As we know metals are classified into 3 types they are : conductors,insulators and semiconductors. conductors allow the flow of electrons, where as the insulators doesn't allow the flow.
Reason is that in conductors the distance between conduction band and valence band is small where as in insulators it is high .when we look at semiconductors which allow partially the flow of electrons. These semiconductors are necessary in these days as they play an important role in modern day electronic goods.
Examples of semiconductors are silicon and germanium which have four valence electrons in their outermost shell.But we mostly use silicon because it has low leakage current(around nA) due to high forbidden gap between conduction band and valence band,and silicon has high temperature withstand capacity(around 1425c) compared to germanium .
construction:
Take a silicon piece and to the left most dope with p-type impurities and to the right, dope with n-type impurities.
Doping means adding of impurities(other metals) to the present one.
Ex:silicon with boran,aluminium or with phosphorus .By proper doping we can design the diode.
working:
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when doping is done, a small junction is formed between the P and N regions before biasing .Reason is P-type has majority holes and minority electrons where as the N-type has majority electrons and minority holes due to force of attraction and repulsion small layer is formed and is called as "depletion layer".
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=>when the potential at anode is greater than cathode then we can say diode is in "forward bias" and act like as closed switch with threshold voltage of 0.6V
=>If we apply lower potential at anode compared to cathode then the diode acts as a "Reverse bias" and is in open state that is it offers infinite resistance.
Reason is that lesser voltage applied at anode will attract the holes(positive charges) towards negative charge and in turn increases the depletion layer so conduction stops.
=>Applications of a diode is it can act as a open or closed switch.
Reason is that in conductors the distance between conduction band and valence band is small where as in insulators it is high .when we look at semiconductors which allow partially the flow of electrons. These semiconductors are necessary in these days as they play an important role in modern day electronic goods.
Examples of semiconductors are silicon and germanium which have four valence electrons in their outermost shell.But we mostly use silicon because it has low leakage current(around nA) due to high forbidden gap between conduction band and valence band,and silicon has high temperature withstand capacity(around 1425c) compared to germanium .
construction:
Take a silicon piece and to the left most dope with p-type impurities and to the right, dope with n-type impurities.
Doping means adding of impurities(other metals) to the present one.
Ex:silicon with boran,aluminium or with phosphorus .By proper doping we can design the diode.
working:
Reason is that when positive potential(greater) is applied at anode due to force of repulsion between positive charges and holes(positive charges) the depletion layer contracts and allow the electrons to recombine with holes.
=>If we apply lower potential at anode compared to cathode then the diode acts as a "Reverse bias" and is in open state that is it offers infinite resistance.
Reason is that lesser voltage applied at anode will attract the holes(positive charges) towards negative charge and in turn increases the depletion layer so conduction stops.
=>Applications of a diode is it can act as a open or closed switch.
