Recently, ACS Nano published an article jointly contributed by research teams led by SPST Professors Xue Jiamin and Professor Guo Yanfeng and Shanghai Institute of Technical Physics Professor Hu Weida. Their work, “Nb2SiTe4: A Stable Narrow-Gap Two-Dimensional Material with Ambipolar Transport and Mid-Infrared Response,” reported an important research advance in new narrow-bandgap two-dimensional (2D) materials.
The narrow-bandgap 2D materials possess gate-tunable carrier types and responses to the infrared spectrum, and have high research and application potentials. However, most of the 2D semiconductors studied to-date have bandgaps on the order of 1 eV or larger. A few of the 2D materials with narrow bandgaps, such as black phosphorus and black arsenic phosphorus, have stability issues in ambient conditions. Therefore, obtaining a new stable narrow-bandgap 2D material is of great importance.
With close collaboration, Xue, Guo and Hu's research teams found that a ternary layered material Nb2SiTe4 (lattice structure as shown in the inset of Figure 1) has a suitable band gap (~ 0.4 eV).
Figure 1: The carrier type of Nb2SiTe4 FET is controlled by the back gate voltage Vg.
By studying few-layer Nb2SiTe4 field-effect transistors (FETs), they found that the carrier type can be continuously tuned from hole to electron with the back gate, and the conductivity of the two types of carriers is comparable (as shown in Figure 1).
Figure2: The responses of few-layer Nb2SiTe4 FET to laser pulses with wavelengths of 532 nm and 3.1 ?m, respectively.
Nb2SiTe4 exhibits excellent mid-infrared detection capability due to its suitable bandgap size. The responses to electromagnetic waves at 532 nm and 3.1 μm are shown in Figure 2. More importantly, Nb2SiTe4 FET devices also show better stability than other narrow-gap 2D materials. As Figure 3 shows, after 10 days of exposure to the atmosphere, the carrier mobility decreased by only about 40%. Previously discovered narrow-bandgap 2D materials lose their electrical properties completely when stored in air for several hours.
Figure 3: Few-layer Nb2SiTe4 FET device shows better stability.
This work provides a new material choice for the 2D material research community. As the reviewers of the manuscript pointed out, the discovery of this material will inspire more research efforts.
More details of the work can be found online: https://pubs.acs.org/doi/10.1021/acsnano.9b05080