Electronic Devices And Circuits MCQ Questions & Answers | ECE

The question asks about the depletion layer width in a junction (like a diode). Think of the depletion layer as a region with very few free charge carriers.

Let's look at each option:

Option A: Decreases with light doping
This is incorrect. Lighter doping means fewer charge carriers are available. To create the depletion region, more of the semiconductor needs to be depleted of its free carriers, so a lighter doping requires a *wider* depletion region.

Option B: Is independent of applied voltage
This is incorrect. The width of the depletion layer *definitely* changes with applied voltage. Applying a voltage will affect how easily charge carriers can move across the junction, and thus the size of the depletion region.

Option C: Is increased under reverse bias
This is correct. Reverse bias *widens* the depletion layer. Applying a reverse voltage pulls the charge carriers away from the junction, making the depletion region bigger and offering greater resistance to current flow.

Option D: Increases with heavy doping
This is incorrect. Heavier doping means more charge carriers are available. Only a *narrow* depletion region needs to be created to deplete the available carriers.

Therefore, the answer is Option C.

In an intrinsic semiconductor like silicon,
the number of free electrons is equal to the number of holes.
This is because electrons are freed when a covalent bond is broken,
creating both a free electron and a hole (a missing electron in the bond).

As the temperature increases,
more covalent bonds are broken due to increased thermal energy.
This generates more electron-hole pairs.
For every broken bond, one electron and one hole are created.

Therefore, the number of free electrons and holes increases,
and they increase by the same amount because they are generated in pairs.

So, the correct answer is Option C.

The correct answer is D: Holes and electrons.
Here's why:
Intrinsic semiconductors are pure semiconductors, meaning they haven't been doped with any impurities.
At room temperature, some of the electrons in the semiconductor gain enough energy to break free from their bonds.
When an electron breaks free, it leaves behind a hole in the crystal structure.
Both the free electrons and the holes can move through the material under the influence of an electric field.
Therefore, the current in an intrinsic semiconductor at room temperature is due to the movement of both holes and electrons.
Ions are not the primary charge carriers in intrinsic semiconductors.