Extrinsic Semiconductor vs. Intrinsic Semiconductor

Attribute	Extrinsic Semiconductor	Intrinsic Semiconductor
Doping	Doped with impurities to alter conductivity	Not intentionally doped
Conductivity	Varies based on the type and concentration of dopants	Relatively low
Charge Carriers	Majority and minority charge carriers	Only majority charge carriers
Electrical Resistivity	Can be controlled by doping	Higher resistivity
Band Gap	Can be modified by doping	Fixed band gap
Applications	Transistors, diodes, integrated circuits	Photovoltaic cells, sensors

Introduction

Semiconductors are materials that have properties between those of conductors and insulators. They are widely used in electronic devices due to their ability to control the flow of electric current. Semiconductors can be classified into two main types: intrinsic and extrinsic. In this article, we will compare the attributes of these two types of semiconductors and explore their differences and applications.

Extrinsic Semiconductors

Extrinsic semiconductors are created by intentionally adding impurities to intrinsic semiconductors. This process is known as doping and is done to modify the electrical properties of the material. The impurities added are typically atoms of other elements that have either fewer or more valence electrons than the atoms of the intrinsic semiconductor. The two most common types of extrinsic semiconductors are n-type and p-type.

N-type Extrinsic Semiconductors

N-type extrinsic semiconductors are created by doping an intrinsic semiconductor with atoms that have more valence electrons than the host material. This creates an excess of negatively charged electrons, which are the majority carriers in n-type semiconductors. The most commonly used dopants for n-type semiconductors are phosphorus and arsenic. These dopants have five valence electrons, one more than the four valence electrons of silicon, which is a commonly used intrinsic semiconductor material.

The additional electron of the dopant atom becomes a free electron that can move freely within the crystal lattice of the semiconductor. This results in increased electrical conductivity. N-type semiconductors are commonly used in devices such as transistors, diodes, and solar cells.

P-type Extrinsic Semiconductors

P-type extrinsic semiconductors are created by doping an intrinsic semiconductor with atoms that have fewer valence electrons than the host material. This creates a deficiency of electrons, known as "holes," which are the majority carriers in p-type semiconductors. The most commonly used dopants for p-type semiconductors are boron and gallium. These dopants have three valence electrons, one less than the four valence electrons of silicon.

The missing electron in the crystal lattice creates a positively charged hole that can move through the semiconductor. This movement of holes contributes to the electrical conductivity of the material. P-type semiconductors are commonly used in devices such as diodes, transistors, and integrated circuits.

Intrinsic Semiconductors

Intrinsic semiconductors are pure semiconducting materials without any intentional impurities. They are typically made of a single element, such as silicon or germanium. In their pure form, intrinsic semiconductors have a balanced number of electrons and holes, resulting in a zero net charge. The electrical conductivity of intrinsic semiconductors is relatively low at room temperature.

When an intrinsic semiconductor is exposed to heat or light, some of the covalent bonds between atoms can be broken, creating free electrons and holes. This process is known as generation and recombination. The concentration of free electrons and holes in an intrinsic semiconductor depends on the temperature and the energy of the incident photons. Intrinsic semiconductors are commonly used in devices such as diodes, transistors, and integrated circuits.

Comparison of Extrinsic and Intrinsic Semiconductors

Now that we have explored the characteristics of extrinsic and intrinsic semiconductors, let's compare them in terms of various attributes:

Electrical Conductivity

Extrinsic semiconductors have higher electrical conductivity compared to intrinsic semiconductors. This is because the intentional addition of impurities in extrinsic semiconductors creates an excess of free charge carriers, either electrons or holes, which significantly enhances the conductivity of the material. Intrinsic semiconductors, on the other hand, have a lower concentration of free charge carriers, resulting in lower electrical conductivity.

Doping

Extrinsic semiconductors undergo the process of doping, where impurities are intentionally added to modify their electrical properties. This allows for precise control over the conductivity and other characteristics of the material. Intrinsic semiconductors, on the other hand, do not undergo the doping process and are in their pure form.

Majority Carriers

In extrinsic semiconductors, the majority carriers are either electrons or holes, depending on whether it is an n-type or p-type semiconductor. The concentration of these majority carriers is significantly higher than that of the minority carriers. In intrinsic semiconductors, the concentration of free electrons and holes is balanced, resulting in an equal number of majority carriers of both types.

Applications

Extrinsic semiconductors find extensive applications in various electronic devices. N-type semiconductors are commonly used in transistors, diodes, solar cells, and sensors. P-type semiconductors are used in diodes, transistors, integrated circuits, and light-emitting diodes (LEDs). Intrinsic semiconductors are also used in similar devices, but their lower electrical conductivity limits their applications in certain high-performance electronic components.

Temperature Dependence

The electrical conductivity of both extrinsic and intrinsic semiconductors is temperature-dependent. As the temperature increases, the number of free charge carriers also increases, leading to higher conductivity. However, the temperature coefficient of extrinsic semiconductors is generally higher than that of intrinsic semiconductors, making them more sensitive to temperature changes.

Cost

Extrinsic semiconductors, particularly those used in the electronics industry, are more expensive compared to intrinsic semiconductors. This is mainly due to the additional processing steps involved in the doping process and the higher purity requirements for extrinsic semiconductors.

Conclusion

In summary, extrinsic and intrinsic semiconductors have distinct attributes that make them suitable for different applications. Extrinsic semiconductors, created through the intentional addition of impurities, offer higher electrical conductivity and precise control over their properties. N-type and p-type extrinsic semiconductors have excess electrons and holes, respectively, as their majority carriers. Intrinsic semiconductors, on the other hand, are pure semiconducting materials with balanced concentrations of free electrons and holes. While intrinsic semiconductors have lower electrical conductivity, they are still widely used in various electronic devices. Understanding the differences between these two types of semiconductors is crucial for designing and developing advanced electronic components.