This PDF file contains the front matter associated with SPIE Proceedings Volume 12003, including the Title Page, Copyright information, Table of Contents, and Conference Committee listings.

We present two multi-color optical excitation techniques to probe quantum emitters in the two-dimensional semiconductor, hexagonal boron nitride. Firstly, we demonstrate controllable optical switching with different color lasers between optically bright and dark states of the color centers. Secondly, we use stimulated emission depletion (STED) as a spectroscopic probe, complementary to photoluminescence excitation spectroscopy, and reveal differences between the electron-phonon interaction in the ground and excited states. Finally, we show that hBN color centers are a viable fluorophore for STED imaging, achieving a spatial resolution of ∼ 50 nm.

First principle DFT-based microscopic many-body models are used to investigate inter- and intra-valley carrier dynamics in the monolayer transition-metal dichalcogenide MoTe₂. Electron-electron and electron-phonon scatterings are calculated for transitions within the full Brillouin zone to determine overall carrier relaxation timescales as well as intra- and inter-valley transition rates. For excitation above the barriers separating bandstructure valleys carriers are found to relax on a ten femtosecond timescale into hot quasi-Fermi distributions at the band minima. Subsequently, the hot carrier plasma is cooled down on a picosecond timescale predominantly through emission of optical phonons. Local carrier occupations lead to strong energy renormalizations in momentum space. However, for the material investigated here, the global energy minimum remains at the K-points once carriers relax into global quasi-Fermi distributions. No transition from a direct to an indirect bandgap is observed.

The integration of atomically thin materials into semiconductor and photonic foundries is crucial for their use in commercial devices. However, current integration approaches are not compatible with industrial processing on wafer level, which is one of the bottlenecks hindering the breakthrough of 2D materials. Here, we present a generic methodology for the large-area transfer of 2D materials and their heterostructures by adhesive wafer bonding for use at the back end of the line (BEOL). Our approach exclusively uses processes and materials readily available in most largescale semiconductor manufacturing lines. Experimentally, we demonstrated the transfer of CVD graphene from Cu foils to 100-mm-diameter silicon wafers, the stacking of two monolayers of graphene to 2-layer graphene, and the formation of MoS₂/graphene heterostructures by two consecutive transfers. We expect that our methodology is an important step towards the commercial use of 2D materials for a wide range of applications in optics and photonics.

The potential for establishing energy gaps by pseudo-magnetic fields in strain-engineered graphene has sparked much interest recently. However, the limited sizes of induced pseudo-magnetic fields and the complicated platforms for straining graphene have thus far prevented researchers from harnessing the unique pseudo-magnetic fields in optoelectronic devices. In this work, we present an experimental demonstration of triaxially strained suspended graphene structures capable of obtaining quasi-uniform pseudo-magnetic fields over a large scale. The novel metal electrode design functions as both stressors and current injectors. We also propose a hybrid laser structure employing a 2D photonic crystal and triaxially strained graphene as an optical cavity and gain medium, respectively.

The field of UV-C LEDs based on AlGaN semiconductors is rapidly progressing due to increasing demands for disinfection. Viruses and bacteria are eradicated efficiently and sustainably when exposed to UV-C radiation. The current worldwide pandemic has shed light on the growing need for solutions to prevent both fomite and airborne transmission of pathogenic microbes, and UV-C radiation from LEDs presents a safe and sustained solution for a future beyond the current crisis. Most market leaders are based on thin-film technology that has intrinsic challenges of dislocation densities, heat extraction, and internal polarization, thus leading to limited internal quantum efficiencies. Graphene, with its outstanding properties of high thermal conductivity, high transparency to the light of all wavelengths, combined with a low sheet resistance, promises to solve some of these challenges in AlGaN-based UV-C LEDs. We report the demonstration of graphene as both the substrate and transparent electrode of a functional AlGaN nanowire-based UV-C LED. Graphene, as the substrate and electrical contact for UV-C flip chip LED, also gives the potential to use its high thermal conductivity for efficient heat dissipation. Moreover, in comparison to thin-film UV-C LEDs, our AlGaN-based nanowire array on graphene results in dislocation-free devices with semi-polar orientation, which provides us the ability to achieve high internal quantum efficiency in our LEDs.

We report Second Harmonic Generation (SHG) enhancement in a custom-designed vertically stacked multilayer Gallium Selenide with a low-index PMMA spacer layer. The structure obtained using an evolutionary optimization algorithm consists of two 40 nm GaSe layers separated by a 195 nm PMMA layer, with a 130 nm Silicon-dioxide layer on a Silicon substrate. This results in 11x and 303x enhancement in SHG signal when compared to a single 40nm GaSe on a 130nm and 300nm SiO₂/Si substrate, respectively. This work underscores the importance of micro-cavity engineering in choosing appropriate 2D material and interspacer thickness to enhance SHG emission from popular 2D materials.

Pseudo-magnetic field in strained graphene has emerged as a promising route to allow observing intriguing physical phenomena that would be inaccessible with laboratory superconducting magnets. However, experimental observation of the impact of pseudo-magnetic field on optical and electrical properties of graphene has remained unknown. Here, using time-resolved infrared pump-probe spectroscopy, we provide unambiguous evidence of slow carrier dynamics enabled by a giant pseudo-magnetic field (~100 T) in periodically strained graphene. Our finding presents unforeseen opportunities towards harnessing the new physics of graphene in previously unachievable high magnetic field regimes.

Two-dimensional (2D) materials are getting a lot of attention in the nonlinear optics research due to their excellent structural characteristics and nonlinear effects. Here, the layered dependent second harmonic generation (SHG) of 2D-gallium sulfide (GaS) nanosheets are demonstrated for the first time. According to the obtained findings, SHG signal was identified exclusively for the odd layer GaS-nanosheets due to the existence of broken inversion symmetry. The even layer, on the other hand, generated no SHG signal due to its centrosymmetric structure. Moreover, the layered dependent damaged threshold of the prepared sample is also discussed here.

Localized surface plasmon resonance (LSPR) shows great promise in optoelectronic devices, solar steam generation, and medical treatment owing to its strong enhancement of light-matter interactions. Herein, for the first time, 1D-2D metallic MWCNTs and HfTe₂ van der Waals (vdW) heterostructure are used for demonstrating the LSPR to enhance the temperature of a solar absorber. The proposed vdW heterostructure is synthesized by a facile self-grown hydrothermal method and grown on top of a copper (Cu) foam. The HRTEM image and EDS spectrum confirm the formation of the vdW heterostructure on the Cu foam. The synergic effect of Te-based TMD with MWCNT provides a broadband absorbance of approximately 92% weighted by the standard air mass 1.5 global solar spectrum and takes full advantage of LSPR to confine heat in a small area. Moreover, the ultrathin nature of MWCNT endows them with the super permeability of water vapor. The solar-driven steam generation performance of the prepared vdW heterostructure demonstrates an excellent evaporation efficiency of 87.43% and an increment of the surface temperature to 79.8 °C in less than 20 mins under 1 kWm^–2 solar illumination. Therefore, the proposed vdW heterostructure can be realized in high-temperature steam generation applications.