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Ultra-thin CuO islands on the surface of SnO2 thin films, exhibit a high sensitivity and
a fast response speed for trace level (20 ppm) detection of H2S gas as compared to other
sensor structures. Thickness of the CuO islands in the nano-scale range yields a
significant improvement in the sensor characteristics and studies on ultra-thin CuO
islands in the range (2.5 to 20 nm) are reported. Optimized performance is observed with
8 nm thick CuO islands showing a high sensitivity of 8.065 x 103 at a low operating
temperature of 150° C. The response speed is 12 seconds and a recovery time of 366
seconds is observed under static air conditions (106 seconds in flowing air). Response
time of the sensors is found to be proportional to the CuO thickness, however recovery
time and sensitivity show a maximum at 8 nm CuO thickness. Modulation of the depletion
regions formed between the p-type CuO and n-type SnO2 are found to govern the
sensitivity values along-with spill over of hydrogen available from the dissociated H2S
gas molecule. Thickness of the CuO islands is shown to influence the amount of adsorbed
oxygen present on the uncovered SnO2 surface and plays an important role in determining
the sensitivity values of the sensors.
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