  The pn junction is a fundamental electrical component in modern electronics
and optoelectronics. Currently, there is a great deal of interest in the
two-dimensional (2D) pn junction. Although many experiments have demonstrated
the working principle, there is a lack of fundamental understanding of its
basic properties and expected performances, in particular when the device is
driven out of equilibrium. To fill the current gap in understanding, we
investigate the electrostatics and electronic transport of 2D lateral pn
junctions. To do so we implement a physics-based simulator that
selfconsistently solves the 2D Poisson's equation coupled to the
drift-diffusion and continuity equations. Notably, the simulator takes into
account the strong influence of the out of plane electric field through the
surrounding dielectric, capturing the weak screening of charge carriers.
Supported by simulations, we propose a Shockley-like equation for the ideal
current voltage characteristics, in full analogy to the bulk junction after
defining an effective depletion layer (EDL). We also discuss the impact of
recombination generation processes inside the EDL, which actually produce a
significant deviation with respect to the ideal behavior, consistently with
experimental data. Moreover, we analyze the capacitances and conductance of the
2D lateral pn junction. Based on its equivalent circuit we investigate its
cut-off frequency targeting RF applications. To gain deeper insight into the
role played by material dimensionality, we benchmark the performances of
single-layer MoS2 (2D) lateral pn junctions against those of the Si (3D)
junction. Finally, a practical discussion on the short length 2D junction case
together with the expected impact of interface states has been provided. Given
the available list of 2D materials, this work opens the door to a wider
exploration of material dependent performances.
