Characterization of magnetic Ni/n-Si Schottky contact for hydrogen gas sensing applications

Abstract

In this paper, the sensing characteristics of magnetic and non-magnetic Ni/n-Si contacts as Schottky-type hydrogen gas sensors are discussed. The Ni/n-Si Schottky contacts were prepared using electron beam deposition of Ni films with a thickness of 50–400 nm onto n-type Si substrates. To improve the gas sensitivity, an appropriate profile as a function of magnetic field ( B), temperature ( T) and time ( t) was used to magnetize the ferromagnetic Ni contact. From both forward and reverse current–voltage ( I– V) characteristics, we have found that the magnetic Ni/n-Si contact exhibited much higher sensitivity than the non-magnetic Ni/n-Si sensor in the response to hydrogen gas of different concentrations. Moreover, the responsivity to hydrogen of the magnetic Ni/n-Si sensor was investigated at various operating temperatures between 25 and 230 °C. Although, the sensor showed a large sensitivity of 51 to hydrogen at room temperature, a higher sensitivity of 62 was measured at 80 °C. An explanation was proposed to explain how the magnetization of Ni could affect the sensing response of the magnetic Ni/n-Si sensor significantly. Further, the relationship between the sensitivity and the thickness of the Ni film deposited on Si was also investigated. The sensitivity was inversely related to the film thickness and a higher sensitivity was recorded for thinner Ni layers. Moreover, the sensitivity of the magnetic Ni/n-Si contact to hydrogen was compared with that to CO at room temperature. We found that the magnetic Ni/n-Si contact was much more sensitive to hydrogen than to CO.