Transmission electron microscopy and X-ray diffraction investigation of In segregation in MOVPE-grown InGaAs-based MQWs with either GaAs or AlGaAs Barriers

Surface In segregation and related interface roughness were studied in metal-organic vapour-phase epitaxy-grown lnGaAs-based multi-quantum well (MQW) structures, with either AlGaAs or GaAs barriers, by dark-field and high-resolution transmission electron microscopy (TEM) and high-resolution X-ray diffraction. By analysing intensity profiles taken across the MQW stacks on TEM images, it is shown that In segregation in the growth direction takes place irrespective of whether the barrier is AlGaAs or GaAs, being slightly more efficient when the barrier is AlGaAs. This makes the (Al)GaAs-on-lnGaAs very rough whereas the InGaAs-on- (Al)GaAs interface is much sharper. The (Al)GaAs-on-InGaAs interface is spread over about three monolayers, the InGaAs well size being of the order of 2 nm. Indium segregation at the growth surface is not laterally uniform as islanding of the (Al)GaAs-on-InGaAs interface occurs. Islanding at the AlGaAs-on-InGaAs interface seems to be slightly more pronounced than that at the GaAs-on- InGaAs interface.