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

Simon Pfaehler,Arzu Angı,Marc Tornow,Bernhard Rieger,Anna Cattani-Scholz,Domenikos Chryssikos

doi:10.1088/1361-6528/ab2c28

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.

Highlights

Semiconductor nanoparticles and nanocrystals (NCs) have gained much significance in electronics and optoelectronics, ranging from fundamental studies on the intriguing transport phenomena in NC arrays to applications in thin-film transistor devices, photovoltaic devices, LEDs, [1, 2] and as fluorescent labels [3]
We describe the fabrication and electrical characterization of all-silicon electrode devices to study the electronic properties of thin films of silicon nanocrystals (SiNCs)
Our demonstrated Si electrode fabrication technique combined with the controlled gap filling method can serve as a platform for the electrical characterization of nm-thin films comprising different NCs passivated with various functional organic groups

Summary

Introduction

Semiconductor nanoparticles and nanocrystals (NCs) have gained much significance in electronics and optoelectronics, ranging from fundamental studies on the intriguing transport phenomena in NC arrays to applications in thin-film transistor devices, photovoltaic devices, LEDs, [1, 2] and as fluorescent labels [3]. The systematic investigation of undoped SiNCs which are functionalized with aliphatic (electrically insulating) molecules poses a particular challenge on the experimental realization: (1) due to the high resistance of the SiNC films, the spacing between the electrical contacts needs to be small (100 nm regime), (2) the space between the contacts (gap) needs to be filled with the SiNC material in a controlled, homogeneous and reproducible manner, and (3) the electrode contact material has to be inert, both chemically and physically with respect to the high electric fields that need to be applied. Our demonstrated Si electrode fabrication technique combined with the controlled gap filling method can serve as a platform for the electrical characterization of nm-thin films comprising different NCs passivated with various functional organic groups

Experimental methods

Preparative methods

Characterization methods

Results and discussion

Conclusion