MORPHOLOGY OF INGAAS INP QWS - FROM EXCITONIC SPECTROSCOPY TO HR-TEM ANALYSES/

We report on the non-squared composition profiles of three series of t hin (L(Z)<30 angstrom) InGaAs/InP quantum wells grown with interruptio n sequences at, both, the lower and the upper interfaces. First is a s eries 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 L(Z)=30 angstrom and gal lium compositions x=0.47 (LM) and x=0.73 (gallium rich). Comparing spe ctrometric data collected at 2 K with high-resolution transmission ele ctron microscope (HR-TEM) pictures, we find that the lower interface m orphology (InP/InGaAs) can be easily probed from excitonic absorption and luminescence spectra. Nothing similar is found for the higher inte rface (InGaAs/InP), even if a considerable amount of interface roughne ss is resolved from HR-TEM. We show that this upper interface roughnes s originates from unperfected 2-dimensional growth kinetics of InGaAs.