On a transistor-type hydrogen gas sensor prepared by an electrophoretic deposition (EPD) approach

• We form Pd-gate by an electrophoretic deposition (EPD) as catalysis metal.
• We examine the EPD-based Pd morphologies by SEM, AFM, XRD, and EDS analyses.
• Low-temperature EPD could provide low surface defects and excellent Schottky contact property.
• EPD demonstrates advantages of low cost, simple apparatus, easy process, and adjustable alloy grain size.

A Pd/GaN/AlGaN heterostructure field-effect transistor (HFET)-type hydrogen gas sensor, based on an electrophoretic deposition (EPD) approach, is fabricated and studied. Due to the formation of good Schottky gate contact by an EPD approach, the studied HFET shows improved DC performance including the suppressed gate current and better thermal stabilities on current–voltage (I–V) characteristics. This is mainly attributed to the reduction of interface trap density and improved Pd morphology. The EPD-based Pd morphologies are examined by X-ray diffraction, energy dispersive spectroscopy, Auger electron spectroscopy, scanning electron microscopy, and atomic force microscopy. For the used gate-dimension of 1 μm × 100 μm, an EPD-based HFET shows low gate current of 2.9 nA, maximum drain saturation current of 490 mA/mm, and maximum extrinsic transconductance of 78.9 mS/mm at room temperature. Also, solid thermal stabilities on maximum drain saturation current (−0.46 mA/mm K) and maximum extrinsic transconductance (−0.08 mS/mm K) are found as the temperature is increased from 300 to 600 K. For hydrogen gas sensing application, at 370 K, the maximum hydrogen sensitivity of 600.1 μA/mm ppm H2/air under a 5 ppm H2/air ambiance and fast response time (30 s) and recovery time (47 s) under a 10,000 ppm H2/air ambiance are obtained. The EPD approach also demonstrates advantages of low cost, simple apparatus, easy process, little restriction on the shaped substrate, composited deposition, and adjustable alloy grain size. Therefore, the proposed EPD approach gives the promise for fabricating high-performance HFET devices and hydrogen gas sensors.