In the framework of density functional theory （DFT）, we have studied the electronic properties of alkene/alkyne- hydrosilylated silicon nanocrystals （Si NCs） in the size range from 0.8 nm to 1.6 nm. Among the alke...In the framework of density functional theory （DFT）, we have studied the electronic properties of alkene/alkyne- hydrosilylated silicon nanocrystals （Si NCs） in the size range from 0.8 nm to 1.6 nm. Among the alkenes with all kinds of functional groups considered in this work, only those containing -NH2 and -C4H3S lead to significant hydrosilylation- induced changes in the gap between the highest occupied molecular orbital （HOMO） and the lowest unoccupied molecular orbital （LUMO） of an Si NC at the ground state. The quantum confinement effect is dominant for all of the alkene- hydrosilylated Si NCs at the ground state. At the excited state, the prevailing effect of surface chemistry only occurs at the smallest （0.8 nm） Si NCs hydrosilylated with alkenes containing -NH2 and -C4H3S. Although the alkyne hydrosilylation gives rise to a more significant surface chemistry effect than alkene hydrosilylation, the quantum confinement effect remains dominant for alkyne-hydrosilylated Si NCs at the ground state. However, at the excited state, the effect of surface chemistry induced by the hydrosilylation with conjugated alkynes is strong enough to prevail over that of quantum confinement.展开更多
A Raman frequency upshift in the nc-Si phonon mode is observed at room temperature, which is attributed to a strong compressive stress in the Si nanocrystals. The 10-period amorphous-Si（3 nm）/amorphous-SiO2 （3 nm）...A Raman frequency upshift in the nc-Si phonon mode is observed at room temperature, which is attributed to a strong compressive stress in the Si nanocrystals. The 10-period amorphous-Si（3 nm）/amorphous-SiO2 （3 nm） layers are deposited by high-vacuum radio-frequency magnetron sputtering on quartz and sapphire substrates at different temperatures. The samples are then annealed in N2 atmosphere at 1100 ℃ for 1 h for Si crystallization. It is demonstrated that the presence of a supporting substrate at the high growth temperature can induce different types of stresses in the Si nanocrystal layers. The strain is attributed to the difference in the thermal expansion coefficient between the substrate and the Si/SiO2 SL film. Such a substrate-indueed stress indicates a new method for tuning the optical and electronic properties of Si nanocrystals for strained engineering.展开更多
An investigation was conducted into the effect of hydrogen dilution on the microstructure and optical properties of silicon nanograins embedded in silicon nitride （Si/SiNx） thin film deposited by the helicon wave pl...An investigation was conducted into the effect of hydrogen dilution on the microstructure and optical properties of silicon nanograins embedded in silicon nitride （Si/SiNx） thin film deposited by the helicon wave plasma-enhanced chemical vapour deposition technique. With Ar-diluted SiH4 and N2 as the reactant gas sources in the fabrication of thin film, the film was formed at a high deposition rate. There was a high density of defect at the amorphous silicon （a-Si）/SiNx interface and a relative low optical gap in the film. An addition of hydrogen into the reactant gas reduced the film deposition rate sharply. The silicon nanograins in the SiNx matrix were in a crystalline state, and the density of defects at the silicon nanocrystals （nc-Si）/SiNx interface decreased significantly and the optical gap of the films widened. These results suggested that hydrogen activated by the plasma could not only eliminate in the defects between the interface of silicon nanograins and SiNx matrix, but also helped the nanograins transform from the amorphous into crystalline state. By changing the hydrogen dilution ratio in the reactant gas sources, a tunable band gap from 1.87 eV to 3.32 eV was obtained in the Si/SiNx film.展开更多
Si-rich silicon nitride films are prepared by plasma-enhanced chemical vapor deposition method, followed by thermal annealing to form the Si nanocrystals（Si-NCs） embedded in Si Nx floating gate MOS structures. The c...Si-rich silicon nitride films are prepared by plasma-enhanced chemical vapor deposition method, followed by thermal annealing to form the Si nanocrystals（Si-NCs） embedded in Si Nx floating gate MOS structures. The capacitance–voltage（C–V）, current–voltage（I–V）, and admittance–voltage（G–V） measurements are used to investigate the charging characteristics. It is found that the maximum flat band voltage shift（△VFB） due to full charged holes（～ 6.2 V） is much larger than that due to full charged electrons（～ 1 V）. The charging displacement current peaks of electrons and holes can be also observed by the I–V measurements, respectively. From the G–V measurements we find that the hole injection is influenced by the oxide hole traps which are located near the Si O2/Si-substrate interface. Combining the results of C–V and G–V measurements, we find that the hole charging of the Si-NCs occurs via a two-step tunneling mechanism. The evolution of G–V peak originated from oxide traps exhibits the process of hole injection into these defects and transferring to the Si-NCs.展开更多
