P-type surface charge transfer doping of black phosphorus field-effect transistors

In this work, a new approach to chemically dope black phosphorus (BP) is presented which significantly enhances device performance of few-layer BP field-effect transistors (FETs). By applying 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ), low on-state resistance and high field-effect mobility are achieved, where the mobility has been increased from 181.1 cm2/Vs to 228.5 cm2/Vs and the on-state resistance has been decreased from 7.4 Ω·mm down to 3.2 Ω·mm achieving a record high drain current of 531.8 mA/mm with a moderate channel length of 1.5 μm. In addition, transfer length method (TLM) structure has demonstrated a 2.9 times reduction in sheet resistance, and nearly 1.3 times decrease in contact resistance upon p-type surface charge transfer doping of BP FETs.