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# NCERT Solutions for Class 12 Physics Chapter 14 - Semiconductor Electronic: Material, Devices and Simple Circuits - PDF Download

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The NCERT Solutions for Class 12 Physics Chapter 14 Semiconductor Electronics: Materials, Devices and Simple Circuits are important chapters if you want to score well on the Class 12 Physics examination. NCERT solutions for class 12 Physics have answers to questions which are given in the textbook. These solutions are freely available on our website where you can download this in pdf form and use them in future.

These Solutions for Class 12 Physics help you to sort out your weaknesses and strengths in the topic of Semiconductors. By this solution you can also learn the right methods to solve numerical problems.

In chapter 14 you will learn about semiconductors, about metals, semiconductor and non metals, p-type, n-type semiconductors, p-n junction, junction as rectifier.

## Subtopics involved in Class 12 Physics Chapter 14 Semiconductor Electronics

1. Introduction

2. Classification of Metals, Conductors, and Semiconductors

3. Intrinsic Semiconductor

4. Extrinsic Semiconductor

5. P-n Junction

1. p-n junction formation

6. Semiconductor Diode

1. p-n junction diode under forward bias

2. p-n junction diode under reverse bias

7. Application of Junction Diode as a Rectifier

### Classification of Metals, Conductors, and Semiconductors

(i) Metals: Metals possess very low resistivity and high conductivity.

(ii) Semiconductors: Semiconductors have resistivity or conductivity intermediate to metals and insulators.

(iii) Insulators: Insulators have high resistivity and low conductivity.

### Intrinsic Semiconductor

An intrinsic or pure semiconductor, also known as an undoped semiconductor or i-type semiconductor, is a pure semiconductor without any crucial dopant species present.

### Extrinsic Semiconductor

The conductivity of an intrinsic or i-type semiconductor depends on temperature, but at room temperature the conductivity is very low. As such,there are no important electronic devices that can be developed using these types of semiconductors. Therefore, there is a necessity to improve the conductivity of semiconductors, which can be done by making use of impurities. When a small amount, like a few parts per million (ppm), of a suitable impurity is added to the pure semiconductor, the conductivity of the semiconductor is increased. Such semiconductors are known as extrinsic semiconductors or impurity semiconductors.

There are two types of dopants used in doping the tetravalent Ge or Si:

(i) Pentavalent (valency 5); like Antimony (Sb), Arsenic (As), , Phosphorous (P), etc.

(ii) Trivalent (valency 3); like Boron (B), Indium (In), Aluminium (Al), etc.

### p-n Junction

Let us consider a thin p-type silicon (p-Si) semiconductor wafer. By adding a very small quantity of pentavalent impurity, part of the p-Si wafer can be converted into n-Si. There are many processes by which a semiconductor can be formed. The wafer now consists of the p-region and n-region and a metallurgical junction between the p-, and n- region. Two important processes happened during the formation of a p-n junction: one is diffusion and another is drift.

As we all know that in an n-type semiconductor, the concentration of electrons (number of electrons per unit volume) is more compared to the concentration of holes. Likewise, in a p-type semiconductor, the concentration of holes is more than the concentration of electrons. During the formation of p-n junction, and due to the concentration gradient across p-, and n- sides, holes diffuse from p-side to n-side and electrons diffuse from n-side to p-side.

### Semiconductor Diode

A semiconductor diode is generally a p-n junction with metallic contacts provided at the ends for the application of an external voltage. Diode is a two terminal device, the direction of the arrow indicates the conventional direction of current when the diode is under forward bias. The equilibrium barrier potential can be changed by applying an external voltage V across the diode. The situation of the p-n junction diode under equilibrium (without bias).

#### p-n junction diode under forward bias

When an external voltage V is applied across a semiconductor diode such that the p-side is connected to the positive terminal of the battery and the n-side of the semiconductor is connected to the negative terminal, it is said to be forward biased. The applied voltage almost drops across the depletion region and the voltage drop across the p-side and n-side of the junction is negligible.

If the applied voltage is very small, the barrier potential will be reduced only slightly below the equilibrium value, and only a small number of carriers in the material—those that happen to be in the uppermost energy levels—will possess enough energy to cross the junction.

So the current will be small. If we increase the applied voltage, the barrier height will be reduced and more carriers will have the required energy. Therefore the current increases.

#### p-n junction diode under reverse bias

When an external voltage V is applied across the diode such that n-side is positive and p-side is negative, it is known to be reverse biased. The applied voltage almost drops across the depletion region. The direction of applied voltage is the same as the direction of barrier potential. As a result, the barrier height increases and the depletion region widens due to the change in the electric field. Thus, diffusion current decreases enormously compared to the diode under forward bias.

The electric field direction of the junction is such that if electrons on p-side or holes on n-side in their random motion come close to the junction, they will move to its majority zone. This drift of carriers gives rise to current. The drift current is of a few mA. This current is quite low because it is due to the motion of carriers from their minority side to their majority side across the junction. The drift current is also there under forward bias but it is negligible (mA) when compared with current due to injected carriers which are usually in mA. The diode reverse current is not very much dependent on the applied voltage. Even a small voltage is sufficient to sweep the minority carriers from one side of the junction to the other side of the junction.

### Application of Junction Diode as a Rectifier

From the Voltage and current characteristic i.e. V-I of a junction diode we see that it allows current to pass only when it is forward biased. So if an alternating voltage is applied across a diode the current flows only in that part of the cycle when the diode is forward biased. This property is used to rectify alternating voltages and the circuit used for this purpose is called a rectifier. If an alternating voltage is applied to a diode in series with a load, a pulsating voltage will appear across the load only during the half cycles of the ac input during which the diode is forward biased. Such a rectifier circuit is called a half-wave rectifier. The secondary of a transformer supplies the desired ac voltage across terminals A and B. When the voltage at A is positive, the diode is forward biased and it conducts. When A is negative, the diode is reverse-biased and it does not conduct. The reverse saturation current of a diode is found negligible and can be considered as equal to zero for practical purposes.

## Benefits of NCERT Solutions for Class 12th Physics

Chapter 14 Semiconductor Electronic: Material, Devices and Simple Circuits of Class 12th Physics is not very tough and not very easy; it is a moderate chapter. After clearing the concepts and practising the maximum number of questions, you would find questions very easy. Some benefits of Chapter 14 are listed down below:

• Chapter 14 solutions reveal all possible methods of solving concerned problems given in the following chapter.

• These NCERT solutions are solved by our expert physics teachers hence they are completely accurate.

• These solutions covered almost all the tips and tricks for quick problem solving.

• Chapter 14 will help you learn all the important formulas at one hand only.

• These solutions are very well explained in detail with their logics; so each solution explains itself the method of solving.

Question 1 : What is Intrinsic Semiconductor?

Answer : An intrinsic or pure semiconductor, also known as an undoped semiconductor or i-type semiconductor, is a pure semiconductor without any crucial dopant species present.

Question 2 : What are the topics in chapter 14 Semiconductor Electronic: Material, Devices and Simple Circuits?

Answer : Subtopics involved in Class 12 Physics Chapter 14 Semiconductor Electronics

1. Introduction

2. Classification of Metals, Conductors, and Semiconductors

3. Intrinsic Semiconductor

4. Extrinsic Semiconductor

5. P-n Junction

1. p-n junction formation

6. Semiconductor Diode

1. p-n junction diode under forward bias

2. p-n junction diode under reverse bias

7. Application of Junction Diode as a Rectifier