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AN OVERVIEW OF THE SUBJECT Semiconductor Material & Devices Usman Ali Khan.

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Presentation on theme: "AN OVERVIEW OF THE SUBJECT Semiconductor Material & Devices Usman Ali Khan."— Presentation transcript:

1 AN OVERVIEW OF THE SUBJECT Semiconductor Material & Devices Usman Ali Khan

2 Contents 1. Subject Information 2. The study of Electronics 3. History 4. Semiconductor Materials 5. Atomic Structure

3 Subject Information Code: EE120 Text Book: Electronic Devices & Circuits by Theodore F. Bogart 6 th ed. Electronic Devices & Circuits by David A Bell 4 th ed. Electronic Devices & Circuits by Floyd Electronic Devices & Circuits by Manzar Saeed Basics of Electronic Device by NIIT

4 Marks distribution Total Marks: 150 Theory: 100 Practical: 50 Session Marks: 20 Assignments: 05 Quiz: 05 Project + Presentations: 05 Attendance: 05

5 Introduction Semiconductor Devices Building blocks of useful electronic devices Semiconductor devices include: Diodes PN junction Light Emitting Diode (LED) Zener Diode Tunnel Diode Varactor Diode Laser Diode Photo Diode

6 Transistors Bipolar Junction Transistor (BJT) NPN BJT PNP BJT Junction Field Effect Transistor (JFET) Amplifier Fundamentals Small Signal Transistor Amplifier Integrated Circuits (ICs) Analog ICs Digital ICs

7 Basic Atomic Theory Every chemical element is composed of atoms All atoms within a single element have same structure Every element is unique because the structure of its atoms is unique Atom is composed of three basic particles: Protons (+ive charge) Neutrons Electrons (-ive charge) Nucleus

8 Silicon Atom P=14 N=14 Orbits or Shells K, L, M,N Valence Shell N e ( Electrons in nth orbit) = 2n 2 + Draw the atomic structure of Ge (32)

9 Sub-shells ShellSub-shellCapacity Ks2 L s2 p6 M s2 p6 d10 N s2 p6 d f14

10 Free Electrons + When electrons get enough energy (e.g. from heating), they leave their parent atoms and become free electrons. Flow of free electrons is called current. Therefore more free electrons and more current. Free electrons in (i) conductors (ii) Insulators & (iii) Semiconductors Valence electrons have more tendency to become free electrons because of less attraction force between nucleus and valence shell

11 Flow of Free Electrons (Current) Material containing free electrons Excess of electrons Lack of electrons - Force of repulsion Force of attraction

12 Silicon Crystal (Covalent Bonding) + For stability there should be 8 electrons in valence shell **** **** * + **** **** + **** **** + **** **** + **** **** **** + **** + **** + + **** **** + **** **** + **** + Si Crystal

13 HOLE CURRENT Current in Semiconductors Usman Ali Khan

14 Contents 1. Basics 2. Electron Energy 3. Energy Bands 4. Temperature & Resistance 5. Holes & Hole Current

15 Basics: Rupturing of covalent bond The unit of energy is electronvolt(eV) Energy acquired by one electron if it is accelerated through potential difference of one volt 1 eV = x J Valence Electron energy considerably large and need a few amount of energy to release Electrons in inner shell possess little energy and need a large amount of energy to release Electrons can lose energy in the form of heat and light Free electrons can alco lose and fall into valence shell

16 Important Quantities QuantitySymbolUnitUnit Symbol CurrentIAmpereA VoltageVVoltV ChargeQCoulombC EnergyW,EJouleJ Electric Field StrengthEVolt/meterV/m VolumeVCubic meterm3m3 AreaASquared meterm2m2 ResistanceROhm ConductanceGMoh, SiemensS ResistivityρOhm-meter-m ConductivityσSiemens/meterS/m

17 Important Relations V = IR (Ohm's Law) I = Q/t W = QV R = ρ l/ A G = 1/R σ = 1/ ρ Charge on electron = e = X C Electron energy = 1 eV = X J

18 Rupturing of Covalent Bonds Electron Freed (Conduction Band) Hole created Covalent bond ruptured Valence band Energy is supplied in the form of heat to rupture covalent band

19 Electron Energy P=14 N=14 E1 E2 E3 Electrons closer to nucleus are more tightly bound and need more energy to become free Therefore: E1 > E2 > E3 If free electron loses energy and falls back to valence band, this process is called Annihilation or Recombination Lost energy emits as light

20 Energy Bands: Quantum theory explain these bands as Conduction Band : Free electrons accommodate there Valence Band : Electrons having lesser energy accommodate there Forbidden band: The region between valence and conduction band No electrons can stay at this energy levet

21 Energy Bands eV Valence Band (Electrons in Valence Shell) Forbidden Band Conduction Band (Free Electrons) Energy Gap Energy gap is the energy required to rupture covalent bond

22 Energy Bands for Different Materials Valence Band Forbidden Band Conduction Band Valence Band Forbidden Band Conduction Band Valence Band Forbidden Band Conduction Band Valence Band Forbidden Band Conduction Band Insulators Conductors Silicon Germanium 1.1eV 0.67eV Temperature dependent 0.01eV

23 Temperature & Resistance T I R ConductorsSemiconductors R I T Temp. Coeff. = α α = +ive α = -ive

24 Holes & Hole Current Hole Movement Electron Movement

25 Hole Current Vs Electron Current The movement of holes and electrons is in opposite directions There are no holes in pure conductors, they are only created in semiconductors There are two currents in semiconductors: Hole current (Band ? Charge ?) Free electron current (Band ? Charge ?) The total current in semiconductor materials is the sum of hole current and electron current Number of holes = ?

26 Charge Carriers Holes are called positive charge carriers Free electrons are called negative charge carriers For pure (Intrinsic) semiconductors: Number of positive charge carriers = Number of negative charge carriers Is there any way to make charge carriers unequal? Let hole density be p i (holes/m 3 ) and electron density be n i (electrons/m 3 ) where i denotes intrinsic semiconductor, then: n i = p i Intrinsic Semiconductor

27 Charge Carriers at Room Temperature Silicon Carriers/m 3 Germanium Carriers/m 3 Copper Carriers/m X X X 10 28

28 Thank You


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