiation for a study of the interface morpholog y and migration of constituent atoms in a heterojunction formed between CdS and CuInSe2 single crystals. The advantage of using a single crystal for t his study is to avoid the usually complicated problems arising from multipl e phases of the Cu-In-Se compounds. By a comparison of the results obtained with a bare CuInSe2 single crystal, the changes of interface microstructur es in the CdS/CuInSe2 heterojunction system with well-defined stoichiometry can therefore be investigated. Prominent features in the ADXRF data clearl y demonstrate that both Cu and Se atoms have migrated into the CdS layer in the heterojunction while In atoms remain intact in the CuInSe2 single crys tal. The local structures around Cu in the system also show a significant c hange after the deposition of CdS, as manifested by the appearance of new C d near neighbors in the XAFS spectra. (C) 1999 American Institute of Physic s. [S0021-8979(99)02223-9].