2D semiconductors give solar panels, video cameras a boost

Visual entertainment and manufacturing are placing their bets on 3D. However, electronics and photonics are going 2D. In fact, one of the latest advancements in these fields focuses on molybdenum disulfide (MoS), a 2D semiconductor that, while generally used in lubricants and steel alloys, is demonstration remarkable potential in optoelectronics.

Recently, engineers placed a single layer of MoS molecules on top of a photonic structure called an optical nanocavity made of aluminum oxide and aluminum. (A nanocavity is an arrangement of mirrors that allows beams of light to circulate in closed paths. These cavities help us build things like lasers and optical fibres used for communications.)

The results, described in the paper "MoS monolayers on nanocavities: Enhancement in light-matter interaction" published in April by the journal 2D Materials, are promising. The MoS nanocavity can increase the amount of light that ultrathin semiconducting materials absorb. In turn, this could help industry to continue manufacturing more powerful, efficient and flexible electronic devices.

"The nanocavity we have developed has many potential applications," said Qiaoqiang Gan, PhD, assistant professor of electrical engineering in the University at Buffalo's school of engineering and applied sciences. "It could potentially be used to create more efficient and flexible solar panels, and faster photodetectors for video cameras and other devices. It may even be used to produce hydrogen fuel through water splitting more efficiently."

Figure 1: An optical nanocavity made, from top to bottom, of molybdenum disulfide (MoS2), aluminum oxide and aluminum. Credit: University at Buffalo.

A single layer of MoS is advantageous because unlike another promising 2D material, graphene, its bandgap structure is similar to semiconductors used in LEDs, lasers and solar cells.

"In experiments, the nanocavity was able to absorb nearly 70% of the laser we projected on it. Its ability to absorb light and convert that light into available energy could ultimately help industry continue to more energy-efficient electronic devices," said Haomin Song, a PhD candidate in Gan's lab and a co-lead researcher on the paper.

Industry has kept pace with the demand for smaller, thinner and more powerful optoelectronic devices, in part, by shrinking the size of the semiconductors used in these devices.

A problem for energy-harvesting optoelectronic devices, however, is that these ultrathin semiconductors do not absorb light as well as conventional bulk semiconductors. Therefore, there is an intrinsic tradeoff between the ultrathin semiconductors' optical absorption capacity and their thickness.

The nanocavity, described above, is a potential solution to this issue.

Zhiwen Liu, PhD, professor of electrical engineering at Penn State University Park, is the paper's other co-lead author. Additional authors include UB graduate students Haomin Song and Dengxin Ji; and Penn State University Park students Corey Janisch (also a co-lead researcher), Chanjing Zhou, Ana Laura Elias and Mauricio Terrones.

The research was supported by grants from the National Science Foundation, the U.S. Army Research Office and the U.S. Air Force Office of Scientific Research.

- Cory Nealon
  University at Buffalo