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# Important Questions and Answers: Semiconductor Diode

Electronic Devices - Semiconductor Diode - Important Questions and Answers: Semiconductor Diode

SEMICONDUCTOR DIODE

1.     Give the value of Charge, Mass of an electron.

Charge of an electron – 1.6 x 10 -19 coloumbs. Mass of an electron - 9.11 x 10 -31 Kgs

2.     Define Potential.

A potential of V volts at point B with respect to point A, is defined as the work done in taking unit positive charge from A to B , against the electric field.

3.     Define Current density.

It is defined as the current per unit area of the conducting medium. J = I / A

4.     Define Electron volts.

If an electron falls through a potential of one volt then its energy is 1 electron volt. 1 eV = 1.6 x 10 -19 joules

5.     What is atomic number?

The number of protons or electrons in an atom is atomic number.

6.     What are valence electrons?

Electron in the outermost shell of an atom is called valence electron.

7.     What is forbidden energy gap?

The space between the valence and conduction band is said to be forbidden energy gap.

8.     What are conductors? Give examples?

Conductors are materials in which the valence and conduction band overlap each other so there is a swift movement of electrons which leads to conduction. Ex: Copper, silver.

9.  What are insulators? Give examples?

Insulators are materials in which the valence and conduction band are far away from each other. So no movement of free electrons and thus no conduction. Ex glass, plastic.

10.                        What are Semiconductors? Give examples?

The materials whose electrical property lies between those of conductors and insulators are known as Semiconductors. Ex germanium, silicon.

11.                        Give the energy band structure of Insulator.

In Insulators there is a wide forbidden energy gap. So movement of valence electron from valence to conduction band is not possible. 12.            Give the energy band structure of Semi conductor. In Semiconductors th ere is a small forbidden energy gap. So movement of valence electron from valence to conduction band is possible if the valence electrons are supplied with some energy.

13.                        Give the energy band structure of conductor.

In conductors there i s no forbidden energy gap, valence band and conduction and overlap each other. so there is a heavy movement of valence electrons. 14.                        What are the types o f Semiconductor?

1. Intrinsic semiconductor 2. Extrinsic semiconductor.

15.                        What is Intrinsic Sem iconductor?

Pure form of semiconnductors are said to be intrinsic semiconductor. Ex: germanium, silicon.

16.                        What is Extrinsic Se miconductor?

If certain amount of i mpurity atom is added to intrinsic semiconduuctor the resulting semiconductor is Extrinsic or impure Semiconductor.

17. Define Mass action law.

Under thermal equili brium the product of free electron concentr ation (n) and hole concentration (p) is constant regardless of the individual magnitude.

n.p = ni2

18.                        What are the types of Extrinsic Semiconductor?

1.P-type Semiconductor 2. N- Type Semiconductor.

19.                        What is P-type Semiconductor?

The Semiconductor which are obtained by introducing pentavalent impurity atom (phosphorous, antimony) are known as P-type Semiconductor.

20.                        What is N-type Semiconductor?

The Semiconductor which is obtained by introducing trivalent impurity atom (gallium, indium) are known as N-type Semiconductor.

21.                        What is doping?

Process of adding impurity to a intrinsic semiconductor atom is doping. The impurity is called dopant.

22.                        Which charge carriers is majority and minority carrier in N-type Semiconductor?

Majority carrier: electron and minority carrier: holes.

23.                        Which charge carriers is majority and minority carrier in P-type Semiconductor?

Majority carrier: holes and minority carrier: electron

24.                        Why n - type or penta valent impurities are called as Donor impurities?

n- type impurities will donate the excess negative charge carriers ( Electrons) and therefore they are reffered to as donor impurities.

25. Why P type or trivalent impurities are called as acceptor impurity?

p- type impurities make available positive carriers because they create holes which can accept electron, so these impurities are said to be as acceptor impurity.

26. Give the energy band structure of n- type semiconductor. 27. Define drift current?

When an electric field is applied across the semiconductor, the holes move towards the negative terminal of the battery and electron move towards the positive terminal of the battery. This drift movement of charge carriers will result in a current termed as drift current.

28. Give the energy band structure of P- type semiconductor. 29. Give the expression for the Fermi level energy in n – type semiconductor. Where,

EF - Fermi level energy

EC – Conduction band energy

K – Boltzmann constant

T – Temperature

NC – dimension of concentration in n – type

ND - concentration of donor atoms

30. Give the expression for drift current density=µ due to electron. 31. Give the expression for drift current densitydue to holes. 32. Define the term diffusion current?

A concentration gradient exists, if the number of either electrons or holes is greater in one region of a semiconductor as compared to the rest of the region. The holes and electron tend to move from region of higher concentration to the region of lower concentration. This process in called diffusion and the current produced due this movement is diffusion current.

