**Current through an Ideal Diode:**

The diode equation gives an
expression for the current through a diode as a function of voltage. The Ideal
Diode Law, expressed as shown below

Where,

I = the net current flowing
through the diode

I

_{0}= Reverse Saturation Current
V = applied voltage across
the terminals of the diode

q = absolute value of
electron charge

k = Boltzman’s constant and

T = absolute temperature
(K).

The Reverse Saturation
Current (I

_{0}) is an extremely important parameter which differentiates one diode from another. I_{0}is a measure of the recombination in a device. A diode with a larger recombination will have a larger I_{0}.
Note that,

I

_{0}increases as T increases and
I

_{0}decreases as material quality increases.
At 300K, kT/q = 25.85 mV, called
Thermal Voltage.

**Current through Non Ideal Diodes:**

For actual Diodes, the
expression becomes,

Where,

n = ideality factor, a
number between 1 and 2 which typically increases as the current decreases.

**Effect of Temperature on Forward Characteristics of Diode:**

The characteristics curve of
a Si diode shifts to the left at the rate of -2.5 mV per degree centigrade
change in temperature in forward bias region.

As shown in the graph above the
curves at different temperatures are shown far apart just for illustration
purpose. The curve shifts to the left at the rate of -2.5 mV per degree
centigrade change in temperature. Hence if the temperature increases from room
temperature (25° C) to 80° C, the voltage drop across the diode will be (80-25)
x 2.5 mV = 137.5 mV.

**Effect of Temperature on Reverse Characteristics of Diode:**

In the reverse bias region,
the reverse saturation current of Si and Ge diodes doubles for every 10° C rise
in temperature. Suppose an increase of temperature from 25 °C to 85 °C, where
the reverse saturation current at 25 °C is 100 nA. The temperature increases by
60 °C (25 °C to 85 °C), which is 6 x 10. Hence the reverse saturation current
would increase by a factor of 26 = 64. Hence the reverse saturation current at
85 °C will be 100 nA x 64 = 6400 nA.

A graph showing the
variation of reverse saturation current with temperature is shown below.

From the above graph it is
clear that the reverse saturation current increases with increase in
temperature. The graph also shows how the reverse breakdown voltage changes
with temperature. It is indicated in the above graph that the reverse breakdown
voltage increases with an increase in temperature. However it is only true for
avalanche diodes. The reverse breakdown voltage for Zener diodes decreases with
an increase in temperature.

Thank you!

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