Extrinsic Semiconductors - Definition, Types, FAQs

Updated on Jul 02, 2025 04:47 PM IST

A semiconductor is a type of substance having electrical conductivity between conductors and insulators. In semiconductors electrons from the valence band get energy and jump to the conduction band, then the current starts flowing through the semiconductor. Semiconductors generally have 4 valence electrons in their outermost shells. The addition of a trivalent impurity to a semiconductor creates many p-type semiconductors and the addition of a pentavalent impurity to a semiconductor creates many n-type semiconductors. In this article, we will discuss types of semiconductors, what is extrinsic semiconductor, extrinsic semiconductor examples, n-type semiconductor diagrams, p-type semiconductor diagrams, factors affecting extrinsic semiconductors, difference between n-type and p-type semiconductors, and application of extrinsic semiconductor

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What is Extrinsic Semiconductor?
Types of Extrinsic Semiconductors
N-type Semiconductor
P-type Semiconductor
Factors Affecting Extrinsic Semiconductors
Applications of Extrinsic Semiconductor
Energy Band Diagram For P-type and N-type Semiconductor
Difference Between P-type and N-type Semiconductors

Extrinsic Semiconductors - Definition, Types, FAQs

Types of Semiconductors

Intrinsic semiconductor
Extrinsic semiconductor

Semiconductors are of two types: intrinsic semiconductors and extrinsic semiconductors.

What do you mean by doping?

Doping is known as the controlled mixing of impurities in semiconductors. The impurities are called dopants.

What is Extrinsic Semiconductor?

Extrinsic semiconductor definition: Extrinsic semiconductor is a special kind of semiconductor that drastically increases the electric conductivity of the semiconductor by mixing impurities in a controlled manner. When the conductivity of a semiconductor gets increased by doping, then the semiconductor is called an extrinsic semiconductor.

If we define impurity, impurities meaning in a semiconductor is not the constituent particle of the semiconductor, it means other substances like arsenic, phosphorus, etc.

Extrinsic semiconductor examples: Germanium (Ge) and silicon (Si) doped with arsenic (As), phosphorus (P), etc.

Related Topics,

Types of Extrinsic Semiconductors

Extrinsic semiconductors are classified into two types depending on the doping and the majority charge carriers.

n-type semiconductor
p-type semiconductor

N-type Semiconductor

If pentavalent impurities or elements are dropped as impurities in the crystal of an intrinsic semiconductor in a controlled manner, the crystal thus formed is called an n-type semiconductor or n-type extrinsic semiconductor.

Pentavalent impurities are called donors as they have five electrons in the outermost shell.

Examples of n-type semiconductors

Arsenic (As), and phosphorus (P) act as an n-type semiconductor in pure silicon (Si) or germanium (Ge).

P-type Semiconductor

If trivalent impurities or elements are doped as impurities in a crystal in an intrinsic semiconductor in a controlled manner, the crystal thus formed is called a p-type semiconductor or p-type extrinsic semiconductor.

Trivalent impurities examples/ Examples of p-type semiconductors

Boron (Br), aluminum (Al) doped in pure silicon (Si), or germanium (Ge) which works as a p-type semiconductor.

Factors Affecting Extrinsic Semiconductors

Doping Element type
Amount of impurities added
Temperature
Energy band gap
Mobility of charge carriers
Type of semiconductor material

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Applications of Extrinsic Semiconductor

Diodes (P-N junction diode, Zener diode, LED)
Transistors
Photodiodes
Solar cells
Lasers
Phototransistors
Rectifiers
Light detectors

Energy Band Diagram For P-type and N-type Semiconductor

P-type Semiconductor Diagram

N-type Semiconductor Diagram

Difference Between P-type and N-type Semiconductors

n-type Semiconductor	p-type Semiconductor
Pentavalent impurities	Trivalent impurities
Electrons are the majority of charge carriers	Holes are the majority of charge carriers
Holes are the minority charge carriers	Electrons are the minority charge carriers
Donor impurities that donate free electrons.	Acceptor impurities that create holes.
Conductivity is due to the movement of electrons.	Conductivity is due to the movement of holes.
Donor energy levels are close to the conduction band.	Acceptor energy levels are close to the valence band.
Used in transistors, diodes, and other electronic devices.	Used in LEDs, photodiodes, and other electronic devices.
Silicon is doped with phosphorus or arsenic.	Silicon doped with boron or gallium.

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Frequently Asked Questions (FAQs)

1. What is semiconductor?

The substances having electrical conductivity intermediate between conductors and insulators are called semiconductors.

2. What is hole?

The release of an electron creates a position known as hole , which is opposite in charge of an electron.

3. What is a forbidden band?

The separation between two consecutive energy levels in a solid is known as a forbidden band.

4. What is valence band?

The energy band that is formed by energy levels in which the electrons of a substance can reside, is called valence band.

5. What is a conduction band?

The energy levels possessed by the free electrons or conduction electrons of a substance constitute the band which is known as conduction band.

6. What happens when germanium doped with indium?

When germanium doped with indium, p-type semiconductor is obtained.

7. What is the number of valence electrons in a semiconductor?

A semiconductor has generally valence electrons of 4.

8. How does doping affect the optical properties of semiconductors?

Doping can significantly affect the optical properties of semiconductors. It can introduce new absorption and emission bands, alter the refractive index, and change the semiconductor's response to light. These effects are utilized in various optoelectronic devices such as LEDs and photodetectors.

9. What is the Hall effect, and how is it used to characterize extrinsic semiconductors?

The Hall effect is the production of a voltage difference across a conductor when a magnetic field is applied perpendicular to the current flow. In extrinsic semiconductors, the Hall effect can be used to determine the type of majority carriers (electrons or holes), their concentration, and mobility, providing crucial information about the doping characteristics.

10. What is hot carrier injection in heavily doped semiconductors?

Hot carrier injection occurs when charge carriers gain high kinetic energy in the presence of strong electric fields, typically in heavily doped regions. These energetic carriers can overcome potential barriers and inject into adjacent regions, affecting device performance and reliability, particularly in small-scale semiconductor devices.

11. How does doping affect the thermal conductivity of semiconductors?

Doping generally reduces the thermal conductivity of semiconductors. This is because the impurity atoms introduce scattering centers for phonons (lattice vibrations), which are the primary carriers of heat in semiconductors. The effect becomes more pronounced at higher doping concentrations.

12. How does doping affect the breakdown voltage of a semiconductor?

Higher doping concentrations generally lead to lower breakdown voltages in semiconductors. This is because the increased number of charge carriers allows for easier avalanche multiplication under high electric fields. However, the relationship is complex and depends on the specific device structure and doping profile.

13. What is the difference between n-type and p-type extrinsic semiconductors?

N-type extrinsic semiconductors are doped with donor impurities that provide extra electrons, making electrons the majority charge carriers. P-type extrinsic semiconductors are doped with acceptor impurities that create extra holes, making holes the majority charge carriers.

14. Why are extrinsic semiconductors more conductive than intrinsic semiconductors?

Extrinsic semiconductors are more conductive because doping introduces additional charge carriers (electrons or holes) that are readily available for conduction. This increases the number of free charge carriers compared to intrinsic semiconductors, where charge carriers must be thermally excited across the full band gap.

15. What is the Fermi level, and how does it change in extrinsic semiconductors?

The Fermi level is the energy level at which the probability of electron occupancy is 50%. In n-type semiconductors, the Fermi level shifts closer to the conduction band, while in p-type semiconductors, it shifts closer to the valence band. This shift reflects the change in charge carrier concentrations due to doping.

16. What is charge neutrality in extrinsic semiconductors?

Charge neutrality in extrinsic semiconductors means that the total positive charge (holes and ionized donors) equals the total negative charge (electrons and ionized acceptors). This principle ensures that the semiconductor remains electrically neutral overall, despite the introduction of dopants.

