Tin diselenide (SnSe2) is a two-dimensional (2D) semiconductor with a high electron affinity (∼5.2 eV) and inherent n+-type conductivity. While conventional chemical vapor deposition (CVD) has been investigated for the growth of SnSe2, the domain sizes are typically limited to ∼50 μm. This limitation arises primarily from difficulties in precise control of the thermodynamics of nucleation and growth along with the kinetics of vapor-phase transport. To address this issue, we employed flux-assisted growth (FAG) to facilitate liquid-phase precursor transport via a molten flux. As a result, we achieved crystalline SnSe2 flakes with significantly enlarged domain sizes exceeding 300 μm. The synthesized SnSe2 exhibits a well-ordered 1T-phase lattice structure, a high Hall mobility of 262.5 cm2·V-1·s-1, and an electron concentration of 8.23 × 1013 cm-2, confirming its degenerate n-type nature. Furthermore, the SnSe2-based devices show reproducible photoresponse cycles governed by trap-mediated processes yielding a multitime scale fading memory. Our findings provide insights into the feasibility of flux-grown SnSe2 for p-n+ van der Waals tunneling heterostructures and in-sensor reservoir computing.

Two-dimensional (2D) materials have emerged as promising candidates for next-generation integrated single-photon emitters (SPEs). However, significant variability in the emission energies presents a major challenge in producing identical single photons from different 2D SPEs, which may become crucial for practical quantum applications. Although various approaches to dynamically tuning the emission energies of 2D SPEs have been developed to address the issue, the practical solution to matching multiple individual 2D SPEs is still scarce. In this work, we demonstrate precise emission energy tuning of individual SPEs in a WSe2 monolayer. Our approach utilizes localized strain fields near individual SPEs, which we control by adjusting the volume of a stressor layer through laser annealing. This technique allows continuous emission energy tuning of up to 15 meV while maintaining the qualities of SPEs. Additionally, we showcase the precise spectral alignment of three distinct SPEs in a single WSe2 monolayer to the same wavelength.

Complementary metal-oxide-semiconductor (CMOS)-compatible photonic integrated circuits (PICs) capable of operating at visible wavelengths are critical for advanced quantum systems, including trapped-ion quantum computers. However, standard silicon (Si) PICs are fundamentally unsuitable for this task due to silicon's strong intrinsic material absorption, which prevents the efficient propagation of visible light in Si waveguides. In this work, we present a hybrid two-dimensional (2D) integrated silicon-on-insulator (SOI) PIC platform that enables out-of-plane visible light emission through second-harmonic generation (SHG). This emission arises from a monolayer tungsten diselenide (WSe2) with broken inversion symmetry, which is encapsulated within hexagonal boron nitride (hBN) to avoid degradation. Our approach bypasses Si absorption by leveraging the transparency of Si waveguides at the infrared pump wavelength, while nonlinear frequency conversion occurs exclusively in the 2D material at the out-coupling interface to convert the infrared photons into visible light. This work opens a promising pathway toward realizing CMOS-compatible, on-chip visible light sources for quantum technologies.

Semiconductor nanowires have shown great potential for enabling ultra-compact lasers for integrated photonics platforms. Despite the impressive progress in developing nanowire lasers, their integration into Si photonics platforms remains challenging largely due to the use of III-V and II-VI semiconductors as gain media. These materials not only have high material costs, but also require inherently complex integration with Si-based fabrication processing, increasing overall costs and thereby limiting their large-scale adoption. Furthermore, these material-based nanowire lasers rarely emit above 2 um, which is a technologically important wavelength regime for various applications in imaging and quantum sensing. Recently, group-IV nanowires, particularly direct bandgap GeSn nanowires capable of emitting above 2 um, have emerged as promising cost-effective gain media for Si-compatible nanowire lasers, but there has been no successful demonstration of lasing from this seemingly promising nanowire platform. Herein, we report the experimental observation of lasing above 2 um from a single bottom-up grown GeSn nanowire. By harnessing strain engineering and optimized cavity designs simultaneously, the single GeSn nanowire achieves an amplified material gain that can sufficiently overcome minimized optical losses, resulting in a single-mode lasing with an ultra-low threshold of 5.3 kW cm-2. Our finding paves the way for all-group IV mid-infrared photonic-integrated circuits with compact Si-compatible lasers for on-chip classical and quantum sensing and free-space communication.

