ALL RIGHTS RESERVED Total current density in a semi

All rights reserved total current density in a semi

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ALL RIGHTS RESERVED Total current density in a semi conductor For 2 / n n n dn J nq qD A cm dx For holes 2 / p p p dp J pq qD A cm dx diffusion length n n L D cm Hole diffusion length P P L D cm Conductivity In Metals: Metals are uni-polar, so current is carried only by n nq In metal, conductivity decreases with temperature. In Semi Conductors n P nq pq Concentration of in CB Concentration of holes in VB Mobility of holes and electrons Conductivity of pure semi-conductor increases with temperature In Extrinsic Semi-conductor For n type D n N q = donor concentration For p type A p N q = acceptor concentration In extrinsic semiconductor (SC) below the room temperature, conductivity increases. But above the room temperature their conductivity decreases. Direct Band Gap Semiconductor During the re-combinations the falling from the conduction band will be releasing energy in the form of light. Momentum and direction of will remain same. : , , Example GaAs InP ZnS Indirect Band Gap Material Most of falling will directly releasing energy in the form of heat J J J (Total current) (Current carried by ) (Current carried by holes) n p e J J J current due to drift current density diffusion current density n n n e e e  e e e n e e , n p D N A N e e e
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ECE FORMULA BOOK 5. ELECTRONIC DEVICES & CIRCUITS [141] Published by: ENGINEERS INSTITUTE OF INDIA . ALL RIGHTS RESERVED Moment of will change Direction of will change : Example Ge and Si Direct band gap materials having higher carrier lifetime and are used for fabrication for LED, laser, tunnel diode, photodiode. General Properties of Ge and Si Properties Ge Si Atomic number 32 14 Density of atoms Intrinsic concentration n at 300 K 1300 2 cm Vsec p at 300 K 1800 500 Leakage current nA Temperature range 60º to 75º C 60º to 175º C Power handling capacity Less High doubles for 50º C 75º C For 1º C conductivity Increases by 6% Increases by 8% Cut in voltage 0.2 V 0.7 V Applications High conductivity and high frequency Switching applications ratio 2.1 : 1 2.6 : 1 2 cm Vsec n D 99 34 2 cm Vsec p D 47 13 e e 22 4.42 10 22 5 10 13 2.5 10 10 1.5 10 2 cm 3800 V sec A n p
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ECE FORMULA BOOK 5. ELECTRONIC DEVICES & CIRCUITS [142] Published by: ENGINEERS INSTITUTE OF INDIA . ALL RIGHTS RESERVED Hall Effect If a specimen (metal or semi conductor) carrying the current I is placed in transverse magnetic field B, an electric field intensity is induced in a direction perpendicular to both I and B. Force experience by the charge carriers is always same direction irrespective of their polarity.
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  • Summer '16
  • Jam Adam Scalin
  • Binary numeral system, Binary-coded decimal, Voltage source, ECE FORMULA BOOK,  Power dissipation

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