17. How do donor and acceptor atoms differ in their effect on semiconductor properties?

Donor atoms (used in n-type doping) provide extra electrons to the semiconductor, increasing electron concentration and shifting the Fermi level closer to the conduction band. Acceptor atoms (used in p-type doping) create extra holes, increasing hole concentration and shifting the Fermi level closer to the valence band.

18. How does doping affect the energy band structure of a semiconductor?

Doping introduces new energy levels within the forbidden gap of the semiconductor. For n-type semiconductors, donor levels are created near the conduction band, while for p-type semiconductors, acceptor levels are created near the valence band. This reduces the energy required for charge carrier generation and increases conductivity.

19. How does band bending occur in extrinsic semiconductors?

Band bending refers to the curvature of energy bands near the surface or interface of a semiconductor. In extrinsic semiconductors, it occurs due to the difference in Fermi levels between the bulk and the surface/interface, leading to charge redistribution and the formation of depletion or accumulation regions.

20. How does carrier mobility differ between n-type and p-type semiconductors?

Generally, electron mobility is higher than hole mobility in most semiconductors. This means that n-type semiconductors often have higher carrier mobility than p-type semiconductors of the same material. However, the exact values depend on factors such as doping concentration, temperature, and crystal structure.

21. What is the difference between majority and minority carriers in extrinsic semiconductors?

Majority carriers are the charge carriers (electrons or holes) that are more abundant due to doping. In n-type semiconductors, electrons are majority carriers, while in p-type semiconductors, holes are majority carriers. Minority carriers are the less abundant charge carriers in each case.

22. What is the depletion region in a p-n junction, and how is it affected by doping?

The depletion region is an area at the junction between p-type and n-type semiconductors where mobile charge carriers have diffused away, leaving behind fixed ions. Higher doping concentrations result in a narrower depletion region, while lower doping leads to a wider depletion region.

23. How does temperature affect the conductivity of extrinsic semiconductors?

At low temperatures, the conductivity of extrinsic semiconductors is dominated by the dopant-induced charge carriers. As temperature increases, more intrinsic charge carriers are generated, eventually leading to intrinsic behavior at very high temperatures. This results in a complex relationship between temperature and conductivity.

24. How does doping concentration affect the electrical properties of extrinsic semiconductors?

Increasing doping concentration generally increases conductivity by providing more charge carriers. However, very high doping levels can lead to impurity scattering, reducing carrier mobility. The relationship between doping concentration and conductivity is therefore non-linear and has practical limits.

25. What is compensation in extrinsic semiconductors?

Compensation occurs when both donor and acceptor impurities are present in a semiconductor. The donors and acceptors can partially cancel each other's effects, resulting in a reduced net doping level. This can be intentional or unintentional and affects the overall electrical properties of the semiconductor.

26. What is the difference between direct and indirect doping in semiconductors?

Direct doping involves intentionally adding impurities to the semiconductor during its growth or through ion implantation. Indirect doping refers to the creation of defects or vacancies in the crystal structure that act like dopants. Direct doping is more common and provides better control over semiconductor properties.

27. What is the drift current in extrinsic semiconductors?

Drift current in extrinsic semiconductors is the flow of charge carriers (electrons or holes) due to an applied electric field. The magnitude of drift current depends on the carrier concentration, mobility, and the strength of the electric field. It is a key component of current flow in semiconductor devices.

28. What is the difference between uniform and graded doping in semiconductors?

Uniform doping involves a constant concentration of dopants throughout the semiconductor, while graded doping creates a varying concentration profile. Graded doping can be used to create built-in electric fields, modify carrier transport, and optimize device performance in applications like solar cells and bipolar transistors.

29. How does doping affect the resistance of a semiconductor?

Doping generally decreases the resistance of a semiconductor by increasing the number of charge carriers available for conduction. The relationship between doping concentration and resistance is typically inverse, but not linear. At very high doping levels, the resistance may not decrease as rapidly due to increased carrier scattering.

