[en] Hybrid quantum well–dots (QWD) nanostructures have been formed by deposition of 7–10 monolayers of In_0_._4Ga_0_._6As on a vicinal GaAs surface using metal–organic chemical vapor deposition. Transmission electron microscopy, photoluminescence and photocurrent analysis have shown that such structures represent quantum wells comprising three-dimensional (quantum dot-like) regions of two kinds. At least 20 QWD layers can be deposited defect-free providing high gain/absorption in the 0.9–1.1 spectral interval. Use of QWD media in a GaAs solar cell resulted in a photocurrent increment of 3.7 mA cm"−"2 for the terrestrial spectrum and by 4.1 mA cm"−"2 for the space spectrum. Diode lasers based on QWD emitting around 1.1 μm revealed high saturated gain and low transparency current density of about 15 cm"−"1 and 37 A cm"−"2 per layer, respectively. (paper)