Vertical Cavity Surface Emitting Lasers

Quoting from InGaAs/GaAs vertical cavity surfa http://dumbo.sc.ic.ac.uk/Microcavities/VCSELS.html ce emitting lasers by G Hill, J Hunt, A Khan, G Parry, M Pate and C Roberts.

"Vertical cavity surface emitting lasers and LEDs are promising devices for free-space and fibre communication systems. Their advantages include low threshold, single mode operation, a circularly symmetric beam profile and efficient coupling into fibres. Commercially they are attractive because they can be processed readily and tested on wafer. Figure 1 shows an SEM image of a VCSEL structure which has been etched to show the Bragg reflectors and gain region."
Structure of a Vertical Cavity Laser (Source)

Scanning electron micrograph of a vertical cavity surface emitting laser structure grown by MBE.
The Bragg reflectors are produced using GaAs (694 A) and AlAs (828A) and the activie region
between tha two Bragg stacks contains three quantum wells of InGaAs/GaAs (approximately
80A well width and 18% In). The laser is designed for emission at 980 nm. The structure has
been etched to show the components of the Bragg stack. (Source)

The reflectivity of a voltage tunable Bragg reflector is shown as function of wavelength and
bias voltage. The curves correspond to voltage steps of 1 V. The Bragg mirror consists of
(from the substrate):20 x GaAs/AlAs (694A/828A) n-doped, 14 x InGaAs/GaAs (50A/9OA
and 23% In) undoped, 4 x GaAs/AlAs (694A/828A) p doped. (Source)