30. How does doping affect the width of the band gap in semiconductors?

Doping typically does not significantly change the width of the band gap itself. However, it introduces energy levels within the band gap, effectively reducing the energy required for charge carrier generation. This can make the semiconductor behave as if it had a smaller effective band gap.

31. What is the concept of freeze-out in extrinsic semiconductors?

Freeze-out occurs at low temperatures when there is insufficient thermal energy to ionize the dopant atoms. As a result, the charge carriers "freeze" into their dopant atoms, significantly reducing the semiconductor's conductivity. This effect is more pronounced in semiconductors with deeper dopant energy levels.

32. How does doping affect the minority carrier lifetime in semiconductors?

Doping generally reduces the minority carrier lifetime in semiconductors. This is because the increased number of majority carriers enhances recombination rates. Additionally, dopant atoms can act as recombination centers. The relationship between doping and minority carrier lifetime is crucial for devices like solar cells and bipolar transistors.

33. What is the concept of compensation ratio in extrinsic semiconductors?

The compensation ratio is the ratio of the concentration of acceptor impurities to donor impurities (or vice versa) in a semiconductor. A fully compensated semiconductor has equal numbers of donors and acceptors, resulting in behavior similar to an intrinsic semiconductor. Partial compensation can be used to fine-tune semiconductor properties.

34. How does doping affect the electron affinity of a semiconductor?

Doping can slightly modify the electron affinity of a semiconductor, which is the energy required to remove an electron from the conduction band to the vacuum level. The changes are typically small but can be significant in heterostructures and at interfaces where band alignment is crucial.

35. What is the effect of doping on the effective mass of charge carriers?

Doping can indirectly affect the effective mass of charge carriers in semiconductors. While it doesn't directly change the band structure, high doping levels can lead to band tailing and non-parabolicity, which can alter the apparent effective mass of carriers. This effect is more pronounced in heavily doped semiconductors.

36. How does doping influence the Seebeck coefficient in semiconductors?

The Seebeck coefficient, which measures the thermoelectric effect, is strongly influenced by doping. Generally, increasing the doping concentration reduces the magnitude of the Seebeck coefficient. This relationship is important in the development of thermoelectric materials and devices.

37. What is the concept of modulation doping in semiconductor heterostructures?

Modulation doping is a technique used in semiconductor heterostructures where dopants are introduced in one layer but the charge carriers are free to move into an adjacent, undoped layer. This separates the carriers from the ionized impurities, reducing scattering and enhancing mobility, which is crucial for high-speed electronic devices.

38. How does doping affect the recombination mechanisms in semiconductors?

Doping influences various recombination mechanisms in semiconductors. It can introduce new recombination centers, alter the rates of radiative and non-radiative recombination, and affect Auger recombination rates. Understanding these effects is crucial for optimizing the performance of optoelectronic devices like LEDs and lasers.

39. What is the relationship between doping and the built-in potential in a p-n junction?

The built-in potential in a p-n junction increases with higher doping concentrations on either side of the junction. This is because the difference in Fermi levels between the p-type and n-type regions becomes larger, resulting in a greater potential difference when the junction is formed.

40. How does doping affect the Franz-Keldysh effect in semiconductors?

The Franz-Keldysh effect, which describes the change in optical absorption of a semiconductor in the presence of an electric field, can be influenced by doping. Higher doping levels can enhance the effect by allowing for stronger built-in electric fields, particularly important in electro-optic modulators and certain types of photodetectors.

41. What is the impact of doping on the noise characteristics of semiconductor devices?

Doping can significantly affect the noise characteristics of semiconductor devices. Higher doping levels generally lead to increased shot noise due to the larger number of charge carriers. However, they can also reduce certain types of noise, like generation-recombination noise, by minimizing fluctuations in carrier concentrations.

42. How does doping influence the surface properties of semiconductors?

Doping can alter the surface properties of semiconductors by changing the surface charge, modifying surface states, and affecting band bending at the surface. These changes can impact surface recombination velocities, work function, and chemical reactivity, which are crucial for device performance and semiconductor processing.

