Characterization of the superlattice region of a quantum cascade laser by secondary ion mass spectrometry.

Secondary ion mass spectrometry is applied to the depth profiling of the superlattice active region of lattice matched (∼9.2 μm) AlInAs/InGaAs/InP quantum cascade lasers. The developed measurement procedure is capable of characterizing the quality of each individual layer in the superlattice region, including layers as thin as 0.7 nm. The oxygen level for AlInAs and InGaAs layers is in the range of 1-3 × 10 atms per cm and below the detection limit (∼1 × 10 atms per cm), respectively. Oxygen is not uniformly distributed in the AlInAs layers - more oxygen is embedded into the structure during the very first stage of the growth of the AlInAs layer and thus the corresponding interface is 1.83 ± 0.31 times more contaminated than the other. The procedure can also be operated in 3D imaging mode which proves to be invaluable for failure analysis.