UNTRANSLATED .. 3.11

Diode I-V characteristics

Objective

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

Procedure

_images/diode_iv.svg _images/diode-iv-screen.png

Discussion

The IV characteristic of an ideal PN junction diode is given by equation I = I_0 \times e^{(qU/kT) − 1}, where I_0 is the reverse saturation current, q the charge of electron, k the Boltzmann constant, T the temperature in Kelvin. For a practical, non-ideal, diode, the equation is I = I_0 \times e^{(qU/nkT) − 1}, where 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 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 E = h\nu  = hc/\lambda . This energy is equal to the energy of an electron that overcomes the junction barrier and is given by E = eV_0. So Planck’s constant h = eV_0 \times \lambda / c, where \lambda is the wavelength of light from the LED, e the charge of electron and c the velocity of light.

Repeat the experiment by heating the diode to different temperatures.