Abstract
We achieve sharp excitonic resonances near 1.3 μm in InGaAs quantum wells grown on a GaAs substrate by molecular beam epitaxy using a slowly graded InGaAs buffer layer. Our results indicate that linear grading is preferable to step grading for high In composition InGaAs on GaAs. SIMS results confirm the linearity of the grading. Cross-section TEM analysis of the graded sample reveals dislocations within the buffer but none which are threading up to reach the quantum wells. In addition to a well-defined exciton at 1.25 μm under zero bias, we observe pronounced quantum confined Stark effect in the absorption spectrum of a sample including a graded buffer layer while the spectra from samples with step-graded buffers exhibit no excitonic features. We demonstrate a transmission electro-absorption modulator with a relative transmission modulation (Δ T/ T) of 12% at 1.3 μm.
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