Light emitting diode (LED) is an extensively used device in electronic circuits. GaAs is used for the fabrication of LED. A simple p-n junction of GaAs can be used as an LED. This type of LED is called planar LED. In hemispheric LED, a hemisphere of n-type GaAs is surrounded by a diffused p-type region. Truncated ellipsoid LED couples with a truncated spherical microlens made from oxides of silica and titanium with the InGaAsP surface emitting LED. Low output, low bandwidth and presence of harmonic distortion are the main disdavantages of LED. Buthey have advantages like high reliability, economical and linearity. Edge emitting LED is a diode based on double heterostructure LED. This LED can provide an increase in order-of-magnitude in radiome from a very small emission area. GaAs in 5 layers can act as an edge emitting LED. This diode gives more output power from a small active area. Here self absorption of photon is very less since the active region is very thin. The structure of this LED is similar to that of stripe edge type laser diode.
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