This Small Business Innovation Research (SBIR) Phase I project will examine a novel approach to semiconductor diode laser operation in the increasingly important 2-5 micron band and beyond. Using indium thallium phosphide (InTlP), in conjunction with well-developed indium gallium arsenide phosphide (InGaAsP) epitaxial materials on InP substrates, high performance laser structures may be made to operate at room temperature or near-room temperature at mid-infrared (IR) wavelengths. In Phase I InTlP will be grown by metallo-organic chemical vapor deposition (MOCVD). Electrical and optical properties of the materials will be characterized, and simple light-emitting diodes (LEDs) with an InTlP active region will be fabricated to determine suitability for IR lasers. Preliminary laser structures will be designed. Phase II would fabricate, characterize, and optimize laser structures for many useful applications. Phase I is expected to provide information for robust, high-performance, III-V mid-infrared semiconductor lasers by MOCVD Highly reliable, low cost diode lasers, capable of room temperature operation in the important 2-5 micron wavelength range would impact many technological areas. In particular, this development would make possible compact, robust, state-of-the-art diode lasers for environmental pollution monitoring, wind shear sensing, manufacturing process control, communications, military countermeasures, and IR molecular spectroscopy.