Optimizing fabrication and performance of liquid-processed carbon nanotube photodetectors on various substrates

Abstract

Carbon nanotubes (CNTs) have attracted interest for optoelectronic applications due to their unique electronic and optoelectronic properties. In particular, multiwall (MW) CNTs film acts as perfect photo-collector surface with the possibility to tune the absorbance by controlling the film thickness. In this work, we demonstrate two types of hybrid Si-MWCNTs photodetectors. The MWCNTs are solution-processed and deposited on n-silicon substrate covered by two different dielectrics (Si₃N₄ or SiO₂). The MWCNTs/SiO₂/n-Si device is used here as reference, since the SiO₂/Si system is the most widely investigated structure in microelectronics. The electrical and optical characteristics of the reference device are compared with the corresponding of our basic MWCNTs/Si₃N₄/n-Si device. The MWCNTs are deposited on the substrate with the drop casting technique. Optical performance of the SiO₂ device is comparable to the Si₃N₄ device thus revealing a quite interesting response under UV illumination. The Si₃N₄ device exhibited a peak equivalent quantum efficiency (EQE) of 57% at 3 μW of source illumination power, thus demonstrating a superior performance as compared to the SiO₂ device (EQE of up to 55%, which is also promising for future applications). This performance can be attributed to the great absorption in UV region of CNTs layer. Apart from this technological goal, we also investigated how MWCNTs/Si₃N₄ or MWCNTs/SiO₂ heterojunctions perform using standard electrical characterization techniques and how the presence of the CNTs change the dielectric characteristics of both substrates.