Low-Temperature Iron-Induced Crystallization of Germanium Thin Films: Substrate-Dependent Structural and Electrical Properties

Abstract

This study investigates iron-induced crystallization (Fe-IC) of amorphous germanium (α-Ge) thin films deposited on aluminum-doped zinc oxide (AZO) and crystalline silicon (c-Si) (100) substrates. A thin Fe interlayer effectively promotes the crystallization of α-Ge thin films during post-annealing at 400°C–500°C. Raman spectroscopy and X-ray diffraction (XRD) analyses reveal a clear amorphous-to-crystalline transition, accompanied by peak sharpening, linewidth reduction, and the development of a preferential Ge(111) orientation. The combined Raman–XRD analysis demonstrates progressive strain relaxation and grain growth, with significantly enhanced crystallization observed on c-Si compared to AZO substrates. Electrical measurements further show that Fe-assisted crystallization markedly improves charge transport, leading to ohmic behavior in AZO-based films and rectifying characteristics in c-Si–based structures. These findings establish Fe as an effective catalyst for low-temperature crystallization of Ge thin films and highlight the critical role of substrate properties in governing microstructural evolution and electrical performance.