Forming single-photon emitters (SPEs) in insulating hexagonal boron nitride (hBN) has sparked wide interests in the quantum photonics. Despite significant progress, it remains challenging to deterministically create SPEs at precise locations with a specific type of element for creating defects. In this study, we present a straightforward approach to generate site-deterministic carbon-functionalized quantum emitters in hBN by harnessing ultrasonic nanoindentation. The obtained SPEs are high-quality and can be scaled up to large arrays in a single fabrication step. Comprehensive experimental analyses reveal that the insertion of carbon atoms into the hBN lattice is the source of the robust quantum emission. Complementary theoretical studies suggest possible candidates for the structural origin of the defects based on our experimental results. This rapid and scalable nanoindentation method provides a new way to create SPE arrays with specific types of atoms, enabling the comprehensive investigation of the origins and mechanics of SPE formations in two-dimensional (2D) materials and beyond.

Single-photon emitters (SPEs) hold the key to many quantum technologies including quantum computing. In particular, developing a scalable array of identical SPEs can play an important role in preparing single photons - crucial resources for computation - at a high rate, allowing to improve the computational capacity. Recently, different types of SPEs have been found in various 2D materials. Towards realizing scalable SPE arrays in 2D materials for quantum computation, it is required to develop tunable SPEs that can produce identical photons by precisely controlling emission properties. Here, we present a brief review of the recent progress on various tuning methods in different 2D materials. Firstly, we discuss the operation principle of different 2D SPEs along with their unique characteristics. Secondly, we introduce various dynamic strain engineering methods for tuning the emission wavelengths in 2D SPEs. We also present several electric field-induced wavelength tuning methods for 2D SPEs. Lastly, we discuss the outlook of dynamically tunable 2D SPEs towards scalable 2D SPE arrays for realizing practical quantum photonics applications.

Despite the potential of graphene for building a variety of quantum photonic devices, its centrosymmetric nature forbids the observation of second harmonic generation (SHG) for developing second-order nonlinear devices. To activate SHG in graphene, extensive research efforts have been directed towards disrupting graphene's inversion symmetry using external stimuli like electric fields. However, these methods fail to engineer graphene's lattice symmetry, which is the root cause of the forbidden SHG. Here, we harness strain engineering to directly manipulate graphene's lattice arrangement and induce sublattice polarization to activate SHG. Surprisingly, the SHG signal is boosted 50-fold at low temperatures, which can be explained by resonant transitions between strain-induced pseudo-Landau levels. The second-order susceptibility of strained graphene is found to be larger than that of hexagonal boron nitride with intrinsic broken inversion symmetry. Our demonstration of strong SHG in strained graphene offers promising possibilities for developing high-efficiency nonlinear devices for integrated quantum circuits.

We present a strain engineering platform that allows the dynamic tuning of the emission wavelength of a monolayer WSe2. A large and localized strain was induced in monolayer 2D materials by patterning a photoresist layer with internal stress into two elliptical shapes with a finite gap in between, which is referred to as a dimer in this work. By applying laser annealing on the dimer stressor while monitoring the exciton emission, we demonstrate the capability to dynamically tune the emission wavelength of the bright exciton in the monolayer WSe2.

Despite its superior physical properties, graphene’s optical properties still possess crucial drawbacks for both classical and quantum photonics applications. For example, graphene’s gapless band structure prohibits efficient light emission, while its centrosymmetric nature renders it impossible to obtain strong second-order nonlinearity. In this work, we discuss our latest results on strained graphene that provides a new pathway towards solving the two key above-mentioned problems.

Tensile strained GeSn alloys are considered a key enabler for the realization of complementary metal-oxide-semiconductor laser sources. However, the tensile strained GeSn lasers reported to date require complex fabrication processes for applying tensile strain in GeSn, preventing tensile GeSn lasers from becoming the mainstream technology for integrated photonics. Here, a unique strain engineering method is presented that can introduce a uniform tensile strain in GeSn lasers by harnessing a widely developed atomic layer deposition (ALD) process. 1D photonic crystal nanobeam lasers under homogenous tensile strain induced by an ALD HfO2 all-around stressor layer show a single-mode lasing peak with a approximate to 31 nm redshift and approximate to 2 times intensity increase. The lasing threshold of tensile strained GeSn lasers is approximate to 12% improved compared to the unstrained GeSn lasers. It is believed that the approach offers a new path toward the realization of practical group-IV laser sources for photonic-integrated circuits.

We enable second harmonic generation in pseudo-Landau quantized graphene that achieves strong strain-induced sublattice polarization. A strong temperature-dependent behavior of the observed second harmonic generation is attributed to resonant optical transitions between discrete pseudo-Landau levels.

The photonics-based approach has recently become a strong candidate for realising a large-scale, practical quantum processor. Particularly in recent years, two-dimensional (2D) materials have become a strong candidate for developing an ideal integrated light source owing to their several unique advantages such as convenient on-chip integration. In this work, we study the effect of strain on the emission wavelength and carrier lifetime. We first show that the geometry of stressors can adjust the amount of strain and emission wavelength. Using this strain engineering technique, we demonstrate that the emission wavelength can be significantly shifted by ~10 nm while the carrier lifetime can also be engineered by ~30 %.

