Biomedical Engineering Reference
In-Depth Information
x
0
0.2
0.5
Wells
Barriers
p + - GaAs
Au/Zn
p-AI 0.5 Ga 0.5 As
n-AI 0.5 Ga 0.5 As
n + - GaAs
Au-Ge
FIGURE 2.29
Cross-section and energy band diagram for ridge waveguide MQW laser.
have shown room temperature operation with 15 mA thresholds and differ-
ential quantum efficiencies of 60%. For this particular integration scheme,
the laser will be implemented as a surface emitter as shown in Figure 2.30.
The laser light is coupled from the laser to a passive AlGaAs waveguide.
The light in the waveguide is coupled from the surface either with an etched
V-groove or a grating. This technique allows the user to fabricate lasers
at any position on the chip rather than only at the edge of the chip. The
method is more difficult to implement if fibers are to be used as the transmis-
sion medium; however, it does provide the flexibility for utilizing the third
dimension and directing the optical signals via holographic techniques.
The photodetector used in this development was a PIN structure grown by
MOCVD. The device was a six-layer stack consisting of GaAs and AlGaAs
layers. Initial tests on this device [75] have shown a dark current of <10 pA
and a breakdown voltage of 80 V. A current gain of 10 was demonstrated at a
voltage of 95% of breakdown.
 
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