ELECTRONIC DEVICES AND CIRCUITS (2131006) ENERGY BAND IN SEMICONDUCTOR DEVICES

MADE BY :- PATEL ARTH (140110111032) MISTRY CHINTAN (140110111024) KACHHIYA KEVIN (140110111019) N KARTHIKEYAN(140110111026) GUIDED BY :- Parthesh Mankodi EC Department  

Types of energy band VALANCE BAND :- In this energy band there are large no of free electrons available. Filling of the valence band can be partial or complete. These bands never get empty. The major disadvantage of the electrons present in this band is that these electrons are unable to attain energy from any external source of electric field.

CONDUCTION BAND :- The density of the electrons is very few. As compared to the electrons present in the valence energy bands, these electrons can gain energy from the external field of electric field. ENERGY GAP BAND :- Electrons are absent in this energy band. Some little amount of energy is needed for electron shifting to conduction band from valence band. This type of gap is known as band gap. Symbol used to represent band gap is Eg.

ENERGY BAND IN SEMICONDUCTOR The energy gap band in semiconductor is more than the energy band gap of metals but is lesser than the energy band gap of insulators.

ENERGY BAND IN SEMICONDUCTOR AFTER DOPING P -TYPE SEMICONDUCTORS :- The addition of acceptor impurities contributes hole levels low in the semiconductor band gap so that electrons can be easily excited from the valence band into these levels, leaving mobile holes in the valence band . This shifts the effective fermi level to a point half way about the acceptor levels and the valence band.

Electrons can be elevated from the valence band to the holes in the band gap with the energy provided by an external source. Since the electrons can be exchanged between the holes, the holes are said to be majority carriers for current flow in p type semiconductor.

N- TYPE SEMICONDUCTOR :- The addition of donor impurities contributes electron energy level high in the semiconductor band gap so that electrons can be easily excited into the conduction band. This shifts the effective fermi level to a point about halfway between the donor levels and the conduction band.

Electrons can be elevated to the conduction band with the energy provided by an applied voltage and move through the material. The electrons are said to be the majority charge carrier for current flow in N – type semiconductor.

Energy bands in a unbiased diode Depletion layer Energy P N Conduction band Valence band

Forward Biased diode P type N type - Anode + Cathode - R + - Vγ - + VB

Energy bands of a forward biased diode Smaller depletion layer Energy P N Conduction band Valence band

Forward Biased diode The diode behaves like a ‘ON’ switch in this mode Resistance R and diode’s body resistance limits the current through the diode VB has to overcome Vγ in order for the diode to conduct

Energy bands in a reverse biased diode Larger Depletion layer Energy P N Conduction band Valence band

Reverse Biased diode The diode behaves like a ‘OFF’ switch in this mode If we continue to increase reverse voltage VB breakdown voltage of the diode is reached Once breakdown voltage is reached diode conducts heavily causing its destruction

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