Ground state lasing at 1.34 μ m from In As ∕ Ga As quantum dots grown by antimony-mediated metal organic chemical vapor deposition Appl. Phys. Lett. 90, 241110 (2007); 10.1063/1.2748082Ground-state lasing of stacked In As ∕ Ga As quantum dots with GaP strain-compensation layers grown by metal organic chemical vapor deposition Quantum dot lasers based on a stacked and strain-compensated active region grown by metal-organic chemical vapor depositionWe report on the lasing characteristics of three-and five-stack InAs/ GaAs quantum dot ͑QD͒ lasers grown by metal organic chemical vapor deposition. By increasing the number of stacked dot layers to 5, lasing was achieved from the ground state at 1135 nm for device lengths as short as 1.5 mm ͑no reflectivity coatings͒. The unamplified spontaneous emission and Z ratio as a function of injection current were also investigated. While the five-stack QD lasers behaved as expected with Z ratios of Ϸ2 prior to lasing, the three-stack QD lasers, which lased from the excited state, exhibited Z-ratio values as high as 4. A simple model was developed and indicated that high Z ratios can be generated by three nonradiative recombination pathways: ͑i͒ high monomolecular recombination within the wetting layer, ͑ii͒ Auger recombination involving carriers within the QDs ͑"unmixed" Auger͒, and ͑iii͒ Auger recombination involving both the QD and wetting layer states ͑"mixed" Auger͒, which dominate once the excited and wetting layer states become populated.