Role of reducing environment in the chemical growth of zinc selenide thin films

Chemical deposition of ZnSe (Zn/Se ratio, 0.57≤x≤0.99) thin films highlighting influence of reducing environment on the structural properties and surface morphology is presented. Hydrazine hydrate was used as a reducing agent to initiate growth process and to reduce selenosulfate to Se2− ions that permits formation of non-stoichiometric ZnSe film layers. ZnSe films thus obtained are adherent, homogeneous and diffusely reflecting with light brown coloured tinge. These films were characterized through XRD, SEM, EDS and AFM techniques to reveal the structural and morphological informations. As-grown films are polycrystalline wurtzite with (1 0 1) preferred orientation. d-values change considerably whereas I/Imax is more or less constant. The average lattice parameters have similar trend of variation with Zn/Se ratio. Non-uniform distribution of spherical ZnSe crystallites was observed through SEM. The micrographs further indicated marginal agglomeration of crystallites forming globule like overgrowth. AFM studies spotlighted influence of reducing environment on the surface roughness of the films. The bulk ZnSe exhibits LO and TO phonon bands at 252 cm−1 and 205 cm−1 respectively as indicated by Raman studies. The optical band gap is decreased a little and is correlated to variation in the excess metallic Se-phase.

► ZnSe film growth from a chemical bath is unique and key technology today.
► Excellent quality ZnSe thin films can be grown under reducing atmosphere.
► As-grown ZnSe exhibits hexagonal phase with crystallite size in the nano range.
► SEM showed nonuniformly distributed spherical growth of the crystallites.
► Lack of centre of symmetry confirms polycrystalline nature of ZnSe films.