Field-Effect Transistors based on Silicon Nanowire Arrays: Effect of the Good and the Bad Silicon Nanowires

Aligned arrays of silicon nanowires (aa-Si NWs) allow to exploit their nanoscale properties in a scalable way. Previous studies explored the influence of the number, doping density, and diameter of the Si NWs on the electrical performance. Nevertheless, the origin of the observed effects still not fully understood. Here, we aim to explore the reasons behind the effect of channel number on the fundamental parameters of aa-Si NW field effect transistors (FETs). Towards this end, we have fabricated and characterized 87 FET devices with varied Si NW number. The results show that FETs with Si NWs above a threshold number (n > 80) exhibit better device uniformity, but generally lower device performance, than FETs with lower number of Si NWs (3 ≤ n < 80). Complementary analysis indicates that the obtained discrepancies could be explained by a weighted contribution of two main groups of Si NWs, which exist in a specific, arbitrary Si NWs batch: (i) a group that includes Si NWs with no gold impurities and exhibit high and uniform electrical characteristics; and (ii) a group that includes Si NWs with gold impurities in their cores and, therefore, exhibits inferior electrical characteristics. These findings are validated by a binomial model that consider the aa-Si NW FETs via a weighted combination of FETs of individual Si NW. Overall, the obtained results suggest that the criterions used currently for evaluating the device performance (e.g., uniform diameter, length and shape of a grown batch of Si NWs) do not necessarily guarantee uniform electrical characteristics, raising the need for new growth processes and/or advanced sorting techniques of electrically homogenous Si NWs.