Graded Buffer Layers for Molecular Beam Epitaxial Growth of High in Content InGaAs on GaAs for Optoelectronics

Abstract

ABSTRACTLinearly-graded buffer layers are used to achieve exciton resonances in InGaAs/GaAs at the 1.3 μm dispersion minimum of optical fibers. We investigate the effect of various gradients in the linearly-graded InGaAs buffer layer of a p-i-n structure designed as an optical modulator. Samples were grown by molecular beam epitaxy on GaAs substrates at 450°C. Each consisted of an n-type graded buffer region followed by thirty In0.5Ga0.5 As quantum wells with Alo.35Ga0.65As barriers, and 5000 Å of ρ-type InGaAs. Gradients of 7.5%, 15%, and 30% In/μm, or 0.5%, 1%, and 2% misfit/μm were used to grade the In concentration from 0% to 35%. Room temperature absorption measurements reveal well-defined zero-field excitonic features near 1.3 μm for all samples. The exciton resonance becomes sharper as the gradient decreases. Analyses of these samples by TEM and double crystal X-ray diffraction confirm the trend that a slower grading yields better quality material.