Post Implantation Treatment of Silicon Carbide-Based Sensors for Hydrogen Detection Properties Enhancement
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Post Implantation Treatment of Silicon Carbide-Based Sensors for Hydrogen Detection Properties Enhancement I. C. Muntele *, C. I. Muntele *, D. Ila *, R. L. Zimmerman *, D. B. Poker **, D. K. Hensley ** * Center for Irradiation of Materials, Alabama A&M University, Normal, AL ** Solid State Division, Oak Ridge National Laboratory, Oak Ridge, TN ABSTRACT Palladium ion implantation was performed at energies of 35 keV, 50 keV and 100 keV, at both room temperature (RT) and 500 °C, on two identical sets of 6H, n-type silicon carbide samples. Then, one set of samples was subjected to a post-implantation sputtering process, in order to eliminate the substrate layer damaged by the palladium ions during implantation. Electrical and micro-Raman measurements have been performed on both sets of samples, aiming for a better understanding of the chemical processes that take place in the presence of hydrogen atmosphere in the chemical sensors prepared this way.
INTRODUCTION Using silicon carbide as a semiconductor substrate for hydrogen sensor prototyping has been an ongoing research project at the Center for Irradiation of Materials of Alabama A&M University for the past few years. The goal is to design and to prototype a sensing device that can operate at elevated temperatures, using palladium as a chemically active element (catalyst). In pursuing this goal, there are two approaches in developing this kind of sensor: to deposit a thin palladium layer on the surface [1, 2], or to implant palladium ions below the surface of a silicon carbide substrate material [3, 4, 5]. The first approach has been proven to yield devices that gave a very good response in current in the presence of hydrogen, but are not stable with time, the deposited layer of palladium deteriorated after the long exposure to oxygen at temperatures above 300 °C [5]. This brought into consideration the second approach of placing palladium ions inside the extremely stable substrate material forming a sensitive layer of silicon carbide doped with palladium. This yielded devices that proved to be much more stable at elevated temperatures and oxygen exposure, with a fairly good current response to hydrogen. However, the response time of the signal is quite slow, of the order of tens of seconds, as compared to tenths of seconds for the sensors with palladium deposited on the surface. Also, the signal is reversed in the sense that for constant positive voltage applied on the face opposite to the one implanted/deposited, in the presence of hydrogen the current decreases for the implanted sensors, and increases for the deposited sensors. Assumptions that led us throughout this study were that the increase in the response time of the signal is due to the time needed by the hydrogencontaining gas to diffuse through the surface silicon carbide layer before reaching the palladiumcontaining region of the sensor, and that the modification of the current signal is governed by a p-n junction-like behavior of the structure created by ion implantation. Also, the possibility of hydr
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