Synthesis and characterization of polycrystalline GeS thin films for optoelectronic applications

Layered semiconductors are promising for new optoelectronic applications due to their unique optical and electronic properties. This study focuses on the synthesis of thin germanium monosulfide (GeS) films and the characterization of their structural and optoelectrical properties. We show that rapid thermal evaporation (RTE) enables effective synthesis of large-area polycrystalline GeS thin films on glass, fluorine-doped tin oxide and interdigitated array (IDA) electrode substrates. However, the one-step deposition process leads to uncontrolled, randomly oriented crystal growth. We have developed a two-step process that involves the initial deposition of an amorphous film at a temperature below 350 °C and subsequent annealing at 370 °C, ensuring complete GeS crystallization and the formation of high-quality polycrystalline GeS films with controlled thickness and layer orientation. Photoelectric characterization using current-voltage (JV) characteristics, transient photocurrent and time-delayed collection field (TDCF) measurements revealed that polycrystalline GeS is a photosensitive material with long carrier lifetimes but with rapidly decreasing mobility. GeS is potentially promising for optoelectrical applications. • A rapid thermal evaporation (RTE) method allows synthesizing large-area polycrystalline GeS films. • The two-step deposition process enhances GeS film crystallinity and orientation controll. • Light sensitivity and long carrier lifetimes show the potential of polycrystalline GeS films for optoelectronic applications.