Analysis of the α-factor in 1.55-µm vertical-cavity surface-emitting lasers based on InGaAs/InAlGaAs quantum wells

Subject of study. Semiconductor-based vertical-cavity surface-emitting lasers (VCSELs) fabricated using a combined wafer-fusion and molecular beam epitaxy technique are studied. Aim of study. The aim was to determine the linewidth enhancement factor ( α -factor) of single-mode VCSELs operating in the 1.55-µm spectral range. These VCSELs were based on strained InGaAs/InGaAlAs quantum wells and fabricated using a combined wafer-fusion and molecular beam epitaxy method. Method. The α -factor was estimated by direct measurements of the laser emission linewidth with a scanning Fabry–Pérot interferometer, small-signal frequency analysis, and analysis of the shifts in the resonant wavelength in the spontaneous emission spectra with changes in the charge carrier concentration. Main results. An increase in the inverse population factor or charge carrier lifetime leads to a decrease in the α -factor for VCSELs fabricated using the combined wafer-fusion and molecular beam epitaxy technique. For the studied lasers, the α -factor values lie in the range of 3 to 4.5, depending on the photon lifetime in the cavity. Practical significance. The obtained results make it possible to correlate the photon lifetime in the cavity to the α -factor of VCSELs operating in the 1.55-µm spectral range. This correlation is crucial for designing gas sensors and high-speed optical transceivers based on such lasers.