33. Give the expression for diffusion current= density due to electron. Where

Jn - diffusion current density due to electron

q - Charge of an electron

Dn – diffusion constant for electron

dn / dx – concentration gradient

34. Give the expression for diffusion current = density due to holes. Where

Jp - diffusion current density due to holes

q - Charge of a hole Dp – diffusion constant for hole

dn / dx – concentration gradient

33.                        What is the other name of continuity equation? What does it indicate?

The other name of continuity equation is equation of conservation of charge.This equation indicates that the rate at which holes are generated thermally just equals the rate at which holes are lost because of recombination under equilibrium conditions.

34.                        Define Hall effect?

If a metal or semiconductor carrying current I is placed in a transverse magnetic field B , an electric field E is induced in the direction perpendicular to both I and B , This phenomenon is known as Hall effect.

35.                        Give some application of Hall Effect.

i.                   hall effect can be used to measure the strength of a magnetic field in terms of electrical voltage.

ii.                 it is used to determine whether the semiconductor is p – type or n- type material

iii.              it is used to determine the carrier concentration

iv.              it is used to determine the mobility.

36.                        What is depletion region in PN junction?

The region around the junction from which the mobile charge carriers ( electrons and holes) are depleted is called as depletion region.since this region has immobile ions, which are electrically charged , the depletion region is also known as space charge region.

37.                        Give the other names of depletion region? i.space charge region

ii.Transition region

38.                        What is barrier potential?

Because of the oppositely charged ions present on both sides of PN junction an electric potential is established across the junction even without any external voltage source which is termed as barrier potential.

39.                        Give the other names of depletion region? i.space charge region

ii.Transition region

40.                        What is barrier potential?

Because of the oppositely charged ions present on both sides of PN junction an electric potential is established across the junction even without any external voltage source which is termed as barrier potential.    41.                        What is meant by biasing a PN junction?

Connecting a PN junction to an external voltage source is biasing a PN junction.

42.                        What is forward bias and reverse bias in a PN junction?

When positive terminal of the external supply is connected to P region and negative terminal to N region ,the PN junction is said to be forward biased. under forward biased condition the PN region offers a very low resistance and a large amount of current flows through it.

43.                        What is reverse bias in a PN junction?

When positive terminal of the external supply is connected to N type and negative terminal to P type then the PN junction is said to be in reverse bias. Under reverse biased condition the PN region offers a very high resistance and a small amount of current flows through it.

44.                        What is Reverse saturation current?

The current due to the minority carriers in reverse bias is said to be reverse saturation current. This current is independent of the value of the reverse bias voltage.

45.Why a contact difference of potential exist in PN junction?

When a pn junction is formed by placing a p-type and n-type material in intimate contact, the Fermi level throughout the newly formed specimen is not constant at equilibrium. There will be transfer of electron and energy until Fermi levels in the two side did line up. But the valence and conduction band in pside cannot be at the at the same level as in n side .this shift in energy level results in contact difference of potential.

46. Give the expression of contact difference= of potential? Where, E0 - contact difference of potential,

K – Boltzmann constant ,

T – Temperature

ND - concentration of donor atoms ,

NA - concentration of acceptor atoms

ni – intrinsic concentration

47. Give the diode current equation?

The diode current equation relating =the voltage V and−1current I is given by I – diode current, Io – diode reverse saturation current at room temperature V – External voltage applied to the diode, η - a constant, 1 for Ge and 2 for Si

VT = kT/q = T/11600, thermal voltage,

K – Boltzmann‘s constant (1.38066x10^-23 J/K)

q – Charge of electron (1.6x10^-19 C)

T – Temperature of the diode junction

INTRODUCTION

ELECTRON

It is a stable elementary particle with a charge of negative electricity, found in all atoms and acting as the primary carrier of electricity in solids.

ELECTRONICS

·        Electronics is the movement of electrons in a vacuum, gas, semiconductor, etc., in devices in which the flow is controlled and utilized.

·        Electronics deals with electrical circuits that involve active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection technologies.

ELECTRON DEVICES

·        An electronic component is any physical entity in an electronic system used to affect the electrons or their associated fields in a manner consistent with the intended function of the electronic system.

·        Components are generally intended to be connected together, usually by being soldered to a printed circuit board (PCB), to create an electronic circuit with a particular function (for example an amplifier, radio receiver, or oscillator). Components may be packaged singly, or in more complex groups as integrated circuits.

·        Some common electronic components are capacitors, inductors, resistors, diodes, transistors, etc. Components are often categorized as active (e.g. transistors and thyristors) or passive (e.g. resistors and capacitors).

ELECTRONIC CIRCUITS

Circuits and components can be divided into two groups: Analog and Digital. A particular device may consist of circuitry that has one or the other or a mix of the two types.

Analog circuits are constructed from combinations of a few types of basic circuits. Analog circuits use a continuous range of voltage as opposed to discrete levels as in digital circuits. The number of different analog circuits so far devised is huge, especially because a 'circuit' can be defined as anything from a single component, to systems containing thousands of components.

Digital circuits are electric circuits based on a number of discrete voltage levels. Digital circuits are the most common physical representation of Boolean algebra, and are the basis of all digital computers. To most engineers, the terms "digital circuit", "digital system" and "logic" are interchangeable in the context of digital circuits.

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