A new method was developed to passivate defects in next-generation optical materials. The new photocatalytic reaction enables the integration of high-quality, optically active, atomically thin material in a variety of applications such as electronics, electro-catalysts, memory, and quantum computing.
The laser processing technique significantly improves the optical properties of monolayer molybdenum disulphide (MoS2) — a direct gap semiconductor — with high spatial resolution. The process produces a 100-fold increase in the material’s optical emission efficiency in the areas “written” with the laser beam.
Atomically thin layers of transition metal dichalcogenides (TMDs), such as MoS2, are promising components for flexible devices, solar cells, and optoelectronic sensors due to their high optical absorption and direct band gap. The semiconducting materials are particularly advantageous in applications where weight and flexibility are a premium; however, their optical properties are often highly variable and non-uniform, making it critical to improve and control the optical properties of the TMD materials to realize reliable, high-efficiency devices.
Defects are often detrimental to the ability of monolayer semiconductors to emit light. These defects act as nonradiative trap states, producing heat instead of light; therefore, removing or passivating these defects is an important step toward high-efficiency optoelectronic devices.
In a traditional LED, approximately 90 percent of the device is a heat sink to improve cooling. Reduced defects enable smaller devices to consume less power, which results in a longer operational lifetime for distributed sensors and low-power electronics.
Water molecules passivate the MoS2 only when exposed to laser light with an energy above the band gap of the TMD. The result is an increase in photoluminescence with no spectral shift. Treated regions maintain a strong light emission compared to the untreated regions that exhibit much a weaker emission. This suggests that the laser light drives a chemical reaction between the ambient gas molecules and the MoS2.