Impurity-Free Vacancy Diffusion of InGaAsP/InGaAsP Multiple Quantum Well Structures Using SiH4-Dependent Dielectric Cappings

Abstract

We report the impurity-free vacancy diffusion (IFVD) behaviors of In0.86Ga0.14As0.64P0.36/In0.88Ga0.12As0.25P0.75 multiple quantum well (MQW) structures using dielectric films as a capping layer. The effects of SiOx and SiNx films deposited using different SiH4 flow rates on the IFVD are investigated by photoluminescence measurements and ellipsometry analysis. The properties of dielectric capping layer play a key role in the intermixing of this MQW structure, indicating that the increased porosity of SiOx and SiNx layers enhances the bandgap energy shift of MQWs. A significant blue shift of 173 nm (i.e., 106 meV) for the sample capped with a relatively more porous SiNx, which was deposited using 20 sccm SiH4, was obtained after a thermal annealing of 850 °C for 30 s. The mechanism was analyzed by using transmission electron microscopy and energy dispersive X-ray spectroscopy. It is believed that the enhanced blue shift is ascribed to the dominant interdiffusion of group V atoms because the compositions of group III atoms are kept almost identical in the wells/barriers.