Dilute Hydrogen Sulfide Sensing Characteristics of a Pt/GaN Schottky Diode

Tuesday, 26 May 2015: 16:00
Conference Room 4G (Hilton Chicago)
J. F. Xiao, C. P. Hsu, and Y. L. Wang (National Tsing Hua University)
Hydrogen sulfide is a colorless, flammable and highly toxic gas with the characteristic foul odor of rotten eggs, often results from the bacterial breakdown of organic matters. Because of its toxicity, many personal safety gas detectors are set to alarm at 10ppm[i]. A number of sensors based on Schottky diode have been investigated as gas sensors since 1980s. In 2011, Professor Liu studied a Pt/AlGaN/GaN Schottky diode, which can exhibit ammonia detection limit lower than 35ppm NH3/air[ii]. There are also many papers research in H2S sensing with Schottky diode or metal oxide, most of their detection limit is higher than 10 ppm, expect one sensor made by thin film of CuO-SnO2, which can reach to 0.02ppm[iii].

The sensor studied in this paper contains four layers, which is showed in Figure 1 in detail. The Ohmic contact was formed by lift-off of e-beam evaporated Ti(200 Å)/Al(800Å)/ Ni(400Å)/Au(1000Å) and annealed at 850°C for 42 s under a flowing N2 ambient in a Premtek / ARTs 150. 100Å of Pt was deposited by e-beam evaporation to form Schottky contact as well as used as catalytic metal. Figure 2 shows three sets of Pt/GaN Schottky diode in different size and the size for the whole device is about 2×2mm. As the result of experiment, all of these three diodes are sensitive to H2S. Figure 3 shows real-time detection of 0.7ppm H2S in air. Figure 4 shows the relation between current change and concentration of H2S from 0.1-1ppm. All of the devices are tested in 200℃ and applied with 0.5ms width 1.5V pulse every second. With this Pt/GaN Schottky diode we can detect H2S down to 0.05pp.

[i] Agency for Toxic Substances and Disease Registry (July 2006)."Toxicological Profile For Hydrogen Sulfide". p. 154. Retrieved 2012-06-20.

[ii] T. Y. Chen, H. I. Chen, Y. J. Liu, C. C. Huang, C. S. Hsu, C. F. Chang, and W. C. Liu, “Ammonia sensing properties of a Pt/AlGaN/GaN Schottky diode,” IEEE Trans. Electron Devices, vol. 58, no. 5, pp. 1541–1547, May 2011.

[iii] Jun Tamaki , Kengo Shimanoe, Yoshihiro Yamada, Yoshifumi Yamamoto, Morio Miura, and Noboru Yamazoe,” Dilute Hydrogen Sulfide Sensing Properties of Copper Oxide-Tin Oxide Thin Film Prepared by Low-Pressure Evaporation” Solid State Sensors and Actuators, 1997 International Conference