1.

On which factors does the wavelength of light emitted by a LED depend?

Answer»

The intensity of the emitted light is directly propor-tional to the recombination rate and hence to the diode forward current. The colour of the light emitted by an LED depends on the compound semiconductor material used and its composition (and doping levels) as given below :

Table: Typical semiconductor materials and emitted colours of LEDs

MaterialEmitted colour(s)
Gallium arsenide (GaAs), Indium gallium arsenide phosphide (InGaAsP)Infrared
Aluminum gallium arsenide (AlGaAs)Deep red, also IR laser
Indium gallium phosphide (InGaP)Red
Gallium arsenide phosphide (GaAsP), aluminum indium gallium phosphide (AlInGaP)Orange, red or yellow
Gallium phosphide (GaP)Green or yellow
Aluminium gallium phosphide (AlGaP), zinc selenide (ZnSe), zinc selenide telluride (ZnSeTe), nitrogen impregnated gallium phosphide (GaP:N)Green
Indium gallium nitride (InGaN), gallium nitride (GaN), sine sulphide (ZnS)Blue and violet Longer wave lengths (green and yellow) are obtained by increasing the indium (In) content. Phosphor encapsulation produce white light.
Aluminium gallium nitride (AlGaN)Ultraviolet



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