Channeled substrate buried heterostructure GaAs- (GaAl)As injection lasers

Abstract

A technique for fabricating stripe geometry GaAs/(GaAl)As injection lasers with optical and carrier confinement not only in the plane perpendicular but also parallel to the p‐n junction is reported. This independently developed channeled substrate technique is a simple extension of conventional liquid phase epitaxy requiring no regrowth and relies on the strong tendency of epitaxial layers to smooth out as they grow. The active regions of the preliminary 10‐ and 20‐μm‐wide stripe lasers that have been fabricated to date are parabolic in cross section, tapering gradually to zero at the edges and completely embedded in GaAlAs. Unlike the ’’etched buried heterostructure lasers’’ recently reported by Burnham and Scifres, the n‐ (GaAl)As layer is continuous, thus preventing the direct injection of carriers into the substrate. Room‐temperature pulsed threshold currents are in the range 150–350 mA with efficiencies up to 30%. This paper describes the LPE growth techniques that we used to produce the two preliminary wafers. A first‐order theory is presented which describes the transverse mode structure of the unusually shaped waveguide which forms the active region of the lasers. The observed mode structure agrees closely with that calculated. A mode selection effect has been observed which favors low‐order transverse mode operation close to threshold in the multimode waveguides which we produced. Finally, we report the cw operation of these lasers and discuss the more significant aspects of their operation.