43. What are extrinsic semiconductors?

Extrinsic semiconductors are semiconductors that have been intentionally doped with impurities to modify their electrical properties. Unlike intrinsic semiconductors, which are pure, extrinsic semiconductors have additional charge carriers (electrons or holes) introduced by the dopants, which significantly alters their conductivity.

44. What is the impact of doping on the quantum confinement effects in semiconductor nanostructures?

Doping can modify quantum confinement effects in semiconductor nanostructures by altering the potential well shape and depth. It can shift energy levels, change oscillator strengths, and affect carrier localization. Understanding these interactions is crucial for designing advanced optoelectronic devices based on quantum dots, wells, and wires.

45. How does doping affect the spin properties of charge carriers in semiconductors?

Doping can influence the spin properties of charge carriers in semiconductors, which is important for spintronics applications. It can affect spin relaxation times, spin polarization, and spin-dependent transport. The type and concentration of dopants can be used to engineer these spin-related properties.

46. What is the relationship between doping and the Fermi velocity in semiconductors?

The Fermi velocity, which is the velocity of electrons at the Fermi level, can be affected by doping. In heavily doped semiconductors approaching degeneracy, the Fermi velocity can increase as the Fermi level moves into the conduction or valence band. This effect is particularly important in high-speed electronic devices.

47. How does doping influence the thermionic emission properties of semiconductors?

Doping can significantly affect thermionic emission from semiconductors by altering the work function and the position of the Fermi level. Higher doping levels generally enhance thermionic emission by reducing the effective barrier for electron emission. This is important in devices like Schottky diodes and certain types of electron emitters.

48. How does doping affect the capacitance of semiconductor devices?

Doping affects the capacitance of semiconductor devices by changing the width of the depletion region and the charge distribution. Higher doping concentrations generally lead to higher capacitance due to narrower depletion regions. This relationship is crucial in the design of capacitors and other semiconductor devices.

49. What is the concept of degeneracy in heavily doped semiconductors?

Degeneracy occurs in heavily doped semiconductors when the Fermi level moves into the conduction band (for n-type) or valence band (for p-type). This leads to metallic-like behavior, where the semiconductor no longer follows classical statistics and requires quantum mechanical treatment. Degenerate semiconductors have unique electrical and optical properties.

50. What is the effect of doping on the piezoelectric properties of semiconductors?

While doping primarily affects electrical properties, it can also influence the piezoelectric response of certain semiconductors. In some cases, doping can enhance or suppress piezoelectric effects by altering the crystal structure or introducing strain. This is particularly relevant for materials used in MEMS devices and acoustic wave sensors.

51. How does doping affect the plasmon resonance in semiconductors?

Doping can significantly influence plasmon resonance in semiconductors. Higher doping levels increase the free carrier concentration, which can lead to the emergence of plasmon resonances in the infrared or terahertz range. This effect is used in plasmonic devices and can be tuned through careful control of doping levels.

52. What is the relationship between doping and the Burstein-Moss shift in semiconductors?

The Burstein-Moss shift is an increase in the apparent band gap of a semiconductor due to heavy doping. As the doping level increases, the Fermi level moves into the conduction band (for n-type) or valence band (for p-type), blocking low-energy transitions and effectively increasing the observed optical band gap.

53. How does doping affect the magnetoresistance of semiconductors?

Doping can significantly influence the magnetoresistance of semiconductors. The type and concentration of dopants affect carrier mobility and concentration, which in turn modify how the material's resistance changes in a magnetic field. This relationship is important for magnetic field sensors and magnetoresistive devices.

54. What is the impact of doping on the thermal expansion coefficient of semiconductors?

Doping can slightly modify the thermal expansion coefficient of semiconductors. While the effect is generally small, it can be significant in certain applications, particularly in heterostructures or devices where thermal mismatch is critical. The changes are due to alterations in the crystal lattice and electron-phonon interactions.

55. How does doping influence the photorefractive effect in semiconductors?