Characteristics of highly sensitive Au/porous-GaAs Schottky junctions as selective CO and NO gas sensors

Abstract

In this paper an excellent selectivity towards polar CO and NO gases is achieved with an Au/porous-GaAs gas sensor, resulting from reaction kinetics between the polar gases and the pore structures on the Schottky contact. Au/porous-GaAs based on metal-semiconductor Schottky junctions were fabricated and systematically studied as CO and NO gas sensors at different temperatures. The effects of CO and NO adsorption on the reverse biased current–voltage ( I– V) characteristics were investigated, indicating a larger decrease in breakdown voltage towards CO than to NO. Particularly, low CO and NO concentrations could be detected at room temperature in contrast to gases without a dipole moment like N 2, O 2, H 2 and CO 2. Moreover, this sensor exhibited high response towards polar CO and NO gases at elevated temperatures. This means that the device reported here can be used in detecting gases with a dipole moment at various temperatures—an advantage for monitoring engine-exhaust emissions and hazardous gases emitted at different temperatures. The response time of the Au/porous-GaAs Schottky junction sensor was around 0.1 s towards both CO and NO whereas the recovery time was around 8 s. The gold contact for formation of the Au/porous-GaAs Schottky junction senor was deposited using a dc magnetron sputtering system with various film thicknesses between 10 and 125 nm, and was compared with Ag/porous-GaAs and Au/GaAs contacts. We found that the Au/porous-GaAs contact with a thickness of 20 nm showed the best results in response to CO and NO.