Wednesday, October 8, 2008

Fundamentals: LED-light emiting diode

A diode is a pn junction. The depletion region prevents the electron to cross over to the p region and vice versa. When a voltage is applied, the electrons overcomes the internal electric field and crosses over to the p region. When the electron recombine with the hole in the p region, photon energy is released. This photon energy corresponds to the visible light region. Hence light is emitted. A typical voltage applied is 1.71V hence electron has E = 1.71eV which is later emitted as photon energy E= 1.71eV corresponding to red light. Hence red LED.