Question

Determine the silicon pn junction diode current for the forward bias voltage of 0.27 v at room temperature 27 c with reverse saturation current equal to 20 a.

Answer 1

Answer:

If a metal or a semiconductor carrying a current I is placed in a transverse magnetic field of a flux density B, an electric field is developed along a direction perpendicular to both B and I. This phenomenon is known as Hall Effect. This is used for:-

Determining the type of semiconductor p or n-type

Finding out the carrier concentration

Measuring the conductivity of the material

Determining the carrier mobility

Detecting and measuring magnetic field 1000000 times smaller than that of the earth(with Hall-effect magnetic meters)

Under the influence of an applied magnetic field of a certain force electrons end to crowd towards one side of the semiconductor and consequently gives rise to a potential gradient. This prevents additional electrons from accumulating there. And it reaches a steady state when the two oppositely acting magnetic and electric forces become equal.

Volt - Ampere characteristics

For a p-n junction, the current I is related to the voltage V by equation

I = Io [e ( v / ξVT) -1](3.3)

Where,

I = diode current

Io = diode reverse saturation current at room temperature

V = External voltage applied to the diode

ξ = a constant, 1 for germanium and 2 for silicon

VT= KT/q = T/11600, volt equivalent of temperature i.e. thermal voltage;

where K is the Boltzmans constant (1.38066-23 J/K)

q is the charge of electron (1.6021910-19C)

T is the temperature of diode junction (oK)

At from temperature (T=300oK), VT = 26mv. Substituting this value the equation we get

I = Io [e ( 40 v / ξ )-1]

Therefore for germanium diode

I = Io [e ( 40 v )-1] (3.4)

and for silicon diode it is

I = Io [e ( 20 v )-1] (3.5)

If the value of applied voltage is greater than unity, then the equation of diode current for germanium becomes

I=Ioe40v and

for silicon it is

I = Ioe20v.

Explanation: