Crystallization dynamics of Ge in In/Ge bilayer films under Swift Heavy Ion irradiation: Experimental and Density Functional Theory Studies

Indium (In) metal induced crystallization (MIC) of a-Ge in In/poorly-crystalline Ge bilayer thin films under 120 MeV Ni7+ swift heavy ion (SHI) irradiation at different fluences of 1 × 1011 ions-cm-2, 5 × 1011 ions-cm-2, 1 × 1012 ions-cm-2, 5 × 1012 ions-cm-2, followed by thermal annealing at 200 ℃, is presented. The ion irradiation followed by thermal annealing leads to crystallization of a-Ge. The crystallization of a-Ge is decreasing with increasing ion fluence. Further, it changes the lattice plane of In (101) to In (110), but that of Ge (111) remains the same. The interface mixing due to the ion irradiation is confirmed and explained using the thermal spike model. A new approach to explain the mechanism of MIC, Density Functional Theory (DFT), is employed. The electronic and thermodynamic properties of the pristine and post-thermal annealed samples are compared. The interaction between the 4p orbital of Ge and the 5p orbital of In leads to the weakening of Ge-Ge bonds, which produces many free Ge atoms. The change in enthalpy is redistributed to lower entropy and a higher change in Gibbs free energy, which is responsible for the crystallization of a-Ge at a relatively lower temperature of 200 ℃.