Ultrafast laser heating for controlling the optoelectronic properties of sulfur hyperdoped black silicon

Ultrashort pulse laser processed sulfur hyperdoped black silicon represents a promising silicon-based material for infrared optoelectronic applications due to its high sub-bandgap optical absorptance. Non-thermal melting and resolidification processes associated with such laser processing, however, result in amorphous and polycrystalline phases which may be detrimental for this purpose. Furthermore, the sulfur impurities are electrically inactive, impeding the formation of a rectifying junction. This work demonstrates an ultrafast laser heating process based on heat accumulation with laser pulses of 10 ps pulse duration at high repetition rates of 41 MHz and peak fluences between 33% and 66% of the ablation threshold as a method to (i) recrystallize the material and (ii) electrically activate the sulfur dopants while (iii) maintaining the sub-bandgap absorption. Furthermore, laser heating recovers the optical activity of sulfur states that have been previously deactivated by thermal annealing. The demonstrated process can have versatile applications in material functionalization due to its highly localized heat input accompanied by high cooling rates.

Automated summary

Ultrashort pulse laser processing can improve the optical absorptance of sulfur hyperdoped black silicon for infrared optoelectronic applications, but it may also result in amorphous and polycrystalline phases and electrically inactive sulfur impurities. This study demonstrates an ultrafast laser heating process that recrystallizes the material, activates the sulfur dopants, and maintains sub-bandgap absorption. The process also recovers the optical activity of sulfur states deactivated by thermal annealing, making it highly applicable for material functionalization due to its localized heat input and high cooling rates.