"Resonant Tunneling in Black Phosphorus Homojunction"

Most common resonant tunnel devices (RTDs) consist of a quantum well formed between double barrier structures. Here for the first time, we demonstrate the RTD in a homojunction. By taking highly anisotropic nature of black-phosphorous (BP) into account, we have fabricated RTDs by sandwiching a thin (4-7 nm)-BP layer between two thick (40-72 nm)-BP flakes. We have observed that RTD could be realized in a BP homojunction by careful alignment of BP flakes. Moreover, a formation of a quantum well at the junction derives from the work function tunability of BP with flake thickness. Work function difference of thick-BP and sandwiched thin-BP layers results in band bending near the junction creating a quantum well. Under certain bias conditions, an electron can tunnel from one side to other through bound states in the quantum well. Such RT has been manifested by observation of negative differential resistance (NDR) in the current-voltage characteristics. The observed NDR peak in the current-voltage characteristics shifts to a higher voltage with decreasing quantum well thickness. Temperature-dependent current-transport reveals that momentum conservation for resonant tunneling is satisfied with acoustic/optical phonon scattering of electrons in the quantum well.