Low-temperature laser crystallization of Ge layers grown on MgO substrates

The crystallization of amorphous Ge layers grown at room temperature was investigated using continuous-wave green laser irradiation. The most favorable crystallization conditions for the 40-nm-thick Ge layer were determined by adjusting the laser power density, laser beam shape, and laser scan direction. The optimized laser irradiation crystallizes the amorphous Ge layer in a significantly long-range ordered structure on MgO (001) substrate, whereas that on SiO2/Si substrate becomes polycrystalline. The line-shaped flat-top beam profile of the laser along the MgO [100] scan direction is a decisive factor for uniform crystallization on the MgO substrate. A SiO2 capping layer suppresses heat dissipation from the surface of the amorphous Ge layer and facilitates a lower temperature at the Ge/MgO interface, resulting in the initiation of crystallization from the Ge/MgO interface after laser irradiation. Our analysis indicates that the Ge layer crystallized on MgO (001) substrate exhibits an in-plane epitaxial relationship of Ge [110] // MgO [100] with 45° misorientation.