Cw electro-optical characteristics of graded-index waveguide separate-confinement heterostructure lasers with proton-delineated stripe

Abstract

Shallow proton-bombarded stripe-geometry (5 μm wide, 380 μm long) lasers were fabricated from graded-index waveguide separate-confinement heterostructure (GRIN-SCH) laser wafers grown by molecular beam epitaxy (MBE). Low median cw threshold currents of ∼50 mA were obtained for this stripe-geometry gain-guided structure. Such threshold currents represent a reduction by 25% from those of similar geometry lasers fabricated under the same technologies from the lowest threshold regular double heterostructure (DH) lasers wafers grown by MBE or liquid phase epitaxy (LPE). Up to the maximum measured output power of 10 mW/mirror (cw) the linearity is good and the symmetry of the output powers from both mirrors of these GRIN-SCH (gain guided) lasers compares well to those lasers of the buried heterostructure type (index guided). The average intrawafer variation in the symmetry of the two end mirror outputs can be characterized by the average of the quantity 〈α〉, which is the deviations from unity of the A/B power output ratio measured at 3 mW. For three LPE grown DH wafers 〈α〉 is about ±20%, and varies from ±5% to ±8% for three MBE grown DH wafers. For three GRIN-SCH wafers, 〈α〉 between ±3% and ±0.8% was obtained. The standard deviations of the cw threshold current distributions for MBE grown lasers (σ≂4 mA dc) are one-half that for LPE grown lasers. This documents the improved layer thickness and composition control achievable with the MBE growth procedure.