Impact of Pulse Duration on the Properties of Laser Hyperdoped Black Silicon

The impact of three different pulse durations (100 fs, 1, and 10 ps) on the formation of laser hyperdoped black silicon with respect to surface morphology, sub-bandgap absorptance, the sulfur concentration profile, and the effective minority carrier lifetime after Al₂O₃ surface passivation is investigated. The current flow behavior is compared through the hyperdoped layer by I–V measurements after hyperdoping with different pulse durations. For conditions that give the same absolute sub-bandgap absorptance, an increase in pulse duration from 100 fs to 10 ps results in a shallower sulfur concentration profile. Findings are explained by an increasing ablation threshold from 0.19 J cm⁻² for a pulse duration of 100 fs to 0.21 J cm⁻² for 1 ps and 0.34 J cm⁻² for 10 ps. The formation of an equally absorbing layer with a shallower doping profile results in a reduction in contact and/or sheet resistance. Despite the higher local sulfur concentration, the samples show no decrease in carrier lifetime measured by quasi-steady-state photoconductance decay on Al₂O₃ surface-passivated samples. The investigation shows that longer pulses of up to 10 ps during laser hyperdoping of silicon result in advanced layer properties that promise to be beneficial in a potential device application.