Spreading resistance at the nano-scale studied by scanning tunneling and field emission spectroscopy

We explore the capability of scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) to study nanoscale Si(100) device layers in silicon-on-insulators (SOIs). These device layers are a macroscopic 2D silicon sheet, and understanding the effective coupling of charge in and out of this sheet allows the determination of whether it is possible to accurately measure the electronic properties of the sheet. Specifically, we examine how the spreading resistance is manifested following the processing of SOI device layers with various doping levels. Depending on the doping level, ultra-thin SOI can exhibit significant blue shifts of the peaks in the tunneling and field emission spectra. By comparing these peak shifts with the film resistivity, it is possible to estimate the contribution of the spreading resistance in STM and STS. We show that STM can be used to study the effective n-type dopant concentrations in the 10¹³–10¹⁶ cm⁻³ range. Furthermore, we demonstrate that with a sufficiently high doping level, 5 nm thick SOI device-layers can be measured and exhibit bulk like electronic characteristics.