A photomemory by selective-assembling hybrid porphyrin-silicon nanowire field-effect transistor

Dear editor, Recently, the integration of photosensitive material and electronic nanodevice has been the center of attention with Internet of things (IoT) technology development [1–3]. The immobilization of such photoactive molecules on the semiconductor surface was necessarily adopted to employ their photoelectric characteristics which can be observed in the solution. Porphyrin-based hybrid transistors have emerged as promising candidates for photonic sensing application due to the confirmed photo-induced charge transfer (PCT) behavior between porphyrin molecules and electronic platforms [4]. Silicon nanowire is also considered as an ideal configuration to detect stimulus due to large suface-to-volume ratio and excellent transport property [5]. However, most of existing porphyrin/Si nanowire transistor showed transient light response only when the illumination occurred [6–8], and yet an entire photoelectric microsystem is constructed by not only photonic sensor but also other memory counterpart. In this case, an extra number of memory devices were necessary to keep the transformed electrical information recorded, which makes the whole system redundant and complex. In this study, we successfully proposed and fabricated a porphyrin/si hybrid photomemory by a novel selective-assembling silicon nanowire transistor. Thanks to the hydrophobicity difference between SiO2 and Si3N4, the enrichment of water soluble porphyrin onto nanowire surface can be achieved, and a wealth of porphyrin layer is also the key to realize photomemory because molecular orbits in a wealthy and ordered porphyrin layer tend to split so that PCT behavior can be more easily triggered from nanowire to porphyrin’s redox energy level. It is demonstrated that our photomemory could store charge under illumination and also dissociate it by applying electrical field, which can be ignored in a conventional hybrid nanowire device since its molecular orbits in porphyrin layer can hardly split. Experiment. From the very beginning, p-type (1 0 0) silicon wafer was used. For the selectiveassembling porphyrin-silicon nanowire field-effect transistor (PSNFET), LPCVD SiO2/Si3N4/SiO2 stack was firstly implemented as the isolation layer with thicknesses of 10/150/7 nm. For the control sample, only an oxide layer was deposited. Then, a poly-si layer of 25 nm was deposited as the channel material, and the nanowire widths were defined by electron beam lithography (EBL) ranging from 40 to 450 nm. The source and drain regions were patterned by optical lithography and followed by heavy As implantation with energy and dosage of