Morphological and compositional study of CBD-ZnSe thin films by microscopytechniques and angle resolved XPS

A morphological and compositional study is carried out on ZnSe thin films o btained by the chemical bath deposition (CBD) method. SEM, TEM and AFM imag es are shown for the morphological characterisation. Angle-resolved XPS (AR XPS) measurements are used for the study of surface and subsurface composit ion of the films. The composition underneath is studied with XPS analysis o f films eroded by sputtering. It is found that films have a mixed ZnSe-ZnO (or Zn(OH)(2)) composition. The Zn/Se ratio iii the film increases with dep th, indicating that Zn is preferentially as ZnO-Zn(OH)(2) close to the film -substrate interface, and that the ZnSe proportion increases above. Such co mposition inhomogeneity is attributed to a change in the deposition mechani sm during film growth. At first, it proceeds via reaction of adsorbed Zn an d Se precursors, and then by deposition of ZnSe clusters formed in the bulk of the solution. Apparently the first mechanism is less efficient for the formation of a pure ZnSe film, at least under the experimental conditions u sed here, hence gives rise to higher concentration of Zn oxides close to th e film-substrate interface. At longer times during the deposition process, the fluster precipitation mechanism predominates and, consequentially, the top layers of the him become richer in ZnSe but less compact. Other compoun ds detected by ARXPS are Se-0 occluded in the bulk of the film, and some Se O2 at the surface. Annealing at 300 degrees C results in structural and com positional changes which involve compaction of the films, the loss Elf the occluded Se-0, the increment of the SeO2 overlayer and the transformation o f Zn(OH)(2) into ZnO and/or Zn(O, Se) compounds. (C) 2000 Elsevier Science S.A. All rights reserved.