TEXAS ADVANCED TECHNOLOGY PROGRAM GRANT

Title: Integrated Multifunctional Fluorescence Sensors for Real Time Environmental Effluents & Water Analysis

Project Summary

Several EPA reports on the status of the nation's lakes, rivers, and estuaries state that the world's greatest environmental threat is chemically contaminated water. While filtering systems continue to improve, new contaminants and at much lower levels should be detected. Rapid and accurate methods are needed for assessing environmental (water/air) chemical quality in closed recycle life support systems on extended space flight missions. Other water contamination issues relate to employment of deionized (DI) water in semiconductor processing, biomedical, and other industrial applications, where measurements at high temperatures and in corrosive environments are required. These concerns indicate that continuous improvement of water analysis systems is of highest importance. Large size and weight, high costs, low reliability of the existing fluorometers makes it difficult to apply them in rapidly changing and harsh environments. Integration of the fluorometer components in a single chip would allow for the fabrication of miniature, inexpensive, rugged multifunctional devices, ideally suited for environmental analysis and control. Such integration was not possible up to recently due to the absence of UV/blue LEDs and tunable photodetectors technology. The recent development in the group III nitrides materials growth techniques allows now for the fabrication of ultraviolet/blue light emitting structures and tunable photodetectors on a single substrate. High chemical and thermal strength of III-V Nitrides combined with other high stability materials used in sensor design will result in advanced applications of the proposed devices at extreme field conditions and in harsh environments. In this proposal we intend to apply our results in both UV/blue light emitting diodes and photodetectors for the development of a III-V Nitrides-based single-chip integrated hardened multifunctional sensor capable to detect various organic and metal contaminants and other harmful chemicals in water, measure the concentration of water contaminants, water flow, and water temperature.

Summer 2000 Progress Report

During completion of Task1, epitaxial growth of nitride layers on sapphire has been optimized. Closer attention was paid to the growth of acceptor type layers, since they exhibited better characteristics. Optoelectronic diode structures based on such layers have been fabricated and characterized. The photosensitivity to the ultraviolet (UV) light and UV/blue optical emission was observed on these structures. The total UV power measured from a packaged Light Emitting Diode (LED) was comparable to the power of commecial blue LEDs. To avoid absorption by the base nitride material in the UV part of the spectrum and extend the spectral characteristics of our structures further into the UV part of the spectrum, we have developed a process for deposition of electrically conductive UV-transparent electrodes based on oxide semiconductor materials, that demonstrated more than 80% of the optical transmittance in the UV part of the spectrum. The described above results indicate, that both UV/blue light emitting and UV-photosensitive diode structures based on nitrides can be fabricated on the same substrate in a single technological process. A match between the optical emission and photosensitivity spectra of the developed diode structures allows realization of a one-chip-integrated optoelectronic chemical sensor working in the absorption/reflection mode.