Substrate bias effect on Al–Si and Al–Ge thin film structure

Phase-separated Al–Si and Al–Ge films, composed of Al cylinders embedded in an amorphous Si and Ge matrix, respectively, were investigated by sputtering method with substrate bias voltage. In the Al–Si system, the period of Al cylinders was increased by applying a negative bias voltage to the substrate, which is consistent with the simulation results. On the other hand, the diameter of Al cylinders increased up to a bias voltage of − 80 V, and then it began decreasing beyond − 100 V accompanied by the appearance of a chain-like arrangement of Al cylinders. In the Al–Ge system, the period and diameter of Al cylinders increased by applying a negative bias voltage. However, in the Ge-rich film prepared at a high bias voltage, relatively large dots with low area density were observed. Transmission electron microscope observation revealed that the film was composed of AlGe γ2 phase as a matrix and Al-rich amorphous dots.