Development and characterization of nitride-based devices Task Leader: Dr. David Starikov This task integrates the group's capabilities toward the realization of devices and systems that fall within the main objectives of the project. The focus is on the development of miniature integrated chemical sensors, field emission-based cold cathodes for electron and ion sources working at pressures close to atmosphere, and high temperature electronics for environmental, space, military, industrial, and biomedical applications. Integrated chemical sensors. Wide band of GaN, AlN, InGaN, BN and CN semiconductor materials allow for the development of Light Emitting Diodes (LEDs) and tunable photodiodes with an optical spectra ranging from near UV to near IR. The RF-assisted Molecular Beam Epitaxy (MBE) used for the material growth allows for fabrication of these components on a single Si or sapphire chip. The possibility to "tune" the band gap, and employment of various material combinations permit fabrication of absorption and fluorescence-based sensors capable to detect species that interact with the UV/blue light. Employment of Si substrates for III-V Nitrides growth together with the high chemical and thermal strength of the III-V Nitride materials result in development of miniature, rugged , "smart" sensors integrated with Micro-Opto-Electro-Mechanical Systems (MOEMS) being currently developed for several environmental, biomedical, industrial, military, and space applications. The completed EIH_Project, and ongoing Texas_ATP, ISSO, TSGC [click here to view the project highlights in powerpoint], and Post Doctoral Program projects are dedicated to development of chemical sensors for detection and measurement of contaminants in water and air and characterization of several effluents in closed space environments. Advanced particle detectors based on WBGS We are investigating possibilities of using aluminum nitride and gallium nitride compounds as novel materials for fabrication of particle detectors. The research is performed in three main areas:
Preparation of Phase II proposals for continuation of these projects are currently underway. Field emission-based devices The main goal of this subtask is to develop and characterize nitride-based cold cathode materials for rugged electron and ion sources which operate with low power at pressures up to 0.1 Torr. Implementation of novel Nitride materials with negative electron affinity can further improve performance of cold cathode devices by enhancing the electron emission at lower operating voltage and improvement of the cathode material strength to low-vacuum and gaseous environments. We have already observed field emission with current densities over 30 A/cm2 and turn-on at fields lower than 30 V/m from metallic and Si substrates coated with our BN, CN, AlN, and GaN layers. In collaboration with Ionwerks, Inc. we have completed two Phase I projects: NASA SBIR "Filamentless Molecular Beam Ionizer for Time-of-Flight Mass Spectroscopy" and DOE SBIR "Nitride-Baed Cold Cathodes for Miniature and Rugged Electron Sources." Possibilities to employ the field emission of the nitride-based materials in MEMS-compatible pressure sensors is under investigation. High temperature electronics As a part of this subtask, development and characterization of alternative dielectric materials for the realization of high temperature electronic devices (diodes and transistors) is on the way. Boron nitride and gallium nitride thin films are well matched (thermal expansion coefficients and lattice structure) to Silicon Carbide (SiC) that is recognized as superior material for high temperature applications. The BN films are stable up to 1300°C and have the widest energy gap (6.4 eV) among IV and III-V materials. BN thermal conductivity is estimated to be close to 13 W/cmK and compares well with that of copper (4 W/cmK) and diamond (20 W/cmK). As a result, our Metal Insulator Semiconductor (MIS) Schottky barrier structures based on GaN with interfacial BN layers maintain their rectification properties at temperatures up to 600 °C. The integration of such structures in three terminal electronic devices is the next step in the development of advanced III-V Nitride materials for high temperature electronics. Projects:
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