GaAs integrated optical circuits by wet chemical etching

Abstract

An integrated optical circuit containing a laser, passive waveguide, and extra-cavity detector is described. These devices are fabricated from Al <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf> Ga <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</inf> 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 <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</inf> = 16 percent and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J_{t} = 2.4</tex> kA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , whereas these values are <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\eta_{t} = 6.5</tex> percent and J <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</inf> = 3.0 kA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> 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, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R_{e} \simeq 1-2</tex> percent, but transfer efficiencies into the external passive waveguide as large as <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T = 50</tex> percent have been observed. The effect of small R <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</inf> on device performance is examined both experimentally and theoretically. The fabrication of ribbed interconnections between active circuit components is also described.