Novel single-crystalline-like germanium thin films on flexible, inexpensive substrates: Influence of architecture and film thickness

Single-crystalline-like germanium films have been demonstrated on flexible metal substrates. Using MgO templates made by ion beam assisted deposition (IBAD), germanium films with grain-to-grain misorientation as small as 1° have been demonstrated. The out-of-plane texture of the germanium film has been found to be sensitive to the intermediate buffer layers used in the architecture. Germanium films are grown epitaxially on CeO₂ films which are deposited on the MgO templates without or with intermediate layers such as LaMnO₃ and SrTiO₃. It is found that the strongest preferred (400) orientation of Ge is achieved with SrTiO₃ intermediate layer. Additionally, the highest hall mobility in the single-crystalline-like germanium has been achieved in architectures with SrTiO₃ intermediate layer. Hall mobility values of the germanium film are found to increase with film thickness and reach as high as 518 cm²/Vs. Cross sectional transmission electron microscopy (TEM) images of thick germanium films on IBAD templates show a high density of defects near the CeO₂ interface and a decrease in defect density in the mid and top part of the film.