The P–N junction characteristic can be demonstrated using the
electrical voltammetry. That is, for a P–N junction sample under
forward bias, the internal electric field facilitates the flow of current,
fering only minimum resistance. However, when it is undereversed bias, the junction becomes a barrier, offering high resistance
current to flow through. Zhang et al. have exerted this concept in
their non-uniform Mn doping in TiO
2