Fig. 1: Laser writing of in-plane longitudinal SiGe heterostructures via scan-speed-dependent spatial redistribution of the composition.
a Optical microscope image showing laser-written microstripes on a Si0.5Ge0.5 thin film (epi-SiGe) epitaxially grown on Si substrates, for scan speeds in the range of 0.1–200 mm s-1. b Results of finite-element-method (FEM)-based phase-field simulations for laser-driven phase segregation are given as composition color maps showing the Ge molar fraction x(r) for the short transient (blue) and indefinitely-long steady-state regions (yellow/orange) solidified behind the laser-induced molten zone (red) traveling at a constant scan speed in the range of 1–500 mm s−1. c Simulated spatial redistribution of the alloy composition in the cross-section and on the top surface of a laser-written microstripe. An in-plane longitudinal SiGe heterostructure was formed with a Ge-rich strip core and Si-rich under-cladding along the scan direction. The image size in the transverse direction was rescaled accordingly to match the width of the laser-written microstripe in d. d Optical microscope image showing the angle-polished cross-section and top facet of a longitudinal SiGe heterostructure laser-written at 200 mm s−1 for qualitative comparison with the simulation result.
