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Abstract:
Femtosecond-laser hyperdoping of sulfur in silicon typically produces a concentration gradient that
results in undesirable inhomogeneous material properties. Using a mathematical model of the
doping process, we design a fabrication method consisting of a sequence of laser pulses with
varying sulfur concentrations in the atmosphere, which produces hyperdoped silicon with a
uniform concentration depth profile. Our measurements of the evolution of the concentration
profiles with each laser pulse are consistent with our mathematical model of the doping
mechanism, based on classical heat and solute diffusion coupled to the far-from-equilibrium
dopant incorporation. The use of optimization methods opens an avenue for creating controllable
hyperdoped materials on demand.