LED structures

Light emitting diode (LED) is component its convert the electrical signal into a corresponding light that be injected into the fiber. Basically light emitter are a key element in any fiber optic system. Essentially LED is a PN junction diode.

Hetero junctions

A (hetero junction) is an interface between two adjoining single crystal semiconductors device with different band gap.


Hetero junctions are of two types, Antisotype ( p-n ) or,  Isotype (n-n or p-p)

Double Hetero-junctions (DH) 

In order to achieve efficient confinement of emitted radiation double hetero-junctions are used in LED structures.


In double hetero-junction the crosshatched regions represent the energy levels of free charge recombination occurs only in active InGaAsP layer.

A hetero-junction is a junction formed by dissimilar semiconductors. Double heterojunction ( DH) is formed by two different semiconductors on each side of the active region. Figure shows double heterojunction (DH) light emitter.

Double heterojunction emitter ( DH )
The two materials have different refractive indices and different band gap energies. This structure can changes in band gap energies create the potential barrier for both holes and electrons and also some free charges can recombine only in narrow band, well defined active layer side.

A double hetero-junction structure will confine both holes and electrons are narrow active layer. So in DH junction under forward bias, it will be a large number of carriers injected into active region where they are efficiently confined. One of the most advantages of LED is serves to narrow the output beam.

Advantages of LED structure :
  • Carrier recombination occurs in a small region 
  • light emission occurs in an optical wave guide, which serves to narrow the output beam.