Comparison of luminescent efficiency of InGaAs quantum well structures grown on Si, GaAs, Ge, and SiGe virtual substrate

Abstract

In order to study the luminescent efficiency of InGaAs quantum wells on Si via SiGe interlayers, identical In0.2Ga0.8As quantum well structures with GaAs and Al0.25Ga0.75As cladding layers were grown on several substrates by an atmospheric metalorganic vapor deposition system. The substrates used include GaAs, Si, Ge, and SiGe virtual substrates. The SiGe virtual substrates were graded from Si substrates to 100% Ge content. Because of the small lattice mismatch between GaAs and Ge (0.07%), high-quality GaAs-based thin films with threading dislocation densities <3×106 cm−2 were realized on these SiGe substrates. Quantitative cathodoluminescence was used to compare the luminescent efficiency of the quantum well structure on the different substrates and cross-sectional transmission electron microscopy was used to characterize dislocation densities. Our results show that the InGaAs quantum wells grown on the GaAs substrates have the highest luminescent efficiencies due to the lowest dislocation densities. Interestingly, InGaAs quantum wells grown on the SiGe virtual substrates outperform those on Ge substrates, both in terms of luminescent efficiency and dislocation density. This difference is attributed to the variation in thermal expansion coefficient (α) and its impact on defect structure during the process cycle. The SiGe virtual substrate has a smaller α compared to a Ge substrate because of the smaller α of the Si substrate, which helps minimize compressive strain in the quantum well layer during the temperature decrease from the growth temperature. Consequently, fewer misfit dislocations are created between the quantum well and cladding interfaces. These misfits can greatly affect the luminescent efficiency since they can act as recombination sites. In general, the efficiencies of the quantum wells on the SiGe and Ge substrates were affected only by higher misfit dislocation densities, whereas the quantum wells on the Si substrate had low efficiency due to high threading dislocation density.