Implementing Lateral MoSe₂ P-N Homojunction by Efficient Carrier-Type Modulation

High-performance p-n junctions based on atomically thin two-dimensional (2D) materials are the fundamental building blocks for many nanoscale functional devices that are ideal for future electronic and optoelectronic applications. The lateral p-n homojunctions with conveniently tunable band offset outperform vertically stacked ones, however, the realization of lateral p-n homojunctions usually require efficient carrier-type modulation in a single 2D material flake, which remains a tech challenge. In this work, we have realized effective carrier-type modulation in a single MoSe₂ flake, and thus, a lateral MoSe₂ p-n homojunction is achieved by sequential treatment of air rapid thermal annealing and triphenylphosphine (PPh₃) solution coating. The rapid thermal annealing modulates MoSe₂ flakes from naturally n-type doping to degenerated p-type doping and improves the hole mobility of the MoSe₂ field effect transistors from 0.2 to 71.5 cm²·V^-1·s^-1. Meanwhile, the n-doping of MoSe₂ is increased by drop-coating PPh₃ solution on the MoSe₂ surface with increased electron mobility from 78.6 to 412.8 cm²·V^-1·s^-1. The as-fabricated lateral MoSe₂ p-n homojunction presents a high rectification ratio of 10⁴, an ideality factor of 1.2, and enhanced photoresponse of 1.3 A·W^-1 to visible light. This efficient carrier-type modulation within a single MoSe₂ flake has potential for use in various functional devices.