Space charge-limited current transport in thin films of alkyl-functionalized silicon nanocrystals

Abstract

Abstract We describe the fabrication and electrical characterization of all-silicon electrode devices to study the electronic properties of thin films of silicon nanocrystals (SiNCs). Planar, highly doped Si electrodes with contact separation of 200 nm were fabricated from silicon-on-insulator substrates, by combination of electron beam lithography and reactive ion etching. The gaps between the electrodes of height 110 nm were filled with thin-films of hexyl functionalized SiNCs (diameter 3 nm) from colloidal dispersions, via a pressure-transducing PDMS (polydimethylsiloxane) membrane. This novel approach allowed the formation of homogeneous SiNC films with precise control of their thickness in the range of 15–90 nm, practically without any voids or cracks. The measured conductance of the highly resistive SiNC films at high bias voltages up to 60 V scaled approximately linearly with gap width (5–50 μm) and gap filling height, with little device-to-device variance. We attribute the observed, pronounced hysteretic current–voltage (I–V) characteristics to space-charge-limited current transport, which—after about twenty cycles—eventually blocks the current almost completely. We propose our all-silicon device scheme and gap filling methodology as a platform to investigate charge transport in novel hybrid materials at the nanoscale, in particular in the high resistivity regime.