Junction Potential or Barrier Potential

Recombination of diffusing carriers across the junction only proceeds up to a point, beyond which the depletion layer's own electric field acts as a barrier to further diffusion: an electron trying to cross into the p-region meets a wall of negative immobile ions repelling it back, and only electrons with enough energy can punch through and recombine with a hole (creating yet another negative ion in the process). The strength of the potential difference across the depletion region keeps increasing with every carrier that manages to cross, until an equilibrium is reached at which the internal repulsion of the depletion layer stops further net diffusion. This equilibrium potential difference across the depletion layer is called the barrier potential $V_b$; at $25^\circ$C it is approximately 0.7 V for silicon …