High-throughput synthesis of terahertz quantum cascade lasers

The proposed Phase I program is aimed at design and fabrication of a robust, AlGaAs-based epitaxial layer structure for terahertz quantum cascade (QC) lasers that can be grown by the metalorganic chemical vapor deposition (MOCVD) process. The ability to produce such epitaxial wafers at low cost is critical to the future widespread use of QC lasers. There are currently only three groups in the world that are capable of producing terahertz QC laser wafers, and each of these groups uses epitaxial wafers grown by molecular beam epitaxy (MBE), a slow and inherently expensive method of wafer growth. This severely limits the availability of this material. Demonstrating MOCVD growth of terahertz QC laser structures will stimulate the rapid development of terahertz QC lasers. The growth of complex AlGaAs epitaxial layers grown on GaAs substrate wafers has developed into a relatively mature technology, and is currently used to produce large volumes of complex-structure wafers. Phase I will concentrate on the design of terahertz QC laser epitaxial layer structures compatible with the MOCVD growth capabilities, as well as demonstrate growth and evaluation of such structures. Phase II will further develop this growth capability and demonstrate operational QC laser devices. Coherent sources of radiation in the terahertz spectral region are useful for scientific, medical, and communication applications. Many complex molecules have resonant absorption lines in this spectral region, making it possible to analyze molecular structures in gaseous, liquid, or solid form. Such spectroscopic applications have been demonstrated for DNA, RNA, and protein identification. Other potential applications include chemical and biological agent detection. Due to the transparency of many materials in this spectral region, terahertz sources can be used for imaging systems as a safe alternative to x-ray sources, for detection of hidden objects, dental cavities, and similar applications. The strong water absorption at terahertz frequencies prevents long-distance transmission through the atmosphere, thus make this a safe medium of wireless communication for short distances, such as Wi-Fi. Skin cancer identification has been demonstrated with terahertz radiation, opening the possibility of a new, safe, non-invasive medical diagnostic modality.