Preparation Of Silicon Nanowires And Their Application In NH₃Gas Sensors

One-dimensional (1D) silicon nanostructure materials have many unique features due to the small size effect, surface and boundary effect, quantum size effect and so on. What’s more, silicon nanowires are easily compatible with current integrated circuit technology, so it becomes the hot issue and front studied by the domestic and international researchers. Comparing with bulk silicon materials, silicon nanowires have better photoelectric properties and sensing property which can make up for some lack of bulk silicon material. So in the future, it will have a good prospect in nano-electronic devices and nano silicon integrated circuit.Today more and more researchers have a strong interest in silicon nanowires. The major preparation methods of silicon nanowires include:laser ablation method, chemical vapor deposition (CVD), thermal evaporation, solution method, template method, electrochemical method, silicon substrate direct growth method and so on. In this paper, we use two methods based on SLS and VLS growth mechanism to prepare the silicon nanowires. We prepared the silicon nanowires using high-temperature tube furnace which has the advantages of simple operation, easy control and requiring not harsh experiment conditions. Through SEM, XRD and EDS, we characterized the grown silicon nanowires. We analyzed the factors influencing the silicon nanowires growth such as temperature, carrier gas flow rate, temperature gradient, the thickness of Au and so on. By the process of SLS, we got that the best growth temperature was1000℃. When the carrier gas flow rate was75sccm and temperature was1000℃, a mass of silicon nanowires were prepared. By the process of VLS, if the thickness of Au was within the dozens of nanometers, the thicker Au is, the faster the growth rate is. In addition, the temperature gradient is also an important factor to affect the growth of silicon nanowires. If there is no temperature gradient, the silicon nanowires will not be observed on the sapphire substrate. Through XRD, it was found that the [111] is the preferential growth orientation compared with others.We also used the silicon nanowires grown on Si substrate and sapphire substrate to make the NH3gas sensors, respectively. By comparing the two sensors, the performance of the sensor based on sapphire is better. It has better repeatability and its recovery-time may be less than10s. By means of the I-V curves of the sensor under different NH3concentrations, it was estimated that the response time and recovery-time are25s and6s respectively, for the NH3concentration of25ppm, which are faster than these for higher concentrations. So we think this gas sensor is more suitable for working in the lower gas concentration. What’s more, operating at room temperature, the sensor was found to have good sensing characteristics. And also this sensor has advantages of low cost and low power consumption, it will play an important role in the practical application of silicon nanowire sensors.