Size and Surface Modification Effects on the pH Response of Si Nanowire Field-Effect Transistors

Abstract

We investigated the effects of Si nanowire (SiNW) dimensions and their surface modifications on the pH-dependent electronic transport characteristics of SiNW Electrolyte-Insulator-Semiconductor Field-Effect Transistors (EISFETs). The threshold voltages, V-th's, of all devices were extracted from the I-d-V-g characteristics with V-g applied to the reference electrode immersed in different pH solutions, and their pH-dependences were analyzed for various devices. We found that our devices produce the systematic pH-dependence of V-th with respect to the SiNW's length and show significant changes in a linear pH region and a pH sensitivity upon the Si surface modifications. Particularly in the case of the APTES-treated surface, the linear variation was observed in the wide region of pH = 2 similar to 11 with the sensitivity of 54.7 +/- 0.6 mV/pH. Also we compared our data to a theoretical result based on the Gouy-Chapmam-Stern-Graham model and found a reasonable agreement between them.