About the strain state of different metal oxide layers epitaxially grown on Si(1 1 1)

The strain state of metal oxides Pr(2)O(3), Y(2)O(3) and Sc(2)O(3) used as buffer material in different heteroepitaxially grown semiconductor-oxide-Si(1 1 1) layer stacks was studied by x-ray diffraction techniques at room temperature (RT) and near the growth temperature of 625 degrees C. A broad spectrum of different strain states was found depending on preparation conditions, layer combination and layer thickness. Pr(2)O(3) behaves differently from the other two investigated oxides as it grows in a hexagonal phase on Si(1 1 1) and must be transformed into the stable cubic phase by annealing processes. This transformation is accompanied by the creation of an amorphous silicate interface layer that leads to a decoupling of substrate and oxide lattices and finally to a partial relaxation of the cub-Pr(2)O(3) layer only. High-temperature measurements demonstrate that there exists a measurable difference between the strain state at RT, where x-ray measurements are typically performed, and at growth temperature. The coefficient of thermal expansion of different metal oxides was measured in thin film structures for the first time. These coefficients are significantly higher compared with that of Si, which leads to an additional tensile strain component when the samples are cooled down to RT.