Question

Which compound is used for making LED’s?

Answer 1

The recombination of the charge carrier occurs in the LED. The light is emitted at a specified wavelength of spectral when the LED is forward biased. Depending on the energy gap, the wavelength of the light emitted has its colour.

Complete step-by-step solution:
A light emitting diode (LED) is a forward biased p-n junction diode which emits visible light once energized working on the process of electroluminescence. The colour of light emitted depends on the semiconducting used. Once the light emitting diodes are forward biased, the electrons from the n-type material cross the p-n junction and recombine with holes within the p-type material. These free electrons are present in the conduction band and at a higher energy level than the holes within the valence band. The recombination of electrons produces energy in the form of heat and light. In Germanium and Silicon diodes, mostly the entire energy is released up in the form of heat and emitted light is in the IR region.
The V-I characteristics of a LED is same as that of a Si or Ge junction diode. But the threshold voltages are much higher. Also, the reverse breakdown voltage of LED is very low (i.e.about 5V).
Wavelength of the light emitted, and its colour, depends only on the energy gap of the materials forming the p-n junction.
Wavelength of light emitted,[lambda = left[ {frac{{hc}}{{{E_g}}}} right]]
Where, [{E_g}] is the energy gap of the materials forming the p-n junction, [h] is Planck’s constant, [c]is the speed of light. Visible LEDs are available for variety colours. The energy range of the visible region is from 1.8eV to 2.8eV. Therefore, those materials with energy gaps in this range can be used. We cannot use Si and Ge in LED, because their energy gaps are less than 1.8eV. Gallium arsenide-phosphate is used for making LEDs of different colours. Gallium phosphate → red or green, Gallium arsenide phosphide→red or yellow→ red or green, Gallium arsenide phosphide →red or yellow

Note: LCD stands for liquid crystal display. LCDs generally use fluorescent lights which are usually placed behind the screens. Also, all LCDs are not the subset of the LEDs because LCDs are usually thicker and lack energy when compared to LEDs.