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Extrinsic Semiconductors

Last updated date: 23rd May 2024
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What are Semiconductors?

Semiconductors are those materials that have an electrical conductivity value which lies between that of an insulator such as glass and a conductor such as copper. The common examples of semiconductors are Silicon and Germanium which are also known as Elemental Semiconductors. The examples of Compound Semiconductors are Cds, GaAs, CdSe, anthracene, doped phthalocyanines, etc. Diodes, transistors, and integrated circuits are some of the electronic devices in which semiconductors are mainly used. The application of these devices is wide because they are quite affordable, compact, reliable, and power-efficient. There are mainly two types of semiconductors, and they are intrinsic semiconductors and extrinsic semiconductors.


What are Intrinsic Semiconductors?

Intrinsic Semiconductors (Definition) - Intrinsic semiconductors are those semiconductors that are always in extremely pure form. It is also known as an undoped semiconductor. It shows a low electrical conductivity under room temperature and its conductivity depends on its temperature. Therefore, intrinsic semiconductors are generally not used in electronic devices due to their low electrical conductivity. Examples are silicon (Si) and Germanium (Ge). An intrinsic semiconductor acts as a perfect insulator at absolute zero, which means its conductivity is zero.


What are Extrinsic Semiconductors?

Extrinsic Semiconductors (Definition) - An extrinsic semiconductors are those semiconductors that come into existence when a measured and small amount of chemical impurity is added to intrinsic semiconductors. It is also known as doped semiconductor or impurity semiconductors. The doping of the semiconductors increases its conductivity. The process of deliberately adding a desirable impurity is known as doping and the impurity atoms are called dopants. Extrinsic semiconductors are further classified into two types - N-Type semiconductors and P-type semiconductors.


Difference Between Extrinsic and Intrinsic Semiconductors

The major difference between extrinsic and intrinsic semiconductors are as follow:

Intrinsic Semiconductors

Extrinsic semiconductors

1. Intrinsic Semiconductors are always in pure form.

1. Extrinsic Semiconductors are made by doping some impurity in the pure semiconductors.

2. They have low electrical conductivity at room temperature.

2. They have comparatively high electrical conductivity.

3. The no. of electrons are equal to the no. of holes.

3. The no. of electrons is not equal to the no. of holes.

4. It is dependent on temperature only.

4. It is dependent on temperature as well as the amount of impurity.

5. It is not classified further.

5. It is further classified as n-type semiconductors and p-type semiconductors.

6. Examples are Silicon and Germanium.

6. Examples are Si and Ge doped with Al, In, P, As, etc.


Therefore, these are some of the major differences between extrinsic and intrinsic semiconductors.


Did You Know?

Semiconductors are used in various electrical devices like computers, the internet, smartphones, tablet services. They are widely used in the present world. It would be impossible to make all these devices without semiconductors. In 1821, an effect due to semiconductors was first noticed by Thomas Johan Seebeck. Studies regarding semiconductors were carried out in the laboratories in the early 1830s.


In 1833, Michael Faraday experimented with silver sulfide and discovered that the conductivity of silver sulfide increased with the increase of temperature. This behaviour of silver sulfide is opposite to the metals such as copper in which its conductivity decreases with an increase in temperature.


Tips to study Extrinsic Semiconductors

Through the above paragraphs about the meaning of semiconductors, their types and the difference between Extrinsic and Intrinsic Semiconductors, students must have got a lot of information. 

Since this is one of the most important topics of Chemistry, you might need to know about some of the tricks to prepare this subject with ease, read ahead to know about it. 

  • Allocate your time wisely.

Before you make your timetable to prepare for anything, you shall keep a few things in mind. One of the most important of them is to be able to divide time into each topic wisely. Students shall understand that leaving anything from the study content can cost you more than you could even imagine and that is why it is important for you to cover your syllabus with utmost sincerity and understanding. Apart from this, students are also advised to stick to the plan that they have made because delaying tasks doesn’t let you stay consistent and true towards your goal and without that, nothing can be achieved. 

  • Don't cram, understand.

Another important step that the students shall be following at all times, despite the level that they are at, is to understand concepts and not just mug things up. It is because that understanding ensures better memorisation and helps to lay a strong foundation for the upcoming years. Being able to use the knowledge that you’ve understood over the years, is another advantage that you shall be looking forward to. This means that you’ll be able to score better if you decide to understand and learn rather than cramming. 

  • Practice till you master.

One of the most effective techniques that students shall be doing is practising. As a matter of fact, you cannot master anything unless you repeatedly practice the concept. Hence, it is advised that students shall be spending a lot of their time testing their knowledge and attempting as many questions as possible. It also lets the students remember things for a longer time and also makes sure that the information is retained in their minds. This is also one of the most effective ways to maximize the impact of learning. 

  • Attempt and check.

Self-evaluation is a master key, especially in the times when students have some exams around the corner. It lets you take an insight into whatever you have comprehended so far and test your knowledge. This also allows you to study the pattern that you usually follow to study and furthermore helps you to make relevant changes in the plan of action that you’re currently using. Since it is a great way to take control of your learnings and assessments, it helps you to manage your schedule and prepare effective strategies that could help you score better. 

  • Review your work.

Students shall be able to review their work critically because it allows them to know about their exact performance. You shall be able to identify the areas that you’re weak at, areas that are your strengths and the areas that need more attention. All these observations shall further be used to develop a plan which would let you improve your overall performance and enhance your subject understanding. 

FAQs on Extrinsic Semiconductors

1. What are N-type Semiconductors?

N-type semiconductors are those extrinsic semiconductors in which a tetravalent element (elements that have valency 4) such as Silicon or Germanium is doped with a pentavalent element (elements that have valency 5) such as Arsenic (As), Antimony (Sb). As a result, an atom of that pentavalent element occupies the position of an atom in the crystal lattice of the tetravalent element. When the doping is done, four out of five electrons of the pentavalent atom bonds with the four tetravalent element neighbours, and the fifth electron forms a weak bond with the parent atom.

Therefore, a very low amount of ionisation energy is required to set the fifth electron free. Also, the fifth electron moves freely in the lattice of the tetravalent element, even if it is at room temperature.

2. What are P-type Semiconductors?

P-type semiconductors are those extrinsic semiconductors in which a tetravalent element such as Silicon and Germanium is doped with a trivalent element ( elements that have valency 3) such as Aluminium (Al), Indium (In), etc. When the doping is done, three out of four electrons of the tetravalent element forms a covalent bond with the three electrons of the trivalent element. A deficiency of one electron arises, and therefore the fourth electron does not have an electron to bond with.

Thus, a vacancy or hole gets created, and a need arises to fill that vacancy. Hence, there is a chance for an electron in the outer orbit of a neighbouring atom to jump and fill the vacancy. Thus, this creates a hole or vacancy in the place of that electron. As a result, the hole becomes available for conduction.

3. How can I make preparation for the topic of Extrinsic Semiconductors easier?

Students shall not be looking for shortcuts when preparing for tests. The only key to cracking these exams is being clear about the concepts and practising as many times as possible. Vedantu can help you with the detailed notes of the topics so that you’re able to expand the subject knowledge. You can also get many mock tests and quizzes to be able to test your understanding and gain a clear insight into whatever you’ve comprehended.

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5. How should I prepare for the topic of Extrinsic Semiconductors during the last day before my final exam?

You shall have a look and deeply read all the important points of the topic and attempt some short quizzes which helps you to relax your mind for a little while and also prepare you for the exam by testing your knowledge subconsciously. Vedantu offers you access to all the important topics, filtered according to the different subjects and chapters.  It can also help you perform some small quizzes and puzzles.

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