GaAs integrated optical circuits by wet chemical etching

An integrated optical circuit containing a laser, passive waveguide, and extra-cavity detector is described. These devices are fabricated from Al
x
Ga
1-x
As layers grown by liquid-phase epitaxy. Reflectors are formed by a two-step preferential etch procedure. For proper laser orientation on {100} wafers, the mirrors are found to be oblique, tapered so as to enhance coupling into the underlying passive waveguide; this increases the efficiency of radiation transfer to the detector. Device operation with high differential transfer efficiency and low threshold has been achieved; e.g., for devices with one etched mirror and one cleaved mirror, η
t
= 16 percent and
J_{t} = 2.4
kA/cm
²
, whereas these values are
\eta_{t} = 6.5
percent and J
t
= 3.0 kA/cm
²
for devices with two etched mirrors. Other orientations on {100} and {110} wafers have also been investigated. The reflectivity of the etched mirrors is small,
R_{e} \simeq 1-2
percent, but transfer efficiencies into the external passive waveguide as large as
T = 50
percent have been observed. The effect of small R
e
on device performance is examined both experimentally and theoretically. The fabrication of ribbed interconnections between active circuit components is also described.