Growth of epitaxial strontium titanate films on germanium substrates using pulsed laser deposition

The monolithic integration of metal oxide thin films with conventional semiconductors like silicon and germanium enables new functionalities to be introduced to semiconductor devices. In this regard, we used pulsed laser deposition (PLD) to grow epitaxial strontium titanate (STO) films on Ge (001) single crystal. The study of the structure and phase of STO films and of Ge(001) was performed using in situ X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). By optimizing surface preparation and deposition conditions, it was possible to grow epitaxial STO films with a sharp interface without the presence of interfacial amorphous oxide layer. The effects of the Ge(001) surface substrate cleaning, growth temperature, oxygen partial pressure, and laser energy density on the growth of STO films are discussed. In particular, we find that PLD of STO on Ge(001) single crystal in the presence of O-2 leads to growth of (100) and (110) planes while in its absence the growth is largely limited to the (110) plane.