Solution-based fabrication of p-channel and n-channel field-effect transistors using random and aligned carbon nanotube networks

We report both p-channel and n-channel single-walled carbon nanotube (SWNT) film-effect transistors (FETs) using low-cost materials and easy-to-control procedures. The introduction of polyethylenimine (PEI), which has high electron-donating ability, successfully realizes the conversion from p-channel FETs to n-channel devices. The resulting n-channel devices are air-stable outside a vacuum or an inert environment. Instead of conventional chemical vapor deposition method, here in this project, p-channel SWNT FETs are fabricated using two solution-based processes. One method is using layer-by-layer self-assembly to create SWNT random networks and the other is based on dielectrophoresis-aligned SWNTs. By coating a polyethylenimine (PEI) layer on the surface, the transistor demonstrates typical n-channel characteristics. The electrical characteristics of random-network and aligned SWNT transistors are studied comparatively. Our results demonstrate that both p-channel and n-channel devices based on the self-assembly method produce stronger field effects with much higher on/off ratios (I_on/I_off). The combination of fabrication and conversion methods reported here can lead to the development of more complicated SWNT-based devices such as complementary logic gates, which require both p- and n-channel transistors.