Space charge regions (RLZ) are charge regions that build up between differently doped semiconductor layers. They are formed in the pn junction between a positively doped semiconductor region and a negatively doped semiconductor region, which in semiconductors is called a junction.
The junction is characterized by the electrons in the n-doped semiconductor and the holes in the p-doped semiconductor, whose concentration is different. Therefore, an electric field builds up in the space charge region and an electric potential is created, causing the electrons and holes to drift into the other charge region.
The space charge zone can be changed in width by an applied voltage. Depending on the orientation of the voltage, the space charge zone can be widened or narrowed. If the n-doped region is affected with a negative charge, the electrons migrate to the boundary region and thus reduce the space charge zone. The situation is different if the n-doped region is influenced with a positive voltage, then the space charge zone increases. If there is a lack of charge carriers in the space charge zone, it is called a depletion zone.
Space charge zones occur wherever differently doped semiconductor materials such as silicon are adjacent to each other. This is the case with PIN diodes, transistors, FETs, capacitance diodes and Soalr cells, to name but a few.