Comprehensive investigation on planar type of Pd–GaN hydrogen sensors

Palladium/silicon nanowire Schottky barrier-based hydrogen sensors

“…As expected, the formation of a Schottky barrier decreases the conductance of the sensor as H 2 is introduced. The response resembles that of a H 2 sensitive diode in reverse bias, which generally achieves high sensitivity over a wider range than diodes biased in forward bias [16,23,24]. Since a SBNWFET has two back-to-back junctions, one of which is always reverse biased, the current is symmetric around V ds = 0 V. Modulating the backgate voltage can also be used to tune the sensitivity.…”

“…1a shows the structure of the sensor consisting of a Pd/Si/Pd layers. As opposed to the standard metal-semiconductor architecture used in diode-based sensors, the metal-semiconductor-metal architecture was used here because it is simpler to fabricate (since an ohmic contact is not needed), and several other benefits, such as bi-directional sensing and potentially higher sensitivity [24]. A native SiO 2 layer exists at each Pd/Si interface and serves as a diffusion barrier against PdSi formation while concurrently reducing the effect of Fermi level pinning [15], but is too thin to inhibit carrier transport.…”

Unidirectional sensing characteristics of structured Au–GaN–Pt diodes for differential-pair hydrogen sensors

“…A GaN-based hydrogen sensor with a newly proposed metalsemiconductor-metal configuration was fabricated on the same substrate design described in [11]. After removing the native oxide upon an exposed neGaN layer using a solution of HF:H 2 O ¼ 1:1, a multi-finger electrode was formed by thermally depositing a 30 nm Au metal.…”

“…As a result, the measured current of the MS-and MOS-type hydrogen sensors upon exposure to various concentrations of hydrogen was then recorded as the sensing signal. Although a bidirectional sensing property is available, the MSand MOS-type hydrogen sensors exhibit rectifying and asymmetric behaviors in their currentevoltage (IeV) characteristics [11,12]. When these conventional hydrogen sensors are in a forward-biased mode, an undesirable conducting current brings about unnecessary power dissipation.…”

Sensing properties of resistive-type hydrogen sensors with a Pd–SiO2 thin-film mixture

“…Fortunately, various types of semiconductor hydrogen sensors have been reported with fast response, high sensitivity, or low-cost manufacture. They are, for example, metaleoxideesemiconductor (MOS) [2e7], metalesemiconductor (MS) [6e12], metalesemiconductoremetal (MSM) [13,14], and resistive-type hydrogen sensors [15e17]. Although these hydrogen sensors were investigated based on different sensing mechanisms, most of them use palladium (Pd) to absorb hydrogen.…”