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.