Strain-engineered vertical emitting InGaAsSb quantum well lasers at 2–2.4 µm: in-well vs. barrier pumping, silicate bonding, and thermal optimization

We present a comprehensive study of continuous-wave (cw) lasing in GaSb-based membrane external cavity surface emitting lasers (MECSELs) operating in the 2.0-2.4 µm range. Using both in-well and barrier pumping, we investigate the influence of quantum well (QW) strain in eight InGaAsSb-based MECSEL structures. A key advance is the implementation of silicate bonding, which improves fabrication yield from <10% (for direct bonding) to >60% by relaxing surface flatness requirements of GaSb wafers. In addition, we show that only compressively strained QWs with lattice mismatch >1% lase. This is supported by theoretical calculations showing that the imbalance between the density of states (DOS) in the conduction and valence bands limits the ability to reach population inversion, even though sufficient TE-polarized gain is available in all structures. At 2 µm, in-well and barrier pumping provide similar slope efficiencies (∼29% over absorbed power), but in-well pumping achieves a record-low thermal resistance of 0.5 ± 0.1 K/W by eliminating pump-absorbing barrier layers. At 2.35 µm, slope efficiency drops (∼6.8% for in-well, ∼10.7% for barrier pumping), likely due to increased Auger recombination at longer wavelength. The in-well design maintains superior thermal performance (0.6 ± 0.2 K/W thermal resistance). These results position in-well pumped MECSELs as a thermally efficient, wavelength-scalable platform for short-wave infrared (SWIR) applications including gas sensing, medical diagnostics, and molecular spectroscopy.