Fabrication and characterization of zinc oxide light-emitting diodes, indium zinc oxide thin-film transistors, and aluminum gallium nitride/gallium nitride high electron mobility transistor-based biosensors

Hydrogen effects on the electrical and optical properties of p-i-n ZnO light emitting diodes (LEDs) were investigated. There were no diode characteristics or light emission observed from p-i-n ZnO LEDs unless the LEDs were annealed at 350°C after fabrication. Annealed diodes showed band-edge electroluminescence at 385nm and a broad defect band with a peak at 930nm at room temperature. The effects of hydrogen plasma, moisture, water, and phosphoric acid solution on the annealed diode characteristics were investigated and significant degradation of electrical and optical properties were observed in all cases. The plasma-enhanced chemical vapor-deposited (PECVD) SiO2 and SiNx passivation effects on p-i-n ZnO LEDs were also investigated.;Depletion mode and enhancement mode indium zinc oxide (IZO) thin film transistors (TFTs) were fabricated on glass substrates using rf magnetron sputtering deposition at room temperature. Plasma enhanced chemical vapor deposited SiO2 or SiNx was used as the gate insulator. The depletion mode TFTs had a threshold voltage of -2.5V. The drain current on-to-off ratio was >105. The maximum field effect mobility in the channel was 14.5 cm2.V-1.s -1. A unity current gain cut-off frequency, fT, and maximum frequency of oscillation, fmax of 180 and 155 MHz, respectively, were obtained. The equivalent device parameters were extracted by fitting the measured s-parameters to a device equivalent circuit model to obtain the device parameters; intrinsic transconductance, inductances, drain resistance, drain-source resistance, transit time and gate-drain and gate-source capacitance. The enhancement mode TFTs showed an excellent pinch-off and the threshold voltage was 0.75V. The drain current on-to-off ratio of the e-mode TFTs was >106. The maximum field effect mobility in the channel was 39.7 cm2.V-1.s-1.;Antibody-functionalized and Au-gated AlGaN/GaN high electron mobility transistors (HEMTs) were used to detect botulinum toxin. The antibody was anchored to the gate area through immobilized thioglycolic acid. The AlGaN/GaN HEMT drain-source current showed a rapid response of less than 5 seconds when the target toxin in a buffer was added to the antibody-immobilized surface. The detection limit is less than 1ng/ml of botulinum. The sensors could be recycled by washing with phosphate buffered saline (PBS) solution. When the sensors were properly stored at 4°C for several months, they still could work well with an un-degraded sensitivity. By using a similar method, the bacteria, Perkinsus marinus (P. marinus), was also detected by a AlGaN/GaN HEMT-based sensor in sea waters.