Objective To Study I-V characteristics of LED and Diode Laser. To Study P-I characteristics of LED and Diode Laser.
LED and Laser diode Characteristics Apparatus
A light-emitting diode (LED) is a semiconductor light source. Like a normal diode, the LED consists of a chip of semiconducting material doped with impurities to create a p-n junction. As in other diodes, current flows easily from the p-side, or anode, to the n-side, or cathode, but not in the reverse direction. Charge-carriers—electrons and holes—flow into the junction from electrodes with different voltages. When an electron meets a hole, it falls into a lower energy level, and releases energy in the form of a photon. The wavelength of the light emitted, and therefore its color, depends on the band gap energy of the materials forming the p-n junction. Typical I-V Characteristics of LED in forward bias are shown in the fig.
A laser diode is a laser where the active medium is a semiconductor similar to that found in a light-emitting diode. A laser diode, like many other semiconductor devices, is formed by doping a very thin layer on the surface of a crystal wafer. The crystal is doped to produce an n-type region and a p-type region, one above the other, resulting in a p-n junction, or diode.
Procedure: LEDs are connected in forward bias arrangement and applied voltage across LED is varied & corresponding current is measured. Result is tabulated and plotted on the graph. In second part voltage applied across Laser diode is varied and it’s corresponding output is measured & plotted.
Instrument The setup consists of Main Unit having variable power supply, digital voltmeter, digital milliammeter, LEDs (4 nos), Diode Laser with holder, photo detector, bases.