This Small Business Innovation Research Phase I project will demonstrate feasibility of development of laser diodes by MBE, operating in the mid-infrared (MIR) range ((>6ªm) using the InGaAsSb/AlGaAsSb strained quantum well (QW) structure. The development of our MIR laser structures serves a variety of dual-use applications having immediate use in molecular spectroscopy, remote sensing, as well as in optical fiber telecommunications and laser radar systems. The emitting wavelengths are extendible to cover the 6-ªm range. Structured Materials Industries, Inc.'s laser diode is constructed with three regions. In the middle is the active region where undoped AlGaAsSb layers confine the InGaAsSb QWs. The active region is sandwiched by two heavily doped AlGaAsSb cladding layers which form a pn junction and provides the optical confinement. In Phase 1, the laser structure will be grown InP substrates with a buffer layer to which the AlGaAsSb layers are lattice-matched. Using InP substrates with a buffer layer has demonstrated advantages over GaSb and InAs for the antimonides. They anticipate a major increase in laser wavelength by the use of strained QW structures as compared to conventional antimonide based QW or double heterostructure (DH) lasers. The modification of the density of states in QWs associated with the quantum effects can result in lower threshold current and reduced temperature sensitivity. They will study strain and quantum effects as well as the Auger recombination process, an important nonradiative mechanism in low bandgap materials, in order to optimize their laser design. In Phase I, their design will be implemented, characterized and compared to the model. The Phase I effort will create a firm base for the further development in Phase II. The strained QW approach chosen will allow them to develop this material to cover the laser wavelength range from 6 to 10ªm in later Phases. The growth, processing and packaging capability will be refined and a distributed feedback mechanism will be implemented to improve the mode selectivity for single mode operation in Phase II in order to produce lasers suitable for military and commercial applications. They will also implement the lasers in IR spectroscopic Trace Gas Concentration Monitoring and Analysis system.
