Affected by lattice symmetry, the thermal conductivity, conductivity, dielectric constant, Raman tensor and other basic physical quantities in crystal materials often show inherent anisotropy. For example, the conductivity within ab surface in graphite is three orders of magnitude higher than outside (in the C direction), and this strong anisotropy is more common in three-dimensional block van der Waals materials. In recent years, with the development of two-dimensional materials research, new phenomena of anisotropy in various surfaces are emerging constantly.
Among them, the phenomena of Raman anisotropy and in-conductivity anisotropy of two-dimensional van der Waals materials with low lattice symmetry (such as SnSe, GeP, etc.) have received more and more attention and in-depth research, and the prototype devices based on this need to be designed and developed urgently. However, the current reported anisotropy values in the two-dimensional limit (for example, the ratio of the maximum conductivity in one direction to the conductivity in the other direction) are all within 10, which is not conducive to the development and application of new devices. On the other hand, whether the electrical anisotropy can be regulated by some quick and convenient means is also a very challenging problem.
Metal research institute, Chinese Academy of Sciences, shenyang national research center for materials science, researchers in cooperation with the domestic many discovered the two-dimensional shape of the lower limit semiconductor gallium telluride in-plane conductivity of huge anisotropy, and implemented under the gate voltage regulation of the change of electrical anisotropy of several orders of magnitude, finally has carried on the demonstration of relevant prototype device.
Using vertical assembly of atomic layers in an inert atmosphere, the team encapsulated a few layers of gallium telluride between 4.8 nm and 20nm in two layers of boron nitride. The field effect devices were prepared by micro - and nano - processing method, and the electrical measurement was carried out systematically. The experimental results show that the conductivity of a few layers of gallium telluride with holes at room temperature shows an elliptic oscillation behavior with the direction change, that is, the conductivity anisotropy is similar to the reported SnSe and GeP systems. By regulating the gate voltage, the ratio of conductivity anisotropy was able to soar from 10 times to 5,000 times, far more than other systems with in-plane electrical anisotropy reported so far.
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