Material Innovations and Nanoelectronics Research Group, Faculty of Electrical Engineering, Universiti Teknologi Malaysia, 81310 Skudai, Johor, Malaysia.
Sensors (Basel). 2011;11(3):3067-77. doi: 10.3390/s110303067. Epub 2011 Mar 9.
The sensing responses in aqueous solution of an open-gated pH sensor fabricated on an AlGaN/GaN high-electron-mobility-transistor (HEMT) structure are investigated. Under air-exposed ambient conditions, the open-gated undoped AlGaN/GaN HEMT only shows the presence of a linear current region. This seems to show that very low Fermi level pinning by surface states exists in the undoped AlGaN/GaN sample. In aqueous solution, typical current-voltage (I-V) characteristics with reasonably good gate controllability are observed, showing that the potential of the AlGaN surface at the open-gated area is effectively controlled via aqueous solution by the Ag/AgCl gate electrode. The open-gated undoped AlGaN/GaN HEMT structure is capable of distinguishing pH level in aqueous electrolytes and exhibits linear sensitivity, where high sensitivity of 1.9 mA/pH or 3.88 mA/mm/pH at drain-source voltage, V(DS) = 5 V is obtained. Due to the large leakage current where it increases with the negative gate voltage, Nernstian like sensitivity cannot be determined as commonly reported in the literature. This large leakage current may be caused by the technical factors rather than any characteristics of the devices. Surprisingly, although there are some imperfections in the device preparation and measurement, the fabricated devices work very well in distinguishing the pH levels. Suppression of current leakage by improving the device preparation is likely needed to improve the device performance. The fabricated device is expected to be suitable for pH sensing applications.
在 AlGaN/GaN 高电子迁移率晶体管 (HEMT) 结构上制造的开栅 pH 传感器在水溶液中的传感响应进行了研究。在暴露于空气的环境条件下，开栅无掺杂 AlGaN/GaN HEMT 仅显示线性电流区域的存在。这似乎表明在无掺杂 AlGaN/GaN 样品中表面态存在非常低的费米能级钉扎。在水溶液中，观察到典型的电流-电压 (I-V) 特性和相当好的栅极可控性，表明通过水溶液Ag/AgCl 栅电极有效地控制了开栅区域的 AlGaN 表面的电势。开栅无掺杂 AlGaN/GaN HEMT 结构能够区分水溶液中的 pH 值，并表现出线性灵敏度，在漏源电压 V(DS) = 5 V 下获得了 1.9 mA/pH 或 3.88 mA/mm/pH 的高灵敏度。由于漏极电流随着负栅极电压的增加而增加，因此不能像文献中通常报道的那样确定 Nernst 型灵敏度。这种大的漏极电流可能是由技术因素而不是器件的任何特性引起的。令人惊讶的是，尽管在器件制备和测量中存在一些不完美之处，但所制备的器件在区分 pH 值方面表现非常出色。通过改进器件制备来抑制电流泄漏可能需要提高器件性能。所制备的器件有望适用于 pH 感测应用。
