An investigation was performed of columnar InAs quantum dots (CQDs) with modulated tensile-strained InGaAsP barriers in which the amount of tensile strain in the upper parts was higher than in the lower parts, the dots being deposited on an InP substrate grown by metalorganic vapor phase epitaxy. The smaller tensile strain of the barrier layers in the lower parts made the photoluminescence (PL) wavelength longer while the larger tensile strain of the barrier layers in the upper parts increased the strain compensation of the CQDs. Compared to CQDs with uniformly tensile-strained barriers, 1.55 mu m emission was obtained at a higher average strain of barrier layers. By utilizing modulated tensile-strained barriers, triple-stacking of 12-fold CQDs with a PL wavelength of 1.55 mu m using 30-nm-thick spacer layers was achieved with good crystallinity, indicating suitability for fabrication of high density CQDs. (c) 2012 Elsevier B.V. All rights reserved.