We report broadband ultrafast photoluminescence from graphene ranging from visible to telecom wavelengths. We show strongly modified emission spectra owing to the presence of the cavity effect and demonstrate improved thermal stability enabled by hBN.

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.

Strain-engineered graphene has garnered much attention recently owing to the possibilities of creating substantial energy gaps enabled by pseudo-magnetic fields (PMFs). While theoretical works proposed the possibility of creating large-area PMFs by straining monolayer graphene along three crystallographic directions, clear experimental demonstration of such promising devices remains elusive. Herein, we experimentally demonstrate a triaxially strained suspended graphene structure that has the potential to possess large-scale and quasi-uniform PMFs. Our structure employs uniquely designed metal electrodes that function both as stressors and metal contacts for current injection. Raman characterization and tight-binding simulations suggest the possibility of achieving PMFs over a micrometer-scale area. Current-voltage measurements confirm an efficient current injection into graphene, showing the potential of our devices for a new class of optoelectronic applications. We also theoretically propose a photonic crystal-based laser structure that obtains strongly localized optical fields overlapping with the spatial area under uniform PMFs, thus presenting a practical route toward the realization of graphene lasers.

GeSn alloys have been regarded as a promising material for creating a complementary metal-oxide-semiconductor (CMOS)-compatible light source. Despite the remarkable progress in demonstrating GeSn lasers, an unavoidable intrinsic compressive strain introduced during epitaxial growth has prevented researchers from pushing the directness of GeSn gain media to the limit and realizing practical GeSn lasers. In this paper, we demonstrate a GeSn-based 1D photonic crystal nanobeam laser on a high-quality GeSn-on-insulator (GeSnOI) substrate which allows releasing the limiting compressive strain, thus improving the threshold and operating temperature. Pump-power-dependent photoluminescence measurements show a lasing threshold density of 18.2 kW cm−2 at 4 K for the released strain-free GeSn nanobeam, which is ~2 times lower than that of the unreleased GeSn nanobeam with compressive strain. The improved bandgap directness in the released GeSn nanobeam also allows achieving lasing action at higher operating temperatures up to 90 K compared to the unreleased laser device (<70 K). We also report a straightforward geometric strain-inversion technique that harnesses the harmful compressive strain to achieve ultrahigh tensile strain in GeSnOI nanowire, drastically improving the directness of the bandstructure. We achieve ~2.67% uniaxial tensile strain in ~120 nm wide nanowires, surpassing other values reported thus far. We also demonstrate unique superlattices comprising of indirect and direct bandgap GeSn are demonstrated in a single material only by applying a periodic tensile strain. Increased directness in tensile-strained GeSn significantly enhances the photoluminescence intensity by a factor of ~2.5. Our demonstration offers an avenue toward developing practical CMOS compatible light sources.

Combining Sn alloying and tensile strain to Ge has emerged as the most promising engineering approach to create an efficient Si-compatible lasing medium. The residual compressive strain in GeSn has thus far made the simple geometrical strain amplification technique unsuitable for achieving tensile strained GeSn. Herein, by utilizing two unique techniques, we report the introduction of a uniaxial tensile strain directly into GeSn micro/nanostructures. By converting GeSn from indirect to direct bandgap material via tensile strain, we achieve a 10-fold increase in the light emission intensity.

Ultrafast light emission from monolayer graphene shows attractive potential for developing integrated light sources for next-generation graphene-based electronic-photonic integrated circuits. In particular, graphene light sources operating at the telecom wavelengths are highly desired for the implementation of graphene-based ultrahigh-speed optical communication. Currently, most of the studies on ultrafast light emission from graphene have been performed in the visible spectrum, while studies on ultrafast emission at the telecom wavelengths remain scarce. Here, we present experimental observations of strong ultrafast thermal emission at telecom wavelengths from wafer-scale monolayer graphene. Our results show that the emission spectra can be strongly modified by the presence of the cavity effect to produce an enhanced emission at telecom wavelengths. We corroborate our experimental results with simulations and show that by designing a suitable cavity thickness, one can easily tune the emission profile from visible to telecom wavelength regardless of the pump power. In addition, we demonstrate that the insertion of a monolayer of hexagonal boron nitride between graphene and the substrate helps improve the thermal stability of graphene, thereby providing more than five times enhancement of the ultrafast thermal emission. Our results provide a potential solution for stable on-chip nanoscale light sources with ultrahigh speed modulation.

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.