Low-temperature copper-induced lateral growth of polycrystalline germanium assisted by external compressive stress

Copper-induced lateral growth of polycrystalline germanium (poly-Ge) at temperatures as low as 150°C was enabled by the application of an external mechanical stress during the annealing step of sample processing. An equivalent compressive strain of 0.05% was externally applied at 150°C for 10 h to a deposited amorphous Ge layer and crystalline growth rates of 2.5 and 1.8 μm/h were observed in directions parallel and perpendicular to the stress axis, respectively. These results were confirmed by scanning electron microscope and transmission electron microscopy (TEM) analyses. In addition, TEM and x-ray diffraction analyses indicate that a fraction of poly-Ge annealed in the presence of applied compressive stress possessed a tetragonal structure with space-group P4 ₃2 ₁2. The presence of the tetragonal phase is hypothesized to be the primary mechanism responsible for the lateral growth of poly-Ge.