Characterization of the metal-semiconductor and metal-insulator-semiconductor junctions between single-walled carbon nanotube films and Si substrates

Single-walled carbon nanotube (CNT) film is a transparent, conductive, and flexible material that exhibits uniform physical and electronic properties¹. Several promising optoelectronic and photovoltaic device applications of these films have recently been demonstrated². However, in previous works, the properties of the junction between the CNT film and the semiconductor substrate (typically Si) have not been properly characterized². Here, we analyze the interface and transport properties of the junction between the CNT film and Si substrates by fabricating metal-semiconductor (MS) and metal-insulator-semiconductor (MIS) structures, where the CNT film acts as the metal and Si is the semiconductor. Our results help to better understand the electrical properties of the CNT film-Si contacts and to improve the design of optoelectronic and photovoltaic devices which use CNT films as transparent conductive electrodes. Device fabrication begins by preparing CNT films using a vacuum filtration approach^1,3 (Fig. 1a) and opening windows in SiO₂ layers on 10¹⁵-10¹⁶ cm^-3 doped n- and p-type Si substrates (Figs. 1c and 1d). For MIS structures, a thin oxide layer is then thermally grown on the exposed Si areas (Fig. 1d2). Next, the CNT films are deposited over both MS and MIS samples (Figs. 1d) and then patterned by O₂ plasma etching³ to form individual devices (Figs. 1e). Finally, metallic rings are deposited on the films for electrical probing (Figs. 1e). For comparison, control samples in which CNT film is replaced with a Ti/Au layer (10/90 nm) have also been fabricated and characterized. An optical image of a CNT film-Si MS structure is shown in Fig. 1b.