Question

Q. How does the space charge width change with forward and reverse bias? Also,

calculate the space charge width for a reverse bias of 4V on a silicon pn junction at T = 300K and doping concentrations of Na = 5x1015cm-3 , Nd = 5x 1016 cm-3 .

Answer 1

The depletion region is created due to a balance of diffusion and drift current. Diffusion pressure causes holes to travel from the P-side and electrons to travel to the N-side and combine with one another around the junction. This combination leaves behind positive charge on the N-side and negative charge on the P-side. This charge creates an electric field that opposes the diffusion current with a drift current. The width of the depletion region is determined by whatever amount of charge transfer balances the drift and diffusion pressures.

When a forward bias voltage is applied then the space charge region or depletion region width decreases and become zero when applied voltage is equal to built in space charge region voltage. But what a reversed bias is applied the space charge region width increases.