Stress-assisted Copper-induced Lateral Growth of Polycrystalline Germanium

Abstract

Lateral growth of poly-Ge at temperatures as low as 150°C is reported. External mechanical stress has been properly manipulated to drive the low temperature Cu-induced crystallization of poly-Ge wherever Cu is deposited to form the crystallization seed for lateral growth. Uniaxial compressive stress has been externally applied to the Ge layer by bending the flexible PET substrate inward. A 10-hour period thermo-mechanical post-treatment in the presence of 0.05% equivalent compressive strain leads to a growth rate of 2.5 µm/hour in the direction of the applied stress and 1.8 µm/hour in the perpendicular direction, as confirmed by SEM analysis. We believe that partial growth of the Cu-seeded poly-Ge region in the form of tetragonal structures is the key feature which leads to the lateral growth of the pure-Ge strip. Elimination of the compressive stress hinders the lateral growth completely, even at reasonably high temperatures.