First principles research on the dynamic conductance and transient current of black phosphorus transistor

The validity of high frequency technique and time-domain measurement to nanoscale electronic devices provides an imperious demand to explore the ultrafast electron dynamics and nonlinear responses accompanied with material science in theory. In this work, we carried out a first principles calculation to research the dynamic response in both frequency and time domain of a nanoscale Cu/black phosphorus (Cu/BP) transistor. The system shows n-type transport behaviors due to the charge transfer from the Cu/BP contact to the central BP section, which is different from the p-type pristine BP transistor. By adjusting the gate voltage, on-off ratio of conductance can reach up to 10(3) which is expected to further increase with the length of the central BP section. The Cu/BP transistor always shows capacitive-like behaviors even at high frequency. and cut-off frequency is estimated up to 75 THz. Transient current evolution shows abundant quantum scattering behaviors, and two important time scales were analyzed. The tune-on time is comparable to the Fermi velocity of pristine BP, and is roughly independent of the magnitudes of bias voltages. The relaxation time is roughly hundreds of femtoseconds, which corresponds to the cut-off frequency up to a point and can be further reduced by dephasing effect. The rapid response of hundreds of femtoseconds indicates that the Cu/BP transistor maybe work as high frequency nanoscale electronic device.