Based on the charge storage mode,it is important to investigate the scaling dependence of memory performance in silicon nanocrystal（Si-NC） nonvolatile memory（NVM） devices for its scaling down limit.In this work,we...Based on the charge storage mode,it is important to investigate the scaling dependence of memory performance in silicon nanocrystal（Si-NC） nonvolatile memory（NVM） devices for its scaling down limit.In this work,we made eight kinds of test key cells with different gate widths and lengths by 0.13-μm node complementary metal oxide semiconductor（CMOS） technology.It is found that the memory windows of eight kinds of test key cells are almost the same of about1.64 V @ ±7 V/1 ms,which are independent of the gate area,but mainly determined by the average size（12 nm） and areal density（1.8×10^（11）/cm^2） of Si-NCs.The program/erase（P/E） speed characteristics are almost independent of gate widths and lengths.However,the erase speed is faster than the program speed of test key cells,which is due to the different charging behaviors between electrons and holes during the operation processes.Furthermore,the data retention characteristic is also independent of the gate area.Our findings are useful for further scaling down of Si-NC NVM devices to improve the performance and on-chip integration.展开更多
We report the crystallization and photoluminescence （PL） properties of amorphous Si：H/SiNx ：H multilayer （ML） films treated by step-by-step laser annealing. The results of Raman measurements show that the nanocr...We report the crystallization and photoluminescence （PL） properties of amorphous Si：H/SiNx ：H multilayer （ML） films treated by step-by-step laser annealing. The results of Raman measurements show that the nanocrystalline Si （nc-Si） grains are formed in the a-Si：H layers under the constrained growth mechanism. The blue shift of PL peak with grain size is observed and can be attributed to the quantum confinement effect, For comparison, we also report the crystallization and PL of a-Si：H/SiNx：H ML samples by normal one-step treatment, This method of step-by-step laser treatment will be a candidate to make nc-Si quantum dots in amorphous Si：H/SiNx：H ML as an active layer in microcavities.展开更多
Silicon dominates the electronic industry, but its poor optical properties mean that it is not preferred for photonic applications. Visible photoluminescence （PL） was observed from porous Si at room temperature in 1...Silicon dominates the electronic industry, but its poor optical properties mean that it is not preferred for photonic applications. Visible photoluminescence （PL） was observed from porous Si at room temperature in 1990, but the origin of these light emissions is still not fully understood. This paper reports that an Si nanocrystal, silicon nanoporous pillar array （Si-NPA） with strong visible PL has been prepared on a Si wafer substrate by the hydrothermal etching method. After annealing in 02 atmosphere, the hydride coverage of the Si pillar internal surface is replaced by an oxide layer, which comprises of a great quantity of Si nanocrystal （nc-Si） particles and each of them axe encapsulated by an Si oxide layer. Meanwhile a transition from efficient triple-peak PL bands from blue to red before annealing to strong double-peak blue PL bands after annealing is observed. Comparison of the structural, absorption and luminescence characteristics of the as-prepared and oxidized samples provides evidence for two competitive transition processes, the band-to-band recombination of the quantum confinement effect of nc-Si and the radiative recombination of excitons from the luminescent centres located at the surface of nc-Si units or in the Si oxide layers that cover the nc-Si units because of the different oxidation degrees. The sizes of nc-Si and the quality of the Si oxide surface are two major factors affecting two competitive processes. The smaller the size of nc-Si is and the stronger the oxidation degree of Si oxide layer is, the more beneficial for the luminescent centre recombination process to surpass the quantum confinement process is. The clarification on the origin of the photons may be important for the Si nanoporous pillar array to control both the PL band positions and the relative intensities according to future device requirements and further fabrication of optoelectronic nanodevices.展开更多
Indium tin oxide/Si-rich SiO2/p-Si structured devices are fabricated to study the electroluminescence （EL） of the Si-rich SiO2 （SRO） material. The obvious peaks at～1050nm and ～1260nm in the EL are ascribed to lo...Indium tin oxide/Si-rich SiO2/p-Si structured devices are fabricated to study the electroluminescence （EL） of the Si-rich SiO2 （SRO） material. The obvious peaks at～1050nm and ～1260nm in the EL are ascribed to localized state transitions of amorphous Si （a-Si） clusters. The EL afterglow associated with a-Si clusters is observed from this structure at room temperature, while the afterglow is absent in the case of optical pumping. It is believed that carrier-induced defects act as trap centres in the a-Si clusters, resulting in the EL afterglow. The phenomenon of the EL afterglow indicates the limits of EL performance and electrical modulation of the SRO material with a larger fraction of a-Si clusters.展开更多
