ABSTRACT
Tunable single-frequency mid-infrared (IR) diode lasers are ideally suited for highly sensitive detection of trace gases for such applications as pollution or toxic gas monitoring and industrial process control. As the active layer material for mid-IR lasers, GainAsSb has been extensively studied. It has a direct bandgap for all the alloy compositions, and can be grown lattice matched to either InAs or GaSb. For the design of the laser structures, one of the most important parameters is the band offset. Molecular beam epitaxy (MBE) is a nonequilibrium growth process, and offers the advantages of precise control of interfacial chemistry at heterojunctions and essentially no cross contamination between sources. The antimonide-based materials were grown at Lincoln Laboratory in a solid-source 3-inch MBE system equipped with a valved As cracking source and conventional ion pumps. The approach at Lincoln Laboratory is to use the theoretical predictions of critical thickness as rough estimates for the range of lattice mismatch and thicknesses.
