Semiconductor Electronics: Physics Class 12 Chapter-14

Key Features of NCERT Material for Class 12 Physics Chapter 14 – Semiconductor Electronics: Materials, Devices and Simple Circuits

Quick revision notes

In Chapter 13 of Class 12 : you must have learnt about Nuclei . In chapter 14:  you will learn about semiconductor electronics.

What are Semiconductors?

Semiconductors are the core fundamental materials which are used in solid-state electronic devices such as transistors, diodes etc. The material’s atomic structure decides whether the material will turn out to be a metal, semiconductor or insulator. Semiconductors could also be elements such as Ge, Si or compounds such as CdS or GaAs.

Intrinsic Semiconductors

These are the type of semiconductors devices which are pure and have charged electrons and holes which are achieved as a result of thermal excitation. The hole’s number is found equal to that of the number of the electrons.

Types of semiconductors

There are two types of semiconductors:

• N-type- in here, ne>>nh
• P-type- in here, nh>>ne

For metals, Eg≈0 and for semiconductors Eg ranges from 0.2 eV to 3 eV and in the case of insulators Eg>3eV

Diode

Diodes are being for the purpose of AC voltage rectification which means restricting the voltage to follow one direction only using a capacitor or a filter, a dc voltage can be achieved. The types of diodes are:

• Zener Diode- This is used in places where voltage regulation is needed.
• P-N junction diode- It is used in photonic or optoelectronic devices and the entity is the photon. Examples are solar cells, light-emitting diodes etc

Types of Digital Circuits

There are special logic operational digital circuits. They are:

• NOR gate
• NAND
• NOT
• AND
• OR

1. Metals They have low resistivity or high conductivity.

ρ ~ 10-2.10-8 Ωm, σ ~102. 108 Sm-1

2. Semiconductors They have resistivity or conductivity halfway to metals and covers

ρ ~ 10-5. 106 Ωm, σ ~ 10+5 .10-6 Sm-1

Types of Semiconductors Types of semiconductors are given beneath:

(i) Elements Semiconductors  These semiconductors are accessible in common structure, for example silicon and germanium. 

(ii) Compound Semiconductors These semiconductors are made by exacerbating the metals, for example Albums, GaAs, CdSe, InP, anthracene, polyaniline, and so on.

3. Insulators They have high resistivity or low conductivity.

ρ ~ 1011 . 1019 Ωm, σ ~ 10-11. 10-19 Sm-1

4. Energy Band In a gem due to interatomic association, valence electrons of one iota are shared by more than one particle in the gem. Presently, parting of vitality level happens. The assortment of these firmly separated vitality levels are called a vitality band. 

5. Valence Band  Valence band are the vitality band which incorporates the vitality levels of the valence electrons.

6. Conduction Band Conduction band is the vitality band over the valence band. 

7. Energy Band Gap  The base vitality required for moving electrons from valence band to conduction band is called vitality band hole (Eg ).

8. Contrasts between director, protector and semiconductor based on vitality groups are given underneath: 

9. Fermi EnergyIt is the most extreme conceivable vitality controlled by free electrons of a material at total zero temperature (for example 0K) 

10. On the basis of purity , semiconductors are of two types:

(i) Intrinsic SemiconductorsIt is an unadulterated semiconductor with no noteworthy dopant species present 

ne = nh =ni 

where , ne and nh are number densities of electrons and gaps individually and ni is called inborn transporter fixation. 

An inborn semiconductor is likewise called an undoped semiconductor or I-type semiconductor 

(ii) Extrinsic Semiconductors Pure semiconductor when doped with the polluting influence, it is known as extraneous semiconductor. 

Extraneous semiconductors are fundamentally of two kinds: (a) n-type semiconductors 

(b) p-type semiconductors 

NOTE: Both the kind of semiconductors are electrically nonpartisan. 

11. In n-type semiconductor,  lion’s share charge transporters are electrons and minority charge transporters are openings, for example ne> nh . 

Here, we dope Si or Ge with a pentavalent component, at that point four of its electrons bond with the four silicon neighbors, while fifth stays pitifully bound to its parent particle. 

Arrangement of n-type semiconductor is demonstrated as follows:

12. In p-type semiconductor, lion’s share charge transporters are gaps and minority charge transporters are eletron for example nh > ne . 

In a p-type semiconductor, doping is finished with trivalent contamination molecules, for example those iotas which have three valence electrons in their valence shell. 

Arrangement of p-type semiconductor is demonstrated as follows: 

13. At equilibrium condition, ne nh = ni2

14. Least vitality needed to make an opening electron pair, hv > Eg where, Eg is vitality band hole. 

15. Electric flow, I = eA(neve + nhvh) where, An is territory of cross-segment. 

where, ve and vh are speed of electron and opening individually. 

