bei48482_FM

Figure 10.30Operation of a semi-

conductor diode.

(a) When there is no applied

voltage, the thermal electron

current to the right equals the

recombination electron cur-

rent to the left and there is no

net current. Both these cur-

rents are small.

(b) When an external voltage is

applied so that the pend of

the diode is negative, the re-

combination electron current

is less than the thermal elec-

tron current. The result is a

very small net electron cur-

rent to the right.

(c) When an external voltage is

applied so that the pend of

the diode is positive, the re-

combination current can be

much larger than the thermal

electron current to give a large

net electron current to the left.

The conventional current is in

the opposite direction to the

electron current.

free electron

hole

= thermal electron current

= recombination electron current

it

ir

New

holes

created

V

+

it

New

electrons

ir added

Electrons and holes

recombine at junction

eF(n)

eF(p) Ve

(c) Forward bias

(a) No bias

it

ir

p region n region

p-n junction

Electron

energy

Depletion region Valence band

Forbidden

band

iirtConduction band

eF

(b) Reverse bias

Holes

disappear

+

V

it

ir

Electrons

disappear

eF(n)

eF(p) Ve

Figure 10.31Voltage-current characteristic of a p-nsemiconductor diode.

Reverse bias Forward bias

V

I

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