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Electric-field-assisted formation of an interfacial double-donor molecule in silicon nano-transistors.

Samanta A, Moraru D, Mizuno T, Tabe M - Sci Rep (2015)

Bottom Line: In this work, we identify pairs of donor atoms in the nano-channel of a silicon field-effect transistor and demonstrate merging of the donor-induced potential wells at the interface by applying vertical electric field.This is due to the decrease of the system's charging energy, as confirmed by Coulomb blockade simulations.These results represent the first experimental observation of electric-field-assisted formation of an interfacial double-donor molecule, opening a pathway for designing functional devices using multiple coupled dopant atoms.

View Article: PubMed Central - PubMed

Affiliation: Research Institute of Electronics, Shizuoka University, 3-5-1 Johoku, Hamamatsu 432-8011, Japan.

ABSTRACT
Control of coupling of dopant atoms in silicon nanostructures is a fundamental challenge for dopant-based applications. However, it is difficult to find systems of only a few dopants that can be directly addressed and, therefore, experimental demonstration has not yet been obtained. In this work, we identify pairs of donor atoms in the nano-channel of a silicon field-effect transistor and demonstrate merging of the donor-induced potential wells at the interface by applying vertical electric field. This system can be described as an interfacial double-donor molecule. Single-electron tunneling current is used to probe the modification of the potential well. When merging occurs at the interface, the gate capacitance of the potential well suddenly increases, leading to an abrupt shift of the tunneling current peak to lower gate voltages. This is due to the decrease of the system's charging energy, as confirmed by Coulomb blockade simulations. These results represent the first experimental observation of electric-field-assisted formation of an interfacial double-donor molecule, opening a pathway for designing functional devices using multiple coupled dopant atoms.

No MeSH data available.


Related in: MedlinePlus

Vertical electric field effect.(a,b) IDS–VFG characteristics (VDS = 2 mV and 5 mV, respectively; T = 5.5 K) measured for two different SOI-MOSFETs with channels randomly doped (ND ≈ 1 × 1018 cm−3). Noise level in these measurements in ~10 fA (shown as cut off level for the vertical axes). (c,d) Contour plots of IDS as a function of backgate voltage (VBG) and frontgate voltage (VFG) for devices A and B, respectively. Device A shows relatively smooth current traces, while device B shows sudden changes in the current peak positions at positive VBG. (e,f) Illustrations of the energy band diagrams and of the electron wave functions at electric fields corresponding to below and above the flatband condition. μSD is source-drain chemical potential.
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f2: Vertical electric field effect.(a,b) IDS–VFG characteristics (VDS = 2 mV and 5 mV, respectively; T = 5.5 K) measured for two different SOI-MOSFETs with channels randomly doped (ND ≈ 1 × 1018 cm−3). Noise level in these measurements in ~10 fA (shown as cut off level for the vertical axes). (c,d) Contour plots of IDS as a function of backgate voltage (VBG) and frontgate voltage (VFG) for devices A and B, respectively. Device A shows relatively smooth current traces, while device B shows sudden changes in the current peak positions at positive VBG. (e,f) Illustrations of the energy band diagrams and of the electron wave functions at electric fields corresponding to below and above the flatband condition. μSD is source-drain chemical potential.

Mentions: For several lower-concentration devices, source-drain current vs front gate voltage (IDS-VFG) characteristics were measured at low temperature (T = 5.5 K) with backgate voltage (VBG) as a parameter. In order to observe the effect of the electric field on transport through ground-states only, we map the current peaks only in the low-bias (low-VDS) region. At higher biases (higher VDS), more complex behavior is likely to be observed as transport could occur through multiple interactive dopants. Due to the random distribution of dopants, different behaviors are observed for different devices as a function of electric field. In this report, we present two significantly different cases among our observations. Figures 2a-2b show the IDS-VFG characteristics at VBG = 0 V for devices labeled A and B, respectively. Several isolated current peaks can be observed before the onset of higher current. These current peaks have irregular intensities (IDS) and do not exhibit any periodicity, which excludes the possibility of a single multiple-electron QD as their origin. The stability diagrams (plots of IDS in the VFG-VDS plane) for each device are also shown in Supplementary Fig. S1a and S1b. Differential conductance was also numerically extracted from this data and displayed as stability diagrams in Supplementary Fig. S1c and S1d. From these diagrams, Coulomb diamonds can be identified confirming that, at least for low-VDS, transport occurs by single-electron tunneling via a single QD, i.e., most likely the ground state of a donor. At higher VDS, more complex structures can be observed in the stability diagrams. Based on the quantitative analysis of these diagrams in the low-VDS region, we extracted typical parameters for each QD, such as the lever-arm factor, α, and the lateral position along the channel. The results of this analysis are shown in Supplementary Table S1. According to these results, we can conclude that the most reasonable interpretation of our data is for each current peak to be ascribed to single-electron tunneling transport through different individual P-donors acting as QDs, as also described in other works7816. The origin of the complex structures in the stability diagrams at high-VDS can be explained based on transport through multiple dopants. The dynamical modification of the potential profile in such multiple-dopant system with the variation in bias and gate voltages could change the equivalent circuit from a single, isolated dopant to interactive, multiple dopants with increasing bias voltage (VDS). Such modification of the potential profile in a multiple-dopant system has been recently reported based on the potential mapping of doped Si nano-channels by Kelvin probe force microscope (KPFM)2324. The change of the transport path from single dopant in the low-VDS region to a multiple-dopant system in the high-VDS region can explain the occurrence of the complex features in the stability diagram at higher biases. Detailed explanations of the stability diagrams are presented in the Supplementary Information file in Fig. S2. However, in the core part of this work, we avoid such complex configurations by focusing the measurement and analysis in the low-VDS region only.


