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

Abstract

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.