Laser Crystallization of Amorphous Ge Thin Films via a Nanosecond Pulsed Infrared Laser

Understanding the dynamics of the laser crystallization (LC) process of Ge thin films by nanosecond (ns) pulsed infrared (IR) lasers is important for producing homogeneous, crack-free crystalline device-grade films for use in thin-film transistors, photo-detectors, particle detectors, and photovoltaic applications. Our motivation is to describe a ns IR laser-based crystallization process of Ge by implementing suitable parameters to fabricate thin-film devices. Our LC technique was applied to crystallize thin amorphous Ge (a-Ge) films with thicknesses suitable for device applications. The LC process was applied to a 300 nm-thick a-Ge thin film utilizing a 200 ns pulsed IR laser with a wavelength of 1064 nm. Electron-beam-evaporation-deposited a-Ge on glass substrates were subject to successive ns laser pulses with a line focus. The crystallinity of the polycrystalline Ge (pc-Ge) films was evaluated by Raman spectroscopy, optical microscopy, and electron backscatter diffraction (EBSD). LC-Ge exhibited a Raman peak of around 300 cm(-1), confirming successful crystallization of a-Ge. pc-Ge domain sizes exceeding several tens of micrometers were observed in EBSD scans. LC of a-Ge minimizes the thermal energy budget of processing and provides flexibility to locally crystallize the film. Our work is the first demonstration of the LC of a-Ge thin films, resulting in domain sizes exceeding tens of micrometers via a ns pulsed IR laser.