Morphology of InGaAs/InP QWs : from excitonic spectroscopy to HR-TEM analyses

We report on the non-squared composition profiles of three series of thin (Lz[MATH]30Å) InGaAs/InP quantum wells grown with interruption sequences at, both, the lower and the upper interfaces. First is a series of LM (lattice matched) samples with nominal thicknesses ranging from 0 to 8 monolayers. Second is a series of samples with a constant thickness of 5 monolayers and gallium compositions ranging from 0.13 to 0.73. Third are two samples with thickness Lz=30Å and gallium compositions x=0.47 (LM) and x=0.73 (gallium rich). Comparing spectrometric data collected at 2 K with high-resolution transmission electron microscope (HR-TEM) pictures, we find that the lower interface morphology (InP/InGaAs) can be easily probed from excitonic absorption and luminescence spectra. Nothing similar is found for the higher interface (InGaAs/InP), even if a considerable amount of interface roughness is resolved from HR-TEM. We show that this upper interface roughness originates from unperfected 2-dimensional growth kinetics of InGaAs