Laser-Fluence Effect on Morphological Evolution and Optical Response of Ge Microcones Grown on Si by Pulsed Laser Deposition

Microstructured germanium (Ge) coatings on silicon (Si) are promising for enhancing light–matter interactions in optoelectronic devices. This work reports a single-step pulsed laser deposition (PLD) route for fabricating crystalline Ge conical microstructures and nanostructures on Si. A review of the available literature indicates that this microconical morphology has not been previously reported in Ge/Si systems grown by PLD. Laser fluence is the key parameter governing the morphology of the Ge microstructures. Depositions at 1, 2, and 3 J/cm2 produce distinct populations of conical structures, ranging from nanocones (190 ± 10 nm in height and 360 ± 10 nm in base diameter) at 1 J/cm2, to intermediate microcones (1.4 ± 0.1 μm in height and 2.8 ± 0.1 μm in base diameter) at 2 J/cm2, and well-developed microcones (5.8 ± 0.1 μm in height and 16.5 ± 0.1 μm in base diameter) with higher surface density at 3 J/cm2. UV–vis measurements reveal a morphology-dependent optical response, with broadband reflectance reduced to 30–40% over the 550–1200 nm wavelength range. These results show that laser fluence is an easy and effective way to control both the shape and optical properties of Ge microcones, making single-step PLD a scalable method for creating light-trapping Ge/Si interfaces in photonic and optoelectronic devices.