基金supported by the National Basic Research Program of China(Grant No.2013CB632101)the National Natural Science Foundation of China forExcellent Young Researchers(Grant No.61222404)+1 种基金the Research and Development Program of Ministry of Education of China(Grant No.62501040202)the 2012 UAlberta MOST Joint Research Laboratories Program,China
文摘In the framework of density functional theory （DFT）, we have studied the electronic properties of alkene/alkyne- hydrosilylated silicon nanocrystals （Si NCs） in the size range from 0.8 nm to 1.6 nm. Among the alkenes with all kinds of functional groups considered in this work, only those containing -NH2 and -C4H3S lead to significant hydrosilylation- induced changes in the gap between the highest occupied molecular orbital （HOMO） and the lowest unoccupied molecular orbital （LUMO） of an Si NC at the ground state. The quantum confinement effect is dominant for all of the alkene- hydrosilylated Si NCs at the ground state. At the excited state, the prevailing effect of surface chemistry only occurs at the smallest （0.8 nm） Si NCs hydrosilylated with alkenes containing -NH2 and -C4H3S. Although the alkyne hydrosilylation gives rise to a more significant surface chemistry effect than alkene hydrosilylation, the quantum confinement effect remains dominant for alkyne-hydrosilylated Si NCs at the ground state. However, at the excited state, the effect of surface chemistry induced by the hydrosilylation with conjugated alkynes is strong enough to prevail over that of quantum confinement.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 61021003, 61036001, and 51072194)the Foundation of Chinese Academy of Sciences
文摘A Raman frequency upshift in the nc-Si phonon mode is observed at room temperature, which is attributed to a strong compressive stress in the Si nanocrystals. The 10-period amorphous-Si（3 nm）/amorphous-SiO2 （3 nm） layers are deposited by high-vacuum radio-frequency magnetron sputtering on quartz and sapphire substrates at different temperatures. The samples are then annealed in N2 atmosphere at 1100 ℃ for 1 h for Si crystallization. It is demonstrated that the presence of a supporting substrate at the high growth temperature can induce different types of stresses in the Si nanocrystal layers. The strain is attributed to the difference in the thermal expansion coefficient between the substrate and the Si/SiO2 SL film. Such a substrate-indueed stress indicates a new method for tuning the optical and electronic properties of Si nanocrystals for strained engineering.
基金supported by the Natural Science Foundation of Hebei Province,China (E2004000119,E2007000201)
文摘An investigation was conducted into the effect of hydrogen dilution on the microstructure and optical properties of silicon nanograins embedded in silicon nitride （Si/SiNx） thin film deposited by the helicon wave plasma-enhanced chemical vapour deposition technique. With Ar-diluted SiH4 and N2 as the reactant gas sources in the fabrication of thin film, the film was formed at a high deposition rate. There was a high density of defect at the amorphous silicon （a-Si）/SiNx interface and a relative low optical gap in the film. An addition of hydrogen into the reactant gas reduced the film deposition rate sharply. The silicon nanograins in the SiNx matrix were in a crystalline state, and the density of defects at the silicon nanocrystals （nc-Si）/SiNx interface decreased significantly and the optical gap of the films widened. These results suggested that hydrogen activated by the plasma could not only eliminate in the defects between the interface of silicon nanograins and SiNx matrix, but also helped the nanograins transform from the amorphous into crystalline state. By changing the hydrogen dilution ratio in the reactant gas sources, a tunable band gap from 1.87 eV to 3.32 eV was obtained in the Si/SiNx film.
基金Project supported by the National Basic Research Program of China(Grant No.2010CB934402)the National Natural Science Foundation of China(Grant No.11374153)
文摘Si-rich silicon nitride films are prepared by plasma-enhanced chemical vapor deposition method, followed by thermal annealing to form the Si nanocrystals（Si-NCs） embedded in Si Nx floating gate MOS structures. The capacitance–voltage（C–V）, current–voltage（I–V）, and admittance–voltage（G–V） measurements are used to investigate the charging characteristics. It is found that the maximum flat band voltage shift（△VFB） due to full charged holes（～ 6.2 V） is much larger than that due to full charged electrons（～ 1 V）. The charging displacement current peaks of electrons and holes can be also observed by the I–V measurements, respectively. From the G–V measurements we find that the hole injection is influenced by the oxide hole traps which are located near the Si O2/Si-substrate interface. Combining the results of C–V and G–V measurements, we find that the hole charging of the Si-NCs occurs via a two-step tunneling mechanism. The evolution of G–V peak originated from oxide traps exhibits the process of hole injection into these defects and transferring to the Si-NCs.
