Separate device probes 2D electron systems without degrading silicon host surface

In addition to their role in electronics, 2D electron systems permit the study of exotic phases of matter. Silicon surfaces are used to host 2D electron systems, but traditional methods of probing them involve the addition of dopants or metals before high temperature processing, which degrades the silicon surface.

Luke Robertson and Bruce Kane developed a method of probing that does not require the addition of dopants or metals to the silicon surface. All harsh device fabrication takes place on a separate silicon-on-insulator (SOI) chip, preserving the purity of the silicon. Dopants, metals and electrical components, including the ohmic contacts, are located on the SOI piece instead of the silicon surface, but the device is still able to make the electrical contact required for four-terminal transport measurements of the 2D electron system.

“The central motivation for all of this is that we want to have a completely undoped piece of silicon that’s process compatible with all types of existing surface termination techniques, and then use our method to probe those surfaces without destroying the underlying pristine properties of the sample,” Robertson said.

The authors demonstrated the viability of their method at 77 K. At colder temperatures than that, the contact resistance was too high, complicating measurements. Next, they want to figure out how to reduce the contact resistance at lower temperatures. They also plan to use their device to measure 2D electron systems on silicon surfaces passivated with halogens instead of hydrogen.

Source: “A non-invasive gating method for probing 2D electron systems on pristine, intrinsic H-Si(111) surfaces,” by L. D. Robertson and B. E. Kane, Applied Physics Letters (2020). The article can be accessed at https://doi.org/10.1063/5.0024842 .