III-V Nitride Based Micro and Nanoscale Sensors

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Koley, Goutam
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Structural, mechanical, and sensing properties of InN nanowires (NWs) grown by chemical vapor deposition process have been investigated for their applications in nanoscale sensors. It has been observed that the NWs bend spontaneously or upon meeting an obstacle in their growth path at angles that are multiples of 30°. Lithographically patterned barriers served as guides for the NW growth, which depending on the angle of incidence of the NW, made them grow along the barrier or get deflected from it. Diameter dependent electrical properties of InN nanowires (NWs) grown by chemical vapor deposition were also investigated. InN NW based back-gated field effect transistors (FETs) showed excellent gate control and drain current saturation behaviors. Both NW conductance and carrier mobility calculated from the FET characteristics were found to increase regularly with decrease in NW diameter, with values of ~1000 cm²/Vs and ~1050 S/cm, observed respectively, for a 12 nm diameter NW. The observed mobility and conductivity variations have been modeled by considering NW surface and core conduction paths. InN NWs grown with thick In₂O₃ shell layer demonstrated NO₂ detection capability down to 45 ppb in a field effect transistor configuration. Overall, the structural and electrical properties of the NWs are found to be highly suitable for applications in nanoscale sensors and nanoelectromechanical systems. AlGaN/GaN heterostructure based microcantilever sensors on Si (111) substrate are also being developed at USC for harsh environment sensing applications. Initial fabrication and characterization results indicate very high sensitivity for these sensors.
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