Growth and characterization of atypical InGaAs/GaAs quantum dots optimized for room temperature emission in the 935–955 nm range for laser-based water vapor detection

In laser-based optical gas sensing, to exploit the multi-line response of analyzed gases, one needs to employ light sources with wide spectral tunability. This is a complex requirement, since it requires a gain medium with bright and spectrally broad emission. A matrix of tunable vertical-cavity surface-emitting lasers (VCSELs), with an active region made of epitaxially-grown quantum dots (QDs), might satisfy the abovementioned requirements better than conventional quantum wells with a narrowband gain spectrum. Here, we report on growth development, as well as structural and optical characterization, of atypical self-assembled, low-strain InGaAs/GaAs QDs, obtained by metal-organic chemical vapor deposition and optimized to achieve emission in the range of 935–955 nm, where strong and distinct absorption lines of water are found. As the InGaAs/GaAs QDs do not naturally emit at these wavelengths at room temperature, a special structure design and growth procedure, plus a post-processing step involving rapid thermal annealing, are required. Thanks to these steps, we achieved an emission level below 980 nm, which is a milestone on the way to manufacturing a low-cost VCSEL-based spectroscopic water vapor sensing system crucial for many industrial and environmental applications.