Synthesis of ZnO: Ge nanocomposite thin films by plasma gas condensation

In this work, we introduce a new method for the synthesis of Ge nanoparticles embedded ZnO thin films that are considered to be a potential candidate for photovoltaic applications. As opposed to current techniques, for the independent preparation of Ge nanoparticles, we propose using Cluster Deposition Source (CDS), which utilizes gas condensation of sputtered Ge atoms. For the synthesis of ZnO thin film host material conventional sputtering technique is employed. In the proposed technique independently synthesized Ge nanoparticles and ZnO thin films are combined into a composite structure on (100) oriented Si substrates. X-ray diffraction (XRD) patterns of the samples have revealed that Ge nanoparticles preferentially settle on (113) planes on top of the (002) oriented ZnO layer. It is realized that Ge nanoparticles with sizes ranging from 16 nm to 20 nm could be embedded into a well-defined ZnO matrix. In fact, transmission electron microscopy (TEM) studies performed on Ge nanoparticles captured on a Cu grids placed just above the substrate during deposition for about 60 s have manifested that Ge nanoparticles reach to ZnO matrix as clusters composed of particles with sizes of about 7–8 nm and then eventually grow larger due to substrate heating implemented during capping layer deposition. Optical absorption measurements have revealed that Ge nanoparticle inclusion lead to an additional absorption edge at about 2.75 eV along with 3.17 eV edge resulting from ZnO host.