GaAs–AlxGa1−xAs heterostructure laser with separate optical and carrier confinement

Abstract

Heterostructure injection lasers in which the GaAs active region is the center layer of a five-layer dielectric slab waveguide have been investigated. The GaAs active layer is bounded on each side by an AlxGa1−xAs layer to confine the carriers. The two outside layers which are AlyGa1−yAs(y > x) confine the optical field. Lasers with this structure have been fabricated and room-temperature threshold current densities Jth300 as low as 650 A/cm2 have been obtained for 1-mm cavity lengths. Differential quantum efficiencies ηD for these separate optical and carrier confinement heterostructure (SCH) lasers were higher than generally encountered for double-heterostructure (DH) lasers with values as high as 65% for [inverted lazy s]300−μ−long cavities. The external quantum efficiency of several typical units was determined as a function of input current, and for one representative unit a maximum value of 39% was obtained at about four times Jth300. Emission in the fundamental TE mode was obtained for symmetrical structures with optical waveguide thicknesses in excess of 1 μ at currents many times Jth300. The angle of beam divergence perpendicular to the junction plane was found to depend on the thickness of the optical waveguide w with half-power point values varying from 51° to 33° for w between 0.8 and 1.56 μ. Calculation of the optical intensity distributions for the symmetrical SCH structure demonstrated the influence of the AlAs mole fraction and layer thickness on confinement of the optical intensity and suggest that it should be possible to achieve still lower threholds.