INDIUM MIGRATION AND CONTROLLED LATERAL BANDGAP VARIATIONS IN HIGH-POWER STRAINED LAYER INGAAS-ALGAAS LASERS GROWN ON NONPLANAR SUBSTRATES

Strained single quantum well InGaAs-AlGaAs graded-index separate confinement heterostructure lasers have been grown by molecular beam epitaxy over nonplanar (100) oriented substrates. We observed large variations in the effective bandgap of the strained QW as a function of the width of the underlying substrate ridge or groove. These variations are associated with increased In composition in the strained quantum well which arises from incorporation of adatoms migrating from the low growth (311)A side facet to the preferential growth (100) active area facet. We have investigated in more detail the properties of laser structures consisting of two separately contacted segments along the laser cavity with different bandgaps. Using the segment with the larger bandgap as passive waveguide cavity, we were able to measure its bandtail absorption and characteristic Urbach energy by comparing the transmitted to the directly emitted spontaneous emission. The results show the possibility of either building multiple wavelength laser arrays or nonabsorbing mirrors, passive waveguides, and quantum well modulators with single-step molecular beam epitaxy.