基金Project supported by the State Key Development Program for Basic Research of China(Grant No.2010CB934402)the National Natural Science Foundation of China(Grant Nos.11374153,61571221,and 61071008)
文摘Based on the charge storage mode,it is important to investigate the scaling dependence of memory performance in silicon nanocrystal（Si-NC） nonvolatile memory（NVM） devices for its scaling down limit.In this work,we made eight kinds of test key cells with different gate widths and lengths by 0.13-μm node complementary metal oxide semiconductor（CMOS） technology.It is found that the memory windows of eight kinds of test key cells are almost the same of about1.64 V @ ±7 V/1 ms,which are independent of the gate area,but mainly determined by the average size（12 nm） and areal density（1.8×10^（11）/cm^2） of Si-NCs.The program/erase（P/E） speed characteristics are almost independent of gate widths and lengths.However,the erase speed is faster than the program speed of test key cells,which is due to the different charging behaviors between electrons and holes during the operation processes.Furthermore,the data retention characteristic is also independent of the gate area.Our findings are useful for further scaling down of Si-NC NVM devices to improve the performance and on-chip integration.
基金Supported by the National Natural Science Foundation of China under Grant No 90301009, 60571008, 60471021, and 10374049, the National Key Basic Research and Development Programme of China under Grant No 2001CB610503, and the Natural Science Foundation of Jiangsu Province （DK 20042111）.
文摘We report the crystallization and photoluminescence （PL） properties of amorphous Si：H/SiNx ：H multilayer （ML） films treated by step-by-step laser annealing. The results of Raman measurements show that the nanocrystalline Si （nc-Si） grains are formed in the a-Si：H layers under the constrained growth mechanism. The blue shift of PL peak with grain size is observed and can be attributed to the quantum confinement effect, For comparison, we also report the crystallization and PL of a-Si：H/SiNx：H ML samples by normal one-step treatment, This method of step-by-step laser treatment will be a candidate to make nc-Si quantum dots in amorphous Si：H/SiNx：H ML as an active layer in microcavities.
基金supported by the Doctoral Fund of the Ministry of Education of China (Grant No. 20090010120014)the Beijing Natural Science Foundation (Grant No. 1103033)the Fundamental Research Funds for the Central Universities
文摘Silicon dominates the electronic industry, but its poor optical properties mean that it is not preferred for photonic applications. Visible photoluminescence （PL） was observed from porous Si at room temperature in 1990, but the origin of these light emissions is still not fully understood. This paper reports that an Si nanocrystal, silicon nanoporous pillar array （Si-NPA） with strong visible PL has been prepared on a Si wafer substrate by the hydrothermal etching method. After annealing in 02 atmosphere, the hydride coverage of the Si pillar internal surface is replaced by an oxide layer, which comprises of a great quantity of Si nanocrystal （nc-Si） particles and each of them axe encapsulated by an Si oxide layer. Meanwhile a transition from efficient triple-peak PL bands from blue to red before annealing to strong double-peak blue PL bands after annealing is observed. Comparison of the structural, absorption and luminescence characteristics of the as-prepared and oxidized samples provides evidence for two competitive transition processes, the band-to-band recombination of the quantum confinement effect of nc-Si and the radiative recombination of excitons from the luminescent centres located at the surface of nc-Si units or in the Si oxide layers that cover the nc-Si units because of the different oxidation degrees. The sizes of nc-Si and the quality of the Si oxide surface are two major factors affecting two competitive processes. The smaller the size of nc-Si is and the stronger the oxidation degree of Si oxide layer is, the more beneficial for the luminescent centre recombination process to surpass the quantum confinement process is. The clarification on the origin of the photons may be important for the Si nanoporous pillar array to control both the PL band positions and the relative intensities according to future device requirements and further fabrication of optoelectronic nanodevices.
基金Supported by the National Natural Science Foundation of China under Grant No 60336010.
文摘Indium tin oxide/Si-rich SiO2/p-Si structured devices are fabricated to study the electroluminescence （EL） of the Si-rich SiO2 （SRO） material. The obvious peaks at～1050nm and ～1260nm in the EL are ascribed to localized state transitions of amorphous Si （a-Si） clusters. The EL afterglow associated with a-Si clusters is observed from this structure at room temperature, while the afterglow is absent in the case of optical pumping. It is believed that carrier-induced defects act as trap centres in the a-Si clusters, resulting in the EL afterglow. The phenomenon of the EL afterglow indicates the limits of EL performance and electrical modulation of the SRO material with a larger fraction of a-Si clusters.
