Thermionic emission process in carrier transport in pn homojunctions

Thermionic emission is treated in pn homojunctions. Thermionic current over pn junction barrier is derived directly from Maxwell-Boltzmann distribution function as a difference between the majority carrier flow and the flow of excess carriers in the opposite direction. It is shown that the excess carrier concentration is determined as an equilibrium between thermionic and diffusion process, which depends on quasi-neutral region width. Total current is limited by thermionic process for very thin quasi-neutral regions. Such an approach enables the determination of boundary condition for any doping profile.