Barrier Potential across Semiconductor P‐N Junction and Resting Membrane Potential

After the atomic-power accident in Fukushima, utilization of solar energy has drawn renewed attention from society. One of the promising methods to capture solar energy is photovoltaic (solar) cells. Though there are several types of the cells, a present mainstream technology uses semiconductor junctions based on silicon element. Silicon is an atom in the fourth group in the periodic table and has four electrons in valence shell. A valence electron orbits the nucleus and stays in the valence shell at low temperature. However, the electron jumps the energy gap (1.12 eV in silicon) into the conduction band if a photon (sunlight) which has greater energy than the gap strikes the electron, and it gets free in the conduction band. On another front, it also leaves behind an electron hole that can move like a physically charged particle (positive). Figure 1(a) shows a schematic diagram of the electron-hole pair generation from the viewpoint of energy band for electron. These electron and hole are called carriers which have the elementary charge (1:602 10 19 coulombs) with different sign, and