Optoelectronic Semiconductor Devices Principals and Characteristics

 
Figure 11.: Basic structure and material composition of LEDs and ILDs. 
[1]
Depending on the geometrical structures normal to the junction layers, ILDs can be further classified as 
broad area or stripe geometry lasers. 
 

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3 LASER DIODES 
Laser diodes are typical pn-junction devices used under a forward bias. Laser is an acronym for Light 
Amplification by Stimulated Emission of Radiation. 
The basic operating mechanism of laser diodes are based on the electrical and optical properties of pn-
junctions and semiconductor materials. 
Laser diodes are devices emitting coherent light produced in a stimulated emission process. The light 
emission process in laser diodes is more complicated then that in LEDs, where light produced in a 
spontaneous emission process. 
The lasing wavelength ranges from the visible to the infrared wavelength range depending on the material 
of the active layer. 
The 850 nm-band AlGaAs/GaAs and 1300/1550 nm-band InGaAs(P)/InP material systems are commonly 
used in optical fiber communication systems, Whereas AlGaAs/AlGaAs, group-III nitrides, and other 
materials are used in the visible wavelength range. 
On the developmental stage of laser diodes, continuous-wave (cw) lasing at room temperature was 
achieved in an AlGaAs/GaAs double-heterostructure laser in 1970, and since then the double 
heterostructure has been a common one for laser diodes. 
3.1 BROAD AREA LASERS 
Broad area lasers are injection lasers of the most rudimentary form. 
 
Figure 12.: Geometry of broad area injection lasers and stripe geometry injection lasers. 
[1]
 
Since the width is much larger than the thickness, (as we can see on Figure 
12.
) we can assume that the 
optical fields and injection current are distributed uniformly in the y direction and many transverse modes 
can be supported by the structure, if they are not suppressed.