Electronic Devices - Online Test

Answer : Option B
Explaination / Solution:

N-type semiconductors have a larger electron concentration than hole concentration. The term n-type comes from the negative charge of the electron. In n-type semiconductors, electrons are the majority carriers and holes are the minority carriers. N-type semiconductors are created by doping an intrinsic semiconductor with donor impurities (or doping a p-type semiconductor as done in the making of CMOS chips). A common dopant for n-type silicon is phosphorus.

Answer : Option D
Explaination / Solution:

The term p-type refers to the positive charge of the hole. In p-type semiconductors, holes are the majority carriers and electrons are the minority carriers. P-type semiconductors are created by doping an intrinsic semiconductor with acceptor impurities (or doping an n-type semiconductor).

Answer : Option B
Explaination / Solution:

P-type semiconductors have a larger hole concentration than electron concentration. The term P-type refers to the positive charge of the hole. In P-type semiconductors, holes are the majority carriers and electrons are the minority carriers. P-type semiconductors are created by doping an intrinsic semiconductor with acceptor impurities (or doping an n-type semiconductor). A common P-type dopant for silicon is boron. For P-type semiconductors the Fermi level is below the intrinsic Fermi level and lies closer to the valence band than the conduction band.

Answer : Option B
Explaination / Solution:

The number of carriers in the conduction and valence band with no externally applied bias is called the equilibrium carrier concentration.

For majority carriers, the equilibrium carrier concentration is equal to the intrinsic carrier concentration plus the number of free carriers added by doping the semiconductor. Under most conditions, the doping of the semiconductor is several orders of magnitude greater than the intrinsic carrier concentration, such that the number of majority carriers is approximately equal to the doping.

At equilibrium, the product of the majority and minority carrier concentration is a constant, and this is mathematically expressed by the Law of Mass Action.

nenh=n2i

Where ni is the intrinsic carrier concentration and neand ph are the electron and hole equilibrium carrier concentrations.

Answer : Option A
Explaination / Solution:

• In n-type semiconductor, the concentration of electrons is more compared to the concentration of holes. Similarly, in p-type semiconductor, the concentration of holes is more compared to the concentration of electrons
• The first process that occurs in the p-n semiconductor is diffusion
• In the formation of the p-n junction, due to the concentration gradient across the p and the n sides, the electrons diffuse from n region to p region and the holes diffuse from p region to n region.

Answer : Option C
Explaination / Solution:

The depletion region, also called depletion layer, depletion zone, junction region, space charge region or space charge layer, is an insulating region within a conductive, doped semiconductor material where the mobile charge carriers have been diffused away, or have been forced away by an electric field. The only elements left in the depletion region are ionized donor or acceptor impurities. The depletion region is so named because it is formed from a conducting region by removal of all free charge carriers, leaving none to carry a current.

Answer : Option D
Explaination / Solution:
No Explaination.

Answer : Option D
Explaination / Solution:

Materials that have the resistance levels between those of a conductor and an insulator are referred to as semiconductors. They are quite common, found in almost all electronic devices. Good examples of semiconductor materials are germanium, selenium, and silicon. Radium is a chemical element with symbol Ra and atomic number 88. It is the sixth element in group 2 of the periodic table, also known as the alkaline earth metals.

Answer : Option B
Explaination / Solution:

The material which has electrical conductivity between that of a conductor and an insulator is called as semiconductor. Silicon, germanium and graphite are some examples of semiconductors.

In semiconductors, the forbidden gap between valence band and conduction band is very small. It has a forbidden gap of about 1 electron volt (eV).

Answer : Option C
Explaination / Solution:

Forbidden gap plays a major role for determining the electrical conductivity of material. Based on the forbidden gap materials are classified in to three types, they are : 

• Insulators : The forbidden gap between the valence band and conduction band is very large in insulators. The energy gap of insulator is approximately equal to 15 electron volts (eV).
• Conductors: In a conductor, valence band and conduction band overlap each other. Therefore, there is no forbidden gap in a conductor.
• Semiconductors: In semiconductors, the forbidden gap between valence band and conduction band is very small. It has a forbidden gap of about 1 electron volt (eV).