Current in Semiconductors

• The way a material conducts electrical current is important in understanding how electronic devices operate;
• You can’t really understand the operation of a device such as a diode or a transistor without knowing something about current in semiconductors;
• As you have learned, the electrons of an atom can exist only within prescribed energy
  bands;
• Each shell around the nucleus corresponds to a certain energy band and is separated from adjacent shells by band gaps, in which no electrons can exist;
• Figure 1–12 shows the energy band diagram for an unexcited (no external energy such  as heat) atom in a pure silicon crystal;

• This condition occurs only at a temperature of absolute 0 Kelvin;