Ultrahigh Anisotropic Transport Properties of Black Phosphorus Field Effect Transistors Realized by Edge Contact

Highly anisotropic black phosphorus (BP) has recently attracted significant interest for electronic and optoelectronic devices. To date, in-plane anisotropic properties of BP field effect transistors (FETs) have been reported only with top contact. However, the 2D top contact geometry is unable to measure the in-plane electrical conductance precisely, due to the presence of the out-of-plane conductance, resulting in underestimation of anisotropy. Here, 1D edge contact method is employed to measure the in-plane conductance precisely along the armchair and zigzag directions of BP without the contribution of out-of-plane conductance. The conductance and mobility anisotropies for BP FETs are measured with edge contact at 300 K to be approximate to 5.5 and approximate to 7.5, respectively. The results further show that the mobility of BP FETs with edge contact weakly depends on temperature, indicating that the edge roughness scattering limits the mobility. In contrast, the mobility of BP FETs with top contact strongly depends on temperature, showing that the impurity scattering and phonon scattering limit the mobility at below and above 150 K, respectively. Finally, a scattering phase diagram is demonstrated to understand the role of different scattering mechanisms on the modulation of mobility anisotropy in BP FETs with edge and top contacts.