High-quality metamorphic compositionally graded InGaAs buffers

We have investigated the use of a continuous, linear grading scheme for compositionally graded (metamorphic) InxGa1−xAs buffers on GaAs grown using MOCVD, which can be used as virtual substrates for optical emitters operating at wavelengths >1.2 μm. Graded buffer quality, as quantified by threading dislocation density (TDD) measurements, was investigated for a range of different graded buffer designs and growth parameters. The best graded buffers obtained had TDD<9.5×104 cm−2, at a final composition of x=0.346. MOCVD reactor configuration was found to play a key role in obtaining the best graded buffers. Photoluminescence (PL) measurements were carried out on doped and undoped quantum-well separate confinement heterostructures (QW-SCH) that were re-grown on these buffers. The results showed that these buffers can serve as high-quality strain-relaxed templates for optoelectronic devices operating in the 1.2–1.5 μm wavelength region, and it is expected that with further refinement, high-quality virtual substrates can be made that will allow operation even beyond 1.6 μm.