Silicon point contacts: Nanofabrication, molecular beam epitaxial growth, and transport measurements

Abstract

We describe a fabrication process for three-dimensional Si point contacts. The process is based on molecular beam epitaxy to grow electrodes of the devices and on electron-beam lithography and wet etching to produce holes in the insulator. From scanning electron microscopy and transmission electron microscopy analysis we find that the lower electrode has a perfect crystalline structure, while the upper electrode has a composite structure consisting of a single-crystalline column grown out of the hole in the insulator and a poly-crystalline environment. The smallest holes realized have a diameter of 40 nm. I–V curves of point contacts with a boron concentration of about 5×1018 cm−3 and with diameters in the range 200–2000 nm are linear at 300 K and indicate behavior according to the Maxwell resistance, as expected for diffusive transport. Below 40 K variable-range hopping is the transport mechanism. In this temperature range quadratic I–V curves develop, which can be understood from electric field activated hopping in the point-contact geometry.