2022 Fiscal Year Research-status Report
Research on band-to-band tunneling via discrete dopants near pn junctions in Si nanodevices
| Project/Area Number |
22K04216
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| Research Institution | Shizuoka University |
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Principal Investigator |
Moraru Daniel 静岡大学, 電子工学研究所, 准教授 (60549715)
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| Project Period (FY) |
2022-04-01 – 2025-03-31
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| Keywords | Esaki diode / single-electron / donor-acceptor pair / band-to-band tunneling / silicon-on-insulator / nanoscale / dopant quantum dot |
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| Outline of Annual Research Achievements |
The purpose of this research was to elucidate effects of discrete dopants in tunneling currents flowing in Si nanodevices. Exploration of tunneling via dopants in transistors is fundamental for such analysis, for which we studied silicon-on-insulator devices doped with phosphorus (P). As a main target, we also fabricated and studied pn/pin diodes with narrow depletion layers.
We reported room-temperature single-electron tunneling in highly-doped SOI transistors, in which multiple-dopant quantum dots can be formed.
At low concentrations, single-electron tunneling via single dopants has been analyzed experimentally and theoretically.
We also reported steps in band-to-band tunneling current in nanoscale tunnel diodes, ascribed to energy states in the depletion layer.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
By analyzing different silicon-on-insulator (SOI) devices, we could identify signatures of tunneling transport that can be ascribed to the effects of dopants. In transistors doped at low concentrations, we analyzed the possibility of inelastic tunneling through individual donor-atoms each working as a quantum dot (QD). These analyses can provide a base for exploring these effects also in tunnel diodes.
In addition, the demonstration of single-electron tunneling at high temperatures (up to room temperature) in nanoscale highly-doped SOI transistors also provides evidence that multiple-dopant-induced QDs can control the tunneling transport significantly in our device configuration.
The experimental analysis of tunnel diodes revealed that band-to-band tunneling is affected by energy states in the depletion layer in nanoscale. Analysis is still under way to clarify whether or not these states are directly or indirectly related to the presence of a large number of dopants in the depletion layer. New devices have been fabricated for this purpose and are under analysis.
First-principles simulations are being analyzed for gaining a basic understanding of the fundamental physical mechanisms.
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| Strategy for Future Research Activity |
In the next stage of this research, the basic understanding obtained from the analyses of nanoscale transistors will be applied to the nanoscale SOI tunnel diodes. The first target is to clarify the origin of the current steps or inflections observed in band-to-band tunneling by theoretical and experimental studies on the newly fabricated samples.
In parallel, first-principles simulations of Si nanowire pn diodes containing discrete dopants (for instance, a P-donor and a B-acceptor) will be analyzed in detail to develop an insight into the impact of such a donor-acceptor pair on band-to-band tunneling. It is expected that the coupling to the leads and the coupling between the dopants will play key roles in this mechanism.
The analysis of the donor-acceptor interactions will also be extended to codoped Si nanoscale transistors, in which single-electron tunneling mechanism was also reported recently by our group (JSAP Fall Meeting 2022).
In terms of experiments, the material properties of highly-doped SOI samples will also be analyzed by various methods, providing a more solid base for the understanding of device functionality. New batches of diodes / transistors will be fabricated.
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| Causes of Carryover |
The research funding for this project was sufficient to carry out the basic activities for the current fiscal year. Larger amounts will be necessary in the upcoming fiscal year. This is due to purchase of materials for device fabrication, higher costs related to publication of results and business trips for research purposes.
Due to the above reasons, a fraction of the research funding was transferred to be used in the next fiscal year.
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