Structural properties of thin Zn 0.62Cu 0.19In 0.19S alloy films grown on Si(111) substrates by pulsed laser deposition

Abstract

Alloys of Zn 2−2 x Cu x In x S 2 (ZCIS) have been grown on Si(111) substrates by pulsed laser deposition (PLD). The thin films grew epitaxially on chemically treated Si(111) regardless of an about 2–5 nm thick interfacial amorphous layer between the ZCIS and the Si substrate. The particular Zn 0.62Cu 0.19In 0.19S layers under investigation consist of column-like grains propagating from the interface to the layer surface. Despite of the existence of the amorphous layer in the interfacial region each ZCIS grain is precisely oriented to the structure of the underlying silicon substrate and to the neighboring ZCIS grains without any azimuthal misorientation. Each individual column-like grain contains many twin lamellae of various thickness that lie parallel to the interface and, therefore, coherent Σ3{111} twin boundaries occur. Σ3{112} grain boundaries are formed perpendicular to the interface during the intergrowth of the individual columns. Perfect dislocations with their lines parallel to the interface envelop the columns and finally, a dislocation network like a honeycomb can be observed during TEM plane-view observation. However, polycrystalline ZCIS layers exhibiting a distinct 〈111〉 texture have been formed on untreated Si(111) substrates, where the 2–2.5 nm thick intermediate native layer consists of amorphous SiO x . The individual ZCIS grains were found to be polysynthetically twinned too. Amorphisized regions have always been produced inside the chemically treated Si substrates due to the out-diffusion of copper from the layer into the Si substrate that seems to be favored against that of Zn. However, the amorphous native SiO x layer which covers the untreated silicon substrates prevents substantially the out-diffusion of metal atoms from the layer into the substrate and, therefore, no diffusion-induced defects have been generated inside the untreated Si substrate.