In this paper, a high-quality crystalline Ge thin film (~10 nm) is grown on n-Si substrate by employing vapour-liquid-solid (VLS) method. The crystalline quality and the film thickness are measured by XRD and spectroscopic ellipsometry experiments, respectively. The current-voltage characteristics of the Ge/n-Si hetero-junction device are measured and the impact of growth time on the rectification properties is studied.