*Charge supply by a Forward-biased PN Junction*

Related articles:

- Semiconductor as a container of electrical charge
- Charge supply by a Forward-biased pn junction.
- Charge supply by a reverse-biased PN Junction.

In the following applet, use the scroll bar to set a positive bias voltage
(Forward bias), say 0.2 Volts. Now, suppose that you are sitting inside
the p-type Semiconductor (red rectangle in
the top diagram). As you look at the junction, what kind of carriers are
*moving into* the p-type region ? ** Answer**:

Question-1: At a forward bias of 0.2 V, calculate the minority electron
concentration at the junction edge (or depletion edge) of the p-type. Assume
that the minority electron concentration at equilibrium is n_{p0}
= 1000 electrons/cm^{3} and use the formula n_{p} = n_{p0}
exp(V/V_{T}) where V_{T} = 0.025 V at room temperature.
see the answer. Calculate the minority electron
density at the depletion edge at 0.4, 0.55, and 0.7 V of forward bias.
see the answer.

What you see in this applet is the *log *of the number of carriers
moving. So, even though the applet shows a small difference in the numbers
of carriers, it is actually a ** big **difference. Not worrying
about the carriers leaving the p-region, and worrying only about those
moving in, we conclude the following:

Question-2: For N_{d} = 1E17 cm^{-3} (or n = 1E17 cm^{-3}),
calculate the minority hole concentration at equilibrium in Si at 300K
? see the answer. Use this
applet to convince yourself of the small number of minority holes in
the n-side.

** A forward-biased PN Junction supplies a large amount of minority
carrier charge into the semiconductor (injection), and supplies a very
small amount of majority charge (leakage)**.