The evolvement of the transport mechanism with the ensemble density of Si quantum dots

Abstract

Electrical transport mechanisms in three dimensional ensembles of silicon quantum dots Abstract. In this review I will try to suggest a comprehensive understanding of the transport mechanisms in three dimensional systems of Si quantum dots (QDs) from the single QD to the very dense ensembles. This understanding is based on our systematic microscopic and macroscopic electrical measurements as a function of the density of Si nanocrystallites. In particular, the role of quantum confinement and Coulomb blockade effects in the transport will be discussed and the concept of QDs' "touching" will be applied. This consideration will enable to reveal the presence of two transitions, a local carrier deconfinement transition and a percolation transition at which these effects are reminiscent of those found in the single QD. It is hoped that our discussion of the evolvement of the transport with the density of the QDs will provide guidance for the understanding of ensembles of semiconductor QDs in general and ensembles of Si QDs in particular.

Glassy-like Transients in Semiconductor Nanomaterials

“…As detailed previously [ 22 , 75 , 86 ], our nano-Si samples were deposited with the co-sputtering of two source materials (targets): high-purity sintered Si pallets and pure fused quartz. The sputtering process was carried out using a plasma of Ar ions that bombarded the targets with energies that were enough to eject clusters of a few atoms from the targets and deposit them on elongated, 13 cm long and 1 cm wide, quartz slides as substrates [ 75 , 86 ]. Our 3 mm wide and 600–1200 nm thick films were such that, during the sputtering process, one end of the substrate was adjacent to the Si target and the other to the fused quartz target.…”

“…To ensure the formation of Si NCs in the films, the slide samples were annealed at 1100–1200 °C in a N 2 atmosphere for about an hour. In particular, for an annealing temperature T a ≥ 1150 °C, the Si phase of the films practically consists only of NCs [ 16 , 75 , 86 , 87 ]. This conclusion was derived from our Raman [ 10 , 16 ] and HRTEM [ 75 , 86 ] measurements.…”

“…In particular, for an annealing temperature T a ≥ 1150 °C, the Si phase of the films practically consists only of NCs [ 16 , 75 , 86 , 87 ]. This conclusion was derived from our Raman [ 10 , 16 ] and HRTEM [ 75 , 86 ] measurements. For example, as shown by our Raman spectra in Figure 1 , the crystalline Si peak (at 521 cm −1 ) “overcomes” the amorphous Si hump (around 480 cm −1 ) when T a was in the 1100–1200 °C range, thus indicating that the entire Si phase consists of NCs.…”

“…As shown in Figure 2 , for the electrical conductivity measurements and for the definition of the x sectors, we have deposited thin (Al, In, or Ag) contact-finger electrodes perpendicular to the slide-film [ 75 , 86 ]. No significant differences in the resulting I(t) behaviors were found with the use of different metal electrodes.…”

“…No significant differences in the resulting I(t) behaviors were found with the use of different metal electrodes. To establish that the above Raman findings are associated with the Si NCs and not with a continuous Si phase, we obtained HRTEM images for a slide sample that was annealed at 1150 C [ 75 , 86 ]. The variation in the size and concentration of the NCs with x is exhibited in Figure 2 .…”