Gold Nanoparticles Found to Improve Photodetector Performance

Researchers at the National University of Singapore have found a way to boost the performance of molybdenum disulfide (MoS₂) photodetectors with nanoparticles of gold.

The mineral molybdenum disulfide, when solid, behaves in many ways like grease, has semiconducting properties that make it a promising alternative to silicon or graphene in electronic devices. It also strongly absorbs visible light, and has been widely employed in light-sensing photodetectors, which are used in environmental sensing systems, process control equipment in factories, and optical communications devices.

The researchers applied a single, loosely arranged layer of gold nanoparticles to the top of a MoS₂ photodetector. The gold layer is less than 15 nm thick and is made up of fewer than 1000 individual particles.

The gold layer improved the photodetectors' efficiency by a factor of three, according to researchers Wei Chen, an assistant professor of chemistry and physics, along with graduate student Jia Dan Lin, and their colleagues.

"We anticipate orders of magnitude higher improvement of MoS₂ sensitivity using a higher density of coated nanoparticles," Chen said.

Chen suspects that the plasmon oscillations (variations in the electron density) of individual nanoparticles -- which enhance the local optical field -- may be one reason for the improved performance of the photodetectors.

The researchers observed a significantly enhanced photocurrent that peaked at the plasmon resonant wavelength around 540 nm. They claim that their findings offer a possibility to realize wavelength selectable photodetection in MoS₂ based phototransistors.

"The next step will focus on varying the materials used to make the nanoparticles, as well as their size, shape, and arrangement," Chen said. He noted the adjustments will "tune" the plasmon resonance wavelength of the metal nanostructure arrays, making it possible for MoS₂photodetectors to detect multiple colors.

The researchers describe their findings in the journal Applied Physics Letters: "Plasmonic enhancement of photocurrent in MoS₂ field-effect-transistor colors.” The authors on this study are affiliated with National University of Singapore and Nanyang Technological University.