Electric-field-assisted formation of an interfacial double-donor molecule in silicon nano-transistors.

Samanta A, Moraru D, Mizuno T, Tabe M - Sci Rep (2015)

Vertical electric field effect.(a,b) IDS–VFG characteristics (VDS = 2 mV and 5 mV, respectively; T = 5.5 K) measured for two different SOI-MOSFETs with channels randomly doped (ND ≈ 1 × 1018 cm−3). Noise level in these measurements in ~10 fA (shown as cut off level for the vertical axes). (c,d) Contour plots of IDS as a function of backgate voltage (VBG) and frontgate voltage (VFG) for devices A and B, respectively. Device A shows relatively smooth current traces, while device B shows sudden changes in the current peak positions at positive VBG. (e,f) Illustrations of the energy band diagrams and of the electron wave functions at electric fields corresponding to below and above the flatband condition. μSD is source-drain chemical potential.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4663623&req=5

f2: Vertical electric field effect.(a,b) IDS–VFG characteristics (VDS = 2 mV and 5 mV, respectively; T = 5.5 K) measured for two different SOI-MOSFETs with channels randomly doped (ND ≈ 1 × 1018 cm−3). Noise level in these measurements in ~10 fA (shown as cut off level for the vertical axes). (c,d) Contour plots of IDS as a function of backgate voltage (VBG) and frontgate voltage (VFG) for devices A and B, respectively. Device A shows relatively smooth current traces, while device B shows sudden changes in the current peak positions at positive VBG. (e,f) Illustrations of the energy band diagrams and of the electron wave functions at electric fields corresponding to below and above the flatband condition. μSD is source-drain chemical potential.
Mentions: For several lower-concentration devices, source-drain current vs front gate voltage (IDS-VFG) characteristics were measured at low temperature (T = 5.5 K) with backgate voltage (VBG) as a parameter. In order to observe the effect of the electric field on transport through ground-states only, we map the current peaks only in the low-bias (low-VDS) region. At higher biases (higher VDS), more complex behavior is likely to be observed as transport could occur through multiple interactive dopants. Due to the random distribution of dopants, different behaviors are observed for different devices as a function of electric field. In this report, we present two significantly different cases among our observations. Figures 2a-2b show the IDS-VFG characteristics at VBG = 0 V for devices labeled A and B, respectively. Several isolated current peaks can be observed before the onset of higher current. These current peaks have irregular intensities (IDS) and do not exhibit any periodicity, which excludes the possibility of a single multiple-electron QD as their origin. The stability diagrams (plots of IDS in the VFG-VDS plane) for each device are also shown in Supplementary Fig. S1a and S1b. Differential conductance was also numerically extracted from this data and displayed as stability diagrams in Supplementary Fig. S1c and S1d. From these diagrams, Coulomb diamonds can be identified confirming that, at least for low-VDS, transport occurs by single-electron tunneling via a single QD, i.e., most likely the ground state of a donor. At higher VDS, more complex structures can be observed in the stability diagrams. Based on the quantitative analysis of these diagrams in the low-VDS region, we extracted typical parameters for each QD, such as the lever-arm factor, α, and the lateral position along the channel. The results of this analysis are shown in Supplementary Table S1. According to these results, we can conclude that the most reasonable interpretation of our data is for each current peak to be ascribed to single-electron tunneling transport through different individual P-donors acting as QDs, as also described in other works7816. The origin of the complex structures in the stability diagrams at high-VDS can be explained based on transport through multiple dopants. The dynamical modification of the potential profile in such multiple-dopant system with the variation in bias and gate voltages could change the equivalent circuit from a single, isolated dopant to interactive, multiple dopants with increasing bias voltage (VDS). Such modification of the potential profile in a multiple-dopant system has been recently reported based on the potential mapping of doped Si nano-channels by Kelvin probe force microscope (KPFM)2324. The change of the transport path from single dopant in the low-VDS region to a multiple-dopant system in the high-VDS region can explain the occurrence of the complex features in the stability diagram at higher biases. Detailed explanations of the stability diagrams are presented in the Supplementary Information file in Fig. S2. However, in the core part of this work, we avoid such complex configurations by focusing the measurement and analysis in the low-VDS region only.

Bottom Line: In this work, we identify pairs of donor atoms in the nano-channel of a silicon field-effect transistor and demonstrate merging of the donor-induced potential wells at the interface by applying vertical electric field.This is due to the decrease of the system's charging energy, as confirmed by Coulomb blockade simulations.These results represent the first experimental observation of electric-field-assisted formation of an interfacial double-donor molecule, opening a pathway for designing functional devices using multiple coupled dopant atoms.

View Article: PubMed Central - PubMed

Affiliation: Research Institute of Electronics, Shizuoka University, 3-5-1 Johoku, Hamamatsu 432-8011, Japan.

ABSTRACT
Control of coupling of dopant atoms in silicon nanostructures is a fundamental challenge for dopant-based applications. However, it is difficult to find systems of only a few dopants that can be directly addressed and, therefore, experimental demonstration has not yet been obtained. In this work, we identify pairs of donor atoms in the nano-channel of a silicon field-effect transistor and demonstrate merging of the donor-induced potential wells at the interface by applying vertical electric field. This system can be described as an interfacial double-donor molecule. Single-electron tunneling current is used to probe the modification of the potential well. When merging occurs at the interface, the gate capacitance of the potential well suddenly increases, leading to an abrupt shift of the tunneling current peak to lower gate voltages. This is due to the decrease of the system's charging energy, as confirmed by Coulomb blockade simulations. These results represent the first experimental observation of electric-field-assisted formation of an interfacial double-donor molecule, opening a pathway for designing functional devices using multiple coupled dopant atoms.

No MeSH data available.


Related in: MedlinePlus