Microscopic observation of lateral and vertical charge transportation in Si nanocrystals sandwiched by amorphous SiC layers

Abstract

Charge injection and transportation process is a fundamental problem to Si nanocrystals (Si-ncs) based electric and photonic devices. In the manuscript, a single layer of Si-ncs sandwiched by amorphous Si carbide (a-SiC) was prepared by excimer laser annealing of a-SiC/a-Si/a-SiC multilayers, and the charging effect was then characterized by Kelvin probe force microscopy (KPFM) on the microscopic scale. Opposite charges were injected into Si-ncs through the biased tip and formed a core-ring or up-down shaped distribution. The decay characteristics showed that these opposite charges would not only vertically tunnel through the bottom a-SiC layer to substrate but also laterally transport and recombine with each other driven by the attractive Coulomb force. Besides, the charge retention time was also found dependent on the injection biases, which is tentatively ascribed to the charge trapping by the Si-ncs/a-SiC interface states under high bias scanning. The analysis was further supported by conductive atomic force microscopy (CAFM) measurement, in which the current-voltage curves gradually shifted during the repetition test, probably because of bias screening by the trapped charges at these interface states.

Nanoscale Characterization of Active Doping Concentration in Boron‐Doped Individual Si Nanocrystals

“…Although the dual‐pass scan might introduce a problem of charge exchange between the tip and sample during the first pass, Li et al recently proved that the problem can be effectively avoided by increasing the ratio of setpoint amplitude ( A sp ) to the tip free amplitude ( A 0 ) . The ratio A sp / A 0 was set as 0.8 in the first pass of our KPFM measurement, which has been demonstrated to block the tip‐sample charge exchange successfully in our previous work . On the other hand, the FM‐KPFM detects the electrostatic force gradient and thus is expected to have a better resolution than AM mode, however, it suffers a reduced bias sensitivity and usually requires a high AC voltage ( V AC > 2 V) .…”

Anisotropic Diffusion of Charges on Au Nanoclusters Embedded in Al2O3 Dielectrics

“…The retention behavior (i.e., potential change after charge injection) was monitored by customized SKPM with a lock‐in amplifier (Model: SR830, Stanford Research) . In a SKPM measurement, an AFM tip was mechanically resonated with a frequency of ≈75 kHz, and an AC bias was applied to the tip with a frequency of ≈17 kHz and a root‐mean‐square voltage of 2 V.…”

Injection and Retention Characterization of Trapped Charges in Electret Films by Electrostatic Force Microscopy and Kelvin Probe Force Microscopy

“…The charge trapping and retention behaviors of nanomaterials have also been studied by EFM/KPFM, such as isolated germanium nanoislands, [ 63 ] individual few‐layer graphene (FLG) films, [ 101 ] Ti 3 C 2 nanosheets, [ 76 ] individual silicon nanoparticles, [ 69 ] Co granular films, [ 48 ] silicon nanocrystals, [ 64,77 ] silicon nanocrystals embedded in SiO 2 film, [ 49–51 ] silicon quantum dots, [ 109 ] P‐doped Si quantum dots, [ 65 ] and Co nanoclusters embedded in SiO 2 . [ 110 ] Verdaguer et al injected charges in isolated graphene sheets deposited on a SiO 2 /Si wafer by KPFM and investigated the discharge process at different relative humidity (RH) conditions.…”

“…In the past decade, EFM/KPFM has been successfully used to study the injection and retention of trapped charges in inorganic films, [ 16,25,45,46,52–57 ] polymer electrets, [ 47,58–60 ] organic small molecules, [ 42,44 ] the composition of polymer and organic semiconductors, [ 27,41,43 ] nanostructure, [ 48–51,61–78 ] double‐barrier CeO 2 /Si/CeO 2 /Si structures, [ 79 ] DNA molecules, [ 39–80 ] and thin‐film transistors. [ 81–86 ] For example, Heim et al proved that EFM is a useful technique to study the electronic properties of an organic monolayer island at the nanometer scale and found that both carriers are delocalized over the whole island in crystalline monolayer islands, while carriers stay localized at their injection point on a disordered monolayer.…”