Controlling the Spontaneous Emission Rate of Monolayer MoS$_2$ in a Photonic Crystal Nanocavity (1310.0923v1)

Abstract: We report on controlling the spontaneous emission (SE) rate of a molybdenum disulfide (MoS$_2$) monolayer coupled with a planar photonic crystal (PPC) nanocavity. Spatially resolved photoluminescence (PL) mapping shows strong variations of emission when the MoS$_2$ monolayer is on the PPC cavity, on the PPC lattice, on the air gap, and on the unpatterned gallium phosphide substrate. Polarization dependences of the cavity-coupled MoS$_2$ emission show a more than 5 times stronger extracted PL intensity than the un-coupled emission, which indicates an underlying cavity mode Purcell enhancement of MoS$_2$ SE rate exceeding a factor of 70.

Overview of Controlling the Spontaneous Emission Rate of Monolayer MoS$_2$ in a Photonic Crystal Nanocavity

The paper at hand investigates the manipulation of the spontaneous emission (SE) rate of a monolayer molybdenum disulfide (MoS$_2$) when integrated with a planar photonic crystal (PPC) nanocavity. Transition metal dichalcogenides (TMDs) like MoS$_2$ have shown a direct bandgap in a single atomic layer, making them potential candidates for efficient electronic and optoelectronic devices. Despite their promising applications, the photoluminescence (PL) efficiency of monolayer MoS$_2$ remains low due to a dominant nonradiative recombination process over the spontaneous emission.

Methodology

The authors utilize a PPC nanocavity to augment the SE rate of MoS$_2$. The cavity's design involves L3-type defects in a gallium phosphide (GaP) membrane, leveraging the Purcell effect to achieve substantial SE rate enhancement. The MoS$_2$ monolayer is deposited on the PPC nanocavity via mechanical exfoliation and precision transfer techniques. SEM and optical microscopy verified the placement of MoS$_2$ on the nanocavities, providing the spatial association necessary for this paper.

Results and Analysis

The application of the Purcell effect leads to an enhancement of more than a factor of 70 in the SE rate of MoS$_2$. The cavity-coupled system demonstrates more than a five-fold increase in extracted PL intensity compared to the uncoupled emission. This enhancement is well-supported by the cavity's high quality (Q) factor and the small mode volume, aligning with theoretical calculations.

Polarization-dependent measurements further reveal resonant cavity modes, correlating with finite-difference time-domain (FDTD) simulations. The SE modification utilizes the constricted in-plane photonic bandgap of the PPC, redirecting emission into vertical directions and achieving increased photon flux at certain wavelengths, particularly those resonant with the cavity's modes.

Implications and Future Directions

The substantial improvement in the SE rate emphasizes the potential of integrating monolayer TMDs with photonic nanocavities for next-generation optoelectronic devices. This advancement may facilitate efficient photodetectors and electroluminescent systems with considerable light-matter interaction strengths. Moreover, systems demonstrating slow light near the photonic crystal band edge or employing coupled cavity arrays could distribute the Purcell enhancement across broader regions.

Further exploration may focus on extending the effective interaction region of these cavities, possibly achieving uniform, high Purcell enhancement areas. This could broaden the application spectrum, enabling atomically thin lasers and cavity-enhanced nonlinear optics functions.

In conclusion, the paper highlights a pronounced leap towards utilizing atomically thin semiconductor layers for robust photonic integration, underlining the role of nanophotonics in evolving material applications and further cementing the potential of monolayer MoS$_2$ within the context of advanced photonic systems.