GATE ECE (Electronics) Test: N-Type Semiconductor Free Online Test 2026

• Atoms having 5 valence electrons acts as donor impurities 
• Antimony is a donor impurity as it has five valence band electrons.
• Atoms having 3 valence electrons acts as acceptor impurities
• Boron and Indium are acceptor impurities.

Important Points
When we add n-type or donor impurities to the semiconductor, the width of the forbidden energy gap in the lattice structure is reduced. Due to an addition of donor atoms, allowable energy levels are introduced a small distance below the conduction band. These new allowable levels are discrete because the added impurity atoms are placed far apart and hence their interaction is small.

Concept:

• The material which is not a good conductor or a good insulator is called as a semiconductor.
• For example: Silicon
• The charge carriers which are present in more quantity in a semiconductor compared to other particles are called the majority charge carrier.

There are two types of semiconductors:

P-type semiconductor:

• The semiconductor having holes as majority charge carriers and electrons as a minority charge carrier is called a P-type semiconductor.

N-type semiconductor:

• The semiconductor having electrons as majority charge carriers and holes as a minority charge carrier are called N-type semiconductor.

Semiconductor: Semiconductors are the materials that have a conductivity between conductors and insulators.

• Semiconductors are made of compounds such as gallium arsenide or pure elements, such as germanium or silicon.
• There are two types of semiconductor:

1. ​N-type Semiconductor
2. P-type Semiconductor
   

• In an n-type semiconductor, pentavalent impurity from the V group is added to the pure semiconductor.
• Electrons are the majority charge carriers in the n-type semiconductor.
• So when a pentavalent impurity is mixed into the semiconductor, the number of electrons becomes more than the number of holes.

N-type Semiconductor:

• An n-type semiconductor is an intrinsic semiconductor doped with phosphorus (P), arsenic (As), or antimony (Sb) as an impurity.
• Silicon of Group IV has four valence electrons and phosphorus of Group V has five valence electrons.
• If a small amount of phosphorus is added to a pure silicon crystal, one of the valence electrons of phosphorus becomes free to move around (free-electron*) as a surplus electron. When this free electron is attracted to the “+” electrode and moves, current flows.

P-type Semiconductor:

• Impurities such as Aluminium, Gallium, and Indium (elements having three valence electrons) are added to P-type semiconductors.
• Impurities are added to P-type semiconductors in order to increase the number of holes (also known as Acceptor atoms).
• In a P-type semiconductor, the majority of charge carriers are holes whereas the free electrons are in minority.

Semiconductor:

• A semiconductor is a substance that has a resistivity in between conductor and insulator.
• A semiconductor has 4 valance electrons that are C, Si, Ge, Sn, and Pb.

Classification of Semiconductor:

Intrinsic Semiconductor:

• An extremely pure form is known as an Intrinsic Semiconductor.
• In intrinsic Semiconductor, even at room temperature, hole electrons pair are created.
• Electric fields applied across the intrinsic semiconductor cause current conduction due to both Holes as well as Electrons.

Extrinsic Semiconductor:

• The process of adding impurity to the pure semiconductor is called Doping.
• By means of doping Extrinsic semiconductor is formed.
• Normally, 108 atoms of semiconductor added with 1 atom of impurity.
• Depending upon the types of impurity added, the extrinsic semiconductor is classified into N-type and P-Type semiconductors.

​1. N-Type Semiconductor: This type of semiconductor is formed by added pentavalent impurity.

The current conduction in N-Type semiconductor is predominantly by free electron or it has electron type conductivity.

2. P-Type Semiconductor: This type of semiconductor is formed by added Trivalent impurity.

The current conduction in the P-Type semiconductor is predominantly by holes or it has hole type conductivity.

Conclusion: Hence, Pentavalent impurity (Arsenic-As) in Intrinsic semiconductors (Silicon) is used to create an N-type semiconductor.

A semiconductor is a solid substance that has a conductivity between an insulator and metals. Semiconductors have conductivity due to many factors like the addition of an impurity or because of temperature effects.

N-type semiconductors: An extrinsic semiconductor where the dopant atoms provide extra conduction electrons to the host material like Phosphorus (P) in Silicon Si called donor impurities.

This creates an excess of negative (n-type) electron charge carriers that are able to move freely.

 

In the donor replacement atom, the outermost shell ( valance shell) contains 5 electrons.

Example: Phosphorus (P) etc.

Important Points

P-type semiconductors: A semiconductor, when the impurity (acceptor) with tri valency is added to pure semiconductors, then it is known as a p-type semiconductor.

Impurities with tri valency such as Boron (B), Gallium (Ga), Indium(In), Aluminium(Al), etc are called acceptor impurity.

In the acceptor replacement atom, the outermost shell (valance shell) contains 3 electrons.

Example: Boron (B), Gallium (Ga), Indium (In), Aluminium (Al), etc.

So, the value of the valance electron is 3.

The assertion is true: In an n-type semiconductor, the Fermi level moves closer to the conduction band due to the increased electron concentration from donor impurities. The reason is true: Donor impurities add electrons to the conduction band, increasing electron density. The reason explains the assertion, as the higher electron concentration shifts the Fermi level upward to balance carrier populations.

• Option A: Correct, as both are true and R explains A.

• Option B: Incorrect, as R is the correct explanation.

• Option C: Incorrect, as R is true.

• Option D: Incorrect, as A is true.

Semiconductor:

• A semiconductor is a substance that has a resistivity in between conductor and insulator.
• A semiconductor has 4 valance electrons that are C, Si, Ge, Sn, and Pb.

Classification of Semiconductor:

Intrinsic Semiconductor:

• An extremely pure form is known as an Intrinsic Semiconductor.
• In intrinsic Semiconductor, even at room temperature, hole electrons pair are created.
• Electric fields applied across the intrinsic semiconductor cause current conduction due to both Holes as well as Electrons.

Extrinsic Semiconductor:

• The process of adding impurity to the pure semiconductor is called Doping.
• By means of doping Extrinsic semiconductor is formed.
• Normally, 108 atoms of semiconductor added with 1 atom of impurity.
• Depending upon the types of impurity added, the extrinsic semiconductor is classified into N-type and P-Type semiconductors.

​1. N-Type Semiconductor: This type of semiconductor is formed by added pentavalent impurity.

The current conduction in N-Type semiconductor is predominantly by free electron or it has electron type conductivity.

2. P-Type Semiconductor: This type of semiconductor is formed by added Trivalent impurity.

The current conduction in the P-Type semiconductor is predominantly by holes or it has hole type conductivity.

Conclusion: Hence, Pentavalent impurity (Arsenic-As) in Intrinsic semiconductors (Silicon) is used to create an N-type semiconductor.

Donor impurities (e.g., phosphorus) in n-type semiconductors add extra electrons by creating donor energy levels just below the conduction band. These electrons are easily excited to the conduction band, increasing the number of free electrons available for conduction compared to an intrinsic semiconductor, which relies on thermal excitation across the bandgap.

• Option A: Incorrect, as donors don’t create holes.

• Option B: Correct, as donors add conduction electrons.

• Option C: Incorrect, as donors reduce the effective excitation energy, not widen the bandgap.

• Option D: Incorrect, as donors don’t reduce mobility.

II-VI semiconductors are generally p-type semiconductors except for ZnO and ZnTe. II-VI semiconductors are those which contain atoms of materials that have 2 valence electrons and 6 valence electrons.