Presentation on: ELECTROMAGNETISM Topic: SEMICONDUCTORS Presented to: SIR.TARIQ BHATTI Program: BsIT-3rd Department of Computer Science BZU, Multan

Group Members >MOHAMMAD IMRAN KHAN >TAHA KHAN >BEENISH JAHANGIR >TAYYABA JAHANGIR 07-33

MOHAMMAD IMRAN KHAN Roll#07-37 >SEMICONDUCTOR >SILICON CRYSTALS >TYPES OF SEMICONDUCTOR >INTRINSIC SEMICONDUCTOR >EXTRINSIC SEMICONDUCTOR

Semiconductors Materials that are neither conductor nor insulator. Element with 4 valance electrons is the best semiconductor. They contains free electrons. Element with electrical properties between those of conductors and insulators.

Difference between semiconductor and conductor is because of the existence of holes, present in semiconductors. For example; Germanium Silicon

Silicon crystals As an insulator: Perfect insulator at 25°C 8 valance electrons, covalently bonded with the neighboring atoms. As a conductor: act as conductor at ambient temperature (above - 273°C) An electron gains energy, creating a vacancy in valence shell (hole), and move to bigger orbit. Hence, become a free electron.

Recombination: Merging of free electron and a hole. Lifetime: Amount of time for the creation and disappearance of free electron

Intrinsic semiconductor Pure semiconductors. Because of thermal energy, equal numbers of electrons & holes are present. These are often called as ‘carriers’ because they carry charge from one part to another. These holes & electrons move in opposite direction.

Extrinsic semiconductor Doped semiconductor is called extrinsic semiconductor. Doping: A way to increase conductivity of semiconductor. Adding impurity atoms to intrinsic crystal to alter its conductivity.

Increasing free electrons: Adding pantavalent atoms, e.g; Arsenic, Antimony, Phosphorus They are also called donar impurities,as they donate an extra electron. Greater the impurity added, greater will be the conductivity. Lightly-doped semi- conductors has high resistance. Heavily-doped semi- conductors has low resistance.

Increasing the holes: Adding trivalent impurity, e.g; Aluminium, Boron,Gallium. Also called acceptor atom, because hole can accept a free electron.

TAHA KHAN Roll#07-06 >N-TYPE SEMICONDUCTOR >P-TYPE SEMICONDUCTOR >THE UNBIASED DIODE >PN-JUNCTION >DEPLETION LAYER

DEFRENCE BETWEEN INTRINSIC AND EXTRINSIC SEMICONDUCTORS

2 types of Extrinsic semiconductors n-Type semiconductor Doped with pantavalent impurity ‘n’ stands for negative Majority carriers are free electrons Minority carriers are the holes

p-Type semiconductor Doped with trivalent impurity ‘p’ stands for positive Majority carriers are holes Minority carriers are free electrons

Unbiased Diode Diode explains, two electrodes It is electrically neutral Also called junction diode or pn-crystal

pn-junction Border between p-type & n-type semiconductors. Lead to inventions like, diode, transistors, & integrated circuits.

The depletion layer Free electrons diffuses from n-type to p-type, converting the pentavalent atom in ‘n’ into positive ion and trivlent in ‘p’ into negative ion Each pair of negative and positive ions at the junction is called Dipole This depreted region around the junction, having no charges but only ions, is called Depletion region

BEENISH JAHANGIR Roll#07-04 >BARRIER POTENTIAL & TEMPRATURE >FORWARD BIAS >REVERSE BIAS >CURRENT IN REVERSE BIAS

Barrier Potential Electric field between positive and negative ions Act as a barrier and causes no diffusion of free electrons from ‘n’ to ‘p’ The electric field between ions is equivalent to difference of potential At 25°C the Barrier potential for; Germanium Diode is 0.3V Silicon Diode is 0.7V

BARRIER POTENTIAL &TEMPERATURE Junction temperature >Temperature inside the diode Ambient temperature >Temperature outside the diode Conducting diode>when Junction temperature is greater then Ambient temperature >Less barrier potential at higher temperature A barrier potential of a silicon diode decreases by 2mV for each degree celsius rise. V/T=-2mV/°C

Forward bias DC source across diode n-type connected to negative terminal of the battery p-type connected to positive terminal of the battery

Conduction of current is in forward direction because of flow of free electron No current if DC voltage is less then barrier potential Continuous current if DC voltage is greater then barrier potential

Reverse bias n-type connected to positive terminal of the battery p-type connected to negative terminal of the battery negative terminal attracts the holes in ‘p’ Positive terminal attracts the free electrons in ‘n’

Depletion layer gets wider (because of ions created around the junction ) Greater the reverse voltage greater will be the potential

Current in reverse biased semiconductor Saturation current >A very small current because of minority carriers and electron- hole pair inside the depletion layer because of thermal energy.. Surface- leakage current >Caused by surface impurity and imperfection in the crystal structure. Approximately ZERO current.

TAYYABA JAHANGIR Roll#07-33 >ENERGY LEVELS >ENERGY BANDS >ENERGY BAND IN INTRINSIC SEMICONDUCTOR >N-TYPE ENERGY BAND >P-TYPE ENERGY BAND

ENERGY LEVELS Higher energy in larger orbit Electron gain energy when lifted to larger orbit Which has more potential after lifting This Energy is provided by heat,light and voltage Falling electron radiate light Electron lose energy in form of heat,light, radiation when falls to lower orbit

ENERGY BANDS Electron of an isolated silcon atom are bound to the neucleus having distinct energy level In a solid, energy level of these isolated atom splits into sub-levels called discrete states These states are so close that they appear as a continuous energy band

FORBIDDEN GAP A range of energy states between two consective permissible energy bands which cannot be occupied by electron VALANCE BAND The energy band in the outer most shell of an atom occupying free electron It is either completely or partially filled but never empty Conduction is because of movement of holes

CONDUCTION BAND Above the valance band Electron move freely May be empty or partially filled Conduction is because of movement of free electron Bands below valance band take no part in conduction process because they are completely filled

ENERGY BAND IN INTRINSIC SEMICONDUCTOR Partially filled conduction & valance band A narrow forbidden gap of order 1eV between conduction band & valance band

N-TYPE ENERGY BAND P-TYPE ENERGY BAND

COMPARISON