On the Hydrogen Sensing Properties of a Pt-Oxide-In[sub 0.5]Al[sub 0.5]P Schottky Diode

Abstract

A new Pt-InAlP metal oxide semiconductor Schottky diode hydrogen sensor with highly sensitive hydrogen detection among wide operating temperature regime is demonstrated and studied. Experimentally, the studied hydrogen sensor can be operated systematically either under forward or reverse bias conditions. At 30°C, the relatively hydrogen detection ratio S r value is increased from 108.8% ͑107.4%͒ to 943.1% ͑1337.3%͒, under the forward ͑reverse͒ bias of 0.3 V, when the hydrogen concentration is increased from 4.3 to 9970 ppm H 2 /air. Note that even an extremely low hydrogen concentration of 4.3 ppm H 2 /air can be effectively detected at the temperature of 30-250°C.Over past years, semiconductor-type hydrogen sensors have attracted considerable attention in many applications, e.g., industrial fabrication processes, medical installations, laboratories, and fueled motor vehicles. Generally, the criteria used to evaluate a hydrogen sensor include high sensitivity, chemical selectivity, high linearity, short response time, small size, reproducibility, simple operation, ease of fabrication, and wide operating temperature regimes. Previously, metal oxide semiconductor ͑MOS͒ Schottky diodes and MOS field-effect transistors ͑MOSFETs͒ with the catalytic metal were reported to exhibit the impressive hydrogen sensing characteristics. 1-3 To produce more sensitive hydrogen sensing devices, Schottky diodes based on III-V compound semiconductors, such as InP, 4,5 GaAs, 6,7 GaP, 8 InGaP, 9 AlGaAs, 10 GaN, 11,12 and AlGaN, 13,14 have been widely studied. However, little has been reported related to the InAlP material system for microsensor application. Due to the inherent large energy bandgap ͑E g Ϸ 2.3 eV͒, In 0.5 Al 0.5 P-based devices are expected to be operated under high-temperature environments. Also, because the In 0.5 Al 0.5 P material is lattice-matched to GaAs, the In 0.5 Al 0.5 P is suitable for application in heterojunction bipolar transistor ͑HBT͒ and high electron mobility transistor ͑HEMT͒ devices. 15,16 From the hydrogen detection point of view, the high-sensitivity hydrogen sensor based on a Schottky diode with a catalytic Pt metal can be expected, as the Schottky diode current depends exponentially on the change of Schottky barrier height. 17 In addition, Schottky diodes with a thin oxide layer exhibit higher sensitivity and larger modulation of barrier height. 18,19 It has been pointed out that low barrier height and high leakage current resulting from the large surface state density could be improved by the existence of an interfacial oxide layer. 20,21 Therefore, in this work, an interesting InAlP/GaAs MOS Schottky diode hydrogen sensor with highly sensitive hydrogen detection in a wide operating temperature regime is demonstrated and studied. ExperimentalThe studied Pt/In 0.5 Al 0.5 P Schottky diode hydrogen sensor structure was grown on an ͑100͒ oriented semi-insulated ͑S.I.͒ GaAs substrate by a metlalorganic chemical vapor deposition ͑MOCVD͒ system. It consisted of a 5000 Å thick GaAs undoped buffer layer,...

Comprehensive investigation of hydrogen-sensing properties of Pt/InAlP-based Schottky diodes

“…Previously, a smart hydrogen sensor based on the Ptoxide-In 0.5 Al 0.5 P MOS structure was first developed and reported by our group [24]. In this work, the detailed hydrogensensing properties of the interesting catalytic Pt/In 0.5 Al 0.5 P MOS and MS [25] Schottky diode hydrogen sensors are comprehensively studied and compared.…”