Optimizing the performance of extended-gate field-effect transistor (EGFET) pH sensor by regulating the structural properties of the nanostructured porous silicon layer

Abstract

We report the performance of extended-gate field-effect transistor (EGFET) pH sensors based on the properties of nanostructured porous silicon layer (nano PSi). Four different forms of nano PSi layers with different characteristic features are used as a sensor for determining the pH level. The synthesized nano PSi layer was prepared by laser-assisted etching of n-type (100) by using different illumination intensities 15, 30, 45 and 60 mW/cm2 of 530 nm laser wavelength. The structural and morphological properties of nano PSi were investigated through exploring scanning electron microscopy, X-ray diffraction (XRD) and gravimetrical measurements. Nano PSi with pore-like structures of various pore shapes and sizes are as follows: fine circular pores, star full pore, circular pores and rectangular pores; star full pore shape was prepared through varying the laser illumination intensity. The Fourier transform infrared spectroscopy, current–voltage measurements and specific surface area of were employed to describe the density of the hydrogenated dangling bonds (Si–Hx) of the nano PSi layer. The synthesized nano PSi pH sensors were tested and dry out in the pH range from 3 to 11 at room temperature. The performance of nano PSi pH sensors was comparatively analyzed based on the density of (Si–Hx), specific surface area, porosity and layer thickness of nano PSi. Concerning EGFET pH sensor showed noticeably enhanced pH sensitivity and linearity with increasing the density of (Si–Hx) and specific surface area. Higher sensitivity with excellent linearity was obtained for pore-like structures of circular pore shapes when the laser illumination intensity was about 45 mW/cm2.