Speaker
Description
The precise, localized control of semiconductor properties is a central challenge in the development of next-generation nanoelectronics, optoelectronics, and photonic devices. Among the available processing techniques, nanosecond pulsed laser processing has emerged as a uniquely powerful tool, offering spatial and temporal confinement of energy deposition, compatibility with existing Si CMOS infrastructure, and the ability to drive materials far from thermodynamic equilibrium. In this work, we demonstrate two complementary laser-based routes to engineer semiconductor thin films: nanosecond UV pulsed laser annealing (PLA) for the crystallization of sputter-deposited MoS₂, and nanosecond pulsed laser melting (PLM) for the fabrication of supersaturated GeSn alloys.
Wafer-scale synthesis of high-quality layered transition metal dichalcogenides (TMDs) remains a key bottleneck for their integration into functional devices. Sputtering offers a scalable and reproducible route to large-area MoS₂ films; however, as-deposited layers are amorphous and require post-deposition crystallization. Here, we present a two-step process in which stoichiometric MoS₂ films are sputter-deposited on Si/SiO₂ substrates and subsequently irradiated with nanosecond UV (248 nm) laser pulses in a N₂-rich atmosphere [1]. By systematically varying the number of pulses and the energy density, we identify the processing window yielding (002)-oriented nanocrystalline 2H-MoS₂ films with uniform coverage, characterized by Raman spectroscopy, XRD, RBS, AFM, and TEM. Heat flow simulations confirm that laser energy confinement keeps the Si/SiO₂ substrate temperature well below the back-end-of-line thermal budget limit of Si CMOS technology (770 K), enabling direct integration with existing device platforms.
Building on the concept of laser-driven non-equilibrium processing, we further exploit nanosecond PLM to fabricate GeSn alloys with Sn concentrations far exceeding the equilibrium solid solubility in Ge. Above ~8 at.% Sn, GeSn alloys undergo an indirect-to-direct bandgap transition, enabling mid-infrared light emission. Using a two-step ex-situ approach, thin Sn films (<50 nm) are deposited by DC magnetron sputtering onto Ge(100) and Ge-on-Si substrates. Subsequent nanosecond PLM melts the near-surface region, enabling rapid Sn diffusion and incorporation up to 20 at.% [2,3]. SIMS depth profiles confirm box-like, uniform Sn distributions, while TEM reveals Sn segregation along threading dislocations at the GeSn/Ge interface. The substitutional Sn fraction correlates with regrowth velocity: lower energy densities favor substitutional incorporation, while a low-energy corrective pulse (300–400 mJ/cm²) restores substitutional Sn in samples processed at higher fluences (800 mJ/cm²). Reciprocal space maps reveal tensile strain from thermal mismatch, lowering the Sn threshold for the direct bandgap transition.
Together, these results establish nanosecond pulsed laser processing as a versatile and CMOS-compatible platform for the local, tunable synthesis of advanced semiconductors, with direct implications for 2D material integration, mid-infrared photonics, and beyond.
References
[1] E. Di Russo et al., Synthesis of Large-Area Crystalline MoS₂ by Sputter Deposition and Pulsed Laser Annealing. ACS Appl. Electron. Mater. 5 (5) 2862 (2023).
[2] E. Di Russo et al., Synthesis of relaxed Ge0.9Sn0.1/Ge by nanosecond pulsed laser melting. Applied Surface Science 612, 155817 (2023).
[3] D. Fontana et al., Ex-situ n-type heavy doping of Ge1-xSnx epilayers by surface Sb deposition and pulsed laser melting. Applied Surface Science 600, 154112 (2022).
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