High‐Performance Black Phosphorus Field‐Effect Transistors with Controllable Channel Orientation

Black phosphorus (BP) receives extensive attention in many fields such as energy storage, microelectronics, and optoelectronics due to its layer-controlled direct bandgap, excellent carrier mobility, and unique anisotropy. However, in practical applications, atmospheric degradation and the random channel orientation make the actual performance of BP much lower than the theoretical value. Here, clean and complete BP nanosheets with large size and high crystal quality are obtained by poly(dimethylsiloxane)-assisted mechanical exfoliation. Then, angle-resolved polarized Raman spectroscopy is used to distinguish the armchair (AC) orientation of BP and a field-effect transistor (FET) with controllable channel direction can improve the carrier mobility of the device (up to 826.2 cm(2) V-1 s(-1)) because of higher mobility along the AC orientation. Due to the tunneling of electrons through the electron barrier into the conduction band of BP under a positive gate voltage, the transistor possesses a bipolar transport property. In addition, with the change of channel thickness, both the impurity scattering of the substrate and the interlayer resistance will affect the movement of carriers, so the carrier mobility of the device increases first and then decreases with the increase of the channel thickness.