5.1 Depletion region

  Semi-conductor Devices and Electronics

In the vicinity of junction, the region containing the uncompensated acceptor and donor ions is known as depletion region.
There is a depletion of mobile charges (holes and free electrons) in this region.
Depletion region has immobile (fixed) ions which are electrically charged, it is also known as the space charge region.
The electric field between the acceptor and the donor ions is known as a barrier.
The physical distance from one side of the barrier to the other is known as the width of the barrier $(W)$.
The potential difference from one side of the barrier to the other side is known as the height of the barrier $\left( {{V_o}} \right)$.

Note:

• For a silicon $(Si)$ $p-n$ junction, the barrier potential is about $0.7\ V$, whereas for a germanium $(Ge)$ $p-n$ junction is approximately $0.3\ V$.
• The width of the depletion layer and magnitude of the potential barrier depends upon the nature of the material of semiconductor and the concentration of impurity atoms.
• The thickness of the depletion region is of the order of one tenth of a micrometer ${\left( {\frac{1}{{10}}} \right)^{th}}\mu m$.