.. 3.11

Diode I-V characteristics
=========================

**Objective**

Draw the I-V Characteristic of diode and compare the result with the
theory.

**Procedure**

.. image:: schematics/diode_iv.svg
	   :width: 300px
.. image:: pics/diode-iv-screen.png
	   :width: 300px

-  Make connections
-  Click on START to draw the characteristic curve.
-  Analyse the data
-  Plot the IV of LEDs

**Discussion**

The IV characteristic of an ideal PN junction diode is given by equation
:math:`I = I_0 \times e^{(qU/kT) − 1}`, where :math:`I_0` is the reverse saturation
current, :math:`q` the charge of electron, :math:`k` the Boltzmann constant, :math:`T` the
temperature in Kelvin. For a practical, non-ideal, diode, the equation
is :math:`I = I_0 \times e^{(qU/nkT) − 1}`, where :math:`n` is the ideality factor, that
is 1 for an ideal diode. For practical diodes it varies from 1 to 2. We
have used a IN4148 silicon diode. The value of *n* for 1N4148 is around 2.
We have calculated the value of :math:`n` by fitting the experimental data with
the equation.

The voltage at which LED starts emitting light depends on its wavelength
and Planck’s constant. Energy of a photon is given by :math:`E = h\nu  = hc/\lambda` .
This energy is equal to the energy of an electron that overcomes the
junction barrier and is given by :math:`E = eV_0`. So Planck’s constant
:math:`h = eV_0 \times \lambda / c`, where :math:`\lambda` is the wavelength of light from the LED, :math:`e`
the charge of electron and :math:`c` the velocity of light.

Repeat the experiment by heating the diode to different temperatures.
