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Laser-driven phase segregation and tailoring of compositionally graded microstructures in Si-Ge nanoscale thin films

DOI: 10.1021/acsami.9b22135 DOI Help

Authors: Ozan Aktas (University of Southampton) , Swe Z. Oo (University of Southampton) , Stuart Macfarquhar (University of Southampton) , Vinita Mittal (University of Southampton) , Harold M. H. Chong (University of Southampton; Japan Advanced Institute of Science and Technology) , Anna C. Peacock (University of Southampton)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Acs Applied Materials

State: Published (Approved)
Published: February 2020
Diamond Proposal Number(s): 17304

Abstract: The ability to manipulate the composition of semiconductor alloys on-demand and at nanometer-scale resolutions is a powerful tool that could be exploited to tune key properties such as the electronic bandgap, mobility, and refractive index. However, existing methods to modify the composition involve altering the stoichiometry by temporal or spatial modulation of the process parameters during material growth, limiting the scalability and flexibility for device fabrication. Here, we report a laser processing method for localized tailoring of the composition in amorphous silicon-germanium (a-SiGe) nanoscale thin films on silicon substrates, post-deposition, by controlling phase segregation through the scan speed of the laser-induced molten zone. Laser-driven phase segregation at speeds adjustable from 0.1 to 100 mm s-1 allows access to previously unexplored solidification dynamics. The steady-state spatial distribution of the alloy constituents can be tuned directly by setting the constant laser scan speed to achieve indefinitely long Si1-xGex microstructures exhibiting the full range of compositions (0<x<1). To illustrate the potential, we demonstrate a photodetection application by exploiting the laser-written polycrystalline SiGe microstripes, showing tunability of the optical absorption edge over a wavelength range of 200 nm. Our method can be applied to pseudo-binary alloys of ternary semiconductors, metals, ceramics and organic crystals, which have phase diagrams similar to that of SiGe alloys. This study opens a route for direct laser writing of novel devices made of alloy microstructures with tunable composition profiles, including graded-index waveguides and meta-surfaces, multi-spectral photodetectors, full-spectrum solar cells, and lateral heterostructures.

Journal Keywords: laser materials processing; semiconductor alloys; nanoscale thin films; compositionally graded microstructures; phase segregation; silicon-germanium

Diamond Keywords: Alloys; Semiconductors

Subject Areas: Materials, Physics

Instruments: I18-Microfocus Spectroscopy

Discipline Tags:

Material Sciences Metallurgy Physics Surfaces interfaces and thin films

Technical Tags:

Diffraction Imaging X-ray Fluorescence (XRF)