In-situ Oxide Substrate Preparation by Long-wavelength Laser Heating

The film-substrate interface crucially determines the structural quality of the following layers. The substrate needs to provide a chemically uniform structure with a specific surface reconstruction as a functional template for the nucleation of the first epitaxial layer. In contrast to compound semiconductor MBE, the temperature range to reach an adsorption-desorption equilibrium is out of reach for most established oxide substrate heater technologies. Therefore, ex-situ chemical treatments are often performed to obtain a desired substrate surface stoichiometry. We demonstrate that by using a ~10 µm laser substrate heating system that we have developed, typical oxide substrates can be heated with high precision to any temperature below their melting point. This allows the termination of oxide substrates by selectively evaporating the volatile components of the substrate surface [1], thereby foregoing the need for chemical etching. In addition, such a laser heating enables the deposition of virtually any material in a thermal laser epitaxy [2] setup, which uses exclusively lasers as power sources, both for substrate heating and the continuous thermal evaporation from individual, high-purity sources.
[1] https://doi.org/10.1063/5.0008324
[2] https://doi.org/10.1063/1.5111678