Atomistic quantum transport simulation of multilayer phosphorene nanoribbon field effect transistors

Few-layer black phosphorus is a semiconductor material, where its allotrope is called phosphorene; a new two-dimensional material which is discovered in 2014. In this paper, first we use the tight-binding method to implement a matrix representation for single-layer and multilayer structures of phosphorene nanoribbon (PNR) to define the Hamiltonian of the system. Second, we investigate the band structure and the band gap of multilayer PNRs. The band gap of armchair PNRs with 16 atoms across the width of PNR for single-layer, bilayer, and three-layer structures are obtained as 1.899, 1.224, and 0.937 eV, respectively. Third, we use the atomistic description of structure to simulate the performance characteristics of single and multilayer PNR field effect transistors (PNRFETs) by employing the non-equilibrium Green's function (NEGF) formalism. Based on the properties of the material and device structures, I_d-V_gs, I_d-V_ds characteristics, energy band diagram in the channel, and I_ON/I_OFF are analyzed. The ON to OFF current ratio for single-layer, bilayer, and three-layer PNRFETs are increasing when the channel length increases from 5 nm to 15 nm. The current ratio for single-layer increases from 1277 for L_ch=5 nm to 216.7×10⁶ for L_ch=15 nm. The I_ON/I_OFF in single-layer PNRFET is higher in comparison with those values in bilayer and three-layer PNRFETs due to very small off-current in the single-layer PNRFET which in turn resulted from its larger band gap. The results show that the performance of PNRFET changes significantly depending on the number of phosphorene layers and the length of the channel of device.