The most basic semiconductor device is the pn junction. pn junctions are formed by doping one side of the junction with electron donating atoms and the other side with electron accepting atoms. If a side is doped with donator atoms, that side has excess electrons and the electron concentration is denoted by the symbol n. If a side is doped with acceptor atoms, that side has a deficit of electrons (called holes) and the hole concentration is denoted by the symbol p. Electrons and holes respond almost equally to a voltage across the pn junction but, of course, the electrons flow toward the positive voltage end of the junction and the holes flow toward the negative end so that both contribute to the current. The doping results in a barrier potential energy, Vb, which resists flow of carriers even in the forward direction until the carrier kinetic energy exceeds this barrier. The electron and hole kinetic energies can be increased by increasing the voltage across the junction. However the doping of, say, the n side also results in huge ratios (order of 10^12) of electrons to holes and conversely for the p side. So, while the voltage in the forward direction has to exceed the Vb in order for current to flow, forward current with voltage above Vb is typically 10^12 larger than backward current even when the backward voltage is much greater than Vb. This gives the pn junction the properties of a rectifier. For our purposes here the potential energy distribution will consist of the usual peak to peak sinusoid (the doping does not significantly alter the ion potentials) going from one side to the center of the propagation grid and then this same sinusoid will be stepped up so that its mean is the barrier potential Vb. Since there are electrical carriers of both signs, an electron packet (n) will start on the left side and a hole (p) packet will start on the right side. Both of these packets can start with kinetic energy larger than the peak of the sinusoid and run into the stepped potential at the center of the grid. At that point they will be either reflected or transmitted depending on their incident kinetic energy. For simplicity only electron wave packets are animated here. The current through the pn junction is proportional to the transmissivity, T, through the potential barrier. The final transmissivity is saved when the reflected wave packet's centroid is at 1/4 of the x range of the potential. If the kinetic energy is larger than Vb, then sometimes the packet gets reflected from the right hand end instead of the potential barrier and that gives erroneous final transmissivity. This happens only when the lattice potential is included. You have the choice of seeing T either for a single applied voltage (same incident kinetic energy) (press the "Start" button) or for an array of applied voltages (press the "Start Computing T Curve" button). The latter animation requires a several minutes. Note that there is a significant difference between the latter and the former in that the former is monotonic and the latter is somewhat sinusoidal. Note that, to save space, all plots and their legends are color coded.