18. p-n JunctionA p-n intersection is a game plan connected of n-type semiconductor and p-type semiconductor..

19. Formation of Depletion Region in p-n Junction During development of p-n intersection, because of the fixation angle across p and n sides, gaps diffuse from p-side to n-side (p — > n) and electrons diffuse from n-side to p-side (n — > p). 

This space charge locale on either side of the intersection together is known as exhaustion area. 

Exhaustion area is liberated from versatile charge transporters. Width of consumption district is of the request for 10-6 m. The potential distinction created over the exhaustion district is known as the possible hindrance. 

20. Semiconductor Diode/p-n Junction Diode A A semiconductor diode is fundamentally a p-n intersection with metallic contacts gave at the finishes to the use of an outer voltage. 

The course of bolt demonstrates the traditional heading of current (when the diode is under forward inclination). 

21. The graphical relations between voltage applied across p-n intersection and current moving through the intersection are called I-V qualities of intersection diode

22.(I) Junction diode is supposed to be forward predisposition when the positive terminal of the outside 

battery is associated less to the p-side and negative terminal to the n-side of the diode. The circuit outline and I-V qualities of a forward one-sided diode is demonstrated as follows: 

:

The circuit diagram and I-V characteristics of a reverse biased diode is shown below.

23. The DC resistance of a junction diode,

rDC = V/I

24. The dynamic resistance of junction diode,

rAC = ∆V/∆I

25. Diode as Rectifier The way toward changing over rotating voltage/current into direct voltage/current is called correction. Diode is utilized as a rectifier for changing over rotating current/voltage into direct current/voltage. 

There are two different ways of utilizing a diode as a rectifier for example

(i) Diode as a Half-Wave Rectifier Diode conducts comparing to positive half cycle and doesn’t direct during negative half cycle. Henceforth, AC is changed over by diode into unidirectional throbbing DC. This activity is known as half-wave correction. 

Circuit graph of p-n intersection diode as half-wave rectifier is demonstrated as follows: 

(ii) Diode as a Full-Wave Rectifier  In the full-wave rectifier, two p-n intersection diodes, D1 and D2 are utilized. The circuit chart or full-wave rectifier is demonstrated as follows: 

The info and yield wave structures have been given underneath:

Its working dependent on the rule that intersection diode offer exceptionally low obstruction in forward predisposition and high opposition in switch inclination. 

26. The average value or DC value retrieved from a half-wave rectifier,

27. The average value or DC esteemed value retrieved from a full-wave rectifier,

28.The beat recurrence of a half-wave rectifier is equivalent to recurrence of AC. 

29. The beat recurrence of a full-wave rectifier is twofold to that of AC. .

30. Optoelectronic Devices  Semiconductor diodes in which transporters are created by photons, for example photograph excitation, such gadgets are known as optoelectronic gadgets. 

These are as follows:

(i) Light Emitting Diode (LED) It is an intensely doped p-n intersection diode which changes over electrical vitality into light vitality. 

LEDs has the accompanying preferences over traditional glowing low force lights 

(a) Fast activity and no warm up time required 

(b) It is about monochromatic 

(c) Low operational voltage and less force devoured 

(d) Fast ON-OFF exchanging ability. 

(ii) Photodiode  A photodiode is a unique sort of intersection diode utilized for recognizing optical signs. It is an opposite one-sided p-n intersection produced using a photosensitive material. Its image is 

Its V-I qualities of photodiode are demonstrated as follows: 

We observe from the figure that current in photodiode changes with the change in light intensity (I) when reverse bias is applied.

(iii) SolarWe see from the figure that current in photodiode changes with the adjustment in light power (I) when opposite inclination is applied. 

(iii) Solar Cell Solar cell is a p-n intersection diode which changes over sunlight based vitality into electrical vitality. Its image is 

V-I attributes of sunlight based cell are demonstrated as follows: 

The materials utilized for sun oriented cell are Si and GaAs. 

31. Zener DiodeZener diode is a converse one-sided vigorously doped p-n intersection diode. It is worked in breakdown area. 

32. Zener Diode as a Voltage Regulator When the applied converse voltage (V) arrives at the breakdown voltage (Vz) of the Zener diode there is a huge change in the current. Along these lines, after the breakdown voltage Vz, an enormous change in the current can be delivered by practically unimportant change in the opposite predisposition voltage for example Zener voltage stays consistent despite the fact that the current through the Zener diode changes over a wide range. The circuital game plan is appeared as follows.