Optimization of buffer layers for InGaAs/AlGaAs PIN optical modulators grown on GaAs substrates by molecular beam epitaxy

In this work we compare the effect of the buffer layer on the device quality and surface morphology of strained InGaAs/AlGaAs PIN multiple quantum well (MQW) modulators. We examine GaAs buffer layers and linearly graded InGaAs buffer layers. Our results indicate that for lower indium concentrations in the quantum wells (less than about 23%) better device performance and surface morphology are obtained by growing directly on GaAs. PIN MQWs with indium mole fractions higher than about 24% have better properties when a linearly graded buffer layer is used.